In the battle against the bulge, you may want to add flavonoid-rich blueberries and strawberries to your arsenal, new research suggests.
Harvard University researchers found last year specific types of fruit and vegetables could either enhance or curb weight loss efforts. Blueberries and pears, for example, helped with weight loss more than stone fruits.
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Which fruits and veggies are most fattening?
An extra serving of certain fruits and vegetables each day for four years can cause weight gain or weight loss. But which foods cause the most?
But they did not know which element in the fruits was responsible for the differences.
Now the same researchers have published a study in The BMJ that shows certain types of flavonoids - plant-based compounds with antioxidant powers - led to "statistically significant" weight loss.
"Our results suggest that choosing high flavonoid fruits and vegetables, such as apples, pears, berries, and peppers, may help with weight control," lead author Monica Bertoia, from Harvard's School of Public Health, wrote.
The flavonoid subclass 'anthocyanins', largely found in blueberries and strawberries, was linked with the greatest weight loss. An extra daily intake of 10 milligrams of anthocyanins was linked with a 0.1-kilogram loss in weight over a four-year period.
Just half a cup of blueberries provides about 121 milligrams of anthocyanins. This means a participant who ate a handful of blueberries each day on average shed about 1.2 kilograms over four years.
The study was based on responses to regular dietary questionnaires and self-reported weight changes by more than 124,000 adults in the United States every four years between 1986 and 2011.
Two other flavonoid subclasses, flavonoid polymers and flavonols, showed strong links with weight loss. Large amounts of flavonoid polymers can be found in grapes and apples, and for flavonols, in tea and onions.
"Most weight loss studies to date have focused on the flavan-3-ol subclass found in green tea and are limited to small numbers of overweight and obese participants. Here, we examine, to our knowledge for the first time, the associations between habitual consumption of all flavonoid subclasses and weight gain," Ms Bertoia said.
"[Other studies] suggest that flavonoids may decrease fat absorption [and] increase energy expenditure."
The observational study does not show cause-and-effect. The researchers said losing weight or preventing even small amounts of weight gain could reduce risk of diabetes, cancer, hypertension and cardiovascular disease.
And the results could provide guidance on which fruits and vegetables to choose for preventing weight gain.
More than 90 per cent of Australian adults do not eat the recommended five serves of vegetables a day, and half do not eat the recommended two serves of fruit, according to the Australian Institute of Health and Welfare's health report.
"While adult Australians aged 25 to 44 are generally healthy, unhealthy behaviours such as not exercising or not eating enough fruit and vegetables place them at risk of developing long-term conditions in the future," the report said.
The study adjusted for a range of dietary and lifestyle factors that may have influenced the results, such as smoking status and physical activity. Results are consistent across gender and age group.
Nutritionist Rosemary Stanton told Fairfax Media it was important to keep in mind that people who ate more fruit and vegetables were likely to eat less of something else, especially junk food.
"The fact that the benefits of most of the flavonoids paled into insignificance when adjusting the data for the positive (beneficial) effect dietary fibre is significant. There is ample evidence that dietary fibre is nature's obstacle to overeating," she said.
"These are expensive foods and likely to be consumed by those with more disposable income - also a factor in staying slimmer."
She said the study was a reminder the benefits of eating whole foods might not apply when components have been removed and added to something else.
"My concern is that some food company will see it as a sales benefit to add anthocyanins to some junk food and then proclaim it healthy. 'XX brand of popped puffed sugary cereal, now with extra anthocyanin'," she said.