Intake of Potatoes Is Associated with Higher Diet Quality, and Improved Nutrient Intake and Adequacy among US Adolescents: NHANES 2001–2018 Analysis

Potatoes are nutrient rich white vegetables, however, research on their impact on public health is limited. The objective of this study was to provide updated evaluation of the cross-sectional association between potato consumption and diet quality, nutrient intake and adequacy. Twenty-four hour diet recall data from adolescents (n = 16,633; age 9–18 years) were used to assess intakes. Usual intakes of nutrients were determined using the National Cancer Institute method and diet quality was calculated using the Healthy Eating Index-2015 (HEI-2015) after adjusting for demographic factors. Consumers of potatoes (baked or boiled potatoes, mashed potatoes and potato mixtures, fried potatoes, and potato chips) had higher (p < 0.05) HEI-2015 total score and subcomponent scores for total vegetables, total protein foods, and refined grain than non-consumers. Consumers also had higher (p < 0.05) intake of energy, dietary fiber, protein, copper, magnesium, phosphorus, potassium, selenium, sodium, zinc, niacin, vitamin B6, vitamin C, vitamin K and total choline; and higher (p < 0.05) adequacy for protein, copper, magnesium, phosphorus, potassium, zinc, thiamine, niacin, vitamin B6, vitamin C, and vitamin K than non-consumers. In conclusion, adolescent potato consumption was associated with higher diet quality, nutrient intake, and adequacy and therefore encouraging their consumption may be an effective strategy for improving nutritional status.


Introduction
Potatoes are the most widely consumed non-cereal staple food consumed worldwide [1]. They are nutrient-rich, typically white, vegetables providing significant amounts of key essential nutrients, including dietary fiber, potassium, magnesium, vitamin C, vitamin B6, and phytonutrients [2][3][4] and are a more affordable source of nutrients with more favorable overall nutrient-to-price ratio compared to many other vegetables [5]. While potatoes are regarded as vegetables in United States (US) dietary recommendations [6], they are not considered as vegetables by World Health Organization [7] and are grouped as cereals in the United Kingdom National Food guide [8]. In the US, potato consumption is over 100 pounds per year per capita, accounting for~30% of total vegetable intake [9]. Their intake was estimated to be 0.35 cup equivalents/day/person in an analysis of National Health and Nutrition Examination Survey (NHANES) 2009-2010 [10].
Potatoes are classified as starchy vegetables because carbohydrates and especially starch (amylose, amylopectin, and resistant starch) are their predominant macronutrient. While potatoes are rich in carbohydrates (starch), because of their high amount of water they have a low energy density compared to other carbohydrate sources [11]. Cooking, cooling, and re-heating increases resistant starch levels in potatoes. Emerging research suggests that resistant starch may enhance satiety, may affect body composition, blood lipid and blood glucose levels; and stimulate growth and increase number of pro-bacteria in the colon [12,13]. Current scientific research on potato consumption and its impact on public health is controversial. In prospective studies, consumption of potatoes was associated with higher risk of type 2 diabetes and hypertension [14,15]. However, a systematic review published in 2016 did not find any conclusive evidence suggesting an association between potato intake and the risk of developing obesity and type 2 diabetes [16]. A recently published NHANES 1999-2010 data analysis reported positive association of higher potato intake with cardiometabolic risk factors but did not find any significant effects on long-term mortality rates [17]. However, only very limited data are available and a research gap exists in children and adolescents.
White potatoes represented about a third of all vegetable servings consumed by US children and adolescents in an analysis of NHANES 2003-2008 [18]. In another analysis of NHANES 2003-2006, white potatoes including French fries contributed to intake of energy and several shortfall nutrients in the diets of children and adolescents [19]. A dietary modeling analysis of NHANES 2005-2012 indicated that removing potatoes from children's diet might compromise potassium intake [20]. Federal nutrition policies related to the role of white potatoes in the diet of adolescents have been controversial and continuously evolving. In 2009, the Institute of Medicine (IOM) and United States Department of Agriculture (USDA) recommended to limit/excluded potatoes and other starchy vegetables from school meal plan [21,22]; however, in 2012, the proposal was struck down by the US Senate prohibiting USDA from setting any maximum limits on the serving of vegetables in school meal programs and removing the restriction on starchy vegetables (including French fries) in school lunches [22]. Starchy vegetables, including potatoes, were also initially restricted to one cup per week in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and the Health Hunger Free Kids Act [23] and in 2009 the WIC program offered a monthly fruit and vegetable cash value voucher that excluded white potatoes [24]; however, an IOM report in 2015 [25] indicated that white potatoes are particularly high in potassium and their increased consumption may help reduce shortfalls of potassium in the diets of both children and women, and recommended that they should be included as eligible vegetables under WIC program. In a recent analysis of longitudinal data from the National Heart, Lung, and Blood Institute's Growth and Health Study, intake of potassium, magnesium, vitamin B6, and vitamin C increased with increasing intake of potatoes at the baseline in adolescent girls [26].
Given this background, we hypothesize that potatoes as nutrient rich vegetables would be associated with improved diet quality and nutrient intake in all adolescents. Therefore, the purpose of this study was to provide an updated evaluation of the association of potato consumption among adolescents on diet quality, nutrient intake, and nutrient adequacy using NHANES 2001-2018 data. To separate the effects of less processed potatoes from more processed potatoes, we used three different definitions to define potato consumers-(1) those consuming potatoes as baked, boiled, and mashed and mixtures; (2) those consuming potatoes as baked, boiled, mashed and mixtures, and fried; and (3) those consuming potatoes as baked, boiled, mashed and mixtures, fried, and chips.

