August 8, 2014
A common dietary recommendation for weight loss, especially in lay public outlets, is to eat more fruit and vegetables (F/Vs). Without a compensatory reduction in total energy intake, significant weight loss would be unlikely. Therefore, Kathryn Kaiser, PhD, Instructor in the Department of Biostatistics, Section on Statistical Genetics, and David B. Allison, PhD, Distinguished Professor in the Office of Energetics, aimed to synthesize the best available evidence on the effectiveness of the general recommendation to eat more F/Vs for weight loss or the prevention of weight gain. Co-investigators include Andrew W. Brown, PhD, Research Associate in the Nutrition Obesity Research Center; Michelle M. Bohan Brown, PhD, Consultant in the Department of Nutrition Sciences Education; James M. Shikany, DrPH, Professor in the Division of Preventive Medicine; and Richard D. Mattes, MPH, PhD, RD, Distinguished Professor of Nutrition Science, Department of Nutrition Science, and Director of Public Health at Purdue University.
The team searched multiple databases for human randomized controlled trials that evaluated the effect of increased F/V intake on body weight. Inclusion criteria were as follows: 15 or more subjects/ treatment arm, 8+-week intervention, a stated primary or secondary outcome of body weight, the stated goal of the intervention was weight or fat loss or the prevention of weight or fat gain, and food intake provided or prescribed was of a variety of F/Vs that remained minimally processed.
Two studies met all criteria; five other studies met all but one of the criteria (weight change was not a stated outcome of interest but weight data were reported). The primary analysis indicated an effect size of weight change (outcome of interest) from baseline compared to control of -0.16 (95 percent CI:-0.78, 0.46; p = 0.60). The standardized mean difference for seven studies that met all or most criteria was 0.04 (95 percent CI: -0.10, 0.17; p = 0.62).
Studies to date do not support the proposition that recommendations to increase F/V intake or the home delivery or provision of F/Vs will cause weight loss. Conversely, no significant weight gain was observed. On the basis of the current evidence, recommending increased F/V consumption to treat or prevent obesity without explicitly combining this approach with efforts to reduce intake of other energy sources is unwarranted.