Background: Fruit, vegetable, and dietary fiber intake have been associated with lower risk of cardiovascular disease (CVD); however, little is known about their role in obesity prevention.
Objective: Our goal was to investigate whether intake of fruits, vegetables, and dietary fiber is associated with weight change and the risk of becoming overweight and obese.
Methods: We studied 18,146 women aged ≥45 y from the Women’s Health Study free of CVD and cancer with an initial body mass index (BMI) of 18.5 to <25 kg/m2. Fruit, vegetable, and dietary fiber intakes were assessed at baseline through a 131-item food-frequency questionnaire, along with obesity-related risk factors. Women self-reported body weight on annual questionnaires.
Results: During a mean follow-up of 15.9 y, 8125 women became overweight or obese (BMI ≥25 kg/m2). Intakes of total fruits and vegetables, fruits, and dietary fiber were not associated with the longitudinal changes in body weight, whereas higher vegetable intake was associated with greater weight gain (P-trend: 0.02). In multivariable analyses, controlling for total energy intake and physical activity along with other lifestyle, clinical, and dietary factors, women in the highest vs. lowest quintile of fruit intake had an HR of 0.87 (95% CI: 0.80, 0.94; P-trend: 0.01) of becoming overweight or obese. No association was observed for vegetable or dietary fiber intake. The association between fruit intake and risk of becoming overweight or obese was modified by baseline BMI (P-interaction: <0.0001) where the strongest inverse association was observed among women with a BMI <23 kg/m2 (HR: 0.82; 95% CI: 0.71, 0.94).
Conclusion: Our results suggest that greater baseline intake of fruit, but not vegetables or fiber, by middle-aged and older women with a normal BMI at baseline is associated with lower risk of becoming overweight or obese.
Alex’s Notes: If you ask someone about strategies to aid in weight loss, chances are they will give you one of two answers. The first is the smart-ass remark I would probably make, “eat less.” The second would be, “eat more vegetables and fruits.” This advice is not without reason of course. Vegetables and fruits are notoriously nutrient-dense and full of water and fiber, thus making them a powerful tool for reducing the energy density of meals and overall caloric intake. Plus they are very satiating.
Despite this strong theoretical basis, observational studies offer inconsistent results, and few randomized controlled trials have been conducted. One such trial in middle-aged men and women found supplementing the diet with 300 or 600g of fruits (primarily apples, oranges, bananas, pears, and grapes) resulted in no significant changes in body weight after eight weeks, despite improved diet quality. Similarly, a year-long study found no effect of increasing vegetable intake on body composition or healthy parameters when in a caloric deficit. Nonetheless, a recent meta-analysis concluded that,
“Promoting increased fruit and vegetable consumption, in the absence of specific advice to decrease consumption of other foods, appears unlikely to lead to weight gain in the short-term and may have a role in weight maintenance or loss.”
For many people, weight maintenance and satiety are exactly what is needed (and wanted). This brings me to the current study by Rautianen and colleagues from Harvard Medical School, which aimed to examine the association of fruit, vegetable, and dietary fiber intake with weight gain and the risk of becoming overweight or obese in a cohort of middle-aged and elderly women.
The study population included a 18,146 normal-weight women from the Women’s Health Study that were over 45 years old with no history of diabetes, cancer, or cardiovascular diseases. All the data was extracted from questionnaires that the women completed at baseline in 1992, and the final weight change of the women was their last reported weight, with some women being followed for up to 17 years. Already we can see problems, as it is possible that the women changed their diets during the follow-up years, making the baseline food intake irrelevant.
Nonetheless, with an average follow-up of 15.9 years, 8125 women became overweight or obese. Total fruit, vegetable, combined fruit & vegetable, and fiber intake was divided into quintiles. Those in the highest quintile of fruit intake (>3 servings/day) were older, less likely to smoke, more physically active, more likely to use hormone replacement therapy, less likely to have hypercholesteremia, more likely to drink alcohol, more likely to take a multivitamin, and consumed more fiber and calories compared to women who consumed less fruit. A similar pattern was seen for women who had the greatest vegetable intake (>5 servings/day).
Clearly many of these factors would play a role in weight change, which is why Rautianen controlled for them in the statistical analysis. Surprisingly, the only significant association with weight change was that those who consumed the most vegetables gained the most weight. Specifically, those women consumed >5 servings/day gained about 10% more weight than those consuming <2 servings, although the absolute difference is rather small (1.93 vs 1.76 kg). Moreover, those consuming the most vegetables had an 11% greater risk of becoming overweight or obese compared to those consuming less. This risk did not persist when baseline BMI was accounted for, however, suggesting that the effects of vegetable intake vary depending on one’s starting point with weight.
Looking to fruit, for both the BMI-adjusted and unadjusted models, consuming more fruit was protective. Consuming more than 3 servings/day was associated with a 13-14% reduced risk of becoming overweight or obese compared to consumed <1 serving. Total fruit & vegetable intake and fiber intake had no significant associations.
I know what you are thinking, they must include pizza sauce as a vegetable.
Indeed this may very well explain why those who consumed more servings of tomatoes per day had increased risk of becoming overweight or obese. This would also be supported by the fact that adjusting for BMI made the results not significant. The story isn’t that simple, unfortunately, as cruciferous vegetables and green leafy vegetables were also associated with significantly increased risk of becoming overweight or obese. Even berry consumption (>0.7 servings/day) led to a 21% increased risk compared to no berry consumption. In fact, the only protective foods were citrus juices and legumes.
So broccoli, tomatoes, spinach, and strawberries increase the risk of becoming overweight?
If your current age is at least 67 years and you are a female, then technically yes. But let’s think for a moment which scenario is more likely:
- Fibrous vegetables and berries lead to weight gain, or
- The results are biased from measurement error within the self-reported food frequency questionnaires, the possibility that diets changed over the 17 year follow-up, and the lack of information on food processing methods.
We really cannot say for sure, but I am definitely leaning towards the latter. Eating broccoli with melted cheese, tomatoes on pizza, spinach in a casserole, or strawberries on top of a parfait could pretty easily lead to weight gain if habitual. Besides, this was an observational study were causation cannot be determined, and we have the previously mentioned meta-analysis of only eight randomized controlled trials suggesting the outcome of the study at hand is bunk.