Starchy Veggies? It Might Be Better to PICK Them than to Pick ON Them
Two studies on fruits and vegetables were recently published, and they're both worth mentioning in one article. Overall, the benefits of eating a diet high in fruits and vegetables are undisputed. These foods check off all the right boxes—they are plants, they have fiber, and they are loaded with vitamins and minerals. Fruits and vegetables also contain a wide variety of antioxidants and phytochemicals, the plant compounds that help reduce disease risk. There is a mountain of scientific research that extols the benefits of eating lots of these good guys.
Now a new study from Harvard that analyzed data from three cohorts—Nurses' Health Study, Nurses' Health Study II, and Health Professionals Follow-Up Study—found that eating more fruits and vegetables was "associated" with weight loss, but eating starchy vegetables was "associated" with weight gain (1). An increase in total vegetable intake was associated with a loss of about a quarter of a pound after four years—hardly stellar—and an increase in total fruit intake was associated with a loss of about a half of a pound over the same time period.
Within the vegetable group, the authors looked at both individual vegetables and at vegetable subgroups, such as cruciferous, green leafy, legumes, and starchy vegetables. The starchy vegetable subgroup focused specifically on corn, peas, and potatoes (included sweet potatoes, yams, and baked/boiled/mashed white potatoes, but excluded French fries and potato chips). Weight loss was associated with eating more non-starchy vegetables and weight gain with eating starchy vegetables—particularly corn, peas, and white potatoes.
The amount of weight gain associated with eating starchy vegetables was extremely small—only about three quarters of a pound after four years in the case of potatoes. Ironically, cabbage and onions were also associated with a weight gain of about a quarter of a pound after four years, although neither of these vegetables are starchy and both are loaded with fiber. Moreover, the total average weight gain in these cohorts ranged from 2.1 pounds for the Health Professionals Follow-Up Study to 5.0 pounds for the Nurses’ Health Study II, while the overall change in vegetable consumption was negligible. People gained weight regardless of their vegetable and fruit intake, and that's not very surprising.
Looking at these results another way, people who ate starchy vegetables gained LESS weight than the total cohort. What was also interesting is that legumes—another vegetable subgroup consisting of starchy vegetables like peas, lima beans, beans, lentils, and tofu/soy—were generally associated with mild weight loss. The authors postulated that the lower-glycemic load (GL) of these higher-fiber starchy vegetables was likely a reason for their better association with body weight. Then again, one of the three starchy vegetables associated with weight gain were peas—also a higher-fiber, lower-GI vegetable. Confusing? Of course it is. To make things even more confusing, clinical research—such as the OmniCarb Randomized Clinical Trial (2)—doesn't show much of a connection between the glycemic index of an individual food and its impact on insulin resistance or cardiovascular outcomes, especially when these foods are part of a mixed meal, which they nearly always are. When is the last time you ate only a bowl of peas or potatoes?
A study from the Centers for Disease Control and Prevention that was released in July 2015 indicated that only 1 out of 8 Americans consumes enough fruit, and only 1 out of 11 is meeting recommended intakes of vegetables (3). Given the acknowledgement by the Dietary Guidelines for Americans that fruit and vegetable consumption positively impacts various health outcomes and that so few Americans are actually meeting recommended intakes, it is difficult to condone a recommendation to limit the intake of any whole fruit or vegetable, including starchy vegetables.
As a clinician and practitioner, I have to look at the larger and more real-world picture, not just the statistical one. Starchy vegetables—such as potatoes, peas, beans, and corn—are not new foods. They were around long before the obesity crisis, when we actually ate more of them. Moreover, they are absolutely loaded with nutrition. Potatoes happen to be one of the best sources of potassium—a nutrient of concern because most people have potassium-deficient diets—as well as several other essential nutrients. Plus, potatoes are affordable and people actually like them. No, I don't want people to over-consume potatoes or any other food, but given the documented vegetable-deficient diets of most Americans, I'd be loath to discourage cutting back on such a nutrient-packed food.
Making broad nutrition recommendations based on population studies is tricky and usually a bad idea. Once people hear the term "associated with," they can easily and inappropriately make the leap to "cause-effect," and that's a mistake.
(1) Bertoia ML, Mukamal KJ, Cahill LE, Hou T, Ludwig DS, Mozaffarian D, et al. Changes in Intake of Fruits and Vegetables and Weight Change in United States Men and Women Followed for Up to 24 Years: Analysis from Three Prospective Cohort Studies. PLOS Med. 2015 September 22;12(9):e1001878. DOI: http://dx.doi.org/10.1371/journal.pmed.1001878.
(2) Sacks FM, Carey VJ, Anderson CA, Miller ER 3rd, Copeland T, Charleston J, et al. Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity: The OmniCarb Randomized Clinical Trial. JAMA. 2014 December 17;312(23):2531-2541. DOI: http://dx.doi.org/10.1001/jama.2014.16658.
(3) Moore LV, Thompson FE. Adults Meeting Fruit and Vegetable Intake Recommendations: United States, 2013. MMWR Morb Mortal Wkly Rep. 2015 July 10;64(26):709-713.