Monitoring the Mineral Content of Plant Foods in Food Composition Databases

Abstract

Declines in the mineral content of food have been reported in several countries. This study monitored reported changes in the mineral content of plant foods in Australian food composition databases between 1991 and 2022. Commonly consumed plant foods (n = 130), grouped as fruit, vegetables, legumes, grains, and nuts in raw unprocessed form, were matched between three reference databases from 1991, 2010, and 2022. Absolute and percentage differences in mineral content (iron, zinc, calcium, and magnesium) were calculated. During this 30-year period, 62 matched foods had updated mineral content. Iron content decreased significantly for fruit (48%) and vegetables (20%), although absolute differences were small (0.09–0.14 mg/100 g). Zinc content declined by 15% for fruit (absolute difference 0.03 mg/100 g), but no differences were observed for calcium and magnesium content. Potential reasons for any reported differences could not be explored using food composition data alone, due to biological, agricultural, and/or analytical factors. Nutritionally, these small differences are unlikely to have a major impact on the population’s nutritional status, although efforts to improve fruit and vegetable consumption are encouraged to meet recommendations.

1. Introduction

With an increased focus on the environment, sustainability, health, and animal welfare, there has been a steady rise in the popularity of plant-based diets in industrialised countries [1,2,3,4]. Plant-based diets focus on foods primarily derived from plants, such as fruits, vegetables, legumes, whole grains, nuts, and seeds, but may include small amounts of animal products [2]. The number of Australians claiming to ‘eat a diet in which the food is all, or almost all, vegetarian’ rose from 9.7% to 12.1%, according to market research between 2012 and 2018 [5]. In a 2017 US survey, 39% of people were actively trying to eat more plant-based foods [3]. This move towards plant-based diets is driven by global health initiatives such as the United Nations Sustainable Development Goals [6], Guiding Principles for Healthy Sustainable Diets by FAO/WHO [7], and the EAT Lancet report [8], which encourage reducing red meat consumption for a healthy and more sustainable future. Such a dietary shift can impact nutrient intake, in particular, those nutrients already identified as being inadequate in the general population, such as calcium, iron, and zinc [9,10]. A recent review found that whilst plant-based dietary patterns can improve intakes of nutrients abundant in plant foods, they can increase the risk of inadequate intake and status of nutrients which are mainly present or more bioavailable in animal foods [11]. For example, a reduction in meat intake, combined with a higher intake of plant sources of phytic acid, can negatively affect the absorption of iron and zinc, which may have implications for at-risk groups such as children and women of child-bearing age [12,13,14,15].

Internationally, concerns have been raised regarding a historical decline in the mineral content of fruit, vegetables, and grains, as reported in studies in the United Kingdom (UK) [16,17] and the United States (US) [18,19]. A frequently cited UK study by Mayer compared food composition data over a 50-year period between the 1930s and 1991 and found reductions in concentrations of copper (36% in fruit and 82% in vegetables), iron (32% in fruit), and magnesium (35% in vegetables) [16]. Similar studies in the US by Davis reported overall reductions in iron and calcium in vegetables between 1950 and 1999 [19] and iron, magnesium, and copper in fruits between 1950 and 2009 [20]. A declining mineral concentration in wheat varieties was also observed as part of the Broadbalk Wheat Experiment in the UK [21]. This is one of the few experimental studies that used archived wheat grain samples from 1845 onwards to assess changes in nutrient content over time. A decline in the concentrations of zinc, iron, copper, and magnesium was noted in the mid-1960s, coinciding with the introduction of higher-yield cultivars [21]. These cultivars contained higher carbohydrate content without a proportionate increase in other nutrients, thus termed the ‘dilution effect’. Other potential reasons for a decline in mineral content have been proposed, including depletion of micronutrients in soil, which has been largely refuted [21,22], agricultural practices and fertiliser use, changes in climate; or methodological differences in post-harvest handling, sampling and improvements in analytical techniques over time [17,23,24].

Few studies have examined mineral concentration changes in the Australian food supply. The first one by Cunningham et al. found no significant or consistent changes in the mineral content of fruits and vegetables between the 1980s and 2000s [25]. A more recent scoping review examining changes in the iron content of vegetables and legumes in Australia found both increases and declines in individual vegetable types during time periods ranging from the 1930s to 2020s [26]. Another review on the iron content of wheat and rice found some changes over time [27], with potential reasons hypothesised to be differences in cultivars, variability in sampling, environmental factors, and analytical methods.

Given the shifts in population dietary patterns and the possibility of declining nutrient content in plant foods, continued monitoring of at-risk nutrients in the food supply is important. Food composition data can provide a practical insight into the temporal changes reported for the nutrient content of commonly consumed foods. Food samples used in food composition databases are representative of the existing food supply of the country and, therefore, provide a snapshot in time [28]. Although these data have limited validity in assessing accurate changes in the mineral content of various individual crops and cultivars due to many biological and methodological differences, they can provide an overview of trends in the food supply over time.

The aim of the present study was to investigate reported changes in the mineral content of plant foods, including fruits, vegetables, legumes, grains, and nuts, using reference food composition databases available in Australia at three time points from 1991 to 2022. Iron, zinc, calcium, and magnesium content were examined as these minerals are often consumed at sub-optimal intakes by vegetarians and other population subgroups. Monitoring the mineral composition of plant foods as the population is becoming more reliant on plant-based diets can provide useful information for dietary guidance, particularly for those following plant-based diets.

2. Materials and Methods

2.1. Food Composition Databases

Data were obtained from three electronic Australian reference food composition databases published by Food Standards Australia New Zealand (FSANZ), Nutrient Tables for Use in Australia (NUTTAB) 1991–1992 [29], NUTTAB 2010 [30], and the Australian Food Composition Database (AFCD) Release 2.0, 2022 [31].

The NUTTAB 1991–1992 database (n = 1580) was the first electronic database in Australia and contains over 90% laboratory analysed data. These data were obtained from the Composition of Foods, Australia, the first large collection of analysed data on Australian foods, collected in the 1980s [32], replacing previously used international data [33]. The sampling procedure considered the geographical density of the population (mostly capital cities Sydney, Melbourne, and Adelaide), retail outlets across the socioeconomic spectrum, food origin, and factors influencing the variability of the nutrients at the time of purchase, during and after sampling, to ensure a reasonable representation of the food sample [32,33]. Composite samples were analysed, comprising a proportionately combined sample of cultivars or brands, typically 2–6 brands for grains, and 5 samples or cultivars for fruit and vegetables. Some samples were constructed to reflect individual varieties (e.g., Granny Smith apples), and some to reflect whatever was available for retail sale under a common name (e.g., broccoli). The values for calcium, magnesium, iron, and zinc were determined by atomic absorption spectrophotometry (AAS) of a hydrochloric acid solution of ash [32].

The NUTTAB2010 database (n = 1534) is a continuation of NUTTAB 1991–1992, incorporating new analytical data as appropriate. These data may include new foods or updated analysis as a result of changes in formulation, processing, or growing conditions of food or an improved analytical method. Sampling differences were reported over time, with the purchasing of samples becoming more nationally representative compared with older data collected in the 1980s and composite sampling of unpackaged foods generally consisting of 6 to 12 purchases. For some staple foods, FSANZ conducted a number of analytical programs over time, and results may be presented as either the average results of these programs or as newer data. Minerals in this database were analysed using AAS or inductively coupled plasma optical emission spectroscopy (ICP-OES).

AFCD Release 2.0 (n = 1616 foods) is the most recent reference database. Mineral content was measured using ICP mass spectrometry (ICP-MS) or ICP-OES in 2022 [31].

