Can fruit help keep you slim?

Berries

Eating certain fruits and vegetables could help people avoid gaining weight, a new study has suggested.

The study, published in the BMJ and carried out by Harvard and the University of East Anglia, looked at the effect of dietary flavonoids, which are natural compounds found in fruits and vegetables.

We all need to be eating more fruit and vegetables, rather than focusing on particular types

Tracy Parker
Heart Health Dietitian at the BHF

Prof Aedin Cassidy, from UEA’s Norwich Medical School, said: “Most adults gain weight as they age and even small increases in weight can have a substantial impact on risk of high blood pressure, developing heart disease, cancer or diabetes - so strategies to help individuals maintain a healthy weight in middle age are needed.

“We found that an increased consumption of most flavonoids were associated with weight maintenance, and even a modest weight loss.

“Just a single portion of some of these fruits per day would have an important impact on health at a population level.

“The greatest association was found for anthocyanins - which are found in blueberries, strawberries, cherries, blackberries, grapes, radishes and blackcurrants. We also found that flavonoid polymers - found in tea and apples - were particularly beneficial, along with flavonols – found in tea and onions.”

How the story was covered

This story was covered widely, including BBC News, the GuardianIndependentTelegraphEvening Standard and others. Most of the coverage was reasonably accurate – although the Telegraph coverage was arguably misleading, with the headline “Eat more food to lose weight – as long as it’s fruit” and opening sentence “It might seem like the last thing dieters should do, but eating more could be the key to losing weight.”

The study did not find that those with a greater intake of flavonoids were consuming more food overall, which is what the article seems to suggest. Also, flavonoids are found in vegetables (and tea and red wine) as well as fruit, although the article did go on to clarify this

Overall, the news coverage did not focus on the fact the weight loss was achieved over 24 years, rather than as part of a crash diet for example. And there was little emphasis on the fact that in most cases those who ate more flavonoids either kept a constant weight or reduced by a modest 1lb to 2lbs.


Strengths and weaknesses

Strengths of the study were that it covered a large number of people – more than 100,000 – with up to 24 years of follow up.

The researchers said that their studies had limitations, including the fact that the food quantities may not always have been measured accurately. The flavonoid content of foods varies depending on ripeness, storage conditions, food processing, and season.

Some sources of flavonoids were not captured by the questionnaire, although the researchers said they included the main sources. The other possibility is that there were other factors which could have caused the effects seen.

Efforts were made to adjust for this, but they say this might not have been total. The study said: “The source of 325 confounding most difficult to control is other constituents for the same foods high in flavonoids.” Fibre, for example, could have been responsible for the effects seen.

Studies like this can only show an association rather than proving cause and effect. The study looked at large populations of middle aged and older adults. Although the results found applied to both genders and to different ages, we don’t know for sure that they would have applied to much younger people, for example.

The BHF view

Tracy Parker, Heart Health Dietitian at the British Heart Foundation, said: "Although the mechanisms of the benefit of eating fruit and vegetables are not well understood, this study suggests that eating fruit and vegetables that contain high levels of flavonoids, such as apples, pears, berries, and peppers, could help people maintain a healthy weight.

"We know that even small increases in weight can have a substantial impact on risk of high blood pressure, developing heart disease, cancer or diabetes. Eating a balanced diet high in fruit and vegetables along with regular physical activity is an essential part of maintaining a healthy weight.

"Unfortunately, most adults in the UK struggle to eat the '5-a-day fruit and vegetables' recommendation, so the take-home message is still that we all need to be eating more fruit and vegetables, rather than focusing on particular types."

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