According to the most recently available data, the age-adjusted prevalence of overweight and obesity in adults was 68% [1]. Consumption of excess energy without a concomitant increase in physical activity is a major reason why there are extremely high obesity rates in the US [2]. Food availability data from 1970 to 2005 suggests, despite an overabundance of healthful foods, such as whole grains, fruit, vegetables, low-fat dairy, and lean meats, too few of these nutrient-dense foods, and too many energy-dense, nutrient-poor foods/beverages were consumed in the US [3]. This finding has been confirmed using nationally representative data from the National Health and Nutrition Examination Survey (NHANES) [4,5,6,7,8].

Consumption of energy-dense, nutrient-poor foods/beverages can increase intake of added sugars [9], fats [9], sodium [10], and alcohol [11] and decrease diet quality [5,12]. Consumption of these foods, in turn, may be associated with increased risk of chronic diseases, including coronary heart disease (CHD) [13], type 2 diabetes [14], and metabolic syndrome [15]. Further, due to low intake of nutrient-dense foods, many adults do not meet the recommendations for certain micronutrients [16]. The 2010 Dietary Guidelines for Americans (DGA) specifically identified dietary fiber, calcium, vitamin D, and potassium as “nutrients of concern” which are underconsumed by the population and present a substantial public health concern [17]. Consumption of dietary fiber has been associated with positive health outcomes, including optimizing gut health [18], reducing risk of cardiovascular mortality [19,20], and modulating blood glucose [21]. Dietary fiber intake has also been linked to lower body weight and protection against weight gain [22,23,24]. Inadequate intake of nutrients, such as calcium and vitamin D, in combination with a sedentary lifestyle can increase the risk of developing osteoporosis [25,26]. Inadequate potassium intake, especially when coupled with high sodium intake, can adversely affect blood pressure [10], and is associated with increased osteoporosis [27], and cardiovascular disease risk [10,28]. The 2010 DGA also identified vitamins A, C, E, and K; choline; magnesium; and folate (in select populations) as shortfall nutrients [17]. In addition to highlighting nutrients of concern and shortfall nutrients, the 2010 DGA also reaffirmed food group intake recommendations, and acknowledged the overconsumption of energy and other dietary components, especially sodium [17]. The recommendation to reduce sodium intake is consistent with a recent Institute of Medicine (IOM) report [29].

Understanding current food selections among the US population is critical for designing strategies to help Americans meet nutrient recommendations within energy needs. The most recent publications that provided a detailed list of the food sources of energy and nutrients among US adults report data from the Continuing Survey of Food Intake by Individuals (CSFII) conducted in 1989 to 1991 [30] and 1994 to 1996 [31]. The purpose of this study was to update previous research by using nationally representative data from the NHANES recently conducted in 2003 to 2006 to examine food sources of energy and 26 nutrients consumed by US adults.

Food sources of energy and 26 nutrients are shown in Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10, Table 11, which appear in this article, and Supplemental Tables S1–S17 which are available online.

Subar et al. [30] and Cotton et al. [31] ranked food sources of energy and nutrients among adults using CSFII data from 1989 to 1991 and 1994 to 1996, respectively. These studies were conducted with data that is now at least 15 years old. Since then, influences in the diets of adults have included food product reformulations in response to consumers’ health concerns [42], food availability and cost [43,44], changing food and beverage preferences [45,46]; increased consumption of meals away from home [47]; and trade liberalization, which has increased the number and types of foods available throughout the year and throughout wider geographic regions [48]. Thus, it was important to re-assess the diets of adults using recent nationally representative data. While both previous studies looked at all adult age groups combined, the five highest ranked sources of energy (for 1994–1996 data) were: yeast bread (8.7%), beef (6.2%), cakes/cookies/quick breads/doughnuts (5.7%), soft drinks/soda (5.2%), and milk (4.2%), which provided approximately 30% of total energy. Compared to the current work, yeast bread (8.7%) and milk (3.8%) were a lower percentage of energy while cakes/cookies/quick breads/doughnuts (7.2%) were now a higher percentage. In our study alcoholic beverages (4.7%) made it into the top five energy sources (was eighth at 3.3% in previous work [31]). Overall, both the current and previous studies showed energy-dense, nutrient-poor foods (e.g., cakes/cookies/quick breads/doughnuts, soft drinks/soda, etc.) as major contributors to dietary energy intake, making it difficult for individuals to achieve nutrient requirements without exceeding energy limits.

The five highest ranked food sources of energy consumed by adults 19–50 y were considerably different from those ranked highest among adults 51+ y. Among adults 19–50 y, the five highest ranked sources of energy were yeast breads/rolls, cake/cookies/quick bread/pastry/pie, soft drinks/soda, beef, and alcoholic beverages. Among those aged 51+ y, soft drinks/soda and alcoholic beverages ranked below the five highest ranked foods; candy/sugars/sugary food and milk were among the five highest ranked sources of energy.

Yeast breads/rolls, especially if whole grain; beef, if lean; and milk were the most nutrient-dense food sources of energy; together, they provided protein, MUFA, PUFA, iron, zinc, calcium, vitamin D, and potassium (some data not shown). The other energy sources provided total sugars, fats, and few micronutrients.

Consistent with these findings, the 2010 DGA indicated the highest ranking food energy source in the US adult population was grain-based desserts (cakes/cookies/doughnuts/pies/crisps/cobblers/granola bars), which contributed 582 kJ/day; and the highest ranking beverage energy source was soda, which contributed 477 kJ/day [17]. The total of 1059 kJ provides 95% of the discretionary calories from these two food groups alone for an individual with an 8368 kJ diet [49]. Meeting nutrient intake recommendations while staying within energy needs has proven to be challenging for many Americans [5], and as a result, individuals may be overweight or obese while being undernourished. To help Americans improve dietary habits and meet nutrient needs through foods, understanding food sources of nutrients is critical.

