Small intestine can sense and react to bitter toxins in food

Toxins in food often have a bad, bitter taste that makes people want to spit them out. A new research finds that bitterness also slows the digestive process, keeping bad food in the stomach longer and increasing the chances that it will be expelled. This second line of defense in the gut against dietary toxins also triggers the production of a hormone that makes people feel full, presumably to keep them from eating more of the toxic food.

The study was performed with mice, and the results probably translate to humans, said Timothy Osborne, molecular biology and biochemistry professor and study senior author. Mammals have evolved to dislike the bitter taste of toxins in food. This response is particularly important when they eat a lot of plant material, which tends to contain more bitter-tasting, potentially toxic ingredients than meat.

Examples of bitter-tasting toxins include phenylthiourea, a compound that destroys the thyroid gland, and quinine, found in tonic water, which can be deadly in large doses. If toxins are swallowed, bitter-taste receptors in the gut sense them and trigger the production of a hormone called cholecystokinin that both suppresses appetite and slows the movement of food from the stomach to the small intestine.

Interestingly, the UCI scientists found that cholesterol regulates the activity of bitter-taste receptors in the intestine, and diets high in plant material and potential toxins naturally are low in cholesterol, compared to low-toxin, high-cholesterol, meat-based diets.

In small intestine cell cultures, low levels of cholesterol triggered a stronger receptor response – meaning they worked better – while high levels caused a weaker response.

The same response was observed in mice that were given drugs to stop the production and absorption of cholesterol. Not only were their receptors more active, their small intestine cells produced two to three times the amount of the appetite-suppressing hormone in the presence of bitter food, compared to normal mice.

In addition to the appetite-suppressing hormone, bitter-taste receptors in the gut activate the production of glucagon-like peptide 1, a protein that stimulates insulin secretion in the pancreas. Drugs currently are on the market that attempt to stabilize this protein in people with diabetes, and therapies aimed at increased production are attractive therapeutic targets.