Nutrient data published in food composition databases represent an average of the nutrient content of a particular sample of foods, determined at a particular time [31], with no measure of variability recorded in the database. It must be noted that nutrient levels in foods can vary substantially between brands and varieties due to factors such as season, geography, origin, growing conditions, agricultural practices, and natural variation. The majority of fruits, vegetables, and grains were, however, grown in Australia [34].

2.2. Food Matching

The foods selected for this study included all raw and unprocessed fruits, vegetables, legumes (dried), grains (unfortified), and nuts that were analysed and re-analysed in Australia between 1991 and 2022. Foods were excluded if sourced from international databases. Foods were matched by food code and/or description. Unspecified varieties of a food, i.e., where individual cultivars or brands were analysed separately and then weighted according to market information to produce a representative sample, were also matched to ensure good coverage of all food types. Data on mineral content were extracted from the three food composition databases.

2.3. Data Analysis

Foods were grouped into broad food groups for analysis, as recommended by previous authors [18,23], due to the uncertainties in the nutrient content data for any single crop. To examine the mean change in nutrient content over time, the medians for each food group were computed for 1991, 2010, and 2022, and absolute differences were calculated between 1991 and 2022 as follows:

$$nutrient content \left(mg\right) in 2022-nutrient content \left(mg\right) in 1991.$$

(1)

The ratio depicting the change in nutrient content for food groups over the 31-year period was calculated as follows:

$$\frac{nutrient content \left(mg\right) in 2022}{nutrient content \left(mg\right) in 1991}.$$

(2)

Statistical testing, using IBM SPSS version 29.0.2.0, was undertaken to test the hypotheses that the ratios equaled 1.0. Median ratios and the sign test were used, as suggested for this analysis by previous researchers, as the distribution of the ratios was not normally distributed [19]. This conservative approach, together with the Bonferroni correction, resulted in statistical significance being set at p < 0.004.

3. Results

The number of foods that were able to be matched between the three databases was 130, and of these, 62 contained updated data for iron, zinc, calcium, or magnesium content. Notably, no legumes and only one type of nut were updated between 1991 and 2022. Table 1, Table 2, Table 3 and Table 4 summarise the changes in mineral content between 1991 (NUTTAB 1991–1992), 2010 (NUTTAB 2010), and 2022 (AFCD 2.0) for all foods that were updated during this time period, both as absolute differences and as a ratio of 2022 to 1991. Figure 1 illustrates the median ratios (2022/1991) for fruits (n = 25), vegetables (n = 28), and grains (n = 8).

3.1. Iron Content

A reduction in median iron content was found for fruit and vegetables from 1991 to 2010 and a further decline to 2022 (Table 1, Figure 1). Between 1991 and 2022, statistically significant reductions were shown for fruit at 48% (p < 0.001) and vegetables at 20% (p = 0.003). The absolute differences over this time were 0.14 mg/100 g for fruit and 0.23 mg/100 g for vegetables.

Table 1. Iron content (mg/100 g) of re-analysed foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Iron Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	0.2	0.03	0.03	0.15	−0.17
Apple, Granny Smith, Raw, Unpeeled	0.2	0.16	0.16	0.80	−0.04
Apricot, Raw, Unpeeled	0.3	0.3	0.28	0.93	−0.02
Banana, Cavendish, Raw, Peeled	0.5	0.29	0.29	0.58	−0.21
Cherry, Raw	0.3	0.28	0.28	0.93	−0.02
Grape, Black/Red Unspec (Red Globe)	0.2	0.42	0.42	2.10	0.22
Grape, Green, Unspec (Thompson)	0.2	0.28	0.36	1.80	0.16
Grapefruit, Raw, Peeled	0.2	0.2	0.2	1.00	0.00
Kiwifruit, Green (Hayward), Peeled, Raw	0.5	0.26	0.26	0.52	−0.24
Mandarin, Unspec, Raw, Peeled	0.3	0	0	0.00	−0.30
Mango, Raw, Peeled	0.5	0.17	0.17	0.34	−0.33
Nectarine, Raw	0.1	0.13	0	0.00	−0.10
Orange, Navel, Raw, Peeled	0.4	0	0	0.00	−0.40
Orange, Valencia, Raw, Peeled	0.4	0	0	0.00	−0.40
Orange, Unspec	0.4	0	0	0.00	−0.40
Peach, Raw	0.2	0.26	0	0.00	−0.20
Pear, Packhams Triumph, Raw, Unpeeled	0.2	0.06	0.06	0.30	−0.14
Pear, Williams Bartlett, Raw	0.2	0.15	0.15	0.75	−0.05
Pear, Unspec, (Green Skin)	0.2	0	0	0.00	−0.20
Pineapple, Raw, Peeled	0.3	0.25	0	0.00	−0.30
Plum, Red Flesh, Raw	0.3	0.22	0.22	0.73	−0.08
Rockmelon, Raw, Peeled	0.3	0.24	0.24	0.80	−0.06
Strawberry, Raw	0.6	0.55	0.55	0.92	−0.05
Tangerine, Raw, Peeled	0.3	0.2	0.2	0.67	−0.10
Watermelon, Raw, Peeled	0.4	0.1	0.1	0.25	−0.30
All fruit, median	0.3	0.2	0.16	0.52	−0.14
Vegetable
Avocado, Hass, Raw *	0.7	0.49	0.49	0.70	−0.21
Bean, Green, Raw	1.0	0.69	0.69	0.69	−0.31
Broccoli, Raw	1.0	0.84	0.84	0.84	−0.16
Cabbage, White	0.6	0.46	0.46	0.77	−0.14
Capsicum, Green *	0.7	0.53	0.23	0.33	−0.47
Capsicum, Red	0.3	0.3	0.28	0.93	−0.02
Carrot, Mature, Peeled, Fresh, Raw	0.3	0.24	0.24	0.80	−0.06
Cauliflower, Fresh, Raw	0.6	0.32	0.32	0.53	−0.28
Celery, Raw	0.2	0.25	0.25	1.25	0.05
Cucumber, Common, Raw, Unpeeled	0.1	0.22	0.22	2.20	0.12
Cucumber, Lebanese, Raw, Unpeeled	0.3	0.27	0.27	0.90	−0.03
Leek, Fresh, Raw	0.7	0.7	0.7	1.00	0.00
Lettuce, Cos, Raw	0.7	0.7	0.7	1.00	0.00
Lettuce, Iceberg	0.6	0.55	0.26	0.43	−0.34
Lettuce, Mignonette, Raw	1.1	1.1	1.1	1.00	0.00
Mushroom, Common, Raw	0.2	0.45	0.45	2.25	0.25
Parsnip, Raw, Peeled	0.3	0.3	0.3	1.00	0.00
Pea, Green, Raw	1.8	1.8	1.8	1.00	0.00
Potato, Pale Skin, Raw, Peeled	0.6	0.45	0.45	0.75	−0.15
Potato, Red Skin, Raw, Peeled	0.5	0.24	0.24	0.48	−0.26
Pumpkin, Butternut, Raw, Peele	0.4	0.32	0.32	0.80	−0.08
Pumpkin, Unspec, Raw, Peeled	0.5	0.39	0.27	0.54	−0.23
Onion, Mature, Brown Skin, Raw, Peeled	0.4	0.24	0.24	0.60	−0.16
Onion, Mature, White Skin, Raw, Peeled	0.4	0.29	0.29	0.73	−0.11
Sweet Corn, On Cob	2.1	1.2	1.2	0.57	−0.90
Tomato, Cherry, Raw	0.5	0.5	0.63	1.26	0.13
Tomato, Common, Raw	0.3	0.23	0.23	0.77	−0.07
Zucchini, Green Skin, Unpeeled, Raw	0.6	0.5	0.5	0.83	−0.10
All vegetables, medians	0.55	0.45	0.32	0.80	−0.09
Grains
Barley, Pearl, Raw	2.7	2.2	2.2	0.81	−0.50
Bulgur, Dry	3.1	2.5	2.5	0.81	−0.60
Flour, Rice	0.2	0.5	0.5	2.50	0.30
Flour, Wheat, White, Plain	1.3	1.2	1.2	0.92	−0.10
Flour, Wheat, Wholemeal, Plain	3.0	3.0	2.8	0.93	−0.20
Oats, Rolled, Raw	3.7	3.5	3.5	0.95	−0.20
Rice, White, Raw	0.7	0.2	0.2	0.29	−0.50
Rice, Brown, Raw	1.2	0.8	0.8	0.67	−0.40
All grains, median	2.0	1.7	1.7	0.87	−0.30
Nuts
Almond, With Skin Raw	3.9	3.75	3.75	0.96	−0.15

* unspec, unspecified type.

