Written by Catharine Paddock PhD
A new study finds that protein, not sugar, stimulates certain brain cells into keeping us awake, and also, by telling the body to burn calories, keeping us thin. Study leader Dr Denis Burdakov, from the University of Cambridge in the UK, and colleagues, write about their findings in the 17 November issue of Neuron. They suggest their discovery will increase understanding of obesity and sleep disorders.
Burdakov, from the Department of Pharmacology and Institute of Metabolic Science at Cambridge, told the media scientists had already established orexin cells in the brain send electrical signals that stimulate wakefulness and tell the body to use up energy. He and his co-authors wanted to take this further and find out if particular dietary nutrients influenced those signals:
“Sleep patterns, health, and body weight are intertwined. Shift work, as well as poor diet, can lead to obesity,” he explained. “Electrical impulses emitted by orexin cells stimulate wakefulness and tell the body to burn calories. We wondered whether dietary nutrients alter those impulses.”
Orexin cells in the brain’s hypothalamus release a stimulant called orexin/hypocretin, which regulates energy balance, wakefulness and reward. We already know that loss of these unique cells results in narcolepsy and weight gain.
For their study, Burdakov and colleagues compared the effect of different nutrients on orexin cells. They discovered that amino acids, the building blocks of proteins, stimulated them much more than any other nutrients.
“We show that orx/hcrt cells are stimulated by nutritionally relevant mixtures of amino acids (AAs), both in brain slice patch-clamp experiments, and in c-Fos expression assays following central or peripheral administration of AAs to mice in vivo,” they write.
To do this, they highlighted the rather elusive orexin cells by breeding mice genetically engineered to have orexin cells capable of fluorescing. They then introduced different nutrients, including amino acid mixtures similar to egg white, and tracked the orexin cell impulses by observing the fluorescence.
Work they had done before this study had already established that glucose blocked the activity of orexin cells, which had led to the idea that this was the cause of sleepiness after meals. So in this study they also looked at interactions between sugar and protein.
They found that amino acids prevented glucose from blocking the orexin cell activity:
“… the presence of physiological concentrations of AAs suppressed the glucose responses of orx/hcrt cells,” they write.
In other words, it appears that protein counteracts the after-meal sleepiness induced by sugar or carbohydrate.
The researchers concluded that the orexin cells are sensitive to nutrient balance, rather than just the net calorie content of the fluid that surrounds them.
They suggest the findings help to explain why people seem to feel less calm and more alert after meals high in protein than after meals high in carbohydrates.
Burdakov said the results are exciting because it gives us a “rational” way to “tune” particular brain cells to be more or less active, just by changing the food we eat. It seems that some brain cells at least, respond to dietary composition, and not just to whether nutrients are present or not.
He said we need better information on how diet affects sleep and appetitle if we are to improve our ways of fighting obesity and insomnia in today’s society:
“For now, research suggests that if you have a choice between jam on toast, or egg whites on toast, go for the latter!”
“Even though the two may contain the same number of calories, having a bit of protein will tell the body to burn more calories out of those consumed,” he added.