A new remedy for appetite
Injecting insulin into the nose reduces cravings for treats
German doctors and neuroscientists have found out that under the influence of insulin injected intranasally, food seems less tasty to a person. Scientists have also determined which area of the brain is affected by the hormone.
A person does not always eat to live – sometimes he eats too much just for pleasure. From the point of view of the body, these are two different types of eating behavior, but in both, insulin acts as a signaling molecule – a hormone that is best known for controlling blood sugar levels. It is assumed that its action is associated with the suppression of hedonic eating behavior – eating "goodies", through the control of signals in the mesolimbic system, which is responsible for the feeling of pleasure and the feeling of reward.
However, until now, similar results have been obtained exclusively in animal experiments, and there has also been no direct evidence of the corresponding neural activity. A group of scientists from Germany undertook to conduct such studies with the participation of people.
The experimental sample included 28 people with normal insulin sensitivity and 20 non-insulin sensitive participants. Everyone was sprayed with insulin or placebo into their nose on an empty stomach. The hormone was injected through the nose, because it was previously shown that in this case insulin successfully penetrates the hemato-encephalic barrier and enters the central nervous system.
Then the subjects were given fMRI to record the neural activity of the brain, and asked to answer "yes" or "no" to the question about the attractiveness of a particular image, and then on a special scale to indicate how much they like or dislike it. Both images of food and inedible objects (for example, a rubber duck) were used.
As a result, it turned out that in patients with reduced insulin sensitivity, the attractiveness ratings of food were on average lower – both before and after insulin administration. But people with normal insulin sensitivity found food less attractive only after the introduction of the hormone. Similar effects did not appear for inedible items.
fMRI data showed the critical role of insulin in the regulation of neural signals in the mesolimbic system. Moreover, by how strongly this effect was expressed according to fMRI data, scientists were able to directly predict a decrease in the nutritional attractiveness of products.
The study allowed scientists to link data on neural activity with a decrease in the attractiveness of food, which causes the introduction of insulin in healthy people. The results of this work will help to understand the causes of eating disorders and may have clinical significance for people at risk of developing metabolic disorders.
An article describing the results of the study was published in the journal Nature Communications (Tiedemann et al., Central insulin modulates food valuation via mesolimbic pathways).
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19.07.2017