Considerable evidence has linked an unhealthy diet to obesity, metabolic syndrome, diabetes and cancer.  We now understand how chronic obesity ages us and then underlies the foundation of our death.  Furthermore, obesity leads to body-wide chronic inflammation that predisposes us to depression and dementia.  However, these are all the long-term consequences of our diet upon our body and brain.  What about the short- term consequences?  Can specific nutrients in my breakfast or lunch influence my brain’s function today?  Intuitively, we would all agree that this is certainly likely.  After all, being depressed or anxious can lead to poor dietary habits; conversely, poor dietary choices can lead to depression and anxiety.  Although it can be difficult to determine which came first in some people, most relevant studies indicate that an unhealthy diet is a significant risk factor for future depressive symptoms (Br J Psychiatry 2009;195:408-413).

Unfortunately, there is very limited rigorous scientific evidence in humans that links specific nutrients to our mood.  Although some recent studies have suggested that omega-3 fatty acids and some minerals such as selenium, zinc and magnesium might prevent mood disorders the findings are too inconsistent to draw strong conclusions. Some dietary regimens may be beneficial, for example, the Mediterranean diet has been associated with a lower risk of depression (BMC Med 2013;11:13). An investigation of popular fad diets, such as those recommending either high protein or high carbohydrate intakes, found no relation between mood state and macronutrient content (Genes Brain Behav 2009;8:193-202).  Thus, these diets are not likely to make someone more or less anxious or relaxed, as compared to being an omnivore. 

A recent study (Nutritional Neurosci 2015;18:137-144) investigated for twenty-three months the association between diet and overall mood state in eighty-four adult humans with metabolic syndrome.  The scientists carefully monitored the participants’ daily servings of cereals, vegetables, fruits, dairy products and meat, and the percentage of energy provided by total and saturated fats, as well as the daily amount of cholesterol and sodium.  The number of different foods consumed daily determined the variety of the diet. Daily mood was determined using a Visual Analogue Scale mood thermometer.  Importantly, their results were corrected for the possible effects of caloric intake, age and sex.

The results confirmed that a poor diet that was high in saturate fats and caloric levels lead to depression.  Possibly more important, their analysis of the effects of specific nutrients indicated that people who consumed more water, fiber, ascorbic acid, tryptophan, magnesium and selenium reported a better mood overall.  A diet high in legumes, fruits and vegetables, such as the Mediterranean diet, would provide these nutrients.  One quite interesting finding was that a diet with higher variety of fruits and vegetables was more effective than eating a diet that had a limited variety.  It is unknown what role fiber plays in the control of mood and the finding in this study might be related to the presence of fiber in most legume, fruits and vegetables that were reported by the participants.  Probably the most encouraging point to take away from this and similar studies was that it is never too late to take advantage of the benefits of a healthy diet (Am J Clin Nutr 2013;97:419-427). 

© Gary L. Wenk, Ph.D. Author of Your Brain on Food, 2nd Edition, 2015 (Oxford University Press)

TED talk: The Brain Cafe