The purpose of this preliminary investigation was to examine self-reported dietary ED in OW, NW, and WLM and to determine if WLM had a self-reported diet lower in ED compared to OW and NW. Additionally, self-reported daily food group intake, specifically in those food groups that may contribute to a diet lower in ED, was examined in the three groups. As hypothesized, WLM self-reported consuming a diet lower in ED (calculated by F + AB and F + CB) than OW and NW, with differences in self-reported ED between all three groups. WLM’s self-reported diet was also lower in ED, calculated as FO, than both NW and OW, with no differences between NW and OW. Importantly, self-reported ED mirrored self-reported energy intake, with both self-reported ED and energy intake lowest in WLM, followed by NW, and then OW, and all methods of calculating self-reported ED were positively related to self-reported energy intake. This finding is consistent with previous observational research that showed a positive relationship between ED and energy intake (Ledikwe et al., 2006a
). Because diets characterized by low ED may reduce ad libitum
energy intake, diets lower in ED may aid with maintaining a lower energy intake necessary to prevent weight regain following weight loss (Rolls, Drewnowski et al., 2005
). Low ED diets may be especially important for maintaining energy balance in individuals who were previously overweight/obese, as compared to individuals who are normal weight but have never been overweight, as they are accustomed to eating a larger amount of food, and consuming low ED foods allows individuals to continue to consume a high weight/volume of food relative to energy content. Importantly, these results also indicated that WLM self-reported consuming the largest gram weight of food and beverages, and this combined with their significantly lower self-reported energy intake does suggest that WLM followed an eating pattern that allowed a greater amount of food to be consumed relative to the energy content consumed.
There are several strategies that can be used to lower the ED of the diet, including consumption of low-fat, high-fiber foods. Dietary fat is the most energy dense macronutrient, and therefore has a greater influence on dietary ED than protein and carbohydrate (Rolls, Drewnowski et al., 2005
). While the contribution of dietary fiber to overall ED of the diet is less than that of fat (Rolls, Drewnowski et al., 2005
), the ED of a given food is affected by its fiber content, as fiber increases the weight of a food with minimal alterations in energy content. Our findings showed that in addition to lower self-reported ED, the self-reported diet of WLM was also characterized by lower dietary fat and higher dietary fiber compared to NW and OW, with daily percent calories from dietary fat ~5 % lower and dietary fiber intake ~7 g/1000 kcal higher in WLM compared to OW. Self-reported dietary fat intake of WLM was also lower and self-reported fiber intake was higher than the national average (Food and Nutrition Board, 2005
), and similar to the fat and fiber intake reported in the NWCR (Phelan et al., 2006
; Shick et al., 1998
), whose members are also successful at long-term weight loss maintenance. Self-reported dietary fat intake of both WLM and NWCR participants was < 30% of total calories and in accordance with national guidelines regarding fat consumption (Department of Health and Human Services, 2005
). Other investigations have also shown that a low-fat diet corresponds to a lower ED (Monsivais & Drewnowski, 2009
; Schroder et al., 2008
; Townsend, Aaron, Monsivais, Keim, & Drewnowski, 2009
), suggesting that decreasing fat intake may be an effective dietary approach for prevention of weight regain through the influence of dietary fat on ED.
One method to both decrease dietary fat and increase dietary fiber intake is to focus on increasing consumption from food groups comprised of foods with these attributes and therefore low in ED, including vegetables, and whole grains. Vegetables also tend to have high water content, which further aids in reducing ED independently of fat and fiber. We found that WLM self-reported consuming significantly more servings of vegetables and whole grains, and also self-reported consuming significantly fewer servings of refined grains compared to OW and NW. Moreover, significant negative correlations were found between self-reported vegetables and whole grains and ED. These findings are consistent with previous studies showing that diets lower in ED are associated with higher intake of vegetables and whole grains (Ledikwe et al., 2006b
; Schroder et al., 2008
) and increased nutritional quality (Adam, Pablo, Matthieu, & Nicole, 2007
; Maillot, Darmon, Vieux, & Drewnowski, 2007
; Schroder et al., 2008
). Further, RTs designed to decrease dietary ED have been successful in implementing the dietary intervention by promoting increased consumption of vegetables, rather than focusing on reducing overall dietary ED (Ello-Martin et al., 2007
; Saquib et al., 2008
). Therefore, emphasis on increased intake of vegetables and whole grains may be a simple, easy way to implement dietary strategy to decrease ED, as it decreases fat and increases fiber and water intake.
Results from this study indicate that a diet low in ED may be helpful for weight management. However, several recent prospective observational studies have shown that lower ED diets are not protective against weight gain over time (Bes-Rastrollo et al., 2008
; Du et al., 2009
; Iqbal, Helge, & Heitmann, 2006
; Savage, Marini, & Birch, 2008
). It is possible that low ED diets are only beneficial for long-term weight management in individuals consciously attempting to control their weight or participating in a weight loss program. That is, a low ED diet may only aid with weight control when energy intake is purposefully restricted. Another possibility is that low ED diets are only useful for weight management within the context of an overall diet high in nutritional quality. In the present study, WLM met or exceeded the recommendations for the number of servings of vegetables, including dark green, yellow and red vegetables, whole grains and, consequently, grams of dietary fiber according to the Dietary Guidelines for Americans 2005
(Department of Health and Human Services, 2005
). These results are in contrast to previous investigations, where individuals consuming the lowest ED diets, yet who were unsuccessful at body weight maintenance over time, did not meet these recommendations. In particular, dietary fiber intake for those consuming low ED diets in these studies ranged from 9.0–12.7 g/1000 kcal (Bes-Rastrollo et al., 2008
; Du et al., 2009
; Savage et al., 2008
), below the recommended minimum of 14 g/1000 kcal, whereas in the present study, WLM consumed 17.1 g/1000 kcal.
