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7. What is the role of food in preventing depression and improving mood, performance and cognitive function?
Med J Aust 2000; 173 Suppl 6 November: S104-S105 Omega 3 polyunsaturated fatty acids (PUFAs) largely determine the fatty acid membrane composition in the brain. In humans, the essential PUFAs -- linoleic acid (C18:2 omega 6) and alpha-linolenic acid (C18:3 omega 3) -- are precursors for the longer-chain PUFAs, and must be supplied by the diet. Dietary sources of omega 3 PUFAs include seafood, flax seed, canola oil, soy bean oil and walnuts. A diet low in omega 3 PUFAs could disrupt cell membrane composition and structure, thereby causing alterations in brain receptor function and enzyme activity, as well as biochemical interactions and the movement of nutrients. Direct measures of the fatty acid composition of serum and platelets in depressed patients support the hypothesis that omega 3 PUFAs protect against depression.1 Weight-management strategies Obesity, weight-reduction regimens and dietary fat restriction may all contribute to depression. Interestingly, a population study showed that obesity was associated with an increased risk of depression in women, but a decreased risk in men.2 Researchers have so far been unable to determine a causal relationship between depression and obesity. However, weight reduction should be undertaken slowly, with moderate fat restriction, and with care to maintain omega 3 PUFAs in the diet. The synthesis of serotonin in the brain is dependent on the supply of its amino acid precursor tryptophan, and it has been found that moderate dieting in women lowers plasma tryptophan sufficiently to reduce brain serotonin synthesis.3 This supports previous results in animal and human studies.4 Further, a small, but well controlled, study found reducing fat in the diet from 41% of total energy to 25% of total energy had adverse effects on mood within a month.5 It is possible that these neurochemical changes, combined with altered membrane activity from a reduced intake of omega 3 PUFA in low fat diets, may predispose women to depression. Caffeine Caffeine increases alertness and reduces fatigue. Negative effects have been demonstrated when large amounts are given or when sensitive groups are studied.6,7 Other disease risk factors need to be taken into account when determining level of caffeine intake, but regular consumption of small amounts of caffeine is beneficial. Regular meals Eating breakfast regularly has been reported to improve performance and lead to a more positive mood, better memory and feelings of calmness.8,9 Researchers who compared three studies involving breakfast, memory function and blood glucose levels concluded that "Eating breakfast benefits memory".10 They found that a high blood glucose level after eating breakfast is one of the key reasons for the improvement in mental performance, particularly the speed of recalling new information. Preliminary results in small groups suggest that omitting breakfast and dinner negatively affects cognitive functioning, and that afternoon snacks may improve cognitive performance.11,12 However, it is important to note there are a number of variables, which have not been measured adequately, which can interact with the effects of food intake on subsequent tasks. Vitamin B6 supplements There is little evidence that vitamin B6 supplements are effective in ameliorating depression or mood changes in older women. Anecdotal evidence appears to have been extrapolated from studies on premenstrual syndrome. Even in these studies, the findings are ambiguous, with a double-blind study showing that pyridoxine (vitamin B6) gave poorer results than placebo.13 A systematic review of published and unpublished randomised placebo-controlled trials of the effectiveness of vitamin B6 in premenstrual syndrome and premenstrual depression concluded that doses up to 100mg may be of small benefit.14 However, practitioners need to be aware that sensory neuropathy has been reported with vitamin B6 supplements. Ensure adequate nutrition by including a variety of foods As expected, cognitive performance is related to nutritional status. Good nutrition, both long term and current, may protect cognitive functions as we age.15 This protection may be conferred by a variety of dietary components, including antioxidants. There is some evidence that vitamin E, which prevents oxidative damage induced by beta-amyloid in cell culture, may delay cognitive decline.16 Clinical trials of vitamin E and dementia are ongoing. It is also interesting that women with metabolically significant vitamin B12 deficiency are at twice the risk of severe depression as women without this deficiency.17 Further study is required to determine these mechanisms.
References
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