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The Hungry Brain

 If you think it is a good diet strategy to save calories by skipping meals, think again. A Yale study showed why getting hungry is a bad idea for your diet.

The Yale study investigated how hunger changes our perception of food by correlating blood glucose level with activity in different areas of the brain. The study involved both men and women with normal or obese body weights. A functional MRI scanner showed which areas of their brains were active when the individuals were exposed to various pictures of high-calorie foods (French fries and cakes) or low-calorie foods (tofu and salad). The individuals were asked to rate their desire for the foods shown.

The results? When the subjects’ blood glucose was in the normal range, the prefrontal cortex, a brain region responsible for logic, reasoning, planning, and will power, was highly active. Looking at the pictures of the high-calorie foods while glucose was normal did not cause a desire for the foods. But when blood glucose was low, a deeper area of the brain, the hypothalamus, thalamus and nucleus accumbens, took over. This deep part of the brain is associated with reward, desire and food seeking. When blood glucose was low and the pictures of high calorie foods were shown, intense cravings were reported. Interestingly, the low calorie foods did not provoke cravings.  This is exactly what happens when you skip a meal or grocery shop on an empty stomach!

Take a look at these images:

Figure 1*

Figure 1: This image of the non-hungry brain shows the prefrontal cortex activation, indicating will-power and logic were intact. No cravings were present.

Figure 2*

Figure 2: This image is of the hungry brain. Notice how the prefrontal cortex shows no activation and the deep regions associated with desire and food seeking have become active. Cravings were intense.

The study showed very clearly how the brain responds to low blood sugar: the will power area is over-ruled by the reward center. For the obese individuals in the study, the effect was magnified. Low blood glucose activated a larger area of the reward center and they reported stronger cravings. Even worse, when blood glucose was brought back to normal the obese subjects’ cravings persisted – this was not the case for the normal weight individuals.

The brain’s acute sensitivity to low blood glucose is a survival mechanism, developed over millions of years, which drove us to seek food when little was available. Under famine conditions, those foods which had the most calories provided the greatest protection against starvation. Today, the primitive drive for high calories when blood glucose is low can sabotage even the most self-disciplined.

So, what should you do?  Eating several small meals is a good idea. Blood glucose will begin to fall 3-4 hours after eating, so it is a good idea plan a healthy snack in the afternoon.  Hunger is not your friend. At meals, be sure to include lean protein because it is digested slowly, keeping your blood glucose even. For an afternoon snack, try these protein-rich foods: low-fat cheese, a hardboiled egg, a handful of nuts, a glass of milk or a container of yogurt.

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