NORWICH, United Kingdom — Trendy time-restricted fasting diets — or intermittent fasting — could trigger problems for couples looking to conceive a child, new research warns. The study by researchers at the University of East Anglia focused on the reproductive processes of zebrafish and discovered that there was a negative effect on egg and sperm quality after the fish returned to normal eating.

After the diet, females saw an increase in the number of offspring they produced but saw a drop in egg and offspring quality. The male’s sperm also decreased in quality. Scientists commonly use zebrafish as a comparative tool for humans because the two species are actually very similar on a genetic level.

“Time-restricted fasting is an eating pattern where people limit their food consumption to certain hours of the day. It’s a popular health and fitness trend and people are doing it to lose weight and improve their health,” says Professor Alexei Maklakov from UEA’s School of Biological Sciences in a media release.

“But the way organisms respond to food shortages can affect the quality of eggs and sperm, and such effects could potentially continue after the end of the fasting period.”

“We wanted to find out more about how these sorts of diets can affect fertility in a popular model organism.”

To reach their results the team measured how the zebrafish allocated resources to body maintenance, body production, maintenance of sperm and eggs, and the quality of offspring.

“What we found is that time-restricted fasting affects reproduction differently in males and females. Once the fish returned to their normal feeding schedule, females increased the number of offspring they produced at the cost of egg quality resulting in reduced quality of offspring. The quality of male sperm also decreased,” adds Dr. Edward Ivimey-Cook, also from UEA’s School of Biological Sciences.

“These findings underscore the importance of considering not just the effect of fasting on body maintenance but also on the production of eggs and sperm.”

“Importantly, some of the negative effects on eggs and sperm quality can be seen after the animals returned to their normal levels of food consumption following time-restricted fasting,” Dr. Ivimey-Cook concludes. “More research is needed to understand how long it takes for sperm and egg quality to return back to normal after the period of fasting.”

The findings appear in the journal Proceedings of the Royal Society B: Biological Sciences.

South West News Service writer Alice Clifford contributed to this report.