January 27, 2016

expert reaction to dietary flavonoids and weight maintenance

Publishing in The BMJ a group of scientists have investigated the effects of dietary flavonoids on weight and report that higher intake of foods rich in flavonoids was associated with a reduction in weight over time.

Dr Paul Kroon, Research Leader and Head of the Polyphenols and Health Group, Institute of Food Research, said:

“This report describes the results of a big study that was looking at possible associations between how much flavonoids people consume in their normal diets on their rate of weight gain across a long period of time (>20 years). It is important to understand that these types of studies can find associations between consumption of certain food bioactives (like flavonoids and other polyphenols) with weight gain or other health benefits, but they cannot prove that by increasing your consumption of flavonoids you will put on less weight than if you didn’t. The only way to prove that this is the case is by conducting long-term, well controlled dietary intervention studies, and so far no such trials have been reported in the scientific literature.

“Nevertheless, there is considerable scientific evidence that consumption of flavonoids can cause beneficial changes in other biomarkers of health. For example, there are numerous reports and meta-analyses of data from randomised controlled trials demonstrating that consumption of some flavonoid-rich foods such as those rich in flavan-3-ols (cocoa, dark chocolate green tea, black tea) cause beneficial changes in markers of cardiovascular disease risk including blood pressure and endothelial function, and there is mounting evidence that consumption of anthocyanins from coloured berries and currants causes reductions in plasma cholesterol.”

Prof. Ian Johnson, nutrition researcher and Emeritus Fellow, Institute of Food Research, said:

“This study is broadly in line with public health advice to consume diets rich in fruits and vegetables but in an observational study of this kind it is difficult to be sure that the effects on weight gain can be specifically ascribed to flavonoids.”

Prof. Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“Is there anything magical about flavonoids? I am not convinced by this paper. The current study, as usual, places lots of emphasis on associations of flavonoid rich food and weight change but this type of study cannot and should not be taken as proving a cause-effect relationship. In truth, individuals who eat more high flavonoid foods have other habits which lead them to put in less weight or other effects of high flavonoid foods may be responsible, such as fibre content in fruits and vegetables. Hence, one must be very careful about recommending high flavonoid foods as beneficial to health.  Our lab conducted a recent randomised-placebo controlled trial of polyphenol / flavonoid rich drinks and saw no effect over the short term (one month) on markers linked to heart disease or diabetes, and longer term trials are needed to prove effects on weight. Yes, for those who eat little fruit or veg, we should encourage more fruit and vegetables, but this is common sense. But I do not know of any robust evidence from trials that extra flavonoids over and above what is recommended will benefit health. ”

‘Dietary flavonoid intake and weight maintenance: three prospective cohorts of 124 086 US men and women followed for up to 24 years’ by Bertoia et al. published in The BMJ on Wednesday 27th January. 

Declared interests

Dr Paul Kroon: Member of Health Claims Advisory Board whose remit is to monitor changes in regulations and guidance from EFSA and other authorities in relation to European health claims within the BACCHUS project. Has acted as a one-off consultant for Coressence Ltd, Cambridge Theranostics Ltd, and Kraft Inc. Has received industry grants of work investigating the effects of fruit polyphenols on vascular endothelial cells. Full details here: www.bacchus-fp7.eu/sites/default/files/styles/thumbnail/public/Paul%20A%20Kroon.pdf

Prof. Ian Johnson:  Ian Johnson is an Emeritus Fellow at the Institute of Food Research and was a member of the SACN Working Group on Carbohydrates and Health. He currently has no research grants or commercial affiliations.

Prof. Naveed Sattar: “Our well conducted small placebo-controlled RCT of polyphenol drink was funded by Coca-Cola and is now, eventually, published as negative trial: Mullan A, Delles C, Ferrell W, Mullen W, Edwards CA, McColl JH, Roberts SA, Lean ME, Sattar N. Effects of a beverage rich in (poly)phenols on established and novel risk markers for vascular disease in medically uncomplicated overweight or obese subjects: A four week randomized trial. Atherosclerosis. 2016 Jan 6;246:169-176. doi: 10.1016/j.atherosclerosis.2016.01.004. PubMed PMID: 26797134.”