Yes nuts are good for you

A few years ago, I blogged about a study in The New England Journal of Medicine (NEJM) that found that consuming nuts on a daily basis significantly decreased mortality in an adult population over a 30-year period. More specifically, people who ate nuts at least 7 times per week were 20% less likely to die than people who did not eat nuts.

Importantly the effect was dose-dependent, i.e. the more frequently you ate nuts the better the health outcome. Those who ate nuts once a week had a reduction in mortality of 11% (health hazard ratio of 0.89 compared to non-nut eaters), those who ate nuts 5 or 6 times per week had a mortality rate reduction of 15% (hazard ratio = 0.85), and those who ate nuts 7 or more times per week were 20% less likely to die (hazard ratio = 0.80).

However one important caveat was that the study was sponsored by the NIH and the International Tree Nut Council Nutrition Research and Education Foundation, and so one could argue that a conflict of interest arose with the latter organization that might have influenced the interpretation of the results.

Now there is further evidence for the healthful benefits of nuts from a second study which is a meta-analysis of previously published work (BMC Medicine). Researchers found that combining the data from 20 studies (including the NEJM results) showed that nuts are indeed good for you (EurekAlert):

"A large analysis of current research shows that people who eat at least 20g of nuts a day have a lower risk of heart disease, cancer and other diseases. The analysis of all current studies on nut consumption and disease risk has revealed that 20g a day - equivalent to a handful - can cut people's risk of coronary heart disease by nearly 30 percent, their risk of cancer by 15 percent, and their risk of premature death by 22 percent. An average of at least 20g of nut consumption was also associated with a reduced risk of dying from respiratory disease by about a half, and diabetes by nearly 40 percent, although the researchers note that there is less data about these diseases in relation to nut consumption."

The overall risk reduction for premature death was 22% which was very close to the 20% reduction in hazard ratio in the group that ate nuts at least 7 times a week in the NEJM study. Both studies examined the effects of a handful of nuts, either 20g (BMC) or 1oz = 28g (NEJM), once a day (BMC) or from once a week to once a day (NEJM). The general agreement of the two sets of data is encouraging, and importantly the new study was not sponsored by the International Tree Nut Council Nutrition Research and Education Foundation.

So then why are nuts good for you?

One possibility is that the nuts possess healthful ingredients such as unsaturated fatty acids, high-quality protein, fiber, vitamins, and minerals. Indeed nuts are an important part of the Mediterranean diet which has been shown to be associated with a reduced risk of lethal cardiovascular events like heart attacks and stroke. Another related hypothesis is that nuts might substitute for (and reduce consumption of) junk food like french fries and potato chips, which are unhealthy because of the large number of calories, and high levels of trans and saturated fats which can lead to elevated LDL (bad cholesterol).

One of the authors of the meta-analysis emphasized the healthful aspects of nuts (EurekAlert):

"What makes nuts so potentially beneficial, said Aune, is their nutritional value: "Nuts and peanuts are high in fibre, magnesium, and polyunsaturated fats - nutrients that are beneficial for cutting cardiovascular disease risk and which can reduce cholesterol levels. "Some nuts, particularly walnuts and pecan nuts are also high in antioxidants, which can fight oxidative stress and possibly reduce cancer risk. Even though nuts are quite high in fat, they are also high in fibre and protein, and there is some evidence that suggests nuts might actually reduce your risk of obesity over time."

However, one should not ignore the substitution effects. The key variable is the net benefit of nuts over what you would be eating if you weren't eating nuts. To a certain extent, nuts substitute for food products high in fat because nuts themselves contain a lot of fat. One should not forget that fat is an essential part of the diet, and the daily recommended amount is 70g. But not all fat is created equal; they affect your bad cholesterol (LDL) levels differently. Trans fats are the worst at increasing LDL, followed by saturated fats. Monounsaturated and especially polyunsaturated fats are the best at decreasing LDL levels. Because nuts contain a lot of monounsaturated and polyunsaturated fat they are a better source of fat than a typical substitute such as meat.

For a more direct comparison one can examine the nutritional chart of peanuts versus beef (Figure 1). Peanuts contain a lot more fat, approximately 50% of their total weight (72g of fat per 146g cup). Beef on the other contains 13g of fat per 85g (15% fat) serving of ground beef. The difference though is that in nuts 23g/72g (32%) is the most healthy polyunsaturated fat, whereas with ground beef, only 0.9g/13g (7%) of the fat is polyunsaturated.

The bottom line is that nuts are a much better source of fat than meat or any other animal product (fish is much better than beef or pork) or artificial fat (e.g. margarine which contains trans fat). So eat nuts (but not too many because they contain so many calories) as a substitute for meat, especially red meat.

Figure 1. Peanuts contain a lot of fat but mainly unsaturated fats including a significant fraction of polyunsaturated fat which is the most healthy. Beef on the other hand, contains less fat, but it is mostly saturated fat with only a small amount of polyunsaturated fat.