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1 From the Department of Family, Nutrition, and Exercise Sciences, Queens College of the City University of New York.
2 Presented in part at the 1999 Experimental Biology meeting, Washington, DC, April 18–22. 3 Supported by grant award NYR-9700611 from the US Department of Agriculture, National Research Initiative Competitive Grants Program, and a Professional Staff Congress–City University of New York research award. 4 Reprints not available.Address correspondence to AK Kant, Department of Family, Nutrition, and Exercise Sciences, Queens College of the City University of New York, Flushing, NY 11367. E-mail: ahkqc{at}cunyvm.cuny.edu.
ABSTRACT
Background: Current dietary guidance recommends limiting the intake of energy-dense, nutrient-poor (EDNP) foods, but little is known about recent consumption patterns of these foods.
Objective: The contribution of EDNP foods to the American diet and the associated nutritional and health implications were examined.
Design: Data from the third National Health and Nutrition Examination Survey (n = 15611; age 20 y) were used. EDNP categories included visible fats, nutritive sweeteners and sweetened beverages, desserts, and snacks. The potential independent associations of EDNP food intake with intakes of energy, macronutrients, micronutrients, and serum vitamin, lipid, and carotenoid profiles were examined with linear and logistic regression procedures.
Results: EDNP foods supplied 27% of energy intake; alcohol provided an additional 4%. The relative odds of consuming foods from all 5 food groups and of meeting the recommended dietary allowance or daily reference intake for protein and several micronutrients decreased with increasing EDNP food intake (P < 0.0001). Energy intake and percentage of energy from fat were positively related to EDNP intake. Serum concentrations of vitamins A, E, C, and B-12; folate; several carotenoids; and HDL cholesterol were inversely related (P 0.0005) whereas serum homocysteine concentration was positively related (P = 0.02) to EDNP food intake.
Conclusions: The results suggest that EDNP foods were consumed at the expense of nutrient-dense foods, resulting in 1) increased risk of high energy intake, 2) marginal micronutrient intake, 3) poor compliance with nutrient- and food group–related dietary guidance, and 4) low serum concentrations of vitamins and carotenoids.
Key Words: NHANES III • third National Health and Nutrition Examination Survey • dietary patterns • serum vitamins • serum carotenoids • homocysteine • dietary guidance • nutritional status • energy-dense foods • nutrient-poor foods • high-calorie foods • junk foods
INTRODUCTION
Prevailing dietary guidance for reducing the risk of chronic diseases promotes consumption of fruit, vegetables, and whole grains while limiting energy and fat intakes (1, 2). Therefore, all the dietary guidance communicated to the US public has advocated reduced consumption of energy-dense, nutrient-poor (EDNP) foods containing fats, oils, and sugars; these foods constitute the tip of the food guide pyramid (3). Data from the second National Health and Nutrition Examination Survey (NHANES II) showed that EDNP foods rich in fat, oil, and sugar provided one-third of the total daily energy intake for adult Americans (4). In the period since NHANES II, public awareness of diet and health issues has increased and an enormous variety of fat- and sugar-modified food products have appeared in the American marketplace, resulting in speculation that the intake of EDNP foods may have declined. However, no recent information is available on consumption patterns for EDNP foods. Some studies examined the contributions of added sugar or carbonated beverages to the American diet and found that the trends were the reverse of the expected decline (5, 6). Furthermore, energy intakes in recent national surveys were higher than previously reported (7) and the prevalences of obesity and overweight in the US population have increased (8). Undoubtedly, changing patterns of energy expenditure are important contributors to the trend of increasing adiposity. Highly palatable EDNP foods may also play a role by promoting higher energy intakes. Therefore, it is important to understand the role of EDNP foods in the American diet and the associated health and nutritional implications.
The purpose of this study was to examine, in a nationally representative sample of the adult American population, the contribution of EDNP foods to daily energy and macronutrient intakes and to examine the relations between intake of EDNP foods and intakes of the macronutrients and micronutrients, serum vitamin and carotenoid concentrations, and the lipid profile.