Table 1. Iron content (mg/100 g) of re-analysed foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Iron Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	0.2	0.03	0.03	0.15	−0.17
Apple, Granny Smith, Raw, Unpeeled	0.2	0.16	0.16	0.80	−0.04
Apricot, Raw, Unpeeled	0.3	0.3	0.28	0.93	−0.02
Banana, Cavendish, Raw, Peeled	0.5	0.29	0.29	0.58	−0.21
Cherry, Raw	0.3	0.28	0.28	0.93	−0.02
Grape, Black/Red Unspec (Red Globe)	0.2	0.42	0.42	2.10	0.22
Grape, Green, Unspec (Thompson)	0.2	0.28	0.36	1.80	0.16
Grapefruit, Raw, Peeled	0.2	0.2	0.2	1.00	0.00
Kiwifruit, Green (Hayward), Peeled, Raw	0.5	0.26	0.26	0.52	−0.24
Mandarin, Unspec, Raw, Peeled	0.3	0	0	0.00	−0.30
Mango, Raw, Peeled	0.5	0.17	0.17	0.34	−0.33
Nectarine, Raw	0.1	0.13	0	0.00	−0.10
Orange, Navel, Raw, Peeled	0.4	0	0	0.00	−0.40
Orange, Valencia, Raw, Peeled	0.4	0	0	0.00	−0.40
Orange, Unspec	0.4	0	0	0.00	−0.40
Peach, Raw	0.2	0.26	0	0.00	−0.20
Pear, Packhams Triumph, Raw, Unpeeled	0.2	0.06	0.06	0.30	−0.14
Pear, Williams Bartlett, Raw	0.2	0.15	0.15	0.75	−0.05
Pear, Unspec, (Green Skin)	0.2	0	0	0.00	−0.20
Pineapple, Raw, Peeled	0.3	0.25	0	0.00	−0.30
Plum, Red Flesh, Raw	0.3	0.22	0.22	0.73	−0.08
Rockmelon, Raw, Peeled	0.3	0.24	0.24	0.80	−0.06
Strawberry, Raw	0.6	0.55	0.55	0.92	−0.05
Tangerine, Raw, Peeled	0.3	0.2	0.2	0.67	−0.10
Watermelon, Raw, Peeled	0.4	0.1	0.1	0.25	−0.30
All fruit, median	0.3	0.2	0.16	0.52	−0.14
Vegetable
Avocado, Hass, Raw *	0.7	0.49	0.49	0.70	−0.21
Bean, Green, Raw	1.0	0.69	0.69	0.69	−0.31
Broccoli, Raw	1.0	0.84	0.84	0.84	−0.16
Cabbage, White	0.6	0.46	0.46	0.77	−0.14
Capsicum, Green *	0.7	0.53	0.23	0.33	−0.47
Capsicum, Red	0.3	0.3	0.28	0.93	−0.02
Carrot, Mature, Peeled, Fresh, Raw	0.3	0.24	0.24	0.80	−0.06
Cauliflower, Fresh, Raw	0.6	0.32	0.32	0.53	−0.28
Celery, Raw	0.2	0.25	0.25	1.25	0.05
Cucumber, Common, Raw, Unpeeled	0.1	0.22	0.22	2.20	0.12
Cucumber, Lebanese, Raw, Unpeeled	0.3	0.27	0.27	0.90	−0.03
Leek, Fresh, Raw	0.7	0.7	0.7	1.00	0.00
Lettuce, Cos, Raw	0.7	0.7	0.7	1.00	0.00
Lettuce, Iceberg	0.6	0.55	0.26	0.43	−0.34
Lettuce, Mignonette, Raw	1.1	1.1	1.1	1.00	0.00
Mushroom, Common, Raw	0.2	0.45	0.45	2.25	0.25
Parsnip, Raw, Peeled	0.3	0.3	0.3	1.00	0.00
Pea, Green, Raw	1.8	1.8	1.8	1.00	0.00
Potato, Pale Skin, Raw, Peeled	0.6	0.45	0.45	0.75	−0.15
Potato, Red Skin, Raw, Peeled	0.5	0.24	0.24	0.48	−0.26
Pumpkin, Butternut, Raw, Peele	0.4	0.32	0.32	0.80	−0.08
Pumpkin, Unspec, Raw, Peeled	0.5	0.39	0.27	0.54	−0.23
Onion, Mature, Brown Skin, Raw, Peeled	0.4	0.24	0.24	0.60	−0.16
Onion, Mature, White Skin, Raw, Peeled	0.4	0.29	0.29	0.73	−0.11
Sweet Corn, On Cob	2.1	1.2	1.2	0.57	−0.90
Tomato, Cherry, Raw	0.5	0.5	0.63	1.26	0.13
Tomato, Common, Raw	0.3	0.23	0.23	0.77	−0.07
Zucchini, Green Skin, Unpeeled, Raw	0.6	0.5	0.5	0.83	−0.10
All vegetables, medians	0.55	0.45	0.32	0.80	−0.09
Grains
Barley, Pearl, Raw	2.7	2.2	2.2	0.81	−0.50
Bulgur, Dry	3.1	2.5	2.5	0.81	−0.60
Flour, Rice	0.2	0.5	0.5	2.50	0.30
Flour, Wheat, White, Plain	1.3	1.2	1.2	0.92	−0.10
Flour, Wheat, Wholemeal, Plain	3.0	3.0	2.8	0.93	−0.20
Oats, Rolled, Raw	3.7	3.5	3.5	0.95	−0.20
Rice, White, Raw	0.7	0.2	0.2	0.29	−0.50
Rice, Brown, Raw	1.2	0.8	0.8	0.67	−0.40
All grains, median	2.0	1.7	1.7	0.87	−0.30
Nuts
Almond, With Skin Raw	3.9	3.75	3.75	0.96	−0.15

* unspec, unspecified type.

3.2. Zinc Content

A statistically significant decrease in zinc content was shown for fruits, with an overall median reduction of 15% (p = 0.004) between 1991 and 2022 (Table 2, Figure 1). No significant differences were found for vegetables or grains.

