The time restricted feeding is a kind of intermittent fasting, which has been shown to increase life expectancy in laboratory animal studies. It means that food is consumed only within eight hours each day. However, a new scientific study revealed a risk that can have that way of fasting: could cause fertility problems.
The work was carried out by researchers from the University of East Anglia, in the Kingdom United. He demonstrated that time-restricted fasting differently affects the reproduction of zebrafish male and female. It was published in the specialized magazine Proceedings of the Royal Society B Biological Sciences.
In addition, it yielded another important result: some of the negative effects of fasting on the egg and sperm quality can be observed after the fish have returned to their normal levels of food consumption.
The research team said that although the study was conducted in fish, their findings highlight the importance of considering not only the effect of fasting on weight and health, but also on fertility.
According to Professor Alexei Maklakov, from the University of East Anglia’s School of Biological Sciences, who led the research, “Time-restricted fasting is an eating pattern that limits food consumption to certain hours of the day.” day. It is a very popular trend in the field of health and fitness fashion, and people do it to lose weight and improve their health.
However, the expert clarified: “But the way in which organisms respond to food shortages can affect the quality of eggs and sperm, and those effects could continue after the fasting period is over.”
Before launching the study, Maklakov and his team had several questions to answer. “We wanted to find out more about how these kinds of diets might affect fertility in a popular model organism,” he said.
The research team studied the zebrafish (whose scientific name is danio laughed) to find out what happens when individuals are exposed to food during and after a period of fasting.
They measured how males and females allocate resources to body maintenance versus sperm and egg production and maintenance, and the quality of the resulting offspring.
“What we have found is that time-restricted fasting affects reproduction differently in males and females,” explained Dr. Edward Ivimey-Cook, another co-author. “Once the fish returned to their normal feeding schedule, the females increased the number of pups they produced at the expense of egg quality, which translated into reduced offspring quality. The sperm quality of the males also decreased,” he added.
“These results underline the importance of taking into account not only the effect of fasting on the maintenance of the organism, but also on the production of eggs and sperm. Some of the negative effects on egg and sperm quality can be seen after the animals returned to their normal levels of food consumption following the time-restricted fast,” he stressed.
Likewise, the researchers recognized that more studies are needed to better corroborate the results they reached. “More research is needed to understand how long it takes for sperm and egg quality to return to normal after the fasting period,” said Ivimey-Cook, who worked in collaboration with researchers at the Center for Environmental, Fisheries, and Aquaculture Sciences. (Cephas).
The experimental study with the fish was carried out with funding from the European Research Council (ERC), the Biotechnology and Biological Sciences Research Council (BBSRC) and the Natural Environment Research Council (NERC).
In people, the time-restricted fasting involves limiting food intake to a period of six to eight hours a day, during which you can eat whatever you want. Small studies in people with obesity suggested some time ago that it could help to lose kilos.
But a work that was published in April of last year in the magazine New England Journal of Medicine (NEJM) revealed that time-restricted eating would have no benefit compared to lowering calorie intake throughout the day.
That job lasted a year. They compared a group of people who ate a low-calorie diet between 8 a.m. and 4 p.m. with a group that ate the same number of calories at any time of the day. It has not found any effect.
According to Dr. Ethan Weiss, a diet researcher at the University of California, San Francisco, who was not involved in the study: “There is no benefit to eating in a narrow window.”
The work was led by researchers at the Southern Medical University in Guangzhou, China, and included 139 people with obesity. Women consumed between 1,200 and 1,500 calories a day, and men between 1,500 and 1,800 calories a day. To ensure compliance, the participants were asked to photograph all the foods they ate and to keep a food diary.
Both groups lost weight (an average of 10 to 15 pounds), but there was no significant difference in the amount of weight lost with each dietary strategy (i.e., between consuming only between 8 a.m. and 4 p.m. or consume the same number of calories at any time of the day). There were also no significant differences between the groups in terms of waist circumference, body fat, and lean body mass.
The scientists also found no differences in risk factors such as blood glucose levels, insulin sensitivity, blood lipids or blood pressure.
“These results indicate that restriction of caloric intake explained most of the beneficial effects observed with the temporary restricted diet,” Weiss and colleagues concluded.
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