A major strength of this study was that self-reported ED was calculated by three different methods, using all foods and beverages other than plain water, all foods and energy containing beverages only, and food only. Due to the lack of a standard method for ED calculation (Ledikwe et al., 2005
), the inclusion of more than one calculation method allows for greater ability to compare ED values between studies using different methods. As expected, we found that ED was lowest with the inclusion of all foods and beverages and highest when all beverages were excluded from the ED calculation. This finding is consistent with previous investigations (Ledikwe et al., 2005
), and reflects the influence of beverages, which generally have a low ED due to their high water content, on overall dietary ED. Mean ED values for food only in the present study of 1.39, 1.60, and 1.83 kcal/g for WLM, NW, and OW, respectively, with a mean value for all three groups of 1.60 kcal/g are also comparable to other observational studies where dietary intake and ED were assessed by the same method and ED tertile values ranged from 1.3–2.1 kcal/g with a mean of 1.7 kcal/g (Savage et al., 2008
). Not all observational studies have yielded consistent results with regard to both absolute ED values and the relationship of beverages to overall ED (Bes-Rastrollo et al., 2008
). Although differences in ED values may be due to differences in the study population characteristics and/or the use of different methods to assess dietary intake, a single standardized method for calculating dietary ED would allow for additional inference when directly comparing studies. As it is proposed that a diet lower in ED may help with weight loss and weight loss maintenance by increasing feelings of satiation (Rolls et al., 2006
), and as beverages are not believed to contribute to increased satiation (Wolf, Bray, & Popkin, 2008
), potentially the calculation of ED using food only may help best understand the relationship between ED and weight loss maintenance.
There are several limitations to this study that should be addressed. First, the three groups in this study were not recruited to participate in the same study, thus there may be differences in the characteristics of these participants that were not measured. However, it is important to note that the participants are generally from the same area (New England), recruited and assessed during the same time, and data were collected from all three groups using identical procedures for the dietary assessment. Also, due to the cross-sectional nature of the study, it was not possible to characterize ED in WLM over time as body weight status changed. This study also relied on self-reported weight data (for WLM and NW). The primarily white, middle-class, and middle-aged sample, as well as the treatment seeking OW group, limits the generalizability of the results to other populations. Moreover, because two of the groups were predominantly female, the influence of gender on ED within the differing weight groups could not be examined. Future research should investigate the influence of these variables on dietary ED and weight loss maintenance.
Additionally, the dietary data to assess energy, nutrient, and food group intake was self-reported. As there are many factors that are believed to influence the accuracy of self-reported dietary data (Maurer et al., 2006
; Wansink & Chandon, 2006
), it might be hypothesized that the OW group may under-report intake more so than the other groups, even though this group did report significantly greater energy intake, and significantly lower weekly energy expenditure in physical activity, which was controlled for in the analyses, than the other groups. One hypothesized variable to influence under-reporting is social desirability (Maurer et al., 2006
). If social desirability was a factor for under-reporting in OW participants, then it might be expected that the OW participants would have presented with the lowest in self-reported energy and energy from fat intake, and highest in self-reported fruits, vegetables, and whole grains, which they did not. However, as overweight/obese individuals tend to under-report more so than individuals of other weight status for a variety of hypothesized reasons (Maurer et al., 2006
; Wansink & Chandon, 2006
), it is unclear how this may impact on dietary ED.
Additionally, the multiple pass 24-h dietary recall method that was utilized is currently considered the gold standard for dietary assessment and the large sample size minimizes intraindividual variation in dietary intake. This method of dietary assessment may also help reduce under-reporting since participants can suggest that occurrences of overeating or eating specific foods on any one day are “not usual” for them (Kristal, Andrilla, Koepsell, Diehr, & Cheadle, 1998
). However, to better understand the relationship between ED and weight loss maintenance, future randomized controlled trials directly comparing an ad libitum
low ED diet to an energy restricted diet with and without an emphasis on ED are needed to determine the effectiveness of a reduction in ED alone and a focus on ED within a calorie-controlled prescription for weight loss and/or weight loss maintenance.
Previously, we reported that WLM exercise more (Phelan, Roberts, Lang, & Wing, 2007
) and use more fat restriction strategies to a greater extent than NW (Phelan et al., 2009
). This preliminary study shows that, in addition to these previously mentioned strategies that can assist with weight loss maintenance, WLM also self-report consuming a diet lower in ED. A diet low in ED may be important to help keep energy intake low, while still allowing for a greater volume of food to be consumed, which may protect against weight regain after weight loss. The WLM’s self-reported low ED diet was associated with self-reported consumption of a greater number of daily servings from food groups comprised of foods low in fat and high in fiber, including vegetables and whole grains. This suggests that consuming a diet low in ED via nutrient rich food groups low in fat and high in fiber may be another effective dietary strategy for successful long-term weight loss maintenance. However, as this investigation was cross-sectional, to clarify the relationship between dietary ED and weight loss maintenance, prospective randomized controlled trials are needed.