Table 2. Zinc content (mg/100 g) of plant foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Zinc Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	0.1	0.03	0.03	0.30	−0.07
Apple, Granny Smith, Raw, Unpeeled	0.1	0.07	0.07	0.70	−0.03
Apricot, Raw, Unpeeled	0.2	0.15	0.14	0.70	−0.06
Banana, Cavendish, Raw, Peeled	0.2	0.16	0.1	0.50	−0.10
Cherry, Raw	0.1	0.1	0.1	1.00	0.00
Grape, Black/Red Unspec (Red Globe)	0.1	0.22	0.22	2.20	0.12
Grape, Green, Unspec (Thompson)	0.1	0.08	0.04	0.40	−0.06
Grapefruit, Raw, Peeled	0.1	0.1	0.1	1.00	0.00
Kiwifruit, Green (Hayward), Peeled, Raw	0.2	0.11	0.1	0.50	−0.10
Mandarin, Unspec, Raw, Peeled	0.1	0.06	0.06	0.60	−0.04
Mango, Raw, Peeled	0.3	0.07	0.07	0.23	−0.23
Nectarine, Raw	0.1	0.11	0.13	1.30	0.03
Orange, Navel, Raw, Peeled	0.2	0.07	0.07	0.35	−0.13
Orange, Valencia, Raw, Peeled	0.2	0.07	0.07	0.35	−0.13
Orange, Unspec	0.2	0.07	0.07	0.35	−0.13
Peach, Raw	0.1	0.11	0.1	1.00	0.00
Pear, Packhams Triumph, Raw, Unpeeled	0.1	0.09	0.09	0.90	−0.01
Pear, Williams Bartlett, Raw	0.1	0.1	0.1	1.00	0.00
Pear, Unspec, (Green Skin)	0.1	0.09	0.09	0.90	−0.01
Pineapple, Raw, Peeled	0.2	0.1	0.17	0.85	−0.03
Plum, Red Flesh, Raw	0.1	0.1	0.1	1.00	0.00
Rockmelon, Raw, Peeled	0.1	0.12	0.12	1.20	0.02
Strawberry, Raw	0.2	0.18	0.18	0.90	−0.02
Tangerine, Raw, Peeled	0.1	0.1	0.1	1.00	0.00
Watermelon, Raw, Peeled	0.4	0.06	0.06	0.15	−0.34
All fruit, median	0.1	0.1	0.10	0.85	−0.03
Vegetable
Avocado, Hass, Raw *	0.5	0.53	0.53	1.06	0.03
Bean, Green, Raw	0.7	0.27	0.27	0.39	−0.43
Broccoli, Raw	0.7	0.6	0.6	0.86	−0.10
Cabbage, White	0.3	0.23	0.23	0.77	−0.07
Capsicum, Green *	0.3	0.18	0.11	0.37	−0.19
Capsicum, Red	0.4	0.2	0.13	0.33	−0.27
Carrot, Mature, Peeled, Fresh, Raw	0.2	0.17	0.17	0.85	−0.03
Cauliflower, Fresh, Raw	0.3	0.2	0.2	0.67	−0.10
Celery, Raw	0.3	0.21	0.21	0.70	−0.09
Cucumber, Common, Raw, Unpeeled	0.2	0.18	0.18	0.90	−0.02
Cucumber, Lebanese, Raw, Unpeeled	0.2	0.16	0.16	0.80	−0.04
Leek, Fresh, Raw	0.3	0.3	0.3	1.00	0.00
Lettuce, Cos, Raw	0.5	0.31	0.31	0.62	−0.19
Lettuce, Iceberg	0.2	0.2	0.21	1.05	0.01
Lettuce, Mignonette, Raw	0.4	0.28	0.28	0.70	−0.12
Mushroom, Common, Raw	0.2	0.06	0.06	0.30	−0.14
Parsnip, Raw, Peeled	0.4	0.4	0.4	1.00	0.00
Pea, Green, Raw	1	1.05	1.05	1.05	0.05
Potato, Pale Skin, Raw, Peeled	0.4	0.21	0.21	0.53	−0.19
Potato, Red Skin, Raw, Peeled	0.4	0.28	0.28	0.70	−0.12
Pumpkin, Butternut, Raw, Peele	0.1	0.16	0.16	1.60	0.06
Pumpkin, Unspec, Raw, Peeled	0.2	0.21	0.16	0.80	−0.04
Onion, Mature, Brown Skin, Raw, Peeled	0.1	0.2	0.2	2.00	0.10
Onion, Mature, White Skin, Raw, Peeled	0.3	0.22	0.22	0.73	−0.08
Sweet Corn, On Cob	0.8	0.45	0.45	0.56	−0.35
Tomato, Cherry, Raw	0.2	0.15	0.16	0.80	−0.04
Tomato, Common, Raw	0.2	0.12	0.12	0.60	−0.08
Zucchini, Green Skin, Unpeeled, Raw	0.3	0.33	0.33	1.10	0.03
All vegetables, median	0.30	0.21	0.21	0.78	−0.08
Grains
Barley, Pearl, Raw	0.9	1.2	1.2	1.33	0.30
Bulgur, Dry	1.6	3	3	1.88	1.40
Flour, Rice	1.1	1.45	1.45	1.32	0.35
Flour, Wheat, White, Plain	0.5	0.84	0.84	1.68	0.34
Flour, Wheat, Wholemeal, Plain	1.3	1.3	1.7	1.31	0.40
Oats, Rolled, Raw	1.9	2.35	2.35	1.24	0.45
Rice, White, Raw	1.1	1.2	1.2	1.09	0.10
Rice, Brown, Raw	2.1	1.7	1.7	0.81	−0.40
All grains, median	1.20	1.38	1.58	1.31	0.35
Nuts
Almond, With Skin Raw	3.8	3.63	3.63	0.96	−0.17

* unspec, unspecified type.