Materials and Methods
NHANES, a continuous large survey of a nationally representative sample of the non-institutionalized US population conducted by the National Center for Health Statistics, were used to assess potato intake [27]. 24 h dietary recall data of 16,633 adolescents 9-18 years participating in nine cycles of NHANES 2001-2018 were combined for the analyses to increase the sample size. Data from pregnant or lactating females and those with unreliable or incomplete data determined by the USDA were excluded. NHANES data are collected using a complex stratified multistage cluster sampling probability design. A detailed description of the subject recruitment, survey design, and data collection procedures is available online [27], and all data obtained for this study are publicly available at http://www.cdc.gov/nchs/nhanes/, (accessed on 11 December 2020). All participants or proxies provided written informed consent and the Research Ethics Review Board at the National Center for Health Statistics approved the survey protocol. NHANES has stringent consent protocols and procedures to ensure confidentiality and protection from identification. This study was a secondary data analysis which lacked personal identifiers, therefore, did not require Institutional Review Board review.
Dietary intake of energy, nutrients, and food components was determined using 24-h dietary recalls, which included an in-person interview in the Mobile Examination Center (day 1 recall), followed by a telephone interview conducted 3-10 days after (day 2 recall). Parents or guardians assisted 9-11 years old adolescents, while 12-18 years old adolescents provided their own recalls. Participants were dichotomized into consumers and nonconsumers of potatoes; and consumers were further classified into intake quartiles based on individual usual intakes. Consumers were defined as those individuals consuming any amount of potatoes on either of the two days of dietary recall. Potato intakes were assessed using a total of four What We Eat in America (WWEIA) food categories (numbers indicated assigned by USDA for categorization purposes): baked or boiled potatoes (#6802), mashed potatoes and potato mixtures (#6806), fried potatoes (#6804), and potato chips (#5002). We used three definitions for defining potato intake: Demographic information and physical activity levels were determined from the NHANES interview [27].
Diet quality scores were determined using the USDA Healthy Eating Index-2015 (HEI-2015) [28], which has 13 subcomponents, each reflecting an aspect of the 2015-2020 Dietary Guidelines for Americans [29] recommendations. Dietary intake was expressed per 1000 kcal for all subcomponents, except for fatty acid ratios, which were expressed as ratio of unsaturated to saturated fatty acids, and for saturated fat and added sugars, both expressed as % energy. Subcomponents for total vegetables; greens and beans; total fruit, whole fruit; total protein; and seafoods and plant proteins were scored proportionally from 0 to 5 points and all other subcomponents (i.e., whole grains; dairy; fatty acids; sodium; refined grains; saturated fat; and added sugars) were scored proportionally from 0 to 10 points. Four subcomponents, sodium, refined grains, saturated fat, and added sugars were reverse scored, so that lower intake leads to a higher score, and thus a greater contribution to overall diet quality. The maximum possible score was 100 [28]. The intake on the first dietary recall were used to determine HEI-2015 total and subcomponent scores.
Energy and nutrient intake were determined using the NHANES cycle specific USDA Food & Nutrient Database for Dietary Studies [30,31]. Food components to assess HEI were determined using the NHANES cycle specific USDA MyPyramid Servings Database Food or Food Patterns Equivalents Database [32,33].
Analyses were performed using SAS 9.4 and data adjusted for the complex sampling (clustered sample) design of NHANES, using appropriate survey weights, strata, and primary sampling units. Least-square means (and the standard errors of the least-square means) for diet quality (HEI-2015 score), and for energy and nutrient intake were generated using regression analyses adjusted for key covariates (age, gender, and ethnicity). Usual intakes of energy, nutrients, and food groups were determined using the National Cancer Institute (NCI) method and NCI macros were used to estimate distribution of usual intake [34]. Nutrient adequacy was estimated by assessing the percentage of the population below the Estimated Average Requirement (EAR) or above Adequate Intake (AI) of nutrients using the cut-point method (except for iron, where the probability method was used, which is the recommended approach when assessing iron intake given asymmetrical requirement distribution of iron in menstruating women [35]). Significant differences between consumers and non-consumers were assessed via t-test and regression analyses were used to assess the linear relationship of potato intake quartiles with diet quality and nutrient intake.

