Nutritional Pearls: How Does the Mind Affect Hunger and Satiety?

Thomas is an obese 36-year-old man who has been struggling with his weight since childhood. His frustration is evident as he reports that he only eats until he is satiated, and doesn’t understand why he doesn’t feel full sooner.

How would you advise your patient?

What is the correct answer?
(Answer and discussion on next page)

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Answer: People who are obese often have reduced post-eating ghrelin response, keeping them feeling hungry.

Hunger and Satiety - Ghrelin

Recently one focus of obesity research has been into the way the body registers hunger and satiety.

The peptin ghrelin appears to help signal hunger as well as fullness. When the stomach is empty or immediate stores of energy are low, ghrelin is secreted from the stomach and passed through the bloodstream to the brain, where it connects with receptors to help produce the physical feeling of hunger.
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When the person eats, ghrelin secretion is suppressed and the receptors in the brain stop signaling hunger and start signaling satiety. In short: high levels of ghrelin = hunger, low levels of ghrelin = no hunger.

In theory, the ghrelin response would rise and fall in proportion to the amount of calories a person ate and would help keep the body at a stable weight. In practice, however, it's not that simple. The communications system involved is far more complex than this description, and abnormalities in other gut hormones can profoundly affect the process.

People who are clinically obese, for example, often have reduced or even absent post-eating ghrelin response (when ghrelin levels should fall), keeping the body feeling hunger even though it has consumed fuel enough to create feelings of fullness in those of normal weight.

Further complicating this picture is the fact that what we think and believe can have a profound effect on our experience of food.

The Research

Studies have shown that those who believe they have eaten more calories feel fuller than those who believe they've eaten fewer calories - even when the actual number of calories eaten is the same. And then, of course, there’s the placebo effect: a classic case of the mind influencing the body.

With this in mind, researchers at Yale and Arizona State University recruited 46 adult men and women for a "Shake Tasting Study."¹ On two separate occasions one week apart, the participants taste-tested one of two vanilla milkshakes. They were told that the study was to evaluate whether the two shakes tasted similar and to measure their body's response to the nutrients in the shake by taking regular blood tests over the course of several hours.

The two shakes were actually identical, but on each tasting occasion the milkshake was presented with a different label: one label described the shake as "an indulgence—decadence you deserve" with 620 calories, while the other was labeled "Sensi-Shake: guilt free satisfaction" with 140 calories. Neither label was correct with respect to the actual number of calories in the milkshake.

The Results

The blood tests were taken just before and at regular intervals after the participants drank the milkshake and were used to measure ghrelin levels. In theory each participant's ghrelin levels should have responded in generally the same way regardless of which label the shake had, because they were actually consuming the same beverage. Instead, their bodies seemed to react as though they had actually consumed the higher- or lower-calorie food. Oddly enough, the hunger the participants actually reported feeling was about the same regardless of which shake they believed they were drinking.

What’s the “Take Home”?

It's clear that the hunger-to-satiety process is far more complex than the simple math of the number of calories you eat, but it’s not “mind over matter,” either. The problem is that eating less, and better and moving more is still the best advice we have for weight control.

Reference

Crum AJ, Corbin WR, Brownell KD, Salovey P. Mind over milkshakes: mindsets, not just nutrients, determine ghrelin response. Health Psych 2011;30(4):424-429. http://dx.doi.org/10.1037/a0023467