The recommended daily serving amount for adults is 1.5-2 cups of fruit and 2-3 cups of vegetables, says the United States Department of Agriculture's MyPlate initiative.
Kathryn Kaiser, Ph.D., instructor in the UAB School of Public Health, and a team of investigators at UAB, including Andrew W. Brown, Ph.D., Michelle M. Bohan Brown, Ph.D., James M. Shikany, Dr.PH., and David B. Allison, Ph.D., and Purdue University investigators performed a systematic review and meta-analysis of data of more than 1200 participants in seven randomized controlled trials that focused on increasing fruit and vegetable intake to see effects on weight loss. Their results show that increased fruit and vegetable consumption per se does not reduce body weight.
"Across the board, all studies we reviewed showed a near-zero effect on weight loss," Kaiser said. "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."
Despite the belief of some that increased intake of fruit may increase the risk for weight gain, Kaiser says that was not the case at the doses studied.
"It appears that an increase in servings does not increase weight, which is a good thing for getting more vitamins and fiber in one's diet," Kaiser said.
While Kaiser recognizes the importance of eating fruits and vegetables for their many other health benefits, expectations for weight loss should be kept in check.
"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."
"In public health, we want to send positive and encouraging messages and telling people to eat more fruits and vegetables seems far more positive and encouraging than just saying eat less." Unfortunately, it seems that if we just get people to eat more fruits and vegetables without also taking explicit steps to reduce total food intake, lower weights are not achieved," said senior author, David B. Allison, Ph.D., associate dean for science in the UAB School of Public Health.
Because this recommendation is so widely shared, Kaiser believes these results should bring change to public health messaging.
"There are many studies where people are spending a lot of money figuring out how to increase fruit and vegetable intake, and there are a lot of healthy things that this helps; but weight loss isn't one of them," Kaiser said. "I think working on more multimodal healthy lifestyle interventions would be a better use of time and money."
Kaiser says it is important that more quality research be performed to investigate how multiple foods may interact to create healthy weight loss that can be maintained.
"We need to design mechanistic studies to understand these things better so we can help the public be best informed and know what to do when it comes to weight-loss efforts," Kaiser said. "Overly simplified messages don't seem to be very effective."
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