Fat is hard to resist

A new study in Proceedings of the National Academy of Sciences may help to explain why some of us find fatty foods hard to resist in large amounts, contributing to our difficulties in trying to maintain a healthy weight. The apparent culprits identified in this study were the endocannabinoids (a group of biologically active lipids) produced in the gut.

Knowing that cannabinoid receptors on the tongue influence the transmission of taste signals from the tongue to the brain, so encouraging fat intake once it has begun, the researchers wanted to find out whether post-ingestive production of endocannabinoids in peripheral tissues also influence dietary fat intake.

To avoid the influence of fat on taste signals from the tongue, rats were given corn oil directly into the stomach. Cells in the jejunum, but not in other peripheral tissues or the brain, started producing endocannabinoids. A similar effect occurred in response to a nutritionally complete liquid diet but not to protein or carbohydrate.

In addition, this feeding experiment failed to alter the jeujunal content of oleoylethanolamide, which is a lipid-derived satiety factor formed when dietary fat enters the small intestine.

Cutting the vagus nerve below the diaphragm abolished the endocannabinoid response, indicating that communication between the brain and the gut via the vagus is necessary to drive this biological reaction. The relevance of this study is that further pharmacological strategies aimed at curbing endocannabinoid activity in the gut might selectively lower the intake of fat-rich foods.