Findings from the cross-sectional multi-variable study suggest flavonoids may contribute to an overall healthier fat mass profile.
This definition includes body fat distribution, which may be a stronger influence on insulin resistance and inflammation that is characteristic of metabolic conditions such as diabetes.
The associations were made with achievable dietary intakes of flavonoids in mind. According to the research team, the findings had specific relevance for public health recommendations aimed at reducing body fat composition.
Current European recommendations differ from country to country with health campaigners also debating as to whether eating vegetables over fruit is more beneficial.
The UK’s EatWell guide for example recommends at least 5 portions of a variety of fruit and vegetables a day – an amount also recommended by the World Health Organisation (WHO) and other countries such as Germany and the Netherlands.
France has taken this figure and doubled it with recommendations totalling 10 fruit and veg portions a day as standard.
Further afield the Australian government has set out advice of “two plus five” a day that recommends people consume two portions of fruit and five of vegetables.
Researchers from Kings College London and the University of East Anglia enrolled a total of 2734 healthy, female twins aged 18–83 years.
Intakes of total flavonoids, flavanones, anthocyanins, flavan-3-ols, flavonols, flavones, polymers, and proanthocyanidins were assessed using food-frequency questionnaires.
Dual-energy X-ray absorptiometry—a technique normally used to measure bone mineral density—was used in this case to measure total fat content, including limb-to-trunk fat mass ratio (FMR), fat mass index, and central fat mass index.
Results found a higher intake of anthocyanins, flavonols, and proanthocyanidins were associated with a lower FMR.
Twins with higher intakes of flavan-3-ols, flavonols and proanthocyanidins had a significantly lower FMR than that of their co-twins with within-pair differences of 3–4%.
Further analyses of twins with higher intakes of flavonol-rich foods (onions, tea, and pears), proanthocyanidin-rich foods (apples and cocoa drinks) had a 3–9% lower FMR than that of their co-twins.
This finding was also observed in younger participants (aged 50 years) consuming anthocyanin-rich foods (berries, pears, grapes, and wine).
“We showed that higher intakes of anthocyanins and flavonols were associated with lower fat mass and reduced central adiposity,” said the research team.
“These inverse associations were independent of established dietary and other risk factors, including physical activity,” they added.
One finding of note found the addition of total fruit and vegetable intake and fibre intake to the model did not significantly weaken the relationship.
The team thought this benefit was specific to a food constituent contained within flavonoid-rich foods and not necessarily to subjects who ate large amounts of fruit and vegetables.
Likely mechanisms of action
Such is the strength of evidence of flavonoid efficacy, several plausible mechanisms linking this metabolite to fat distribution were proposed.
Evidence that the bioactive constituent, the flavan-3-ol epigallocatechin gallate (EGCG) prevents lipid absorption, decreases the expression of genes that regulate lipid metabolism and increases energy expenditure have been put forward.
Additional animal studies have provided more explanation on the effects of dietary flavanones, flavonols and anthocyanins on obesity.
Mechanisms mentioned include the inhibition of cell differentiation, the regulation of glucose tolerance, and the adjustment of insulin and inflammatory signalling pathways.
Source: American Journal of Clinical Nutrition
Published online ahead of print: doi: 10.3945/ajcn.116.144394
“Higher dietary flavonoid intakes are associated with lower objectively measured body composition in women: evidence from discordant monozygotic twins.”
Authors: Amy Jennings, Alex MacGregor, Tim Spector, and Aedın Cassidy