The Mediterranean diet, rich in olive oil, fruit and vegetables and fish, has long been linked to lower incidence of heart disease, obesity and certain types of cancers.
The current evidence supports these claims, said Annie Lapointe and colleagues from Laval University in Quebec, in the Journal of Nutritional Biochemistry (doi: 10.1016/j.jnutbio.2006.01.001).
However, the numerous clinical trials that report on individual supplements like vitamins C and E, beta-carotene, polyunsaturated fatty acids, and polyphenol compounds are insufficient to draw firm conclusions.
"Overall, antioxidant vitamin supplements and fish-oil supplements have not been clearly shown to exert a beneficial effect on circulating oxidized-low density lipoprotein (ox-LDL) concentration, which has been identified as a risk factor for CVD," said Lapointe.
The reason the Mediterranean diet has more clear results, say the reviewers, is due to the combination of dietary antioxidant compounds that work together to reduce LDL oxidation.
"The effect of the Mediterranean diet of ox-LDL particles may explain, at least in part, its cardioprotective potential," said Lapointe.
The reviewers called for further intervention trial, particularly to "investigate the possible interaction and synergic effects of the combination of flavonoid consumption as well as the combination of nutrient and flavonoid intakes."