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Why Sugar Makes Us Sleepy

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Consider the orexin system. Secreted by a small cluster of neurons in the hypothalamus, orexin is a neuropeptide that regulates an astonishing array of mental properties, from sleepiness to hunger.

People with chronically low levels of orexin suffer from narcolepsy and obesity; many also have cataplexy, which occurs when the experience of strong emotions triggers a sudden weakening of skeletal muscles.

Studies have shown that injecting mice with orexin increases metabolism, largely because it makes the animals more active.




The reverse is also true: low levels of orexin make people feel rundown and tired. This helps explain the mechanics of sleep deprivation, as keeping monkeys awake for extended periods all but silences their orexin cells.

In many respects, orexin acts like an internal gas pedal, as even slight twitches in the system can dramatically shift levels of activity.

The reason the orexin system is so important is that it links the needs of the body to the desires of the mind.

Several studies have demonstrated that the intake of sugar can decrease the activity of orexin cells, which is probably why we want to nap after a carb heavy lunch.

This phenomenon also begins to explain the downward spiral of obesity triggered by our warped modern diet.

Because we eat lots of refined sugars, washing down Twinkies with cans of Coke, we continually reduce levels of orexin in the brain, which then reduces levels of physical activity.

In other words, we get fat and sleepy simultaneously. However, not every food has such perverse consequences.

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.

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.

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.

These experiments also document, at a biochemical level, why the modern American diet is such a catastrophic mess.

The typical supermarket is filled with processed foods where the only relevant “nutrient” is some form of sweetener.

While such snacks are unfailingly cheap and tasty, they also lead to sudden spikes in blood sugar and a reduction in orexin activity.

We eat them for the energy boost, but the empty calories in these foods make us tired and sad instead.

And so we keep on swilling glucose, searching for a pick-me-up in all the wrong places.

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Pass it on: New Scientist

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