The study finds that 24-hour fasting cycles increase libido in male mice

The study finds that 24-hour fasting cycles increase libido in male mice

Long-term fasting in 24-hour cycles increases the sex drive of male mice by reducing the concentration of the neurotransmitter serotonin in the brain. This effect is associated with a diet-induced deficiency of the precursor substance tryptophan - an amino acid that must be obtained from food. Researchers from Dzne report on this in the journalCell metabolismtogether with a Chinese team from Qingdao University and the University of Health and Rehabilitation Sciences. They suggest that similar mechanisms exist in humans and may view fasting as a potential approach to treating unwanted loss of sexual desire.

Fasting is a recurring theme in research because reduced food intake and therefore calorie restriction have a variety of effects on the organism that go beyond the commonly observed weight loss. Dr. Dan Eehnner, research group leader at Dzne and lead author of the current study, and his team have also been working on this topic for some time.

"We are interested in the effects of fasting on aging. Using mice as a model, we investigate the underlying biological mechanisms. Our goal is to gain insights that can also be relevant for humans," says the Bonn-based scientist.

More offspring than expected

The research results now published are based on an accidental discovery, as Ehrener and his colleagues originally imagined investigating something else. Their goal was to study how fasting affects the offspring of male mice. However, one particular finding took their research in a new direction: Aged male mice - older individuals by human standards - fasted for extended periods resulted in unusually large numbers of offspring. Contrary to initial hypotheses, this phenomenon was not due to fasting effects on reproductive organs or the endocrine state of the animals. Age-related changes in the testicles, reduced sperm quality and lower testosterone levels, for example, counteract high fertility. “It was a bit of detective work to uncover the real thing,” says Eehnner, whose research group collaborated on the current study with experts from Qingdao University and the University of Health and Rehabilitation Sciences led by Prof. Yu Zhou. "Eventually we realized: It's a question of behavior. The fasting men had significantly more sexual contacts than mice that could eat freely. In other words, these animals had an unusually high mating frequency and, as a result, an unusually high number of offspring for their age.

Fasting in a 24-hour rhythm

Starting at two months, these male mice were subjected to a specific form of intermittent fasting. Their access to food followed a recurring 24-hour pattern: animals were allowed to feed ad libitum for 24 hours, followed by 24 hours of access to water. During the 22-month fasting program, the men were housed together with no contact with women. They were later introduced to three-month-old females who had been raised without dietary restrictions.

Effect takes time

Increased mating behavior was also observed in younger mice. These males had also begun intermittent fasting at two months of age, but had only followed this diet for six months before being introduced to the females. They were also more sexually active than cross-age counterparts who had been fed ad libitum. However, the effect was absent in other experimental groups - both young and old - who fasted for only a few weeks.

“Intermittent fasting to increase sex drive takes time,” says Zhou. “Based on our experiments, the minimum duration appears to be between six weeks and six months.”

A question of serotonin

In examining the causes, attention eventually turned to the neurotransmitters that influence sexual behavior. Some have a stimulating effect while others act as inhibitors. Among the sexually active male mice, one factor stood out: serotonin - a chemical messenger generally associated with inhibitory effects - was present at unusually low levels.

These mice were, so to speak, sexually uninhibited, with the usual regulatory restraint reduced. “

Dr. Dan Eehnner, research group leader at Dzne

Serotonin is produced primarily in the gastrointestinal tract, but also in the brain, where it acts as a neurotransmitter mediating communication between neurons. However, its synthesis depends on the amino acid tryptophan, which must be obtained through diet or released through the breakdown of the body's own protein stores, such as those found in muscle tissue. Tryptophan is considered an essential amino acid, meaning that neither mice nor humans can synthesize it themselves. As a result, food intake plays a key role in regulating tryptophan levels in the body. In fact, it can be found in many common foods. “The lack of serotonin was clearly a result of fasting,” explains the DZNE researcher.

Is the fasting regimen relevant?

"All in all, the fasting mice consumed almost fifteen percent less than the animals in the control group. This also roughly applies to their intake of tryptophan," says Zhou. "However, it is currently unclear whether the reduction in serotonin levels is associated with our specific feeding regimen or would also occur with other types of fasting. Future studies will need to clarify this." As the scientist notes, it is also possible that the effect can occur under general calorie restriction, where food is continuously available, but in reduced quantities.

A potential approach for therapy

"Chemical messengers also play an important role in regulating sexual behavior in humans. This is particularly true for serotonin," says Eehnner. As he points out, this is evident, for example, with the use of SSRIs, a class of antidepressants that increase serotonin levels. A possible side effect of this therapy is reduced libido. Conversely, lower levels of serotonin promote sexual desire. "With this in mind, I think it is very plausible that sexual desire in humans can be influenced by fasting - perhaps not just in men, but also in women, as serotonin also affects their libido." According to Eehnner, there are actually few scientific studies on the effects of fasting on human libido. "I think it would be worthwhile to study this in more detail. I see the potential for therapeutic use. A lack of sexual desire is not necessarily perceived as problematic - but some people suffer from it. This condition is called 'hypoactive sexual desire disorder' and particularly affects older adults. Fasting could potentially serve as a useful addition to existing treatment options."

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