SUBJECTS AND METHODS
In this study, data from the third National Health and Nutrition Examination Survey (NHANES III), 1988–1994, were used. NHANES III is a multistage, stratified probability sample of the noninstitutionalized civilian US population aged 2 mo (9). The survey was conducted in 2 phases of equal length and included administration of a questionnaire at home and a full medical examination with a battery of tests in a special mobile examination center (MEC) (9). Demographic and medical history information was obtained during the home interview. The MEC examination included a physical and dental examination, dietary interview, body measurements, and collection of blood and urine samples. Body weight, height, and circumference at various sites were measured by using standardized procedures in the MEC (9).
Dietary assessment method
A 24-h dietary recall was obtained by a trained dietary interviewer with use of an automated, microcomputer-based interview and coding system (9). The type and amount of each food consumed was recalled with the help of recall aids such as abstract food models, charts, measuring cups, and rulers. Probes were used to prompt the recall of commonly forgotten items such as condiments, accompaniments, fast foods, and alcoholic beverages.
Analytic sample
All adults aged 20 y were eligible for inclusion (n = 17030) in this study. From this eligible sample, those without a complete and reliable dietary recall (n = 1051) were excluded, as were women who were pregnant (n = 282), nursing (n = 91), and both pregnant and nursing (n = 5). The final analytic sample consisted of 15611 respondents (7470 men and 8141 women).
Assessment of intake of EDNP foods
To determine the intake of EDNP foods, it was necessary to identify foods that belong in this category from those reported during the 24-h dietary recalls. As a first step, the 4265 foods reported by survey respondents were classified as belonging to 1 of the 5 major food groups (dairy, fruit, grains, meat and beans, and vegetables) or the EDNP foods group by using previously published methods (10, 11). Briefly, the assignment of foods into the various groups was dependent on their nutrient content and uses in the diet. The dairy group included milk, yogurt, cheese, and buttermilk but excluded butter, cream cheese, and dairy desserts. The fruit group included all fresh, frozen, dried, and canned fruits and fruit juices but excluded fruit drinks. The grains group included all breads, cereals, pastas, and rice but excluded pastries. The meat and beans group included meat, poultry, fish, eggs, and meat alternatives such as dried beans, nuts, and seeds. The vegetable group included all raw or cooked fresh, frozen, and canned vegetables and juices. Mixed dishes containing foods from several groups were assigned to all the relevant groups. Foods excluded from these major food groups were assigned to the EDNP foods group. The EDNP foods were further subcategorized into 5 groups as follows: 1) visible fat (eg, butter, margarine, oils, dressings, and gravies), 2) sweeteners (eg, sugar, syrup, candy, and carbonated and noncarbonated sweetened drinks), 3) desserts (eg, baked desserts such as cookies, cakes, pies, and pastries and dairy desserts such as ice cream, puddings, and cheesecake), 4) salty snacks (eg, potato, corn, and tortilla chips), and 5) miscellaneous (eg, coffee, tea, broth, and spices).
The NHANES III nutrient database for individual foods, which is derived from the US Department of Agriculture's Survey Nutrient Database (12), was used for determining the energy and nutrient contents of all the foods. The nutrients examined included vitamins A, E, B-6, B-12, and C; folate; iron; and calcium. The intake of each nutrient was compared with the respective age- and sex-specific standard available. The standards used were the 1989 recommended dietary allowances (RDAs) for protein, iron, and vitamins A, E, and C and the dietary reference intakes (DRIs) for folate, vitamins B-6 and B-12, and calcium (13–15).
Data on serum concentrations of vitamins A, E, C, and B-12; folate; homocysteine; carotenoids; and lipids were obtained from the National Center for Health Statistics public release CD-ROM (16, 17). The methods used for measurement of these serum analytes and their associated errors were described previously (16, 17).
