It seems that prolonged fasting in 24-hour cycles increases sexual desire in male mice, according to a study conducted by researchers at the German Center for Neurodegenerative Diseases (DZNE). Fasting is a recurring topic of research because reducing food intake and, consequently, caloric restriction have various effects on the body beyond the commonly observed weight loss.
Researchers at the DZNE indicate that fasting in 24-hour cycles, for about six months, increases sexual desire in male mice by reducing the concentration of the neurotransmitter serotonin in the brain. This effect, as reported in ‘Cell Metabolism,’ is related to a diet-induced deficiency of tryptophan, an amino acid precursor that must be obtained through food.
The researchers at DZNE, along with a team from Qingdao University in China, suggest that similar mechanisms may exist in humans and consider fasting as a possible approach to treat unwanted loss of sexual desire.
Dr. Dan Ehninger, leader of the research group at DZNE and lead author of the current study, and his team have been working on this topic for quite 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 gather information that may also be relevant to humans,» he explains.
FASTING AFFECTS DESCENDANTS
The research results are based on a serendipitous discovery, as Ehninger and his colleagues had originally set out to investigate something else. Their aim was to examine how fasting affects the offspring of male mice. However, a particular finding redirected their research: older male mice (considered elderly by human standards) who had fasted for extended periods produced an unusually large number of offspring.
Contrary to initial hypotheses, this phenomenon was not due to the effects of fasting on reproductive organs or the endocrine status of the animals. Age-related changes in the testicles, reduced sperm quality, and lower testosterone levels argued against high fertility.
«It was a bit of detective work to discover the true cause,» reflect the researchers. «Ultimately, we realized it was a behavioral issue. Fasting males 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. Their mating behavior compensated for the physiological limitations of age,» he says.
24 HOURS WITH EXCLUSIVE WATER ACCESS
These male mice were subjected to a specific type of intermittent fasting. Their access to food followed a 24-hour recurring pattern: they were allowed to eat ad libitum for 24 hours, followed by 24 hours with exclusive access to water. During the fasting regimen, the males remained together without contact with females. Subsequently, they were introduced to females raised without dietary restrictions.
An increase in mating behavior was also observed in younger mice. These males had also started intermittent fasting at two months of age, but had only followed this diet for six months before being introduced to females. They were also more sexually active than their same-age counterparts who had been fed ad libitum.
However, this effect was not observed in other experimental groups, both young and old, that fasted for only a few weeks. According to these experiments, the minimum duration seems to be between six weeks and six months.
In investigating the causes, attention was focused on neurotransmitters that influence sexual behavior. Some have a stimulating effect, while others act as inhibitors. Among sexually active male mice, one factor stood out: serotonin, a neurotransmitter generally associated with inhibitory effects, was found at unusually low levels.
Overall, the fasting mice consumed nearly 15% fewer calories than the animals in the control group. This also applies, in general, to their tryptophan intake. However, it is currently unclear whether the reduction in serotonin levels is related to our specific feeding regimen or if it would also occur with other types of fasting. Future studies will need to clarify this.
THEY CONSIDER SIMILAR SEXUAL BEHAVIOR POSSIBLE IN HUMANS
As the scientist points out, it is also possible that the effect occurs with general caloric restriction, where food is available continuously but in reduced quantities. «Neurotransmitters also play an important role in regulating sexual behavior in humans. This particularly applies to serotonin,» says Ehninger.
As he points out, this is evident, for example, in the use of SSRIs, a class of antidepressants that increase serotonin levels. A possible side effect of this therapy is reduced libido. Conversely, it is known that low levels of serotonin promote sexual desire.
«In view of this, I consider it very plausible that fasting could influence sexual desire in humans, possibly not only in men but also in women, as serotonin also affects their libido.» According to Ehninger, there are actually few scientific studies on the effects of fasting on human libido.
«In my opinion, it would make sense to investigate this in more detail. I see potential for therapeutic application. The lack of sexual desire is not necessarily perceived as a problem, but some people suffer from it. This condition is known as ‘hypoactive sexual desire disorder’ and particularly affects older adults. Fasting could be a useful complement to existing treatment options.»
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FUENTE