Flavonoid-Rich Fruits and Vegetables Are a Dieter's Best Friend

Flavonoids, which are naturally occurring chemical compounds in fruits and vegetables, have many positive health benefits. REUTERS/ Mariana Bazo

It's well known that fruits and vegetables are essential to a healthy diet. But it turns out the type you choose matters just as much as whether you eat them at all. A new study published Wednesday in BMJ suggests consuming fruits and vegetables rich in certain types of flavonoids may be a simple way to maintain a healthy weight.

Flavonoids are a naturally occurring chemical compound present in many of the foods we eat, and found abundantly in fruits and vegetables. There are at least seven different flavonoid subgroups in fruits and vegetables, and thousands of variants within each category. In nearly all cases, specific flavonoids give a fruit or vegetable it's characteristically bright color.

The study on 124,086 men and women over age 24 is based on data for three large trials. The researchers looked at the impact of eating fruits and vegetables known to contain high amounts of certain flavonoids, and then identified a handful that appear highly beneficial for weight control. These include fruits and vegetables rich in anthocyanins, flavonols, flavonoid polymers, and flavan-3-ols. Anthocyanins are typically found in fruits and vegetables that are a deep purple and red, such as berries and eggplants. Flavonols were derived primarily from onions, while tea and apples were some mains source for flavan-3-ols and flavonoid polymers.

After adjusting for lifestyle factors such as smoking and fitness level, the researchers found these types of flavonoids were associated with 0.16 to 0.23 pounds less weight gained over four years. These findings were consistent for both men and women and across all age groups.

To many people this would seem like an insignificant amount of weight, but when it comes to your health even a little extra bulk around the middle can have a serious long-term impact. Gradual weight gain over time has been shown to increase risk for a number of chronic conditions, including diabetes, heart disease and hypertension.

"Our results show very small changes in weight—even losing small amounts of weight—can have a very big impact on your health," says Monica Bertoia, a research associate at the Harvard T.H. Chan School of Public Health and co-author on the study.

Bertoia says her team took its cue from other research that suggests high levels of flavonoids in green tea decrease fat absorption and increase energy expenditure. An increasing body of research suggests flavonoids also have anti-inflammatory and anti-cancer benefits.

Bertoia and her team also conducted another study last year that helped to identify exactly which fruits and vegetables are a dieter's best bet. Their list includes blueberries, apples, pears, strawberries, bell peppers, cauliflower and pretty much all leafy greens. However, their findings indicated that peas, corn and potatoes have the opposite effect. All of these starchy vegetables were associated with gradual weight gain over time.

The good news is adding more color to your diet probably won't be too challenging. For example, Bertoia and her team found that an increase of 10 milligrams anthocyanins per day was associated with gaining about a quarter-pound less over a four-year period—and just half a cup of blueberries will give you 120 milligrams of this flavonoid, she says.

Bertoia hopes their findings could bear some influence in public health. "Right now U.S. dietary guidelines recommend eating more fruits and vegetables. My co-authors and I think it would be nice to get more specific guidance," she says. "We think these results would lead you to choose fruits like apples and berries that will give you more flavonoids."