Nutrition and the Brain

Nutrition and the Brain Research

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Most of us are aware that our body needs a variety of food to provide it with the nutrition and energy to grow and function properly. Less recognized is how proper nutrition affects our brain’s ability to function. Neurotransmitters are chemical transporters through which the brain’s billions of neurons communicate. Changes in energy or nutrient levels can alter this chemistry, thereby affecting changes in memory, problem solving abilities, and impairing the functions of the brain at all levels of operation. These impaired functions can impact processes throughout the body and may contribute to obesity, diabetes, and other diseases.

Our research investigates the interactions between food nutrients and the brain and their impact on the human body.

The influence of diet on cognitive function, appetite and mood

10 Key Facts

1. Food cravings are difficult to define and measure and the prevalence reported by studies is, therefore, very variable. They are more commonly reported by women than men and appear to decrease with age. As foods that are most commonly craved are energy-dense, sweet and high in fat, there is concern that this may be a contributing factor to the worldwide increase in overweight and obesity.

2. Cravings are often correlated with negative mood states, such as depression and anxiety, and frequently reported by those with mood-related conditions, such as pre-menstrual tension and seasonal affective disorder. The popular ‘self medication’ hypothesis suggests that people crave comforting sweet and high-fat foods because of this poor mood state and mood improves when they give in to their cravings. It is likely that a variety of food-related cues may influence cravings, for example the sight, smell or taste of food. However, little is known about this area and further research is needed.

3. Consumers often claim that some aspects of eating behaviour are beyond their control and the notion that sweetness is ‘addictive’ endures in the scientific literatures and popular press. However, carbohydrate cravings do not meet the current criteria for substance dependence, as formulated in the Diagnostic and Statistical Manual of Mental Disorders – Fourth Edition (DSM IV) and the term ‘addiction’ is being used inappropriately in relation to food cravings.

4. It is often claimed that sugar (refined carbohydrate) makes you drowsy and is less satiating than other foods (e.g. unrefined carbohydrate). However, the impact of refined carbohydrates on satiety and mood remains controversial. This is a very difficult area to research as there are so many other factors that can impact on mood and food intake. The effects of carbohydrate on mood and eating behaviour are fragile and likely to alter, depending on the psychological state of an individual and the setting in which the food is eaten.

5. It has been estimated that 11.5% of 11-16 year-olds in the UK suffer from depression, which is associated with poor academic performance, self-harm and suicide. There is accumulating evidence that a healthy diet is important for mental health, and depression has been associated with low intakes of many vitamins and minerals. The most widely studied nutrients in relation to mental health are omega 3 fatty acids and folic acid. Supplementation with these nutrients has been shown to reduce symptoms in people who are depressed. However, more research is needed to ensure that these supplements are safe and effective in this age group.

6. The health benefits of fibre-containing foods, such as wholegrains, fruit and vegetables and beans and pulses, are well accepted. Fibre adds bulk to the diet and therefore helps to satisfy appetite, reduce hunger and increase feelings of fullness. A high fibre content also helps to reduce the energy density of the diet. There are many different types of fibre which have different effects on satiety. Viscous fibres (e.g. guar gum, psyllium) appear to be most effective, whereas non-viscous fibres (e.g. inulin) may not have any benefit in relation to appetite (although they offer other health benefits).

7. An adequate protein intake is important in the maintenance of a healthy body weight because of its effect on satiety, thermogenesis, body composition and energy efficiency. Greater weight loss and improved body weight maintenance have been observed when diets have included sufficient protein. Weight loss diets that reduce energy intake but preserve the protein content (i.e. keep the absolute grams of protein similar to pre-diet intake) and weight maintenance diets that maintain protein intake can help preserve or increase lean body mass, reduce fat mass and therefore improve overall health.

8. Caffeine is commonly described as a stimulant. However, recent evidence suggests that little or no acute benefit is gained from regular caffeine consumption. This is because caffeine withdrawal (e.g. overnight) lowers alertness and mood and impairs performance, and, while consumption of some caffeine will reverse these effects, it does not boost performance to above ‘normal’ levels. In contrast, some studies have shown that regular coffee drinking is associated with lower age-related cognitive decline and reduced risk of Parkinson’s disease, suggesting benefits amongst the older population. However, further research is needed to ascertain the potential health effects of dietary caffeine before clear public health advice can be given.

9. Despite a substantial amount of research into carbohydrates and mental function, there is still insufficient evidence that consuming carbohydrate improves cognitive function. Recent developments suggest that it is too simplistic to assume that carbohydrates will inevitably improve cognitive function as there is a damping or buffering between glucose changes in the blood and the brain. There is also evidence that cells within the central nervous system (astrocytes) are able to store glucose and release it to brain neurones when needed. Findings of studies investigating the effect of glucose on mental function have been inconsistent, which may be partly explained by some individuals with poor glucose regulation being more susceptible than others to the effects of glucose on mental function, particularly if brain function is increased by challenging cognitive tests. Future research needs to identify the characteristics of susceptible individuals and the carbohydrate manipulations that can predict improvements in specific cognitive functions.

10. Often based on very limited evidence, a number of supplements and diets have been suggested to boost mood, increase energy and improve memory. There is a need to protect consumers against such unsubstantiated claims. Double-blind, placebo controlled trials are needed to demonstrate the efficacy of such supplements, but this type of design is difficult and often impossible for nutritional studies. There is also a lack of widely accepted and sensitive tests to assess cognitive performance and mood state. Scientific consensus on these issues will help to ensure the availability of safe and efficacious dietary supplements and help to eliminate dangerous or ineffective products.

Notes: This is a summary from the BNF conference, held on 6th March 2007, that focused on a special supplement on this topic published alongside the March issue of Nutrition Bulletin to celebrate the 40th year of the British Nutrition Foundation. Speakers were: Ms J Batchelar (J Sainsbury plc); Professor L Christensen (University of South Alabama); Dr F Bellisle (Institut National de la Recherche Agronomique); Dr D Bamber (University of Cambridge); Ms C Stokes (MRC Human Nutrition Research, Cambridge); Professor J Slavin (University of Minnesota); Professor M Westerterp-Plantenga (Maastricht University); Professor R Hammersley (Glasgow Caledonian University); Professor P Rogers (University of Bristol); Dr L Gibson (Roehampton University); Dr H Lieberman (US Army Research Institute of Environmental Medicine). Professor Robert Pickard, Director-General of the BNF, chaired the meeting.