Statistical analyses
The mean percentages of daily energy from the EDNP food groups (separately and combined) adjusted for age, sex, and race were calculated. The percentage of energy from EDNP foods was categorized into tertiles on the basis of the distribution of this variable in the analytic sample. Mean intakes of energy, macronutrients, and micronutrients and concentrations of serum analytes by tertiles of percentage of energy from EDNP foods were obtained after adjusting for age, sex, and race. The method used for obtaining age-, sex-, and race-adjusted estimates and standard errors from the survey data is based on Taylor linearization methods and was described previously (18). All statistical analyses were performed by using SAS, version 6 (19), and software specially designed for the analysis of survey data, SUDAAN, version 7.0 (20). This software generates variance estimates that are corrected for the multistage stratified probability design of complex surveys. Sample weights provided by the National Center for Health Statistics to correct for differential probabilities of selection, noncoverage, and nonresponse were used in all analyses to obtain point estimates (12).
The independent associations of EDNP food intake with nutrient intakes and serum concentrations of vitamins, carotenoids, and lipids were examined by using regression procedures to adjust for multiple covariates. Linear regression procedures were used when the outcome variables were continuous (eg, dietary nutrient intake or serum nutrient concentration). For categorical outcomes, such as whether or not the standard for a nutrient intake was met, logistic regression procedures were used.
Correlates of EDNP food consumption
We used sex-specific linear regression models for identifying significant correlates of intake of EDNP foods; the outcome variable was percentage of energy from EDNP foods. The initial models included several sociodemographic, lifestyle, weight-related, and food consumption–related predictors. The sociodemographic predictors were age, ethnicity, education, income, and participation in Food Stamp or Women, Infants and Children (WIC) programs. The lifestyle variables were smoking status, amount of physical activity, supplement use, and self-perceived health status. The weight-related variables included body mass index (BMI; in kg/m2), waist circumference, and response to several weight-related questions. The food consumption–related variables included total weight (g) of foods and beverages reported, total weight (g) of foods and beverages from the 5 major food groups, alcohol intake, and a measure of underreporting of food intake (ratio of reported energy intake to estimated energy expenditure for resting needs) (21). From these initial models, variables that were not significant predictors were excluded one at a time to arrive at the final models.
RESULTS
Percentage of daily energy and macronutrients from EDNP foods
The contributions to daily energy of all EDNP foods, EDNP food subgroups, and alcohol by sex, ethnicity, and age categories are shown in Table 1. Approximately 27% of total daily energy was contributed by all EDNP foods, with alcohol contributing an additional 4% of energy. Of the EDNP food subgroups examined, desserts and sweeteners contributed nearly 20% of total daily energy intake. Women, non-Hispanic whites, and the age groups 20–34 y and 35–50 y consumed a higher percentage of daily energy from EDNP foods than did men, other ethnicity groups, and other age groups, respectively. In Table 2, the energy and macronutrient contributions of EDNP foods for each tertile of percentage of daily energy from EDNP foods are shown. In the highest third of EDNP food consumption, these foods provided >50% of total daily carbohydrate intake and >45% of total daily fat intake.
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TABLE 1.. Percentage of total daily energy intake from all energy-dense, nutrient-poor (EDNP) foods, subgroups of EDNP foods, and alcohol in the US adult population by sex, ethnicity, and age: third National Health and Nutrition Examination Survey, 1988–19941
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TABLE 2.. Percentage of daily energy and macronutrient intakes contributed by energy-dense, nutrient-poor (EDNP) foods by tertiles of percentage of energy from EDNP foods: third National Health and Nutrition Examination Survey, 1988–1994
Dietary macronutrient and micronutrient profiles associated with EDNP food intake
In Table 3, the daily energy and macronutrient intakes are shown by tertiles of percentage of energy from EDNP foods. With increasing consumption of EDNP foods, mean energy intake and percentage of energy from carbohydrate and fat increased, whereas percentage of energy from protein and intakes of alcohol and fiber decreased (P < 0.0001).
