The health benefits of nuts are well reported in the scientific literature. In particular nuts have been shown to have beneficial effects on blood lipids and are associated with a reduced risk of cardiovascular disease. Nuts may be beneficial because their fat content is mainly monounsaturated and polyunsaturated fatty acids. However, the beneficial lipid lowering properties of nuts may not be the sole reason for the health effects of nuts, as their rather modest roughly 5 % reduction in serum cholesterol can not explain their roughly 30 % reduction in the risk of cardiovascular disease, based on cohort studies. Therefore nuts likely have other effects that may explain their health effects, and of particular interest to researchers are nut antioxidants. Nuts are good sources of vitamin E, and many contain high concentrations of polyphenolic compounds, such as ellagic acid in walnuts.
Nut antioxidants have been extensively investigated by researchers. For example, in a dose response study1 hyperlipidaemic men and women consumed 3 isocaloric (423 kcal/d) supplements which consisted of either full-dose almonds, half-dose almonds with half‑dose muffins, or full-dose muffins. Subjects were assessed at baseline and then again at 2 weeks and at 4 weeks for a number of markers of oxidative stress, and lipid profiles were taken from plasma samples. At the 4 week point, the full-dose almond group experienced reduced serum concentrations of malondialdehyde and creatinine-adjusted iosprostane output, compared to the controls. Both the full and half-dose almond groups experienced reductions in serum total cholesterol in comparison to the control group. In the full-dose almond group, serum low density lipoprotein cholesterol was significantly lower, and high density lipoprotein cholesterol was significantly higher, than in the control group.
As well as their extensively reported lipid lowering effects, these results support previous studies that show benefits to nut antioxidants in vivo. This antioxidant effect is likely to occur through mechanisms other than increases in vitamin E, because baseline levels of α- and γ-tocopherol did not increase with almond supplementation. Previous studies have found an increase in vitamin E levels with nut supplementation, but the subjects started with lower levels of plasma tocopherols at baseline compared to this study. Therefore the antioxidant effects in this study are more likely due to the polyphenolic compounds present. Almonds are a good source of flavonols (isorhamnetin, kaempferol and quercetin), flavan-3-ols (catechin and epicatechin), flavanones (naringenin), anthocyanins (cyanidin and delphinidin), procyanidins (B2 and B3) and phenolic acids (caffeic acid, ferulic acid, ρ-courmaric acid, protocatechuic acid and vanillic acid), located mainly in the skin. Nut antioxidants may therefore confer significant health benefits to humans.
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