Our view of nuts, in particular tree nuts, as dietary components has undergone an evolution. Nuts are an essential ingredient in many formulations because of their richness and subtle flavors. But that richness is due to fat content, which can be 80 percent of the calories in most nuts. If you are counting calories, that’s a whopping 800 per cup, give or take a few. So dieters had to eat nuts with caution.
Recently, the reputation of nuts soared with the dual realization that not all fats are equal (and the fats in nuts happen to be among the healthiest) and that nuts are a rich source of phytochemicals, including some with strong antioxidant action.
- A dominant fatty acid in nuts is monounsaturated oleic acid, the same as in olives and avocadoes. Oleic acid had the reputation of lowering LDL cholesterol without lowering HDL cholesterol.
- Pine nuts and walnuts are rich in omega-6 fatty acids.
- Walnuts are a source of omega-3 fatty acids.
- Many studies confirm that nuts are a wise choice in a diet to reduce the risk of heart disease.
- In an article published last year in Nutrition Research Reviews, Bradley Bolling of the Department of Nutritional Sciences at the University of Connecticut noted that tree nuts contain a variety of phytochemicals, including carotenoids, phenolic acids, phytosterols and polyphenolic compounds such as flavonoids, proanthocyanidins and stilbenes. Carotenoids, phenolic acids and flavonoids function as powerful antioxidants.
- Flavonoids, a subclass of phenolics, includes flavonols, flavones, flavanones, flavan-3-ols (the primary flavonoids in nuts), anthocyanidins and isoflavones. Flavanones and isoflavones are also found in nuts, but in smaller quantities.
- Proanthocyanidins (PACs) are related to anthocyanidins and include catechins, epicatechin, and epigallocatechins — all found in hazelnuts, pecans and pistachios. They also include afzelechin (almonds). The A-type PAC have been found only in almonds.
- The antioxidants in nuts vary with species and preparation method. Total phytochemical content is affected by environment, cultivation practice, climate, processing and storage. The value is further subjected to the methods used to separate and measure them. According to Bolling, almonds, hazelnuts, pecans and pistachios have higher contents of PAC than do other tree nuts, ranging from 184 to 501mg per 100g.
- Flavonoids have been detected in all tree nuts, but pecans, macadamias, almonds and pistachios have the highest concentrations (25 to 2,713mg per 100g). Pecans and walnuts are rich sources of phenolic acids and aldehydes, with 2,052 and 39mg per 100g, respectively.
- Almond skins are the subject of specific study. According to Sam Cunningham, food technologist and co-owner of Nut-trition Inc. (www.nut-trition.com), Hughson, Calif., "At least 33 bioavailable flavonoids and polyphenolic compounds have been identified in almond skins so far. Almond Bran is a rich source of almond sterols and essential minerals such as magnesium, calcium, phosphorus and potassium. The total antioxidant capacity of Almond Bran is more than 13 times greater than that of almonds alone, and it contains less than half the fat and nearly four times the dietary fiber."