Table 2. Zinc content (mg/100 g) of plant foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Zinc Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	0.1	0.03	0.03	0.30	−0.07
Apple, Granny Smith, Raw, Unpeeled	0.1	0.07	0.07	0.70	−0.03
Apricot, Raw, Unpeeled	0.2	0.15	0.14	0.70	−0.06
Banana, Cavendish, Raw, Peeled	0.2	0.16	0.1	0.50	−0.10
Cherry, Raw	0.1	0.1	0.1	1.00	0.00
Grape, Black/Red Unspec (Red Globe)	0.1	0.22	0.22	2.20	0.12
Grape, Green, Unspec (Thompson)	0.1	0.08	0.04	0.40	−0.06
Grapefruit, Raw, Peeled	0.1	0.1	0.1	1.00	0.00
Kiwifruit, Green (Hayward), Peeled, Raw	0.2	0.11	0.1	0.50	−0.10
Mandarin, Unspec, Raw, Peeled	0.1	0.06	0.06	0.60	−0.04
Mango, Raw, Peeled	0.3	0.07	0.07	0.23	−0.23
Nectarine, Raw	0.1	0.11	0.13	1.30	0.03
Orange, Navel, Raw, Peeled	0.2	0.07	0.07	0.35	−0.13
Orange, Valencia, Raw, Peeled	0.2	0.07	0.07	0.35	−0.13
Orange, Unspec	0.2	0.07	0.07	0.35	−0.13
Peach, Raw	0.1	0.11	0.1	1.00	0.00
Pear, Packhams Triumph, Raw, Unpeeled	0.1	0.09	0.09	0.90	−0.01
Pear, Williams Bartlett, Raw	0.1	0.1	0.1	1.00	0.00
Pear, Unspec, (Green Skin)	0.1	0.09	0.09	0.90	−0.01
Pineapple, Raw, Peeled	0.2	0.1	0.17	0.85	−0.03
Plum, Red Flesh, Raw	0.1	0.1	0.1	1.00	0.00
Rockmelon, Raw, Peeled	0.1	0.12	0.12	1.20	0.02
Strawberry, Raw	0.2	0.18	0.18	0.90	−0.02
Tangerine, Raw, Peeled	0.1	0.1	0.1	1.00	0.00
Watermelon, Raw, Peeled	0.4	0.06	0.06	0.15	−0.34
All fruit, median	0.1	0.1	0.10	0.85	−0.03
Vegetable
Avocado, Hass, Raw *	0.5	0.53	0.53	1.06	0.03
Bean, Green, Raw	0.7	0.27	0.27	0.39	−0.43
Broccoli, Raw	0.7	0.6	0.6	0.86	−0.10
Cabbage, White	0.3	0.23	0.23	0.77	−0.07
Capsicum, Green *	0.3	0.18	0.11	0.37	−0.19
Capsicum, Red	0.4	0.2	0.13	0.33	−0.27
Carrot, Mature, Peeled, Fresh, Raw	0.2	0.17	0.17	0.85	−0.03
Cauliflower, Fresh, Raw	0.3	0.2	0.2	0.67	−0.10
Celery, Raw	0.3	0.21	0.21	0.70	−0.09
Cucumber, Common, Raw, Unpeeled	0.2	0.18	0.18	0.90	−0.02
Cucumber, Lebanese, Raw, Unpeeled	0.2	0.16	0.16	0.80	−0.04
Leek, Fresh, Raw	0.3	0.3	0.3	1.00	0.00
Lettuce, Cos, Raw	0.5	0.31	0.31	0.62	−0.19
Lettuce, Iceberg	0.2	0.2	0.21	1.05	0.01
Lettuce, Mignonette, Raw	0.4	0.28	0.28	0.70	−0.12
Mushroom, Common, Raw	0.2	0.06	0.06	0.30	−0.14
Parsnip, Raw, Peeled	0.4	0.4	0.4	1.00	0.00
Pea, Green, Raw	1	1.05	1.05	1.05	0.05
Potato, Pale Skin, Raw, Peeled	0.4	0.21	0.21	0.53	−0.19
Potato, Red Skin, Raw, Peeled	0.4	0.28	0.28	0.70	−0.12
Pumpkin, Butternut, Raw, Peele	0.1	0.16	0.16	1.60	0.06
Pumpkin, Unspec, Raw, Peeled	0.2	0.21	0.16	0.80	−0.04
Onion, Mature, Brown Skin, Raw, Peeled	0.1	0.2	0.2	2.00	0.10
Onion, Mature, White Skin, Raw, Peeled	0.3	0.22	0.22	0.73	−0.08
Sweet Corn, On Cob	0.8	0.45	0.45	0.56	−0.35
Tomato, Cherry, Raw	0.2	0.15	0.16	0.80	−0.04
Tomato, Common, Raw	0.2	0.12	0.12	0.60	−0.08
Zucchini, Green Skin, Unpeeled, Raw	0.3	0.33	0.33	1.10	0.03
All vegetables, median	0.30	0.21	0.21	0.78	−0.08
Grains
Barley, Pearl, Raw	0.9	1.2	1.2	1.33	0.30
Bulgur, Dry	1.6	3	3	1.88	1.40
Flour, Rice	1.1	1.45	1.45	1.32	0.35
Flour, Wheat, White, Plain	0.5	0.84	0.84	1.68	0.34
Flour, Wheat, Wholemeal, Plain	1.3	1.3	1.7	1.31	0.40
Oats, Rolled, Raw	1.9	2.35	2.35	1.24	0.45
Rice, White, Raw	1.1	1.2	1.2	1.09	0.10
Rice, Brown, Raw	2.1	1.7	1.7	0.81	−0.40
All grains, median	1.20	1.38	1.58	1.31	0.35
Nuts
Almond, With Skin Raw	3.8	3.63	3.63	0.96	−0.17

* unspec, unspecified type.

3.3. Calcium Content

No statistically significant changes were seen in calcium content for fruits, vegetables, and grains between 1991 and 2022 (Table 3).

Table 3. Calcium content (mg/100 g) of plant foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Calcium Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	5	5	5	1.00	0
Apple, Granny Smith, Raw, Unpeeled	5	5	5	1.00	0
Apricot, Raw, Unpeeled	16	16	13	0.81	−3
Banana, Cavendish, Raw, Peeled	5	5	5	1.00	0
Cherry, Raw	26	22	22	0.85	−4
Grape, Black/Red Unspec (Red Globe)	9	10	10	1.11	1
Grape, Green, Unspec (Thompson)	12	13	10	0.83	−2
Grapefruit, Raw, Peeled	21	21	21	1.00	0
Kiwifruit, Green (Hayward), Peeled, Raw	24	28	28	1.17	4
Mandarin, Unspec, Raw, Peeled	26	29	29	1.12	3
Mango, Raw, Peeled	7	9	9	1.29	2
Nectarine, Raw	8	9	9	1.13	1
Orange, Navel, Raw, Peeled	25	23	23	0.92	−2
Orange, Valencia, Raw, Peeled	32	23	23	0.72	−9
Orange, Unspec	29	23	23	0.79	−6
Peach, Raw	6	5	5	0.83	−1
Pear, Packhams Triumph, Raw, Unpeeled	4	8	8	2.00	4
Pear, Williams Bartlett, Raw	6	6	6	1.00	0
Pear, Unspec, (Green Skin)	5	8	8	1.60	3
Pineapple, Raw, Peeled	27	20	9	0.33	−18
Plum, Red Flesh, Raw	7	7	7	1.00	0
Rockmelon, Raw, Peeled	7	7	7	1.00	0
Strawberry, Raw	13	22	22	1.69	9
Tangerine, Raw, Peeled	42	26	26	0.62	−16
Watermelon, Raw, Peeled	6	5	5	0.83	−1
All fruit, median	9.0	10.0	9.0	1.00	0
Vegetable
Avocado, Hass, Raw *	20	10	10	0.50	−10
Bean, Green, Raw	42	45	45	1.07	3
Broccoli, Raw	31	32	32	1.03	1
Cabbage, White	33	32	32	0.97	−1
Capsicum, Green *	8	8	6	0.75	−2
Capsicum, Red	2	4	7	3.50	5
Carrot, Mature, Peeled, Fresh, Raw	31	26	26	0.84	−5
Cauliflower, Fresh, Raw	14	18	18	1.29	4
Celery, Raw	36	44	44	1.22	8
Cucumber, Common, Raw, Unpeeled	12	18	18	1.50	6
Cucumber, Lebanese, Raw, Unpeeled	63	42	42	0.67	−21
Leek, Fresh, Raw	33	33	33	1.00	0
Lettuce, Cos, Raw	20	20	20	1.00	0
Lettuce, Iceberg	16	18	18	1.13	2
Lettuce, Mignonette, Raw	20	20	20	1.00	0
Mushroom, Common, Raw	2	3	3	1.50	1
Parsnip, Raw, Peeled	38	38	38	1.00	0
Pea, Green, Raw	31	30	30	0.97	−1
Potato, Pale Skin, Raw, Peeled	3	3	3	1.00	0
Potato, Red Skin, Raw, Peeled	4	6	6	1.50	2
Pumpkin, Butternut, Raw, Peele	23	18	18	0.78	−5
Pumpkin, Unspec, Raw, Peeled	29	24	19	0.66	−10
Onion, Mature, Brown Skin, Raw, Peeled	18	23	23	1.28	5
Onion, Mature, White Skin, Raw, Peeled	19	26	26	1.37	7
Sweet Corn, On Cob	22	16	16	0.73	−6
Tomato, Cherry, Raw	11	11	14	1.27	3
Tomato, Common, Raw	8	11	11	1.38	3
Zucchini, Green Skin, Unpeeled, Raw	19	18	18	0.95	−1
All vegetables, median	20.0	19.0	18.5	1.00	0
Grains
Barley, Pearl, Raw	22	28	28	1.27	6
Bulgur, Dry	24	30	30	1.25	6
Flour, Rice	7	6	6	0.86	−1
Flour, Wheat, White, Plain	18	21	21	1.17	3
Flour, Wheat, Wholemeal, Plain	30	30	29	0.97	−1
Oats, Rolled, Raw	45	40	40	0.89	−5
Rice, White, Raw	7	4	4	0.57	−3
Rice, Brown, Raw	11	7	7	0.64	−4
All grains, median	20.0	24.5	24.5	0.93	−1
Nuts
Almond, With Skin Raw	250	265	265	1.06	15

* unspec, unspecified type.

