Observational studies show that flavonoid rich foods, including fruits and vegetables, are protective of cardiovascular disease. Further, clinical studies investigating the effects of isolated flavonoids in humans and animals show that they are biologically active. The protective effects of flavonoids may centre on the antioxidant capacity they possess. Structurally flavonoids are polyphenols and the presence of hydroxyl groups confers reducing power to the molecules through electron donation, and their polyphenolic structures then dissociate the charge from the unpaired electrons over the entire molecular structure, stabilising any radical effects. Donation of electrons from flavonoids may quench free radical chain reactions thus protecting body tissues. In particular, flavonoids in their antioxidant role may be protective of the vascular system through reductions in systemic oxidation, which in term may decrease the risk of endothelial dysfunction and thus reduce the risk of developing cardiovascular disease.
As with many nutrients that confer health benefits, the doses required to cause beneficial effects in flavonoids is not known. This is confounded by the fact that metabolism rates of flavonoids may vary between individuals and so recommendations are difficult to make. To address these problems one study1 investigated the dose response effects of fruits and vegetables by administering diets with differing flavonoids contents to individuals at high risk of cardiovascular disease. This subjects were selected because they were consuming less than the recommended fruit and vegetable intake daily. Subjects consumed either a high flavonoid diet containing more that 15 mg total flavonoids per day, a low flavonoid diet containing less than 5 mg total flavonoids per day or their habitual diet. Those on the high and low total flavonoid diets had incremental increases in their flavonoid intakes over the course of the 18 week study such that their fruit and vegetable intake increase by 2, 4 or 6 portions per week every 6 weeks.
The results of the study showed that increased consumption of fruits and vegetables improved vascular function and reduced cardiovascular risk profiles in a dose dependent manner. This effects was particularly apparent for fruits and vegetables that contained high concentrations of flavonoids. In men, increasing fruit and vegetable intakes by 2 portions per day increased endothelium-dependent microvascular reactivity (a measure of the ability of the vasculature to react normally), decreased C-reactive protein levels (a marker of inflammation) and reduced E-selectin (a marker of vascular inflammation). In men, increasing fruit and vegetable intake above 4 portions per day also decreased vascular cell adhesion molecule (a measure of the adhesive properties of blood cells). In men and women, more than 4 portions per day of fruits and vegetables increase nitric oxide levels (a marker of endothelial function) and improved the response of the arteries to pulse wave analysis (a marker of endothelial elasticity).
Dr Robert Barrington’s Nutritional Recommendation: This study shows that increasing the fruit and vegetable intake by just 2 portions per day can significantly improve endothelial function in terms of the elasticity of the vasculature. Increasing the amount of fruit and vegetables by a further 2 portions brings the benefits of reduced inflammation and reduced blood adhesion properties. In this study the effects of fruits and vegetables consumption were tested but it is likely that other flavonoid containing foods such as green team red wine and chocolate would have similar effects. The subjects in this study were consuming less than the recommended intake of fruit and vegetables which is perhaps why the effects seen were likely so significant. If the diet is already rich in fruits and vegetables it is unclear if such benefits would be seen. With flavonoids, as with all phytonutrients, the trick is to eat a wide range of chemicals because they tend to have differing and overlapping effects, which may be synergistic in their action.
RdB
