How influential is your diet upon how you feel? In fact, on an individual basis, the effect of your diet upon how happy or sad you are can be difficult to predict. Considerable evidence suggests that the absence of depression is associated with better overall health. For example, within 18 months after having a myocardial infarction about one-fifth of patients will develop a major depressive disorder; nearly two-thirds of patients will experience a depressive episode and about one third will be diagnosed with clinical depression. The key element that links poor health, poor diet and obesity, which are all predictors of having a heart attack, is the presence of pro-inflammatory cytokines. Cytokines are proteins that normally defend you from bacteria and viruses. When you have a poor diet, these cytokines can turn against you!
I was recently honored by an invitation to give a TED talk on this idea. The video is available here. http://www.youtube.com/watch?v=4SvkaK2Al0o&feature=plcp
Hundreds of studies have identified a relationship between the absence of foods rich in polyunsaturated fatty acids from the diet with the presence of inflammation and depression. Why? Polyunsaturated fatty acids are abundant in the brain. One specific fatty acid, called Omega-3 (ω-3), is thought to antagonize the actions of pro-inflammatory cytokines and lessen the symptoms of depression. Three ω-3 fatty acids are nutritionally important, including alinolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Humans cannot synthesize ω-3 fatty acids from scratch; you must obtain them from your diet.
Your brain needs a balance between ω-3 fatty acids and a similar fatty acid called ω-6. Both influence many important brain functions, including depression. The reason you need a balance is because these two fatty acids compete for control of the level of inflammation in your brain and ultimately your level of depression. How? Increasing the number of ω-3 fatty acids at the expense of the ω-6 fatty acids reduces the production of prostaglandins. One prostaglandin in particular, from the "E" series (PGE), plays a crucial role in controlling the severity of depression.
Think back to the last time you were very sick due to a bacterial infection; do you remember those nagging feelings of sadness and fear that the lethargy and melancholy would never go away? Those feelings are called sickness behavior and are due, in part, to the presence of prostaglandin E2. Many effective anti-depressant treatments, such lithium, valproate, carbamazepine, fluoxetine and amitriptyline reduce the levels of PGE2 and various cytokines in the brain and body. It's now thought that the reduction in the levels of these molecules is the actual mechanism underlying the effectiveness of these common anti-depressant drug therapies.
Taking supplements containing ω-3 fatty acids to reduce feelings of depression reduces pro-inflammatory molecules (J Neurosci 2009;29:14; J Lipid Res 2003;44:1984). However, the balance of these fatty acids in your diet matter! People diagnosed with depression show a higher ratio of ω-6 relative to ω-3; furthermore, people diagnosed with major depression have a higher ω-6: ω-3 ratio and lower overall ω -3 than those patients diagnosed with simply a minor depression (J Affect Disord 1996;38:35). Why? Because the balance of these fatty acid levels influences the function of the neurotransmitter systems in your brain that appear to control how you feel, including serotonin, norepinephrine and dopamine (Biol Psychiatry 1998;44:235). All of the currently approved anti-depressant drugs either directly or indirectly interact with one or more of these neurotransmitter systems.
Supplementation ω-3 fatty acids or eating a diet rich in fish oils inversely correlates with the prevalence of mood disorders (Lancet 1998;351:1213). Thus, on a daily basis, what you eat does influence how your feel. Apparently, a diet rich in ω-3 fatty acids also significantly changes the size of brain regions that are critical for controlling mood (Biol Psychiatry 2004;56:140). However, it is imperative to get the proper balance of both ω-3 and ω-6 in order to achieve optimal brain function. Too much ω-3 in relation to ω-6 can be quite harmful (Am J Cardiol 2006;98:3). My advice: include leafy green vegetables, flaxseed, canola oils, kiwi fruit, walnuts or marine fish in your diet every day.
© Gary L. Wenk, Ph.D. Author of Your Brain on Food (Oxford University Press, 2010)