Table 3. Calcium content (mg/100 g) of plant foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Calcium Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	5	5	5	1.00	0
Apple, Granny Smith, Raw, Unpeeled	5	5	5	1.00	0
Apricot, Raw, Unpeeled	16	16	13	0.81	−3
Banana, Cavendish, Raw, Peeled	5	5	5	1.00	0
Cherry, Raw	26	22	22	0.85	−4
Grape, Black/Red Unspec (Red Globe)	9	10	10	1.11	1
Grape, Green, Unspec (Thompson)	12	13	10	0.83	−2
Grapefruit, Raw, Peeled	21	21	21	1.00	0
Kiwifruit, Green (Hayward), Peeled, Raw	24	28	28	1.17	4
Mandarin, Unspec, Raw, Peeled	26	29	29	1.12	3
Mango, Raw, Peeled	7	9	9	1.29	2
Nectarine, Raw	8	9	9	1.13	1
Orange, Navel, Raw, Peeled	25	23	23	0.92	−2
Orange, Valencia, Raw, Peeled	32	23	23	0.72	−9
Orange, Unspec	29	23	23	0.79	−6
Peach, Raw	6	5	5	0.83	−1
Pear, Packhams Triumph, Raw, Unpeeled	4	8	8	2.00	4
Pear, Williams Bartlett, Raw	6	6	6	1.00	0
Pear, Unspec, (Green Skin)	5	8	8	1.60	3
Pineapple, Raw, Peeled	27	20	9	0.33	−18
Plum, Red Flesh, Raw	7	7	7	1.00	0
Rockmelon, Raw, Peeled	7	7	7	1.00	0
Strawberry, Raw	13	22	22	1.69	9
Tangerine, Raw, Peeled	42	26	26	0.62	−16
Watermelon, Raw, Peeled	6	5	5	0.83	−1
All fruit, median	9.0	10.0	9.0	1.00	0
Vegetable
Avocado, Hass, Raw *	20	10	10	0.50	−10
Bean, Green, Raw	42	45	45	1.07	3
Broccoli, Raw	31	32	32	1.03	1
Cabbage, White	33	32	32	0.97	−1
Capsicum, Green *	8	8	6	0.75	−2
Capsicum, Red	2	4	7	3.50	5
Carrot, Mature, Peeled, Fresh, Raw	31	26	26	0.84	−5
Cauliflower, Fresh, Raw	14	18	18	1.29	4
Celery, Raw	36	44	44	1.22	8
Cucumber, Common, Raw, Unpeeled	12	18	18	1.50	6
Cucumber, Lebanese, Raw, Unpeeled	63	42	42	0.67	−21
Leek, Fresh, Raw	33	33	33	1.00	0
Lettuce, Cos, Raw	20	20	20	1.00	0
Lettuce, Iceberg	16	18	18	1.13	2
Lettuce, Mignonette, Raw	20	20	20	1.00	0
Mushroom, Common, Raw	2	3	3	1.50	1
Parsnip, Raw, Peeled	38	38	38	1.00	0
Pea, Green, Raw	31	30	30	0.97	−1
Potato, Pale Skin, Raw, Peeled	3	3	3	1.00	0
Potato, Red Skin, Raw, Peeled	4	6	6	1.50	2
Pumpkin, Butternut, Raw, Peele	23	18	18	0.78	−5
Pumpkin, Unspec, Raw, Peeled	29	24	19	0.66	−10
Onion, Mature, Brown Skin, Raw, Peeled	18	23	23	1.28	5
Onion, Mature, White Skin, Raw, Peeled	19	26	26	1.37	7
Sweet Corn, On Cob	22	16	16	0.73	−6
Tomato, Cherry, Raw	11	11	14	1.27	3
Tomato, Common, Raw	8	11	11	1.38	3
Zucchini, Green Skin, Unpeeled, Raw	19	18	18	0.95	−1
All vegetables, median	20.0	19.0	18.5	1.00	0
Grains
Barley, Pearl, Raw	22	28	28	1.27	6
Bulgur, Dry	24	30	30	1.25	6
Flour, Rice	7	6	6	0.86	−1
Flour, Wheat, White, Plain	18	21	21	1.17	3
Flour, Wheat, Wholemeal, Plain	30	30	29	0.97	−1
Oats, Rolled, Raw	45	40	40	0.89	−5
Rice, White, Raw	7	4	4	0.57	−3
Rice, Brown, Raw	11	7	7	0.64	−4
All grains, median	20.0	24.5	24.5	0.93	−1
Nuts
Almond, With Skin Raw	250	265	265	1.06	15

* unspec, unspecified type.

3.4. Magnesium Content

No statistically significant changes were shown in magnesium content for fruit, vegetables, or grains between 1991 and 2022 (Table 4).

