A study published last week in the New England Journal of Medicine found that the consumption of nuts was tied to lower mortality rates. I love nuts but I hate studies like this.
The research was funded by the International Tree Nut Council Nutrition Research and Education Foundation. Yep, that sounds like an impartial sponsor. I’m sure that didn’t affect the results whatsoever. Yes, they may have had no influence on the design and results but if they study hadn’t found a benefit to eating nuts would it have been published? Would it still have been promoted in the press?
Even putting aside the significant issue of bias, this study wasn’t great. It used the data from the Nurses’ Health Study. Why do I see this as an issue? Well, it relied on self-reported data. We know that self-reported food intake surveys are flawed and tend to provide inaccurate information. Even if the information provided was accurate, we don’t know how generalizable the results from a survey solely of nursing staff is to the general population. These nurses may differ in some fundamental way from the general populace. There’s huge potential for confounding factors in studies like this. Lower mortality rates may be attributed to other aspects of lifestyle, diet, or socioeconomic status. The nut eaters could have been eating the nuts with something else that was the actual health promoter or they may have been eating the nuts in place of something else that was detrimental to health.
It also bothers me that people who had previously had cancer, heart disease, or stroke were excluded from the study. This means that even if eating nuts benefits healthy people (as the study claims) we still don’t know if it benefits those who are, or who have been, ill.
The study also fails to tell us if there is a limit to how many nuts we should eat in a day for maximum benefit. They found that those who eat nuts at least daily had the lowest mortality rates. However, they didn’t say how many nuts people were eating each day. Nuts are undoubtedly delicious and nutrient dense. They are also calorie dense. Having a handful of nuts on your oatmeal or a walnut pesto on your pasta may be beneficial but eating a large bag of trail mix for a snack most likely is not. Simply telling people to eat more nuts is not helpful dietary advice.