How the brain senses nutrient balance

There is no doubt that eating a balanced diet is essential for maintaining a healthy body weight as well as appropriate arousal and energy balance, but the details about how the nutrients we consume are detected and processed in the brain remain elusive. Now, a research study discovers intriguing new information about how dietary nutrients influence brain cells that are key regulators of energy balance in the body. The study, published by Cell Press in the 17 November issue of the journal Neuron, suggests a cellular mechanism that may allow brain cells to translate different diets into different patterns of activity.

'The nutritional composition of meals, such as the protein:carbohydrate (sugar) ratio has long been recognised to affect levels of arousal and attention,' explains senior study author, Dr Denis Burdakov, from the University of Cambridge. 'However, while certain specialised neurones are known to sense individual nutrients, such as the sugar glucose, it remains unclear how typical dietary combinations of nutrients affect energy balance-regulating brain circuits.'

Dr Burdakov and colleagues studied how physiological mixtures of nutrients influenced 'orexin/hypocretin' neurones, which are known to be critical regulators of wakefulness and energy balance in the body. Previous research had demonstrated that orexin/hypocretin neurones are inhibited by glucose. Surprisingly, the current study revealed that physiologically relevant mixtures of amino acids, the nutrients derived from proteins (such as egg white), stimulated and activated the orexin/hypocretin neurones. The researchers went on to show that when orexin/hypocretin neurones were simultaneously exposed to amino acids and sugars, the amino acids served to suppress the inhibitory influence of glucose.

Taken together, these results support a new and more complex nutrient-specific model for dietary regulation of orexin/hypocretin neurones. 'We found that activity in the orexin/hypocretin system is regulated by macronutrient balance rather than simply by the caloric content of the diet, suggesting that the brain contains not only energy-sensing cells, but also cells that can measure dietary balance,' concludes Dr Burdakov. 'Our data support the idea that the orexin/hypocretin neurones are under a 'push-pull' control by sugars and proteins. Interestingly, although behavioural effects are beyond the scope of our study, this cellular model is consistent with reports that when compared with sugar-rich meals, protein-rich meals are more effective at promoting wakefulness and arousal.'