The ability of the brain for processes which in include perception, thinking, memory, learning and attention are understood as cognition (Bhatnagar and Taneja, 2001). Nutritional research today suggests diet and specific nutrients may play a role in the development of the brain during pregnancy (Williamson, 2006) and in infancy (Bellisle, 2004) and also may influence the degeneration of the brain function because some diseases such as Alzheimer’s have been shown to be less common in people with diets high in fish and whole grains (Capurso et al., 2004).

Hence it may be questioned whether diet could also improve cognition or cognitive performance in adults. Chronic malnutrition states such as protein malnutrition and iodine deficiencies have clearly been shown to decrease cognitive performance, however whether a low status of micro nutrients and macro nutrients effects cognition seems to be more complex as many factors may interfere with the ability of the brain to process information (Gibson and Green, 2002). Such factors could be age and vulnerability to stress, time of the day or even poor hydration status.

Breakfast seems to increase mental performance particularly for young children in the first half of the day. The effects of breakfast on cognitive function in older children and adults is less well studied, although there is support for beneficial effects, those studies might be stronger influenced by individual differences such as the ability to wake up early, being used to have or not have breakfast or the type of mental task performed within the study.

Studies investigating the effects of food intake on the post lunch dip of mental capacity seem also to be inconclusive as the performance drop might be strongly influenced by other hormonal changes.

Interesting however are findings suggesting that personality type seems to determine in how far a post lunch attention dip occurs or not. Neurotics appear not to lose their cognitive performance as much as do extroverts. Personality such as neuroticism seems also to interact in studies investigating macro nutrient composition and performance.

Current scientific evidence supports that the mental performance of neurotic or stress prone individuals benefits of meals high in carbohydrates and low in protein. Furthermore it appears that meals high in fats decrease alertness and increase sleepiness particularly about 2h past meal ingestion however effects on mental performance seem to be limited.
Late afternoon snacks appear to increase mental ability yet again it is not clear whether this is down to nutrients or to general arousal, as mid-morning snacks seem to induce no effects at all.

Meal size furthermore might be an important aspect to consider if one would like to improve performance with food intake, as subsequent studies indicate that unusually large meals decrease performance for some mental tasks.

A particular interesting aspect of nutritional effects of cognitive performance is the effect of decreased cholesterol levels. A couple of recent studies put forward diets and drugs which reduce blood cholesterol lead to decreased cognitive ability hence it might be necessary to balance cholesterol levels between health harming levels (high cholesterol levels have been shown to increase heart disease) and cognitive decreasing levels and this balance might be furthermore influenced by the relative proportion of mono and unsaturated fatty acids in the diet.

Finally as stated above micronutrients have regularly been shown to effect cognition however their action might be of particular importance in the maintenance of cognition. Population studies in elderly found low levels of riboflavin, cobalmin, and serum folate are common micro nutrient deficiencies in elderly hence they have been proposed frequently to play a role in the decline of cognitive function. B vitamins play an important role in the regulation of homocysteine levels. Increased levels of homocysteine have been implicated in vascular problems which may decrease blood perfusion and supply to the brain and hence lead to progressive loss of brain cell activity. However supplementation of elderly with B-vitamins did not show significant changes in mental capacity.

Finally the effects of vitamin C and vitamin E as antioxidants preventing oxidative damage on brain cells appears to be more supportive as it has been shown that memory and mood improved in vitamin C supplementation in elderly subjects.

In conclusion a healthy balanced diet is not just vital for the development of the brain and its cognitive abilities but also for its maintenance, the direct effects of food and nutrients onto mental performance is complex and influenced by many factors. Current knowledge suggests that low glucose levels in the blood may impair brain functions. On the other hand large meals are more likely to reduce cognitive function; therefore regular small meals might be the best advice if one would like to maintain good mental capacity throughout the cause of a day. Good micronutrient and antioxidant status moreover appears to be vital to protect oneself of early brain degeneration.

Bellisle, F.  (2004) Effects of diet on behaviour and cognition in children, British Journal of Nutrition, 92, 227-232

Bhatnagar, S. and S. Taneja (2007) Zinc and cognition, British Journal of Nutrition, 85, (Suppl. 2), 139-145
Capurso  A., Panza, F. and V. Solfrizzi (2003) The role of diet in cognitive decline, Journal of Neural Transmission, 110, (1), 95-110

Gibson, E.L.  and M.W. Green (2002) Nutritional influences on cognitive function: mechanisms of susceptibility, Nutrition Research Reviews, 15, 169–206

Williamson, C. (2006) Nutrition in pregnancy, Nutrition Bulletin, 31, 28-59

Andrea Zick  Esteem Fitness Nutritionist London
Esteem Fitness Personal training London and the South East