In a BMJ study of more than 100,000 men and women, researchers discovered that subclasses of powerful antioxidants called flavonoids—namely flavonols, flavan-3-ols, anthocyanins, and flavonoid polymers—found in select fruits and vegetables may prevent weight gain. The fruits with the greatest effect on weight maintenance were chock full of flavonoids called anthocyanins, and blueberries top this list.
About one-quarter cup of blueberries contains 10 milligrams of anthocyanins, and each 10 mg increase is linked with a quarter-pound less weight gain over four years, the BMJ study found. This may seem insignificant, but it can add up with time, the study authors point out. Exactly how flavonoids deter weight gain is not fully understood but eating foods rich in flavonoids—namely produce—may allow us to feel full sooner, and avoid other less-healthy foods that may lead to weight gain.
"I am a blueberry fan for many reasons," says Keri Peterson, MD, an internist at Lenox Hill Hospital in New York City. Antioxidant power aside, blueberries are also rich in fiber which keeps us feeling full longer, she says. "They are among the healthiest fruits to eat." Berries happen to be among the most-filling fruits. Aim for a cup of blueberries a day as part of an overall healthful diet that is rich in lean protein, complex carbohydrates, healthy fats like olive oil, fruits and vegetables, she says.
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Who cares if an apple a day can keep the doctor away if it also helps keep you trim? Apples are rich in flavonoid polymers and are also packed with fiber, making them one of the best fruits for weight loss when part of a healthy diet. One medium-sized apple is considered one serving. Eat them with the skin on (i.e. unpeeled) to get more fiber, antioxidants, and better control over your blood sugar, says SharAd Paul, MD, the Auckland, New Zealand-based author of The Genetics of Health: Understand Your Genes for Better Health. Preventing blood sugar spikes and valleys will help banish food cravings and eating binges, not to mention help protect against diabetes.
Pears rank up there with apples when it comes to preventing weight gain over the years, the study found, and this is largely due to a healthy dose of flavonoid polymers: Every extra 138 mg of flavonoid polymers resulted in less weight gain over the four-year study period. "Fruits that are rich in flavanoid antioxidants and high in fiber are great choices," Dr. Peterson says. "Fiber fills you up and creates satiety, so pears and apples give you a lot of bang for your buck." Make sure to eat the skin too for maximum benefits, adds Dr. Paul. Test your knowledge of the best high-fiber choices—like pears—with this quiz.
Strawberries help maintain weight for the same reason as their blueberry counterparts: They are rich in anthocyanins. Incorporate one cup of strawberries a day into your diet—try them with breakfast over low-fat yogurt or steel-cut oatmeal, as a mid-afternoon snack, or as a dessert after dinner, Peterson says. "The concern has been that eating sweet fruits may cause weight gain due to fructose content, however, certain fruits like green apples, pears and berries like raspberries, strawberries and blueberries are among the best fruits to eat as part of a weight management plan not only because they are less sweet, but due to their high flavonoid content." Some juices are also loaded with flavonoids.
First, yes: Peppers are in fact a fruit. Ranking up there with the healthiest fruits, they can also help put the brakes on weight gain when eaten daily, according to the research. In fact, peppers may even encourage weight loss: Capsaicin, the component that gives chili peppers that kick, seems to encourage white fat cells to convert into ultra-energy-burning brown fat, in one study. Check out cayenne pepper's other health benefits.