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TABLE 3.. Total daily energy, macronutrient, fiber, alcohol, and food group intakes by tertile of percentage of energy from energy-dense, nutrient-poor (EDNP) foods: third National Health and Nutrition Examination Survey, 1988–19941
In Table 4, the percentages of the population that met the recommendation for fat intake and the RDA or DRI for the micronutrients on the survey day are shown by tertiles of percentage of energy intake from EDNP foods. The percentage that reported eating foods from all 5 food groups is also shown by tertiles of EDNP food intake. The data are presented separately for men and women. The odds of meeting the respective nutrient standard (except for vitamin E) or consuming foods from all 5 food groups decreased with increasing intake of EDNP foods.
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TABLE 4.. Percentage of the adult population (adjusted for age and ethnicity) that met the standard for intake of selected nutrients, and the relative odds (odds ratio and 95% CI) of consuming the standard for nutrient intake by tertiles of percentage of energy from energy-dense, nutrient-poor (EDNP) foods, third National Health and Nutrition Examination Survey, 1988–19941
We also examined the relation of EDNP food intake to the estimated absolute amount of nutrient intake, nutrient density (nutrient intake/4184 kJ), and percentage of the standard for the nutrient. In linear regression analyses, each nutrient was the outcome variable and the percentage of energy from EDNP foods, age, sex, race, education, and total energy intake were the predictor variables. For vitamins A, B-6, B-12, and C; folate; calcium; and iron, there was an inverse relation between percentage of energy from EDNP foods and the absolute amount, nutrient density, or percentage of the standard for each nutrient (P < 0.0001). The relation between percentage of energy from EDNP foods and total vitamin E intake (mg) or percentage of the RDA was not significant, whereas the relation with vitamin E density (mg vitamin E/4184 kJ) was inverse and significant (P < 0.005) (data not shown but available from the author.)
Serum vitamin, carotenoid, and lipid concentrations associated with EDNP food intake
In Table 5, the mean (±SEM) serum concentrations (adjusted for age, sex, and race) of vitamins A, E, C, and B-12; folate; homocysteine; ß-carotene; -carotene; ß-cryptoxanthin; lutein and zeaxanthin; lycopene; total cholesterol; LDL cholesterol; and HDL cholesterol are shown by tertiles of percentage of energy from EDNP foods. An independent inverse association between percentage of energy from EDNP foods and serum concentration of each of the vitamins and carotenoids was found after adjustment for age, sex, race, duration of fasting before blood sampling, dietary intake of the respective nutrient, and supplement use in the past month. The percentage of energy from EDNP foods was also an independent positive predictor of serum homocysteine concentration after adjustment for multiple covariates. Mean serum total and LDL-cholesterol concentrations were not associated with EDNP food intake. However, mean serum HDL-cholesterol concentration was inversely related to EDNP food consumption after adjustment for multiple covariates, including alcohol intake.
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TABLE 5.. Serum concentrations of selected vitamins, carotenoids, and lipids by tertiles of percentage of energy from energy-dense, nutrient-poor (EDNP) foods: third National Health and Nutrition Examination Survey, 1988–1994
Characteristics of respondents in different tertiles of EDNP food intake
In Table 6, the characteristics of respondents in the different tertiles of percentage of energy from EDNP foods are shown. The third tertile (highest EDNP food intake) had more non-Hispanic whites, persons <65 y of age, individuals with 12 y of education, and persons with a higher income. No significant differences were seen in the level of physical activity or use of vitamin and mineral supplements in the different tertiles. The relative odds of having a high BMI (>24.9) or a high waist circumference (>88 cm for women; >102 cm for men) were not different in the 3 tertiles (data on odds ratios not shown).