Table 4. Magnesium content (mg/100 g) of plant foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Magnesium Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	4	4	5	1.25	1
Apple, Granny Smith, Raw, Unpeeled	4	4	4	1.00	0
Apricot, Raw, Unpeeled	9	9	12	1.33	3
Banana, Cavendish, Raw, Peeled	19	31	31	1.63	12
Cherry, Raw	10	8	6	0.60	−4
Grape, Black/Red Unspec (Red Globe)	9	8	8	0.89	−1
Grape, Green, Unspec (Thompson)	12	12	8	0.67	−4
Grapefruit, Raw, Peeled	8	8	8	1.00	0
Kiwifruit, Green (Hayward), Peeled, Raw	17	15	15	0.88	−2
Mandarin, Unspec, Raw, Peeled	11	13	13	1.18	2
Mango, Raw, Peeled	7	10	10	1.43	3
Nectarine, Raw	7	7	9	1.29	2
Orange, Navel, Raw, Peeled	11	12	12	1.09	1
Orange, Valencia, Raw, Peeled	11	12	12	1.09	1
Orange, Unspec	11	12	12	1.09	1
Peach, Raw	6	8	8	1.33	2
Pear, Packhams Triumph, Raw, Unpeeled	6	7	7	1.17	1
Pear, Williams Bartlett, Raw	7	7	7	1.00	0
Pear, Unspec, (Green Skin)	6	7	7	1.17	1
Pineapple, Raw, Peeled	11	16	15	1.36	4
Plum, Red Flesh, Raw	6	6	6	1.00	0
Rockmelon, Raw, Peeled	4	8	8	2.00	4
Strawberry, Raw	8	8	8	1.00	0
Tangerine, Raw, Peeled	11	9	9	0.82	−2
Watermelon, Raw, Peeled	4	12	12	3.00	8
All (median)	8	8	8	1.09	1
Vegetable
Avocado, Hass, Raw *	23	26	26	1.13	3
Bean, Green, Raw	25	24	24	0.96	−1
Broccoli, Raw	22	21	21	0.95	−1
Cabbage, White	15	14	14	0.93	−1
Capsicum, Green *	9	10	10	1.11	1
Capsicum, Red	2	6	10	5.00	8
Carrot, Mature, Peeled, Fresh, Raw	10	12	12	1.20	2
Cauliflower, Fresh, Raw	13	16	16	1.23	3
Celery, Raw	7	10	10	1.43	3
Cucumber, Common, Raw, Unpeeled	13	14	14	1.08	1
Cucumber, Lebanese, Raw, Unpeeled	11	10	10	0.91	−1
Leek, Fresh, Raw	14	14	14	1.00	0
Lettuce, Cos, Raw	13	13	13	1.00	0
Lettuce, Iceberg	8	10	9	1.13	1
Lettuce, Mignonette, Raw	13	13	13	1.00	0
Mushroom, Common, Raw	9	11	11	1.22	2
Parsnip, Raw, Peeled	24	24	24	1.00	0
Pea, Green, Raw	30	33	33	1.10	3
Potato, Pale Skin, Raw, Peeled	19	19	19	1.00	0
Potato, Red Skin, Raw, Peeled	19	20	20	1.05	1
Pumpkin, Butternut, Raw, Peele	16	17	17	1.06	1
Pumpkin, Unspec, Raw, Peeled	12	11	16	1.33	4
Onion, Mature, Brown Skin, Raw, Peeled	4	12	12	3.00	8
Onion, Mature, White Skin, Raw, Peeled	12	12	12	1.00	0
Sweet Corn, On Cob	13	12	12	0.92	−1
Tomato, Cherry, Raw	12	12	14	1.17	2
Tomato, Common, Raw	10	10	10	1.00	0
Zucchini, Green Skin, Unpeeled, Raw	15	16	16	1.07	1
All vegetables, median	13	13	14	1.06	1
Grains
Barley, Pearl, Raw	90	95	95	1.06	5
Bulgur, Dry	108	83	83	0.77	−25
Flour, Rice	52	70	70	1.35	18
Flour, Wheat, White, Plain	34	36	36	1.06	2
Flour, Wheat, Wholemeal, Plain	102	102	89	0.87	−13
Oats, Rolled, Raw	130	104	104	0.80	−26
Rice, White, Raw	34	20	20	0.59	−14
Rice, Brown, Raw	120	119	119	0.99	−1
All grains, median	96	89	86	0.92	−7
Nuts
Almond, With Skin Raw	260	266	266	1.02	−1

* unspec, unspecified type.

Table 4. Magnesium content (mg/100 g) of plant foods between 1991 (NUTTAB 1991–1992) and 2022 (Australian Food Composition Database Release (2.0)).

	Magnesium Content, mg/100 g			Ratio	Difference
	1991	2010	2022	2022/1991	2022-1991
Fruit
Apple, Unspec, Red Skin, Raw, Unpeeled	4	4	5	1.25	1
Apple, Granny Smith, Raw, Unpeeled	4	4	4	1.00	0
Apricot, Raw, Unpeeled	9	9	12	1.33	3
Banana, Cavendish, Raw, Peeled	19	31	31	1.63	12
Cherry, Raw	10	8	6	0.60	−4
Grape, Black/Red Unspec (Red Globe)	9	8	8	0.89	−1
Grape, Green, Unspec (Thompson)	12	12	8	0.67	−4
Grapefruit, Raw, Peeled	8	8	8	1.00	0
Kiwifruit, Green (Hayward), Peeled, Raw	17	15	15	0.88	−2
Mandarin, Unspec, Raw, Peeled	11	13	13	1.18	2
Mango, Raw, Peeled	7	10	10	1.43	3
Nectarine, Raw	7	7	9	1.29	2
Orange, Navel, Raw, Peeled	11	12	12	1.09	1
Orange, Valencia, Raw, Peeled	11	12	12	1.09	1
Orange, Unspec	11	12	12	1.09	1
Peach, Raw	6	8	8	1.33	2
Pear, Packhams Triumph, Raw, Unpeeled	6	7	7	1.17	1
Pear, Williams Bartlett, Raw	7	7	7	1.00	0
Pear, Unspec, (Green Skin)	6	7	7	1.17	1
Pineapple, Raw, Peeled	11	16	15	1.36	4
Plum, Red Flesh, Raw	6	6	6	1.00	0
Rockmelon, Raw, Peeled	4	8	8	2.00	4
Strawberry, Raw	8	8	8	1.00	0
Tangerine, Raw, Peeled	11	9	9	0.82	−2
Watermelon, Raw, Peeled	4	12	12	3.00	8
All (median)	8	8	8	1.09	1
Vegetable
Avocado, Hass, Raw *	23	26	26	1.13	3
Bean, Green, Raw	25	24	24	0.96	−1
Broccoli, Raw	22	21	21	0.95	−1
Cabbage, White	15	14	14	0.93	−1
Capsicum, Green *	9	10	10	1.11	1
Capsicum, Red	2	6	10	5.00	8
Carrot, Mature, Peeled, Fresh, Raw	10	12	12	1.20	2
Cauliflower, Fresh, Raw	13	16	16	1.23	3
Celery, Raw	7	10	10	1.43	3
Cucumber, Common, Raw, Unpeeled	13	14	14	1.08	1
Cucumber, Lebanese, Raw, Unpeeled	11	10	10	0.91	−1
Leek, Fresh, Raw	14	14	14	1.00	0
Lettuce, Cos, Raw	13	13	13	1.00	0
Lettuce, Iceberg	8	10	9	1.13	1
Lettuce, Mignonette, Raw	13	13	13	1.00	0
Mushroom, Common, Raw	9	11	11	1.22	2
Parsnip, Raw, Peeled	24	24	24	1.00	0
Pea, Green, Raw	30	33	33	1.10	3
Potato, Pale Skin, Raw, Peeled	19	19	19	1.00	0
Potato, Red Skin, Raw, Peeled	19	20	20	1.05	1
Pumpkin, Butternut, Raw, Peele	16	17	17	1.06	1
Pumpkin, Unspec, Raw, Peeled	12	11	16	1.33	4
Onion, Mature, Brown Skin, Raw, Peeled	4	12	12	3.00	8
Onion, Mature, White Skin, Raw, Peeled	12	12	12	1.00	0
Sweet Corn, On Cob	13	12	12	0.92	−1
Tomato, Cherry, Raw	12	12	14	1.17	2
Tomato, Common, Raw	10	10	10	1.00	0
Zucchini, Green Skin, Unpeeled, Raw	15	16	16	1.07	1
All vegetables, median	13	13	14	1.06	1
Grains
Barley, Pearl, Raw	90	95	95	1.06	5
Bulgur, Dry	108	83	83	0.77	−25
Flour, Rice	52	70	70	1.35	18
Flour, Wheat, White, Plain	34	36	36	1.06	2
Flour, Wheat, Wholemeal, Plain	102	102	89	0.87	−13
Oats, Rolled, Raw	130	104	104	0.80	−26
Rice, White, Raw	34	20	20	0.59	−14
Rice, Brown, Raw	120	119	119	0.99	−1
All grains, median	96	89	86	0.92	−7
Nuts
Almond, With Skin Raw	260	266	266	1.02	−1

* unspec, unspecified type.

