The other afternoon I hit a classic mid-afternoon slump. Sleepy and sluggish, I grabbed for a bit of chocolate. But I probably should have had egg whites or maybe a piece of steak. Because a recent study in mice has found that it's protein, not sugar, that provides the perk. Brain cells called orexin cells secrete a stimulant that makes us energetic and tells the body to burn calories. If the cells' activity decreases, narcolepsy or sudden sleepiness, is the result. The work is published in the journal Neuron. Scientists marked orexin cells in mice brains so they would fluoresce. Then they tracked the cells' activity after feeding the mice different kinds of food. Turns out that glucose blocks the function of the orexin cells. This effect might be the main reason for the desired post-lunch siesta. But the researchers also found that amino acids stop the glucose action, keeping the cells active and the mice alert. So next time I get that 3 p.m. slow down, I'll have an egg. If I'm alert enough to remember.