Results
Mean per capita intake of potatoes for Case 1 (baked, boiled, and mashed and mixtures), Case 2 (baked, boiled, mashed and mixtures, and fried), and Case 3 (baked, boiled, mashed and mixtures, fried, and chips) were 0.11 ± 0.01, 0.22 ± 0.01, and 0.32 ± 0.01 cup eq, respectively, for NHANES 2001-2018. Mean per capita intake of potatoes (for all three definitions) was stable and did not change significantly (p > 0.05) over the last 18 years (9 NHANES cycles) among US adolescents ( Figure 1).  (Table 1). All other demographic characteristics evaluated were similar (p > 0.05) among consumers and non-consumers potatoes in Case 1 (Table 1). Data is presented as Mean ± Standard Error. "Other Hispanic" and "Other" are not sampled in a way to be nationally representative.
Nutrient Adequacy: Compared to non-consumers, a lower (p < 0.05) proportion of adolescent consumers of potatoes in Case 1 (baked, boiled, mashed and mixtures) were below the EAR for carbohydrate, protein, copper, iron, magnesium, phosphorus, selenium, zinc, vitamin A, thiamine, riboflavin, niacin, vitamin B 6 and vitamin C, and a higher (p < 0.05) proportion were above AI for potassium, sodium, and vitamin K ( Table 6). Similarly, compared to non-consumers, a lower (p < 0.05) proportion of adolescent consumers of potatoes in Case 2 (baked, boiled, mashed and mixtures, fried) were below the EAR for carbohydrate, protein, copper, magnesium, phosphorus, zinc, thiamine, riboflavin, niacin, vitamin B 6 , vitamin B 12 and vitamin C; and a higher (p < 0.05) proportion were above AI for potassium, sodium, and vitamin K. However, a higher (p < 0.05) proportion of consumers compared to non-consumers were below the EAR for calcium, vitamin A, and vitamin D; and a lower (p < 0.05) proportion were above AI for dietary fiber (Table 6).
Compared to non-consumers, a lower (p < 0.05) proportion of adolescent consumers of potatoes in Case 3 (baked, boiled, mashed and mixtures, fried, chips) also were below the EAR for carbohydrate, protein, copper, iron, magnesium, phosphorus, zinc, thiamine, niacin, vitamin B 6 , vitamin B 12 and vitamin C, and a higher (p < 0.05) proportion were above AI for potassium, sodium, and vitamin K. However, a higher (p < 0.05) proportion of consumers compared to non-consumers were below the EAR for calcium, vitamin A, and vitamin D ( Table 6).

