Does a higher intake of vegetables result in greater levels of weight loss? In theory, consumption of vegetables are the cornerstone of a low-energy diet – however, how can you be certain that eating more vegetables will contribute positively to weight loss?
This was the question posed by Australian and Swedish researchers who analysed the results of high-quality studies on the topic of vegetable consumption and weight loss published since 1988.
The initial results from the systematic review indicated that of 16 identified randomised controlled trials testing the effect of vegetable consumption on weight loss, 5 showed increased weight loss, 9 showed no difference, 1 showed weight gain, and 1 indicated a positive association. In short, the research is inconclusive when it comes to the impact of increased vegetable consumption on weight loss.
On further investigation into the methodology for each study it was revealed that different research approaches may have had an effect on the results.
For example, trials which showed a positive effect on weight loss considered the whole diet in the intervention – not just the vegetable component. This may be through use and explanation of a dietary framework with participants, such as DASH – which includes broad food groups and guidance on the appropriate number of serves of food to consume from each group. Another study showing positive results from vegetable consumption provided significant behavioural support to participants by explaining vegetables as an alternative to high fat foods.
Studies where participants did not receive support to alter their normal diet, but were provided with vegetables and asked to eat more of them – even where the participants complied with the increased vegetable consumption – did not result in findings supporting intake of vegetables to increase weight loss. Another example where vegetable consumption was not shown to yield increased weight lost was where the alternative intervention was a diet that was also controlled for energy intake.
The authors conclude that trials which increased vegetable consumption together with behavioural support may contribute to increased weight loss, but only when compared with a control diet based on usual consumption patterns.
Tapsell, L. C., Dunning, A., Warensjo, E., Lyons-Wall, P., & Dehlsen, K. (2014). Effects of Vegetable Consumption on Weight Loss: A Review of the Evidence with Implications for Design of Randomized Controlled Trials. Critical Reviews in Food Science & Nutrition, 54(12), 1529.
What advice do you give your weight loss clients when it comes to vegetable intake?