Researchers at the University of Alabama at Birmingham have found that increasing fruit and vegetable intake does not lead to weight loss, despite decades-old popular belief.
A team of investigators performed a systematic review and meta-analysis of data of more than 1,200 subjects in seven randomized, controlled trials to explore the weight loss effects of increasing fruit and vegetable consumption.
"Across the board, all studies we reviewed showed a near-zero effect on weight loss," says study leader Kathryn Kaiser, PhD, instructor in the UAB School of Public Health. "So I don't think eating more alone is necessarily an effective approach for weight loss because just adding them on top of whatever foods a person may be eating is not likely to cause weight change."
According to the United States Department of Agriculture's MyPlate initiative, the recommended daily serving amount for adults is 1.5-2 cups of fruit and 2-3 cups of vegetables, although dieters are often advised to "fill up" on fruits and vegetables based on the assumption that the low-calorie foods will satiate by taking up space in the digestive tract.
"In the overall context of a healthy diet, energy reduction is the way to help lose weight, so to reduce weight you have to reduce caloric intake," Kaiser said. "People make the assumption that higher-fiber foods like fruits and vegetables will displace the less healthy foods, and that's a mechanism to lose weight; but our findings from the best available evidence show that effect doesn't seem to be present among people simply instructed to increase fruit and vegetable intake."
Fruits and vegetables provide many vitamins and fiber, so even if they don't promote weight loss, it seems unlikely they could do harm unless consumed in extreme quantities.
A study comparing the popular Mediterranean diet to a reduced-fat diet says that while the former may not promote weight loss, it significantly reduces risk of type 2 diabetes, significantly more than the latter. Another study, published last year in the New England Journal of Medicine, worked with patients at risk for cardiac disease, concluding that followers of the Mediterranean diet were 30% less likely to experience heart attack or stroke than those on a low-fat diet.
Possibly, though, the attention given to fruits and vegetables casts a shadow over other important dietary foods.
For example, a study published in the International Journal of Obesity found that eating two eggs for breakfast can lead to weight loss, which some might find surprising because eggs are sometimes associated with weight gain.
Kaiser's study was published in the American Journal of Clinical Nutrition.