Discussion
In the current cross-sectional analysis of data from nine cycles of NHANES (NHANES 2001-2018) using a nationally representative sample of over 16,000 US adolescents, potato consumption was associated with better diet quality, higher intake, and adequacy of several nutrients, including shortfall nutrients.
Potatoes are part of the starchy vegetables subgroup and are present in many different forms representing various cooking/processing methods in the diet. Potato chips, boiled potatoes, fries (French fries and home fries), and baked potatoes represent 28.7%, 23.5%, 22.3%, 10.8%, respectively, of starchy vegetables intake among children age 4-18 years [36]. Limited data suggest that different forms of potatoes may have different nutritional and/or health attributes/outcomes [37][38][39][40]. For example, baked potatoes have a low glycemic index due to their high amount of resistant starch-a dietary fiber [41,42]. Potato chips are often considered as junk food, and fried potatoes may contain acrylamide, which is a potential carcinogen [43]. In the present analysis, we used three different definitions to define potato consumers-Case 1: those consuming baked, boiled, mashed, and mixtures; Case 2: those consuming baked, boiled, mashed and mixtures, fried; and Case 3: those consuming baked, boiled, mashed and mixtures, fried, chips and compared them to their respective non-consumers to differentiate specific attributes of different potato forms. Interestingly, irrespective of the potato consumer definition used, the consumers always had better diet quality, nutrient intake, and adequacy.
Potato consumers (by all three definitions) always had better diet quality, albeit in the 1.6-4.7% range) as assessed using HEI 2015. HEI is a validated measure of diet quality and is indicative of compliance/adherence of a person's diet to the eating pattern recommended by the Dietary Guidelines for Americans [29,44] and is commonly used to evaluate diets and dietary interventions [45][46][47], food environments [45], to assess changes in the diet quality over time [46,47], and to validate other nutrition research tools and indexes [48]. It has also been used to understand relationships between nutrients/foods/dietary patterns and health-related outcomes in scientific studies [49][50][51][52]. With this metric, a higher score is indicative of compliance/adherence to dietary recommendations using 13 components (nine for adequacy and four for moderation), each of which relates to key recommendations of the 2015-2020 Dietary guidelines for Americans [29]. In the present analysis, potato consumers of baked, boiled, mashed and mixtures (Case 1) compared to non-consumers had a 2.1-point higher HEI 2015 total score and the score gradually increased with increasing intake quartiles. HEI 2015 total scores were also higher for potato consumers of baked, boiled, mashed and mixtures, fried (Case 2) and for consumers of baked, boiled, mashed and mixtures, fried, chips (Case 3) than their respective non-consumers; however, the difference was smaller (+0.9 and +0.7, respectively). Additionally, compared to Case 1 consumers, Case 2 and Case 3 consumers had more HEI 2015 subcomponent scores lower than non-consumers (2 subcomponents for Case 1 vs. 6 subcomponents for Case 2 and 7 subcomponents for Case 3) suggesting that diet quality for consumers was influences by other foods commonly consumed with fried potatoes and potato chips. However, in all cases, the total HEI score remained below 50 points (out of a possible 100) and indicates the need for broad improvement on many dietary quality components.
Potato consumers had significantly higher intakes of dietary fiber, copper, magnesium, phosphorus, potassium, selenium, zinc, niacin, vitamin B6, vitamin C, vitamin E, vitamin K and total choline, and their intake increased with increasing potato intake quartiles. Additionally, potato consumers also had higher nutrient adequacy for copper, magnesium, phosphorus, potassium, zinc, thiamine, niacin, vitamin B 6 , vitamin B 12 , vitamin C, and vitamin K than non-consumers. Many of these nutrients are currently under-consumed, and especially dietary fiber and potassium are identified as "Dietary Components of Public Health Concern for Underconsumption" due to their inadequate intake [44]. Additionally, Dietary Guidelines for Americans, 2020-2025 [44] indicated that low intake of nutrient dense foods within food groups has led to low intakes of phosphorus, magnesium, and choline. Higher intakes of micronutrients among potato consumers, as observed in the present analysis, were also reported in earlier cross-sectional studies from both US and international cohorts [19,20,26,53]. Since potatoes are a good source of several of the above nutrients [2][3][4], potato consumption is naturally expected to lead to more nutrient dense diets and greater adequacy for nutrients.
Although potato consumers had higher dietary fiber intake than non-consumers, the difference was about 1 g or less and % above AI remained very low (less than 1% population above AI). On the other hand, potato consumption was associated with a 300-400 mg/d increase in potassium and the % of the population above the AI increased 17-25 percentage points. Similarly, potato consumption was also associated with significant and substantial increase in intake and population adequacy for copper, magnesium, phosphorus, vitamin B 6 , vitamin C, and vitamin K. However, potato consumers also had 130-230 more calories (kcal) than non-consumers. Substantially higher intake and higher adequacy of these nutrients among potato consumers indicates that regular inclusion of potatoes in the diet might be an effective strategy to improve the nutritional status of these nutrients.
However, potato consumption was also associated with increased sodium intake. While sodium is an essential nutrient, average intakes of sodium is high across US population compared to the Chronic Disease Risk Reduction Levels [44]. However, starchy vegetables, including potatoes, are a relatively minor source of sodium contributing to about 4% intake, compared to sandwiches or grain-based mixed dishes contributing to 21% and 8% intakes, respectively [44].
The strengths of this study include the use of a large nationally representative sample of adolescents achieved by combining several sets of NHANES data releases and the use of numerous covariates to adjust data to remove potential confounding; however, even with these covariates, some residual confounding may still exist. A major limitation of this study is the use of a cross-sectional study design, which cannot be used to determine cause and effect. The self-reported dietary recalls for dietary intake data relying on memory are potentially subject to reporting bias.

Conclusions
The results show that potato consumption was associated with better diet quality, higher nutrient intake, and improved nutrient adequacy among adolescents. Potatoes are nutrient rich foods and are a major contributor of starchy vegetables. Current intake of vegetables, including starchy vegetables, are less than the recommended levels [39]. Encouraging potato consumption, preferably without a lot of extra fat/sodium, may be an effective strategy for improving intakes and adequacy of vegetables and certain nutrients and achieving a healthier dietary pattern.

Author Contributions:
The authors' responsibilities were as follows-S.A.: project conception, designed research, developed overall research plan, interpretation of the data, prepared the first draft of the manuscript, and revised the manuscript; V.L.F.III: project conception, designed research, developed overall research plan, NHANES database analysis and statistical analysis, interpretation of the data, and revised the manuscript. All authors have read and agreed to the published version of the manuscript.