A research team from Central Europe has found in a study that fasting in the long term can encourage overeating and thus make losing weight more difficult.
A study has shown that abstaining from eating when trying to lose weight is harmful. Researchers discovered this through experiments with fruit flies. The study results were published in the journal “eLife”.
Reminders to consume carbohydrates
A research team at the Institute of Zoology at the University of Cologne led by Professor Dr. Henrike Scholz used behavioral experiments on the fruit fly Drosophila melanogaster to investigate the control of food intake in the brain.
According to a press release, in fruit flies – similar to humans – insulin-like molecules regulate food intake.
This is influenced, among other things, by a neurotransmitter system that mediates decisions. The system uses the messenger substance octopamine, a molecule related to noradrenaline. This messenger substance determines whether the memories of the intake of carbohydrates are stored in the long-term or short-term memory.
Reduced glycogen levels
The scientists investigated how mild fasting and reduced glycogen levels in fat tissue and muscles affect the perception of carbohydrates in the fruit fly.
The storage form of glucose, glycogen, is stored in fatty tissue and is largely used as energy in the muscles.
The information about the energy reserves of these tissues is integrated into the decision system by the octopamine and influences the formation of a memory about a possible food source.
Memory “triggers” increased food intake
Previous scientific research has shown that overfeeding can lead to increased glycogen levels in animals and humans.
In the experiment, the fruit flies had higher glycogen levels due to genetic modifications. When fasting, the increased energy reserves lead to the formation of a very stable memory that does not disappear when food is consumed again.
This is also the case if the nutritional value of the next meal is actually sufficient to compensate for the deficits caused by fasting. The memory thus “triggers” an increased food intake.
Reduced reward effect in the brain
In the experiment, the intake of carbohydrates when glycogen levels were very high also led to only a small reward effect in the brain. The less rewarding effect of food intake thus fueled the need to continue eating.
If food intake was sufficient or if there was sufficient energy in the fruit fly, the decision system suppressed the formation of such a longer-lasting memory regarding the food source.
This was independent of the carbohydrate content or protein enrichment of the diet. The glycogen level generally had no influence on how the animals evaluated protein-enriched foods.
A harmful mechanism today
Octopamine thus integrates the current food intake into memory formation depending on the energy level: foods that normally offer sufficient nutritional value are no longer perceived as sufficiently rewarding. As a result, overeating occurs – regardless of the nutritional value or the type of food.
“In ancient times, when food was a limited or scarce resource, this mechanism may have served to build up energy reserves when food was available,” says lead author Henrike Scholz.
“In times of food surplus, the long-lasting memory of a carbohydrate source can encourage excessive food intake – and thus contribute to the development of obesity.”
Why it is difficult to lose weight
There are currently no studies demonstrating a similar mechanism in humans, but since the molecules involved in the fruit fly and in humans are very similar, the researchers believe that the mechanism also works in a similar way.
The results could therefore explain why it is difficult to lose weight: If the memory of the rewarding effect of food outlasts the rewarding and satiating effect of the actual food intake, this can lead to increased food intake.
“In the future, it may be important to find out how to erase this long-lasting memory so that losing weight becomes easier,” Scholz concludes. (ad)