Our Brain Keeps Track Of How Much Glucose We Eat

A new study in rats has uncovered a chemical in the brain that acts as a regulator for glucose consumption, increasing or decreasing appetite for sugar and starch:

Study: Glucokinase Activity In The Arcuate Nucleus Regulates Glucose Intake, The Journal of Clinical Investigation, 8 December 2014
Press Release: Scientists Discover Brain Mechanism That Drives Us To Eat Glucose, Imperial College of London, 8 December 2014

Glucokinase activation may represent a CNS [Central Nervous System] mechanism that underlies the oft-described phenomena of the “sweet tooth” and carbohydrate craving.

Low glucokinase activity = low glucose appetite.
High glucokinase activity = high glucose appetite.

This was interesting:

The glucose solution has a lower energy content per unit of glucose and thus the overall energy intake of these rats was reduced compared with those that only had access to chow.

The previously observed increase in food intake, energy intake, and body weight gain in iARC-GK rats that occurred with chow alone did not occur when a glucose solution was available in addition to the chow diet.

So, when rats had increased appetite for glucose, they ended up eating more calories when all they had to sate that appetite was chow (a mix of carb/fat/protein). Sating their appetite with just sugar water led to eating fewer calories.

If a similar mechanism applies in humans then trying to satisfy a glucose craving or “sweet tooth” by eating a mixture of carb/fat/protein (say, a donut) will have one eating more (to reach satisfaction) than eating mostly carb (say, a potato or piece of bread). Maybe that’s why McDougall’s starch diet is so satisfying, and so effective in weight management.

Dr. Gardiner said essentially the same thing in the video:

If you have insufficient glucose in your diet, you’ll take in more of a mixed food that will increase weight gain.

And this…

“This is the first time anyone has discovered a system in the brain that responds to a specific nutrient, rather than energy intake in general. It suggests that when you’re thinking about diet, you have to think about different nutrients, not just count calories,” [Dr. James Gardiner who led the study] said.

Dr Gardiner suggested that in humans it might be possible to reduce cravings for glucose by altering one’s diet. … For some people, eating more starchy foods at the start of a meal might be a way to feel full more quickly by targeting this system, meaning they eat less overall.”

If I had a restaurant, I wouldn’t put baskets of bread on tables before people placed their orders. There goes their appetite! On the other hand, if someone didn’t want to eat much that evening, the bread basket would be their salvation.

News Sources:
Scientists find brain mechanism behind glucose greed
Trying to slim? Have your dessert first! Eating sugar-rich food at start of a meal found to help keep appetites in check

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