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Nuts

Archaeological records show that the consumption of tree nuts and peanuts spans several centuries. Today, a wide variety of tree nuts as well as peanuts (a legume) are consumed. Frequent nut consumption is associated with numerous health benefits due to their unique nutrient profile. This entry describes the nutrient composition of nuts, along with the epidemiologic and clinical evidence supporting their cardioprotective benefits.

Nutrient Profile

By botanical definition, the majority of commonly consumed nuts are not really nuts but rather fruits and seeds. “True nuts” therefore are the acorn, chestnut, hazelnut, beech, and filbert. However, in the cornucopia of foods, nuts generally are characterized as a dry fruit comprising an edible kernel or meat encased in a woody or leathery shell. Other nut varieties include walnuts, almonds, macadamia nuts, pecans, pistachios, and hazelnuts. Often these varieties and the “true nuts” named above are collectively referred to as tree nuts. Peanuts are distinctly different from tree nuts in that they grow underground.

Because of their macro- and micronutrient profile, tree nuts and peanuts are nutrient- and energy-dense foods. All nuts are high in unsaturated fatty acids and are good sources of protein. Peanuts share a similar nutrient profile with tree nuts, although they typically contain less fat and more protein. Nuts lack some essential amino acids, and therefore, they are an incomplete protein source. The limiting amino acid is generally threonine, with low levels of isoleucine, lysine, and the sulfur amino acids (e.g., methionine and cysteine). The amino acids, phenylalanine, tyrosine, valine, and histidine, are relatively high in nuts, and peanuts are a good source of arginine. Nuts are low in saturated fatty acids and high in unsaturated fatty acids, particularly monounsaturated fatty acids. Some nuts (such as walnuts and to a lesser extent pecans, pine nuts, pistachios, and peanuts) are important sources of omega-6 and omega-3 fatty acids. Nuts also contain other components that are known to be cardioprotective, including dietary fiber, micronutrients (copper, magnesium, potassium, phosphorus, calcium, and vitamins E and B), and plant sterols. They also are a rich source of bioactive phytochemicals and antioxidants, such as phenolic compounds, resveratrol, and arginine. Antioxidant content is much higher in nuts containing the pellicle (i.e., the skin). Until recently, the health benefits of nuts were largely attributed to their fatty acid composition, but there is increasing evidence that other constituents contribute to their cardiovascular benefits.

Health Benefits

Epidemiologic studies consistently report an association between nut consumption and reduced incidence of disease. Several prospective cohort studies conducted in the United States (The Adventist Health Study, Nurses' Health Study, Iowa Women's Health Study, Physicians' Health Study) have shown an inverse association between nut consumption and incidence of coronary heart disease. A pooled analysis of these studies determined that people who consumed nuts most frequently had a 35% lower risk of developing coronary heart disease than people who never or rarely consumed nuts. Another study that evaluated the independent effects of peanuts on coronary heart disease risk reported that people who consumed peanuts 2 times per week had a lower relative risk of coronary heart disease (respiratory rate [RR] 0.66). Interestingly, the same study reported that this relationship was somewhat less strong for tree nuts (RR 0.79). Nut and seed consumption also has been inversely associated with levels of inflammatory markers, C-reactive proteins, interleukin 6 (IL-6), and fibrinogen. This is important as the progression of atherosclerosis is largely mediated by inflammatory processes that promote lipid accumulation and oxidation and eventually plaque rupture.

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