Pecan Tree, East Ranch, Madill, Oklahoma

A Handful of Nuts

A report was published in the New England Journal of Medicine (NEJM) on November 21, 2013, entitled “Association of Nut Consumption with Total and Cause-Specific Mortality.”  This really caught my eye for a few reasons.  The primary reason was I wondered how it was possible to do such a study.  The second, and perhaps the more important, was I wanted to know if eating nuts could really have an effect on one’s mortality.  The third was whether the study would have been published if they had not proven their hypothesis, i.e., that eating nuts is good for you.

The study has a very impressive pedigree.  It was performed and written by researchers from Brigham and Women’s Hospital and Harvard Medical School, the Dana Farber Cancer Institute, and Indiana University.  It was funded by the National Institutes of Health (the NIH), and the International Tree Nut Council Nutrition Research and Education Foundation.  I was unaware of the Tree Nut Council, but it is an interesting note that they would be funding research showing nuts are really good for you.  On the other hand, the report states “the funders of the study had no role in its design or conduct; in the collection, management, analysis, or interpretation of the data; or in the preparation, review or approval of the manuscript.”

How was it possible to do this study?  The study was done by examining nut consumption in two very large groups of people for whom intimate details of their lives are available.  One is a group called the Nurses’ Health Study, a group of 121,700 female nurses living in 11 states in the U.S.A., enrolled in 1976.  The other is the Health Professionals Follow-up Study, a group of 51,529 male health professionals from all 50 states, enrolled in 1986.  Food frequency questionnaires were regularly filled out by these participants, and were the basis of the data collected.  The examined group was pared down to those for whom good data was available.  People with known heart disease, stroke or cancer were excluded.  Ultimately, they studied 76,464 women, and 42,498 men.  So they had significant numbers of participants to study.  They report that food frequency data was collected from these people using questionnaires administered every 2-4 years, starting with the women in 1980, and the men in 1986.  They asked how often during the preceding year did the person eat a one ounce (28 g) serving of nuts:  almost never, 1-3 times a month, once a week, 2-4 times a week, daily, or more often.  They also asked if the nuts were peanuts (a legume), or tree nuts.  The end point of the study was death.  So, if you were participating and died during the study, your nut consumption, cause of death, and other factors were then compared against the group still alive.  They found some very interesting things about nut eaters.  As a group, they tend to be leaner, less likely to smoke, more likely to exercise and more likely to take a vitamin supplement.  They also consumed more fruit and vegetables, and drank more alcohol.  In other words, they were very much like my running friends.  The researchers state, though, that they were able to tease apart these other factors in order to look at nut consumption alone as a predictive factor.  They found that how often one ate that handful of nuts was inversely proportional to their chance of dying during the study.  This was expressed as a hazard ratio, a way of comparing relative risks, but not the absolute risk, of an event occurring.  During the years of study, 30 for women, and 24 for men, 16,200 women died, and 11,229 men died.  That is around one in four participants in the study, which seems a high number.  The ones who ate the most nuts, more than one ounce a day, had a hazard ratio of dying of 0.8, or 20% lower chance than those who never or rarely ate nuts.  When they examined peanuts versus tree nuts, the reduced risk of mortality persisted.  Brief mention is made in the report that most major causes of death, including heart disease, cancer and respiratory disease, were decreased in the nut eaters, hence the reference to “cause specific” in the title.

They point out some of the strengths and weaknesses of such a study.  The study included a large number of enrollees, so presumably the statistics are meaningful.  They were careful to include methods for ensuring that the data were as reliable as possible, and that their statistical methods compared apples to apples, so to speak.  However, the study is an observational study, so while it can show an association, it cannot show cause and effect.  Another point not mentioned, is that the number of enrollees who died was significant, and makes me think a good number may have been older when they were first enrolled.  Another criticism of the study is that a large percent of the nut eaters were also, in general, more likely to exercise, eat a Mediterranean diet, and be thinner than the nut avoiders who, perhaps, were also were more likely to consume Ho-Ho’s, who knows.   While they state they were able to separate out these variables, intuitively it seems that if someone eats a healthy diet, exercises, and is thinner that person is less likely to develop diabetes, heart disease or cancer. In a related study published in the NEJM February 25, 2013, “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet,” a group of Spanish researchers showed that in a study of people at high cardiovascular risk, but without known heart disease, a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the incidence of cardiovascular events.  This was a prospective study, meaning the study participants were divided into two groups, and studied going forward, rather than observed after the fact.  In fact, the study was stopped at 4.8 years due to the significance of the data being collected.  Of course, that can skew a study also.  It is possible for the healthy eaters to catch up to the poor eaters in their heart disease and mortality given a little more time.

What does this tell us about the value of a handful of nuts, and its effect on our well being?  The researchers give several plausible explanations why nuts may be good for us in general.  They contain unsaturated fatty acids, high-quality protein, fiber, vitamins and minerals.  They also contain certain phytochemicals (plant-based chemicals such as carotenoids, flavonoids and phytosterols) which may be healthful.  They cannot say, based on their research, that if one starts eating a handful of nuts on a daily basis, that person will avoid heart disease or cancer.  If you are my age, 59, much of your fate may already be cast, with regards to eating habits, atherosclerosis, and other long term health issues.  But that doesn’t mean there is no benefit.  In fact, changing one’s dietary ways at any time could have good effects, too.  In general, from numerous other studies cited by the two papers described above, eating a Mediterranean diet which includes olive oil or nuts is a very healthy type of diet.  Does your olive oil need to be “extra-virgin”?  Extra-virgin is cold-pressed and is the first pressing of the olive.  It is less processed than its non-virginal counterparts, and so has more of the natural substances intact.  There are lots of oils that claim extra-virgin status, which don’t quite live up to the name or reputation.  One must shop carefully.

I feel the benefits of a handful of nuts daily are there, but may not be as important as the overall habit of adherence to a Mediterranean diet.  I know at this time of year, close to Christmas, with cold weather and snow, and long nights with short days, the lure of all sorts of dietary indiscretions is strong.  Yet, be mindful of what you eat, as it does become you.  And grab that handful of nuts…

Another Pecan Tree

Citations:

Ying Bao, M.D., Sc.D., Jiali Han, Ph.D. et. al., Association of Nut Consumption with Total and Cause-Specific Mortality.  NEJM, 2013, 369:2001-2011.

Ramon Estruch, M.D., Ph.D., Emilio Ros, M.D., Ph.D., et. al., Primary Prevention of Cardiovascular Disease with a Mediterranean Diet.  NEJM, 2013, 368:1279-1290.