We hear the advice from everywhere. The key to a healthy diet is when we fill at least half our plate with fruits and veggies (see choosemyplate.gov). Or, taking the language of the 2015 report of the Dietary Guidelines Advisory Committee, a healthy and more environmentally-friendly diet is one that’s predominantly plant-based.
But, as I’ve written about before, sometimes easy-to-remember dietary advice that can fit in 140 characters on Twitter doesn’t always reflect prevailing science on the topic. For example, by combining “fruits” and “vegetables” into a single phrase/piece of advice, do we unintentionally portray them as nutritionally equal in the eyes of consumers? Of course this isn’t true, fruits and vegetables often have very different nutritional profiles (take sugar content for example).
Taking this one step further, by generally recommending people consume more fruits and vegetables, do we overlook key differences within these two food groups? The basic question is this: do all vegetables influence health outcomes in the same way? Or taken another way, are there certain fruits or vegetables that might be less healthy than others?
This is the precise question asked by a team of researchers from Harvard University. In particular, they hypothesized, “greater consumption of fruits and vegetables with a higher fiber content or lower glycemic load would be more strongly associated with a healthy weight.”
The study analyzed data from three large, prospective cohort studies of more than 133,000 men and women in the US between 1986 and 2010 to see if intake of specific fruits and vegetables influenced weight gain. Researchers looked at data within 4-year time intervals and took into account a number of other lifestyle factors known to influence weight gain and obesity risk, such as other aspects of the diet, smoking status, and physical activity.
Let’s take a look at what they found.
The first thing that stands out is the variability in how different kinds of fruits and vegetables were associated with varying degrees of weight change.
So what’s the take-away?