Pragma Synesi – interesting bits

Compendium of interesting bits I come across, with an occasional IMHO

Hormones can make it sweeter


From The Economist July 24th, 2008 print edition:

Appetite control

A sweet result

Hormones influence how sensitive taste buds are to sugar

THAT sweetness is pleasant is no coincidence. Sweet food is at a premium in the wild because the sugars it contains provide valuable calories. But even with sugar there can be too much of a good thing, so it would be no surprise if the body were able to regulate the perception of sweetness as its nutritional needs vary. According to two studies presented to the International Symposium on Olfaction and Taste, held in San Francisco this week, that is exactly what happens. The studies, one on mice and one on people, have identified two hormones that seem to fine-tune the perception of sweetness, and thus regulate the intake of sugar independently of the previously known mechanism of satiation that is located in the brain.

The mouse study was done by Steven Munger, a neurobiologist at the University of Maryland, and his colleagues. They picked a hormone called glucagon-like peptide-1 (GLP-1) that is made by intestinal cells in response to sugar and fat. This hormone is already known to act in the pancreas and the brain, where it helps, respectively, to regulate blood-sugar levels and the feeling of satiation that tells you when to stop eating. Dr Munger, though, found that both GLP-1 and the receptor molecule that picks it up and thus allows it to act are found in taste buds too.

To investigate GLP-1’s role in taste, the team used a strain of mice that were genetically engineered to lack GLP-1 receptors. They found that such animals are much less sensitive to sweetness than their un-engineered confrères. Indeed, the mutants were no more interested in a dilute sugar solution (or, indeed, a solution of artificial sweetener) than they were in plain water—though they did respond to concentrated solutions of sweetness. The “wild-type” mice, by contrast, drank significantly more of the sweet solution than they did of the water, even when the sweet solution was dilute. Moreover, the effect was limited to sweetness. The animals’ responses to the other four fundamentals of taste—bitterness, sourness, saltiness and “umami” (the flavour of monosodium glutamate)—were unaffected. That suggests, though it does not yet prove, that there is feedback from the gut to regulate the desirability of eating sweet food.

The human study was done by Yuzo Ninomiya, a neuroscientist at Kyushu University, in Japan. He and his colleagues looked at leptin, another hormone that is known to regulate appetite and metabolism. Leptin levels are also known to fluctuate naturally over a 24-hour period, being lowest in the morning and highest at night, at least in people who eat three meals a day.

In their experiments, Dr Ninomiya and his colleagues found that their volunteers were more sensitive to sweetness when their leptin levels were low. As the level of the hormone increased over the course of a day, the threshold for detecting sweetness rose. And when the researchers shifted the pattern of leptin production by changing the number of meals their volunteers ate, the volunteers’ sensitivity to sweetness shifted as well, suggesting that it was the hormone rather than merely the time of day that was causing the effect. As in the case of the mice, the humans did not show any changes in their sensitivity to other tastes. However, individuals who had lower leptin levels, and thus more sweet-taste sensitivity before a meal, experienced sharper increases in blood-sugar levels when they had eaten.

Whether either of these results cast light on the perpetual search for pain-free ways of cutting calorie-intake in the modern world of abundant sweetness is not yet clear. But they may, at least, explain why so many people like lashings of sugar on their breakfast cereal.


September 23, 2009 - Posted by | behaviour, diet, health, nutrition | , , ,

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