4. Discussion

Food composition databases are essential tools for nutrition professionals and are used for a variety of purposes, including the assessment of dietary intakes of population groups and the planning and evaluation of the dietary adequacy of meals and diets [35]. Consequently, it is important to monitor any shifts in nutrient content in databases over time, particularly when considering changing dietary patterns in the population. This study investigated the changes in four minerals in common plant food groups over an approximately 30-year period using food composition databases as an indication of the food supply available to the population at the respective time points. A total of 62 common plant foods, including fruits, vegetables, grains, and nuts, were updated over this time and represented a good selection of the most commonly consumed plant foods in Australia. Although both increases and decreases were reported in the mineral contents of foods and food groups, as reflected in the 2022:1991 ratios, significant reductions were found in the iron contents of fruits and vegetables, and a reduction in zinc content was found for fruits. No changes were detected in the calcium or magnesium content for any of the food groups. However, all these differences were small in absolute terms and were well within the range of natural variation in mineral nutrient content both within a single food and within the groups of foods reviewed in the literature. This variation can be substantial, and two-fold differences or higher have been reported in fruits, vegetables, and grains [23,36,37].

Our results for fruits and vegetables are largely consistent with those of Cunningham et al., who undertook an earlier comparison between Australian samples studied in 1981-85 and those in 2000-01 [25]. They considered the small differences in mineral levels to be consistent with biological variation and improved analytical sensitivity in modern methods of measuring mineral content. In addition, our results reflect the overall findings of Davis [18] and Marles [23], who reviewed the available scientific evidence for changes in the mineral nutrient composition of fruits, vegetables, and grains over time. Davis [18] re-analysed earlier studies by applying more appropriate statistical testing, as used in the current study. They found that among the 33 mineral ratios tested for fruit and vegetables, 25 (76%) were less than 1.0 (declines), with 11 (33%) of these being statistically significant, whereas for the ratios that slightly exceeded 1.0, none were statistically significant. The strongest evidence was for mineral declines in vegetables between 5–40% and smaller declines for fruit. In their comprehensive review, Marles [23] confirmed these findings and found that any differences in the mineral content of fruits, vegetables, and grains could be attributed to many variables such as data sources, crop varieties, geographic origin, ripeness, sample size, sampling methods, and laboratory analysis. However, well-conducted comparisons of some modern versus old crop varieties grown side-by-side and archived samples revealed that some modern cultivars had lower concentrations of selected nutrients than older cultivars. This dilution effect, where yield is prioritised over nutrients, was particularly evident in semi-dwarf wheat cultivars introduced in the mid-1960s [21]. Conversely, other cultivars were found to have higher concentrations of selected nutrients, likely due to genetically based variation between horticultural crop genotypes [23,38].

Few recent studies have examined nutrient changes in food composition databases in the past 30–40 years. A 2021 study in the US assessed over 1300 matched food items with changed iron values between 1999 and 2015 in the US food composition databases and found that iron content fell in 62% of food types and increased in 38% [39]. Declines were seen in a wide range of foods, including most fruits and vegetables, whereas increases were seen in eggs, milk, rice, and iron-fortified foods such as cereals. Absolute differences were not reported. The declines in iron content were thought to reflect changes in US agricultural practices, such as the diluting effect of increasing crop yield per acre. The authors attributed an increase in the prevalence of iron-deficiency anaemia over this time period partly due to decreases in iron concentration in the food supply and shifts in dietary patterns (e.g., lower consumption of beef and higher consumption of chicken) [39].

It is important to assess the relevance of any changes in the nutrient composition of the food supply within the context of current dietary intakes. The most recent representative dietary survey in Australia showed that intakes of iron, zinc, calcium, and magnesium were inadequate in various population subgroups [9,40]. Iron requirements were not met by 23% of females, rising to 40% in adolescent girls and women of childbearing age. Zinc intakes were inadequate in 37% of males, with the greatest prevalence of inadequacy among males 71 years and over (66%). Calcium requirements were not met by three in four females and one in two males, and magnesium intake was inadequate for over one-third of males and females aged two years and over [9]. The relative contribution of fruit, vegetables, legumes, unfortified grains (flours and other cereal grains, but excluding bread and breakfast cereals), and nuts to the average adult’s intake of these minerals was less than 20%: iron (17%), zinc (12%), calcium (9%), and magnesium (19%) [41].

If the observed differences in mineral content of the present study were assumed to be a true reflection of a decline rather than a sampling or methodological artefact, the impact on nutrient intake would likely be small. For example, for the iron content of fruit, an absolute decrease of 0.14 mg/100 g (or 0.22 mg for a 150 g standard serving of fruit) was observed, and for vegetables, a reduction of 0.09 mg/100 g (or 0.07 mg per 75 g standard serve of vegetable). Based on the typical population’s diet of 1.5 servings of fruit and 2.7 serves of vegetables [42], this could potentially affect daily iron intake by approximately 0.5 mg, depending on the types consumed. However, when interpreted against daily iron requirements of 12–18 mg for adults [43], this is a small change and would easily be corrected by consuming a nutritious diet that meets the recommended minimum number of serves from the five food groups: fruits, vegetables, grains, lean meats and alternatives, and milk and alternatives [44]. Estimated differences for zinc, calcium, and magnesium would have an even lower impact on total dietary intake and nutrient adequacy. National surveys have shown that dietary recommendations are not met, and consumption of energy-dense, nutrient-poor discretionary foods is excessive [42,45]. Particular attention needs to be paid to meeting iron and zinc requirements in a plant-based, vegetarian, or vegan diet, as requirements are 50% higher compared with an omnivorous diet [43] due to lower bioavailability and the presence of phytate and polyphenols that inhibit absorption. Thus, good sources of iron and zinc are recommended to ensure nutritional adequacy.

A key strength of this study was the application of food composition databases that contain analysed nutrient data representative of the Australian food supply. The selection of foods that had been updated over the past 30 years was representative of foods within the food groups (with the exception of legumes and nuts), and the vast majority of foods were Australian-grown [34]. Although food composition databases are able to provide a snapshot of the nutrient content of foods available on the market at a particular time, they are not designed to accurately assess the factors that impact changes over time. For example, changes can occur in the genetic varieties of crops available on the market, variations in nutrient content can be considerable within the same variety of crop, and variations due to geographic origin, season, agricultural practices, degree of ripeness, and storage conditions can occur [23,46]. These factors are difficult to discern in food composition databases as the data are aggregated from various sources. Additionally, modifications in sampling, analytical methods, and data reporting may occur over time, hindering the attribution of changes in mineral content to a specific cause. Current analytical methods, including ICP-OES and ICP-MS, are likely to be more sensitive analytically and have better detection limits than AAS used in the 1980s [25,31]. Foods with mineral values less than 0.5 mg/100 g, such as iron and zinc in fruit and vegetables, may have been particularly vulnerable to this measurement uncertainty, suggesting that the more recent values may more accurately represent mineral content.

5. Conclusions

In conclusion, this study quantified changes in the reported mineral content of plant-based foods published in food composition databases over the past 30 years. These findings can help inform users of food composition databases when monitoring and interpreting population nutritional intake using previous editions of the database. Food composition databases reflecting the nutrient composition of the Australian food supply from 1991 to 2022 have shown minor changes in the iron and zinc content of fruit and vegetables and no changes in calcium or magnesium content. The underlying reasons for these changes cannot be assessed using food composition databases alone as they were not designed for this purpose, as many variables, including updated analytical methods, biological variability, differences in cultivars, growing conditions, geographical location, and agricultural practices, potentially play a role. However, as the intent of food composition databases is to assess the nutrient intakes of individuals and populations, it is important to determine how changes in food composition can affect nutritional intake and nutritional adequacy. Based on our findings, the small reported differences in iron and zinc content of fruit and vegetables are unlikely to have a major impact on the population’s nutritional intake as these foods do not contribute greatly to population intakes of iron and zinc. Future efforts should be placed on improving the population’s dietary intake by meeting the recommended number of servings of a variety of nutrient-dense foods such as fruit, vegetables, grains, lean meats and alternatives, milk and alternatives, and limiting nutrient-poor discretionary foods.