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TABLE 6.. Characteristics of subjects in tertiles of percentage of daily energy from energy-dense, nutrient-poor (EDNP) foods: third National Health and Nutrition Examination Survey, 1988–1994
Correlates of EDNP food consumption
The initial sex-specific regression models that included all the sociodemographic, lifestyle, weight-related, and food consumption–related predictors listed in the Methods section yielded an R2 of 0.35 in men and an R2 of 0.38 in women (data not shown). In men, age, race, education, waist circumference, intake (g) of food from the 5 major food groups, alcohol intake (g), and the ratio of reported energy intake to estimated energy expenditure were significant correlates (P < 0.05) of EDNP food intake with a model R2 of 0.32. In women, race, education, intake (g) of food from the 5 major food groups, alcohol intake (g), the ratio of reported energy intake to estimated energy expenditure, and considering oneself overweight were significant correlates (P < 0.05) of EDNP food intake with a model R2 of 0.36. The strongest inverse predictor of EDNP food consumption in both men and women was the total intake (g) of foods from the 5 major food groups. None of the other sociodemographic, lifestyle, or food consumption–related variables appreciably altered the amount of variability in the percentage of daily energy from EDNP foods that could be explained in men or women (data not shown; available from the author).
DISCUSSION
The results show that energy-dense foods with relatively modest nutrient contents provided 27% and alcohol provided an additional 4% of the total daily energy in the American diet, with one-third of the population consuming an average of 45% of energy from EDNP foods. These estimates are comparable with estimates reported for NHANES II (1976–1980), in which 30% of daily energy came from a combination of EDNP foods and alcohol (4). However, because reported energy intakes were higher in NHANES III than in NHANES II (7), the NHANES III estimates may represent an increase in absolute intake of EDNP foods. Despite the increasing awareness of links between diet and health in the interim since NHANES II and the introduction of foods with modified fat, sugar, and energy content in the American marketplace, these results suggest that EDNP foods continue to play an important role in the American diet.
The estimates of consumption of EDNP foods reported in this study were based on the approach in which whole foods are examined for their energy and nutrient contributions to the diet. Studies that use different methods for identifying EDNP foods (or commodities that are used to prepare EDNP foods) are likely to yield different estimates. For instance, the US Department of Agriculture estimates the consumption of added fat and sugar by disaggregating recipes and assigning the resulting commodities or ingredients to the various food groups (22). This approach generally yields higher estimates of the numbers of servings consumed from the food groups. Also, it is not practical for either assessing the foods actually consumed or educating the public to encourage dietary change. For example, Nestle (23) recently called for translation of the fats, oils, and sweets category (the tip of the food guide pyramid, where EDNP foods belong) into its major food sources.
The implications of high EDNP food consumption are 4-fold. The first implication is that greater EDNP food intake increases the risk of marginal nutrient intakes. This relation is supported by the reported dietary intakes and serum vitamin profiles in the present study. The odds of consuming less than the standard of intake (RDA or DRI) of most micronutrients and the odds of having low serum vitamin concentrations rose with increasing EDNP food intake. The finding of lower nutrient density (nutrient intake/4184 kJ) for most of the studied nutrients with increasing EDNP food intake was expected because of dilution of the nutrients consumed by the energy-dense foods. However, as is evident from the data in Tables 3 and 4, respondents who consumed more EDNP foods were less likely to report eating foods from all 5 major food groups and had a higher likelihood of consuming smaller quantities of foods from all 5 food groups. These results suggest both qualitative and quantitative differences in the food-selection practices of high- and low-EDNP-food consumers and help to explain the inverse relations of EDNP food intake with both the absolute amounts of nutrients consumed and the percentages of the nutrient standards consumed. Collectively, these results support the theory that EDNP foods were consumed at the expense of nutrient-dense foods.
These findings are similar to those reported for NHANES II (4). Other available studies that examined selected foods or commodities in the EDNP group (eg, soft drinks and added sugars) generally agree with the results of the present study (6, 24). However, Naismith et al (25) studied 11- to 12-y-olds and did not report increased risk of micronutrient inadequacy with increasing sugar intake. The authors concluded that high sugar users may be children who eat more overall without adverse nutritional consequences.
