Scientists have warned intermittent fasting diets reduce energy levels and could damage fertility long term.
The University of East Anglia researchers have looked at the impact cutting down on food has on zebrafish, which have similar genetic structure to humans.
Even after the fish were returned to their normal diets, quality of eggs and sperm produced did not go back up.
The experts say the findings reiterate the importance of exploring the possible risks of such diets, despite the potential for weight loss and other health improvements.
Intermittent fasting generally involves eating during a specific window during the day to aid fat loss.
Professor Alexei Maklakov, the lead author of the study, told the Times: "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.”
The study was published in the journal Proceedings of the Royal Society.
It adds to other findings that suggest fasting diets could damage fertility and interfere with female sex organs.
Dr Edward Ivimey-Cook said time-restricted fasting affects reproduction differently in males and females.
He said: “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."
The scientist added that more research is still needed to understand how long it would take sperm and eggs to return to normal quality.
Methods of intermittent fasting include alternate-day fasting, periodic fasting, and daily time-restricted feeding.
Such fasting has been the subject of various studies, but the adverse effects have not been comprehensively explored, with some experts suggesting it is a fad.
Some research shows it could help with obesity, insulin resistance, dyslipidemia, hypertension, and inflammation.
Fasting also exists in various religious practices, including Buddhism, Christianity, Hinduism, Islam, Jainism and Judaism.
