I’ve discovered that most people are usually judicious in how they administer medicines to themselves; in contrast, people are often cavalier in their decisions about which foods they consume.  Thus, the average person is unlikely to abruptly stop taking their medicine, in contrast, many people decide, usually without much forethought, that they are going to stop eating red meat. Is this always a good decision?

When humans consume diets that are low in tryptophan, a condition often seen when someone first goes on a vegetarian diet, the brain produces much less serotonin and humans display many of the symptoms of depression such as anxiety, irritability, and difficulty thinking. I have seen the same thing happen to many of my students who decided to become vegetarians without considering the consequences of such a drastic change to their nutrient intake. Historians now blame low- tryptophan diets, e.g. due to crop failure, for multiple wars and acts of cannibalism (which would have the benefit of restoring their protein intake).  Scientists once thought that drinking a glass of warm milk before bed, or eating lot of turkey meat at the holidays, made us drowsy because of tryptophan loading – the current evidence does not support this explanation (turkey meat is actually quite low in tryptophan) but the claim makes an important point: we must get the right balance of any particular nutrient into our brain in order for us to notice any effects.

Some dietary regimens may be beneficial over the long term, for example, it’s widely known that the Mediterranean diet has been associated with a lower risk of depression. In contrast, a poor diet that is high in saturate fats and caloric levels leads to depression.  In one study, subjects who consumed more water, insoluble fiber, ascorbic acid, tryptophan, magnesium and selenium reported a better mood overall.  A diet high in legumes, fruits and vegetables, such as a typical vegetarian diet, would easily provide these nutrients.  Thus, leading a safe and well-balanced vegetarian diet can be quite beneficial to one’s health.  That’s the most important thing to consider when converting to a vegetarian diet: where will you get the nutrients that others easily obtain from red meats? Good sources for protein with a complex blend of amino acids, long-chain omega-3 fatty acids and bioavailable iron and zinc are frequently missing from vegetarian diets. Furthermore, Vitamin B12 deficiency often develops with normal aging; thus, being an elderly vegetarian might make obtaining this vitamin more problematic.  As long as a vegetarian obtains sufficient quantities of these essential nutrients there is no reason to expect any negative health consequences.  Indeed, there are many positive benefits for the brain (and body of course) in following a vegetarian diet. For example, vegetarians are less likely to develop type 2 diabetes which is a risk factor for dementia and Alzheimer’s disease.

Several studies of people who do not pay attention to their nutrient balance have reported that vegetarian diets are associated with a higher prevalence of major depression. This mood change can be attenuated by eating a whole egg, which often exerts an antidepressant-like effect for vegetarians. In contrast to all of these wonderful indicators is a study published in the journal PLOS ONE  (Vol 9, 2014) that reported some conflicting findings. First, the good news: a vegetarian diet was related to a lower BMI and less frequent alcohol consumption.  However, the authors also discovered that a vegetarian diet was associated with higher incidences of mental health disorders. Why? One study (International Journal of Behavioral Nutrition and Physical Activity, Vol 9, 2012) discovered that the adoption of the vegetarian diet tends to follow the onset of certain mental disorders. These authors concluded that a vegetarian diet is associated with an elevated risk of mental disorders. However, it remains to be determined which came first, a mental disorder or becoming a vegetarian. My advice would be to limit everything from a cow (and any other red meat source) and be very careful about obtaining a balance of the nutrients I mentioned above.

© Gary L. Wenk, Ph.D.  is the author of The Brain: What Everyone Needs to Know (2017) and Your Brain on Food, 2nd Edition, 2015 (Oxford University Press).

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