Nuts

Summary (as seen on HEC.iTV):

A handful of a variety of nuts 2 to 5 times a week has been found to significantly lower the risk of heart disease. If you are worried about your weight, combining nuts/seeds with low calorie foods is a good way to eat them e.g. vegetable stir frys or salads, because when nuts are consumed as a snack the temptation to consume more than a handful is probably greater.Instead of having that biscuit or piece of cake, try a handful of plain unroasted and unsalted nuts; unroasted because nuts are sometimes roasted in saturated fat. Vegetarians/vegans or people who avoid red meat would be advised to eat nuts almost daily because nuts are a good substitute for meat (with respect to protein, fat, iron, zinc and niacin). For example ½ cup of nuts or ¼ cup of seeds or 2 tablespoons of nut/seed spreads like peanut butter or sesame seed paste (tahini) are equivalent to a serve of meat. So, yes, nuts are a healthy inclusion to our diets. See also the HEC healthy eating pyramid.

Nuts and Health

Nut consumption is very low in Australia - less than 4g/day and has been decreasing over the past 20 years. Unfortunately, nuts were given a ‘bad’ name in the 1970's because of their energy density and lack of information about their phytochemical content. As a result they were not recommended for people with coronary heart disease or people trying to lose weight. In the meantime, several studies have shown that nuts can protect against heart disease, but still need to be consumed in moderation by overweight people.

In 30,000 people, a handful of nuts twice per week was associated with 20% less coronary heart disease (CHD) incidence and 5 times/week with 50% less CHD. They can also help lower blood lipids and reduce the oxidation of LDL, probably due to their high content of vitamin E and other phytochemicals, including phytoestrogens.

The Nurses’ Health Study in the US has been going since 1976 and originally monitored a population of over 121 000 nurses. One advantage of this study is that the researchers measured many factors including diet so that they could be compared to the diseases the women later came down with. Women who ate about 30g of nuts at least five times per week were not the same as the average women in the study. They were smoking less, exercising more, more likely to drink alcohol and were thinner. They also ate less meat and had a better profile of fat intake. Clearly the healthier lifestyle reduced the chances of a heart attack, but even so, taking all these and other factors into account, women eating more than 150g of nuts per week had a 35% lower risk of a fatal or non-fatal heart attack.

There was a dose effect up to the five times per week with middling intake offering middling protection. This study did not analyse the data by type of nut (Hu et al., BMJ 1998; 317:1341-45; Tunstall-Pedoe, BMJ 1998; 317: 1332-1333).

There have been several other epidemiological studies showing similar results, in men and women (Fraser et al., Arch Inter Med 1992; 152: 1416-24;Prineas et al., NEJM 1993; 329:359.) Clinical intervention studies with nuts (especially walnuts) have also shown that they lower blood lipids and do not increase the susceptibility of LDL to oxidation (Sabate et al., NEJM 1993; 328: 603-7; Dreher et al., Nut Rev 1996; 54 (8): 241-5).

Nuts are low in saturated fat, naturally cholesterol free and high in monounsaturated fat. Walnuts, however, are high in omega 6 linoleic and omega 3 linolenic acid and brazil nuts are high in the antioxidant selenium and most nuts are high in a variety of phytochemicals (ellagic acid, flavonoids, phenolic compounds, isoflavones). Nuts yield 5-11% by weight of dietary fibre and are an important source of plant protein, providing 10-25% by weight. They also provide vitamin E, folic acid, vitamin B6, niacin, magnesium, zinc, copper and potassium.

Nuts are high in the amino acid arginine. Research has shown that arginine is a dietary precursor of nitric oxide, a potent endogenous vasodilator that acts much like nitroglycerin. Nitric oxide, may have other antiatherogenic properties as well, such as inhibiting platelet aggregation and monocyte adherence (Sabate & Fraser, Prim Cardiol 1993; 19 (11): 65-72).

The vitamin E content of nuts may contribute to the oxidative resistance of LDL cholesterol that is believed to play a role in atherogenesis (Reaven et al., Arteriosclerosis Thromb 1993; 13: 590-600). The folic acid content of nuts may help lower homocysteine levels; high levels have been linked to increased coronary heart disease risk (Selhub et al. NEJM 1995; 332: 286-91). Copper and magnesium found in nuts may be protective against coronary heart disease (Klevay. Arch Int Med 1993; 153: 401-2).

New research on Walnuts (April 2004)

Take home messages

These studies have shed new light on the role of nuts in protecting us against heart disease (despite their energy density). As a result, recommendations regarding nuts have recently changed. Probably the best advice is to have a handful (9-15nuts) of a variety of nuts daily, especially walnuts and almonds.  Instead of having that biscuit or piece of cake, patients can be encouraged to try a handful of plain unroasted nuts (nuts are sometimes roasted in saturated fat). This advice also applies to patients trying to lose weight. Combining nuts with low energy dense foods (e.g. vegetables) in meals is a good way to eat them e.g. Asian style dishes. When nuts are consumed as a snack - the temptation to consume more than a handful is probably greater.

Last Updated: April 2004