Circulating Glucose Levels Control Desire for High-Calorie Foods – Yale Study

Thursday, September 22nd, 2011 at 3:48 am

Yale University

Yale Study Suggests that Obesity Reduces Control Over Desire for High-Calorie Foods

An interesting clinical study by Yale University researchers was published in the Journal of Clinical Investigation this week on September 19, 2010 and is making the news on TV now, on NBC, for example. It dealt with how cravings for high-calorie food are affected by blood sugar (concentration of glucose in the bloodstream). The study was titled: “Circulating glucose levels modulate neural control of desire for high-calorie foods in humans”. It was conducted by Kathleen A. Page, et. al. of the Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut.

The study focused on brain activity related to the craving for high-calorie food. Some regions of the brain “increase desire” and other regions “inhibit desire” for high-calorie food. The study examined how different blood sugar conditions stimulate activity in these regions to influence how we crave high-calorie foods. In other words, how will the “food craving” activity in these regions be affected as blood sugar levels change (from low in-between meals and normal just after meals) – and what differences are there, if any, between the obese and non-obese study participants.

The study found that when glucose levels are slightly low, such as a few hours after a meal, the obese study participants experienced higher activity in the “increase desire” brain regions (relative to non-obese participants). In the same way, when glucose levels were normal, such as after a meal, activity in the “inhibit desire” regions was greater for the non-obese patients (relative to the obese patients). In a nutshell, brain activity in the obese participants may be leading to overeating (relative to the non-obese participants), both when they are hungry (low glucose levels) and satiated (normal glucose levels).

This was the finding from the research study, with the most important statement underlined:

“Obesity is a worldwide epidemic resulting in part from the ubiquity of high-calorie foods and food images. Whether obese and non-obese individuals regulate their desire to consume high-calorie foods differently is not clear. We set out to investigate the hypothesis that circulating levels of glucose, the primary fuel source for the brain, influence brain regions that regulate the motivation to consume high-calorie foods. Using functional MRI (fMRI) combined with a stepped hyperinsulinemic euglycemic-hypoglycemic clamp and behavioral measures of interest in food, we have shown here that mild hypoglycemia preferentially activates limbic-striatal brain regions in response to food cues to produce a greater desire for high-calorie foods. In contrast, euglycemia preferentially activated the medial prefrontal cortex and resulted in less interest in food stimuli. Indeed, higher circulating glucose levels predicted greater medial prefrontal cortex activation, and this response was absent in obese subjects. These findings demonstrate that circulating glucose modulates neural stimulatory and inhibitory control over food motivation and suggest that this glucose-linked restraining influence is lost in obesity. Strategies that temper postprandial reductions in glucose levels might reduce the risk of overeating, particularly in environments inundated with visual cues of high-calorie foods.”

For the study, 5 obese and 9 non-obese study participants were tested at different glucose levels to determine the level of craving for high-calorie foods while their glucose levels were low vs. when they were normal. The participants were shown images of high-calorie foods to stimulate brain activity in the regions under study and MRI scans were used to assess brain activity.

It wasn’t definitive, as is typical with this small a study, but a few points should be noted:

The researchers stated that these results were obtained “in the absence of changes in circulating insulin”.
Both the obese and non-obese participants were observed at the same glucose levels and same insulin levels at various stages in the study. Since the obese patients were likely insulin resistant (which wasn’t mentioned in the study), their fat and muscles cells were likely absorbing less glucose than the non-obese participants. It would be worthwhile to determine if this had a bearing on the outcome of the study.
The researchers acknowledged the influence of carbohydrates in our diet: “These altered obesity-associated neural responses to food cues may contribute to overeating behavior, especially several hours after consumption of high-carbohydrate meals, a time when glucose often declines significantly below baseline levels”.

If you are not familiar with Insulin Resistance, the following video by Joan O’Keefe, RD, the CardoTabs Chief Nutritional Officer is an excellent and compelling introduction to what it is, why it occurs, and what to do about it.

So… to answer the question we always ask “What do We Eat Now?” My take on this is that for those on Low Carb or Paleo Diets, stay on course! This result is consistent with what we’ve come to understand as the impact of carbohydrates on our system. Eat too many carbs at lunch and you’ll drive up your glucose and insulin levels, which will turn off burning fat for fuel. Your glucose levels, though originally high after lunch, will drop dramatically because of the insulin, and you’ll be starving sometime later. Stay away from carbs in the first place and you avoid all this.

So, this is a nicely done study result that fits with what we know. One more stone gets added to the pile of support for low carb dieting.

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Joe Lindley