Obesity is a worldwide public health problem

Obesity has reached epidemic proportions in Western countries, but its prevalence is also rising in developing countries^[1]. Obesity, especially abdominal obesity, is a strong risk factor for several chronic diseases, such as type 2 diabetes, cardiovascular diseases, and certain cancers^[1]. Therefore, it is of high public health relevance to combat this epidemic. Principally, overweight and obesity result from a long-term imbalance between energy intake and energy expenditure. Although many research efforts have been made, the role of certain macronutrients and foods in the development of obesity is still not entirely understood. This article briefly summarizes studies on the relation of fruit and vegetable intake and weight management.

How fruits and vegetables could exert beneficial effects on weight control

Fruits and vegetables are characterized by a low energy density because they contain large amounts of water and little fat. Basic research studies on satiety demonstrated that an increased water content of a food leads to a decreased energy density, increased satiety and decreased energy intake at subsequent meals[2]. Furthermore, many studies have shown that increasing the intake of fiber, which is highly available in fruits and vegetables, also increases satiety and decreases energy intake^{[3, 4]}.

Results from intervention studies

Numerous intervention studies have investigated whether a high consumption of fruits and vegetables is effective in body weight control. Intervention studies of satiety showed that adding fruits and vegetables to the diet, thereby reducing energy density, was associated with enhanced satiety, reduced hunger, and a reduction in energy intake^[2]. Intervention trials investigating body weight development as an outcome can generally be classified into two groups: 1) studies on weight maintenance as the main objective (often conducted in normal-weight subjects) and 2)weight reduction studies (usually conducted in overweight or obese subjects). Trials in which participants were advised to increase their fruit and vegetable intake but without a weight loss prescription demonstrated that most subjects did not gain body weight during follow-up but could maintain their weight^[2]. More consistent weight maintenance and even weight loss was observed when advice to increase intake of fruits and vegetables was combined with advice to decrease fat intake^[2]. Weightreduction studies, in which the advice to increase consumption of fruits and vegetables was part of the weight reduction program were similarly successful in their results. In these studies, the increase of fruit and vegetable intake was associated with weight loss and maintenance of weight loss^[2]. These data are supported by weight reduction trials not advising but providing obese subjects low-energy dense diets with a high content of fruits and vegetables and a low fat content. These studies also reported substantial body weight reductions among participants^[2]. Taken together, intervention studies suggest that fruits and vegetables are beneficial in body weight control. However, most interventions were not designed to specifically investigate the effects of fruits and vegetables on weight control alone, but tested increased intakes in fruits and vegetables along with other dietary changes like a decreased fat content^[2]. Well controlled intervention studies should be designed with a focus on the impact of increasing fruit and vegetable intake while keeping other parts of the diet constant.

Observations from epidemiological studies

Several prospective epidemiological studies investigated the relation of fruit and vegetable intake and weight gain. In the Nurse’s Health Study[5] women with the largest increase in fruit and vegetable intake during the 12-year time interval of follow up had a 24 percent lower risk of becoming obese (defined as BMI >30 kg/m2) compared with those women with the largest decrease in intake. Similarly, in a large cohort of nearly 80,000 white adults, an inverse association of baseline vegetable consumption with a 10-year change in BMI and gain in waist circumference was reported^[6]. However, not all prospective epidemiological studies detected beneficial effects of fruits and vegetables on body weight control. Indeed, two studies found an inverse association of increase in fruit consumption during followup with weight gain^{[7, 8]}, but no relation was observed for vegetable intake, respectively. Moreover, two further studies could not detect a relationship between fruit or vegetable intake and subsequent weight gain at all^{[9, 10]}. However, these studies were limited due to their short follow-up period^[10] and small study population^[7-9].

Conclusion

Although the results are not completely consistent, data from basic research studies, as well as intervention and epidemiologic studies suggest that a high consumption of fruits and vegetables is beneficial in body weight management. However, further well controlled studies are needed to corroborate the data of these investigations. Public health efforts should emphasize the benefit of consuming high amounts of fruits and vegetables in combination with an overall healthy diet and a physically active and health-conscious lifestyle to combat the worldwide epidemic of obesity.