Science and Reason: Peptide YY and appetite

Just about three months ago we came, briefly, across the peptide called PYY (peptide YY), which has been known, for a few years, to suppress appetite. It has also been known that obese people secrete less PYY than non-obese people. On the other hand, attempts to use PYY directly as a weight-loss drug have not met with much success.

About a year ago, research showed that consumption of protein boosts PYY levels, and in that case there was some benefit to experimental subjects in terms of reducing hunger and promoting weight loss. This would help explain the weight-loss experienced with high-protein diets. Here's a press release on that research:

Eating Protein Boosts Hormone That Staves Off Hunger (9/6/06)

The amount of a hunger-fighting hormone can be increased by eating a higher protein diet, researchers report in the September issue of the journal Cell Metabolism, published by Cell Press. The hormone, known as peptide YY (PYY), was earlier found by the researchers to reduce food intake by a third in both normal-weight and obese people when given by injection.

"We've now found that increasing the protein content of the diet augments the body's own PYY, helping to reduce hunger and aid weight loss," said Medical Research Council clinician scientist Rachel Batterham of University College London, who led the new study.

Scientists have known that high-protein content meals make people feel more full and reduce food intake, resulting in improvements in weight loss and weight loss maintenance. However, the mechanism responsible remained elusive.

In a study in normal-weight and obese people, the researchers now show that enhanced-protein meals stimulate greater release of PYY than either high-fat or high-carbohydrate meals and result in a greater reduction of hunger.

Here's another report on that research: Hello Protein, Goodbye Fat (sub. rqd.) And an earlier article on the PYY controversy: New Data on Appetite-Suppressing Peptide Challenge Critics (sub. rqd.)

Now there are additional findings from the same lab that developed the results of a year ago. The findings indicate that a cortical brain center associated with reward and pleasure (the orbital frontal cortex) responds to PYY:

Brain 'hunger pathways' pinpointed (10/15/07)

The brain circuitry that influences how much food a person will eat – whether they feel starving or full – has been revealed by a new imaging study. The results may help target new treatments against obesity, say researchers.

Rachel Batterham at University College London, UK, and her colleagues have previously shown that a hormone called peptide YY or PYY, which is released by the gut in proportion how many calories we eat, is a powerful appetite suppressant. Previous experiments show that treating normal and obese subjects with intravenous PYY decreases food intake by up to 30%.

Batterham's team used functional magnetic resonance imaging (fMRI) to investigate how PYY affects the brain.