In contrast to the highest ranked food sources of energy, the highest ranked food sources of protein were more nutrient-dense foods: poultry, beef, cheese, milk, and yeast bread/rolls. These foods contributed approximately 50% of protein intake; although the rank order was different, the same five sources were reported by Subar et al. [30] and Cotton et al. [31]. Compared with the earlier studies where beef was the first highest ranked food source of protein; in this study, poultry was the first highest ranked food source of protein among all adults and those 19–50 y. Changes in ranking of beef, poultry, and cheese are consistent with temporal trends in intake [3,50]. These foods were also good to excellent sources of B vitamins, vitamin D, calcium, potassium, iron, or zinc; and, when consumed in their lowest fat form, they are consistent with foods recommended by MyPlate [49].

The 2010 DGA recognized low intakes of dietary fiber, calcium, vitamin D, and potassium were of public health concern [25]. Ideally, foods containing a constellation of these micronutrients can be selected without unduly increasing energy intake. If the food groups consumed most frequently are not those most nutrient dense, reformed public policies and better nutrition education programs are needed.

Dietary fiber intake by adults is slightly less than half the recommended amount [16]. Yeast breads/rolls, legumes, and fruit were the three highest ranked food sources of fiber among adults 19–50 y. Among adults 51 y and older, ready-to-eat cereal (RTEC) ranked third and legumes ranked fourth. All of these foods are nutrient dense, and contributed to dietary intakes of B vitamins, vitamin C, folate, or potassium, in addition to fiber. Consumption of legumes [51] and fruit [52] is associated with improved diet quality. Although these foods are nutrient dense and improve diet quality, most Americans do not consume the recommended amount of or legumes [51] or fruit [5,6]. The highest ranked food sources of dietary fiber shown previously [30,31] were yeast breads, dried beans/lentils, potatoes (white), RTEC, and tomatoes. A comparison of the two studies [30,31] with the present one suggests a shift among foods that contribute to fiber intake occurred over time. In this study, vegetables were split into many different categories, however, when the vegetables that were the highest ranked sources of dietary fiber, i.e., potatoes (white) (6.4%), other vegetables (5.5%), tomatoes/tomato/vegetable juice (4.6%), were combined with categories contributing at least 1% of fiber (e.g., broccoli, spinach, greens; lettuce; carrots, sweet potatoes, winter squash; string beans), vegetables would be the highest ranked source, providing at least 20% of fiber intake.

The nutrient contribution of milk and dairy products play an important role in helping Americans meet recommendations for short-fall nutrients [53] and nutrients of public health concern [25]. In our study, milk was an important source of calcium, potassium, vitamin D, and many other nutrients, including vitamin A, thiamin, riboflavin, vitamins B6 and B12, phosphorus, magnesium, and zinc (some data not shown). Subar et al. [30] showed that in 1989–1991, milk provided 34.2% of calcium intake, and Cotton et al. [31] showed that in 1994–1996, 28.3% of calcium was supplied by milk. In our study milk provided only 22.5% of calcium intake and there were a larger number of smaller contributors to calcium intake than seen in previous of studies, primarily due to fortification of various products (e.g., fruit juice, RTEC).

This study had several limitations. Food grouping has a major influence on the ranked order of food groups; thus, caution is advised when comparing these data to previous reports if there were differences in the level of aggregation or disaggregation procedures used to include ingredients in food groups. Study outcomes are based on self-reported data which may underestimate energy intake [54]. A single day’s intake may not necessarily be representative of usual intake; however, the mean of the intake distribution drawn from a large, representative sample of a group is not affected by day-to-day variation [55]. Since the contribution of food sources in this study was based on mean intake data, the use of a single 24-h recall was appropriate [56]. Since the food grouping in the DSN database does not include ingredients of manufactured foods, disaggregated foods represent mixtures that are prepared from recipes. Salt was separated from other ingredients of disaggregated foods. The USDA reduces the sodium content of mixtures if the respondent never, rarely, or occasionally uses salt in cooking, and the food was prepared at home; thus, much of the salt came from disaggregated foods prepared by restaurants, schools, and other establishments. The updated vitamin D database was appropriate for use with the NHANES 2005–2006 dietary intake data; however, since vitamin D intake from foods consumed in 2003–2004 was determined using the updated food composition data, the 2003–2004 intake data may not have been representative of that time period. Any variation in food composition data affects the reliability of dietary intake estimation. Fortified foods provide the major sources of vitamin D in the diet; vitamin D fortification is regulated by a food additive rule [57]. A petition to add vitamin D to calcium-supplemented juices and fruit drinks was approved by the Food and Drug Administration and implemented in 2004 [58]; however, this change was effective only in the NHANES 2005–2006, since the new calcium- and vitamin D-supplemented foods were not reported in the NHANES 2003–2004.

In conclusion, this study showed that adults consumed a large proportion of total energy from energy-dense, low-nutrient food groups, and identified principal sources of energy that were also major sources of nutrients. While some food and beverage choices such as milk, fruit juices, lean beef and poultry are nutrient-dense and food sources of many nutrients, other energy sources such as cakes/cookies/pies and soda/soft drinks are energy-dense and nutrient-poor choices. All health professionals, policy makers, and the nutrition community need to be aware of the types of foods Americans are consuming since this knowledge can help health professionals design effective strategies to improve diet quality, and reduce energy consumption by US adults.