Friday November 18 2011
Eggs are a good dietary source of protein
The proteins in eggs “help us stay awake and feel alert”, the Daily Mail has today reported, adding that the “Go to work on an egg” advertising slogan of the 1960s was good advice. The newspaper says that cracking new research into the effect of nutrients on the brain has suggested that the proteins found in egg whites activate the brain cells that keep us awake and burning calories and trigger the release of a stimulant called orexin.
Eggs are a good dietary source of protein, and this research examined the effect of amino acids, the building blocks of protein, on the activity of certain brain cells that control energy balance and wakefulness. Previous studies have shown that sugar lowers the activity of these cells. The researchers found that mixtures of amino acids activated these cells, as well as reducing the impact of sugar on their activity.
This was an animal study that examined the impact of amino acids, similar to those found in egg whites, on specific cells in the brains of mice. The researchers looked at activation of brain cells that influence wakefulness. These sorts of animal studies make for eye-catching headlines but the results can't be directly extrapolated from mice to humans. As such, we cannot conclusively say from this research whether eating eggs, or other foods that are high in amino acids, will make you more awake or less sleepy. However, it is worth noting that eggs are a good dietary source of:
Where did the story come from?
The study was carried out by researchers from the Universities of Cambridge, Oxford, McGill (Canada), Aarhus (Denmark) and Stanford (US). The research was funded by the European Research Council and was published in the peer-reviewed journal Neuron.
This study was generally reported accurately by the media, although their stories focused on behavioural outcomes that were not directly examined by the research and the media did not report that the study was carried out in mice.
What kind of research was this?
This animal study examined the effect of dietary nutrients, such as amino acids and fatty acids, on a special type of brain cell, known as orx/hcrt neurons, which is involved in controlling energy balance, feeding behaviour and wakefulness. In mammals, these cells are located in an area of the brain called the hypothalamus.
Animal studies are often used in preliminary research that would be difficult or unethical to conduct in humans. Animals were used in this study because its aim was to help us understand the effect of nutrients on brain activity, not behaviour. Future research may confirm whether dietary influences on the activity of these cells in people result in behavioural differences.
What did the research involve?
The researchers took two groups of mice and fed one a mixture of amino acids, similar to that found in egg whites, and the other a control mixture of water. They measured the presence of amino acids in specific brain cells three hours later, and compared these levels between the two groups. The researchers also tested whether consumption of this mixture of amino acids produced changes in behaviour commonly associated with activity in these brain cells. In order to measure activation of these cells, the researchers measured and compared levels of movement and activity in the two groups of mice.
The researchers also examined the effect of amino acids in combination with sugar on these brain cells. Previous research has shown that sugar reduces the activity of these cells. Sugar and amino acid levels in the brain have been shown to increase after a meal. Because of this, the researchers expected that eating sugar and amino acids together would either cancel out the effect on the cells in the hypothalamus, or that the effect of sugar would override the effect of the amino acids and the cells would show reduced activity. To test this they applied a combination of amino acids and sugar to the mice brains, and measured the activity of the cells.
What were the basic results?
The researchers found that feeding mice a mixture similar to egg whites significantly increased the amount of amino acids that reach the hypothalamus, compared with control mice. They also found that mice fed this mixture exhibited significantly higher amounts of movement and activity, compared with control mice.
When the researchers measured brain activity of the mice given a combination of amino acids and sugar they found that the activity of the brain cells of those mice was increased, and not diminished as they had expected. The activity of these cells was similar to that found when only amino acids were used.
How did the researchers interpret the results?
The researchers conclude that brain cells that are involved in controlling energy levels and wakefulness are directly stimulated by common mixtures of amino acids, and that these nutrients can overcome the activity-decreasing effects of sugar.
This controlled animal study is unlikely to mimic human behaviour. The researchers note that the experimental procedures that were necessary for this study may in themselves stimulate the brain cells under investigation. While the researchers made efforts to control for confounding factors such as this, it is important to be cautious before applying the results of animal studies to humans.
The research shows that the types of nutrients present in a diet have an effect on the activity of brain cells that play a key role in controlling energy and wakefulness. The researchers say that the timing and composition of meals is important for achieving a healthy body weight and controlling sleep-wake cycles, and that their study shows that a common mixture of amino acids can play a role in this process.
The researchers say that these key brain cells are influenced in a “push-pull” manner by sugar and amino acids, and that a diet that is made up mainly of sugars would lead to reduced activity of these cells, while a diet with high levels of amino acids would increase their activity.