Why Sugar Makes Us Sleepy (And Protein Wakes Us Up)

By Jonah Lehrer
December 6, 2011

Excerpt:
It’s long been recognized that meals high in protein are both more filling and less exhausting, which is why we’re always being told to snack on almonds and follow the Zone Diet, with its balance of carbs, protein and fat. (This study, for instance, found that protein rich breakfasts significantly improved cognitive performance.) Although the biological mechanism behind this dietary wisdom has always been unclear, that’s beginning to change – we finally understand why consuming protein can be an effective weight loss tool. The answer returns us to orexin.

According to a new paper in Neuron led by scientists at the University of Cambridge, consuming foods high in protein can increase the activity of orexin neurons. This, in turn, leads to increased wakefullness and bodily activity, helping us burn off the calories we just consumed. Furthermore, eating protein in conjunction with glucose – adding almonds to Frosted Flakes, in other words – can inhibit the inhibitory effects of sugar on orexin. The sweetness no longer makes us tired.

The researchers demonstrated this effect in a number of ways. They began in situ, showing that clumps of orexin cells in a petri dish got excited when immersed in a solution of amino acids. (Neighboring cells in the hypothalamus revealed no such effect.) Then, they moved on to in vivo experiments, studying the impact of an egg white slurry of live animals. This protein meal not only increased orexin activity in the brain, but also led to a dramatic surge in locomotor activity, as the animals began scurrying around their cage. The effect persisted for several hours.

The last sequence of experiments explored the impact of different nutrient combinations on the orexin system. Although the scientists assumed that the inhibitory presence of glucose would more than compensate for the excitatory influence of protein, that hypothesis turned out be incorrect. Instead, consuming even a little protein canceled out the curse of sugar, especially when the foods were consumed simultaneously. (When the animals ate protein first, and then swallowed a chaser of glucose, orexin neurons still showed a decrease in activity. So make sure your dessert has some protein in it.) the rest  image by Nagarjun