Fruits and vegetables are the foundational foods for healthy eating, but a select few of them could be potent enough to protect the human body from gaining weight. Thanks to a collaborative effort by researchers from Harvard and the University of East Anglia (UEA), a new body of research reveals an in-depth look at the best plant-based foods for dieters.

For the study, published in the journal BMJ, researchers examined 24 years’ worth of dietary and lifestyle data from 124,086 Americans between the ages of 27 and 65. Between 1986 and 2011, participants were asked to report their weight to researchers every two years, and their diet every four years. They were looking for particular patterns in their diets that would indicate less weight gain. Previous research found foods, including blueberries, apples, prunes, strawberries, grapes, peppers, and celery, were all linked to lower levels of weight gain. But they wanted to know what exactly about these fruits and veggies helps the body shed excess weight?

The results demonstrated a relationship between diets high in flavonoids and less weight gain. Flavonoids are a naturally occurring chemical compound that contributes to the color in certain plant-based foods. They are known to alter the way our cells function by releasing powerful enzymes that improve cell signal pathways in the body. Fruits and vegetables rich in flavonoid polymers and anthocyanins — a type of antioxidative flavonoid — had the biggest impact on weight loss. Anthocyanins are prevalent in dark red foods like blueberries, cherries, grapes, and strawberries. Tea and apples offer a significant amount of flavonoid polymers.

“We wanted to better understand why those particular fruits and vegetables stuck out,” said the study’s lead author Monica Bertoia, a researcher at Harvard T.H Chan School of Public Health. “It’s easy to look at the results and see that they’re really tiny changes in weight. But weight maintenance is really important. Just maintaining weight from adulthood onward would have a significant public health impact, because most people are gaining weight.”

More than 70 percent of adults are obese or overweight in the United States alone. Opting for the few fruits and vegetables that offer the greatest weight loss benefits could help expedite their weight loss goals. Bertoia and her team found flavonoid-packed foods were associated with 0.16 to 0.23 pounds less weight gained over the course of four years. That may seem miniscule, but researchers insist it doesn’t take a diet packed with fruits and veggies to make a difference. Just half  a cup of blueberries or blackberries a day can result in a quarter pound less gained over the course of four years. Over time, those pounds lost add up.

“There’s a lot of interest in flavonoids with cardiovascular health and diabetes,” said the study’s co-author Aedin Cassidy , a researcher at UEA’s Norwich Medical School. “A lot of people, when they go on a diet, have to do something radical. This is basically saying that something which is good for you already may also be good for weight maintenance, particularly in middle age when weight gain is associated with increased chance of getting heart disease and strokes.”

Source: Bertoia ML, Rimm EB, Mukamal KJ, Hu FB, Willett WC, and Cassidy A. Dietary flavonoid intake and weight maintenance: three prospective cohorts of 124,086 US men and women followed up to 24 years. BMJ . 2016.