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Thu, Jun 27, 2019

Obesity
The Health Benefits of Fruits and Vegetables



Over 60% of American adults are overweight (body mass index =25) and of these, 26% are obese (body mass index =30) (70). In young Americans the prevalence of over-weight is also increasing, with the latest estimates suggesting that 11% of children and adolescents are overweight. The total cost of overweight and obesity is estimated to be $99.2 billion, representing 5.7% of annual U.S. health-care costs (70).


A long-term imbalance between energy intake and expenditure is important in the development of overweight and obesity (71). There is a great deal of interest in the specific dietary factors associated with the prevention of overeating. Although not fully understood it is thought that energy density, fiber content, palatability, and dietary variety are thought to be important determinants of energy consumption (71-73). Inclusion of fruits and vegetables in the diet has the potential to affect each of these factors.


McCrory et al. reported that obesity is associated with consumption of foods high in energy density (74). Conversely, intake of fruits and vegetables (fried potatoes excluded) were among the foods that were negative predictors of body mass index. Rolls and colleagues have extensively examined the relationship between varying energy density of foods and subsequent energy intake. Adding vegetables with high water content to lunch and dinner entrées lowered the energy density of the entrées but did not affect palatability or feelings of fullness and hunger compared to the same entrée without the added vegetables (i.e. higher energy density) (72). Importantly, consuming the entrées with the added vegetables resulted in a 30% reduction in total energy intake for the day. Other studies in normal and overweight women have confirmed that total daily energy intake is lowered by up to 20% when consuming foods of low energy density without excessive feelings of hunger (75). These studies suggest that consuming foods of low energy density, including vegetables and some fruits, may be a useful strategy for weight loss.


“… Other studies in normal and overweight women have confirmed that total daily energy intake is lowered by up to 20% when consuming foods of low energy density without excessive feelings of hunger (75). These studies suggest that consuming foods of low energy density, including vegetables and some fruits, may be a useful strategy for weight loss.”


In general, dietary variety is positively associated with higher energy intake. It has been proposed that the rising prevalence of obesity in the United States parallels the increase in variety and number of high-energy foods available to consumers in the U.S. food market (71). McCrory et al. recently reported that subjects consuming diets associated with a greater variety of vegetables but a lower variety of sweets, snacks, etc. were relatively lean individuals. Conversely, people who consume a high variety of sweets, snacks, condiments, entrées, carbohydrates, and a low variety of vegetables tended to be relatively fat (71). Furthermore, the variety ratio of vegetables to sweets and snacks predicted body fatness in the study of subjects and was a more important predictor than dietary fat, energy density, fiber, and energy intake per kilogram bodyweight. This suggests that diets providing a high variety of vegetables and low variety of sweets, snacks, condiments, entrées, and carbohydrates may be important in promoting long-term reduction in food intake and has potential for treatment of overweight and obese individuals.


Adding fruits and vegetables to the diet was explored as a weight loss strategy in a recent study of obese parents with normal weight children (76). The goal of the study was to evaluate the effect of parent-focused behavioral changes on weight changes in families over a one-year period. One group of families increased fruit intake to 2 fruits per day and vegetables to 3 per day while the other group reduced fat and sugar servings to less than 10 per week. The group with increased fruit and vegetable intake had the greatest reduction in percentage of overweight adults. Furthermore, families who increased fruit and vegetable intake also lowered their fat and sugar intake whereas the group that reduced fat and sugar intake did not increase intake of fruits and vegetables. These data support the positive benefits of including fruits and vegetables in weight loss diets and suggest that an effective approach to weight loss might focus on increasing intake of healthy foods rather than emphasizing dietary restriction.


Foods containing dietary fiber have been proposed to slow gastric emptying and favorably impact satiety (77). This results in a sustained feeling of fullness that may reduce overeating (78). Epidemiological studies generally support a role for fiber in bodyweight regulation among free-living individuals consuming self-selected diets (79). Short-term studies of fiber intake and satiety are typically focused on grains as sources of fiber or use isolated fiber supplements [guar, psyllium, pectin, etc., reviewed in (79)]. Although not tested directly, fruits and vegetables, because of their fiber content, would be expected to be positively associated with increased satiety and reduced overall energy intake.

 

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