An extra serving of fruit a day can lead to a weight loss of 0.24 kg.
Being overweight or obese increases the risk of life-threatening chronic diseases. Recent lifestyle changes mean that many people's diets now provide more energy than they need for their daily activities, causing excess weight and body fat.
By following a healthy diet with fewer calories and by exercising more, people should be able to control their weight and body fat more successfully.
The 2010 Dietary Guidelines for Americans, issued by the US Department of Agriculture (USDA) and the Department of Health and Human Services (HHS), recommend consuming a variety of fruits and vegetables to lower the risk of chronic disease and to "help adults and children achieve and maintain a healthy weight."
The current longitudinal study, led by Dr. Monica Bertoia, notes that despite strong evidence that these foods help prevent cardiovascular disease, their contribution to maintaining a healthy weight has been unproven.
What, for example, is the effect of specific fruits and vegetables on weight? Would variations in dietary fiber content and glycemic load (GL) make a difference?
Dr. Bertoia's team, from Harvard T. H. Chan School of Public Health and Brigham & Women's Hospital in Boston, MA, hypothesized that certain fruits and vegetables may be more or less beneficial for maintaining or achieving a healthy weight.
They also proposed that consumption of fruits and vegetable with a higher fiber content or lower glycemic load would be more likely to lead to a healthy weight than consumption of those with a lower fiber content or higher glycemic load.
More than 70 fruits and vegetables surveyed
Three large prospective cohorts of 133,468 American men and women, mostly working in the health profession, participated in the study, which focused on risk factors for chronic diseases.
The participants made self-reported weight changes and completed questionnaires at 4-year intervals for up to 24 years, between 1986 and 2010.
- 34.9% of Americans are classed as obese
- Obesity runs at 39.5% among 40-59 year-olds, but 30.3% among those aged 20-29
- An obese person costs the public health services on average $1,429 per person per year compared with a non-obese person.
More than 70 items were included on the food frequency questionnaire. Fruits and vegetables with similar nutritional value were combined, for example, apples and pears.
Fruits and vegetables were classified as high or low fiber, and as high or low GL, calculated by multiplying the carbohydrate content of each fruit/vegetable (grams per serving) by the glycemic index of that fruit/vegetable.
Fruits were categorized into citrus, melon, and berries, and vegetables into cruciferous, green leafy, and legumes based on similar nutritional content.
Only whole fruits were included, as fruit juice tends to contain added sugar. Unprocessed potatoes were counted as vegetables (baked, mashed and so on), but not fried.
The researchers examined data on weight and diet changes and the association between change in intake of specific fruits and vegetables and change in weight.
Adjustments were made for lifestyle variables, including smoking status, physical activity level, hours of sitting or watching TV and hours of sleep, as well as change in intake of other foods and nutrients such as fried potatoes, juice, whole grains, sweets and alcohol.
Starchy vegetables led to weight gain
The researchers found that overall, eating an extra portion of fruit a day led to a weight loss of 0.24 kg, while eating an extra daily portion of vegetables brought a weight loss of 0.11 kg.
Greater weight loss was linked to higher-fiber, lower-glycemic vegetables, especially cruciferous vegetables, such as broccoli, Brussels sprouts and cauliflower.
Fruits overall, particularly berries, apples and pears, contributed to greater weight loss, compared with vegetables.
However, the researchers found weight gain was linked to lower-fiber, higher-glycemic and starchy vegetables, including corn, peas, and potatoes, carrots and cabbage.
Increased satiety with fewer calories could be partly responsible for the beneficial effects of increasing fruit and vegetable intake.
Limitations include the fact that participants were mostly white, educated professionals. It was also difficult to verify exact portion size or take into account extra exercise and other temporary variations in lifestyle choices.
Overall, however, the findings support recommendations to consume more fruits and vegetables, but highlight the need to show the differences between them. The researchers also call for fruit juices and fried potatoes to be discouraged.
Although the rate of weight change appears small, an extra one to two portions a day of both fruits and vegetables could make a significant difference long term, at least to maintaining a steady weight.
Earlier this year, Medical News Today reported on a study from the Centers for Disease Control and Prevention (CDC) claiming Americans are not eating enough fruits and vegetables.