The second implication of EDNP food intake is its positive association with energy intake. The increasing adiposity of the US population has been recognized as a public health issue (8), and it is probable that highly palatable EDNP foods play a role in promoting positive energy balance. The third implication of EDNP food intake is that higher consumption of EDNP foods was linked to a decreased likelihood of compliance with current dietary guidance for risk reduction. EDNP food consumption was inversely related to the odds of consuming 30% of energy from fat, obtaining <10% of energy from saturated fat, or eating foods from all 5 major food groups. Although the percentage of energy from carbohydrates increased with increasing EDNP food intake, dietary fiber intake did not; instead, it was inversely related. Therefore, higher carbohydrate intake in association with EDNP food intake most likely reflects the addition of refined sugar and is also inconsistent with dietary recommendations. The results reported here support the position of Emmett and Heaton (26) that added sugar serves as a vehicle for dietary fat. Others, however, have observed an inverse association between intake of added sugar and dietary fat (25, 27). The discrepancy among the findings of these reports and the present study brings into focus the need to examine the diet as a whole rather than focusing on isolated components, commodities, or foods. Finally, data from the present study on serum homocysteine and HDL-cholesterol concentrations, both independent risk factors for cardiovascular disease (1, 28), are suggestive of potentially increased coronary heart disease risk with increasing EDNP food intake.
Underreporting of food intake was recognized as a problem in dietary surveys (21, 29) and Briefel et al (7) found underreporting in NHANES III as well. Although the nature of dietary underreporting is poorly understood, available evidence suggests that EDNP foods are more likely to be underreported than other foods (30). Women and individuals with greater adiposity are more likely to underreport (31, 32). However, the dietary data collection methods used in NHANES III included probes to prompt the recall of many foods that are included in the EDNP group, probably improving the accuracy of the estimates. Nevertheless, given that the estimate of underreporting (ratio of estimated energy intake to predicted energy requirement for basal energy expenditure) was a strong positive predictor of EDNP food intake in the present study, it is apparent that the estimates reported here may be underestimates.
Current dietary guidance involves the philosophy that there are no good or bad foods and therefore, many of the foods classified as EDNP in this study are included in the 5 major food groups of the food guide pyramid. Consumers are encouraged to limit their intake of EDNP foods and to decrease visible fat and sugar intake to compensate for their consumption (3). The results reported here suggest that a large percentage of the US population is not paying such careful attention to food selection. The food industry has flooded the market with fat- and sugar-modified foods that are, however, energy dense, and the manufacturers of these products advertise vigorously to promote their use. For example, in a group of health-oriented popular magazines, fat, oils, and sweets accounted for nearly 30% of all food advertisements, whereas the grain, fruit, and vegetable groups combined amounted to only 6% (33). The suggested strategy by which consumers could make fat, carbohydrate, and energy substitutions to incorporate EDNP foods into a sound eating plan may be far too complex for the average consumer to implement. Also, the high degree of consumer preference for EDNP foods further suggests the need for development of simpler and clearer guidelines about the intake of such foods in conjunction with healthful eating patterns. Research on understanding dietary patterns, particularly the joint study of EDNP food intake and consumption of foods from the major food groups, is also needed.
In conclusion, EDNP foods tend to substitute for, rather than supplement, the more nutrient-dense foods in the American diet. This pattern leads to increased risk of the following: 1) high energy intake, 2) marginal micronutrient intakes, 3) poor compliance with current nutrient- and food group–related dietary guidance, 4) low serum concentrations of vitamins, carotenoids, and HDL cholesterol, and 5) high serum homocysteine concentrations. New strategies are needed for educating consumers about how to moderate their intake of EDNP foods and how to include these foods in the diet sensibly.
ACKNOWLEDGMENTS
I thank Lisa Licitra Kahle for expert programming support. I also thank Daniel F Heitjan of the Columbia University School of Public Health and Barry I Graubard of the National Cancer Institute, National Institutes of Health, for statistical consultation.
REFERENCES