Intermittent fasting — one of the most popular celebrity dieting techniques — may cause fertility problems, research suggests.
Hollywood A-listers like Jennifer Aniston, Nicole Kidman, Cameron Diaz, and Mark Wahlberg have jumped on the trend since it rose to prominence in the early 2010s.
But despite numerous studies suggesting it works, experts have remained divided on its effectiveness and potential long-term health consequences.
Now, an animal study suggests that while fasting is good for your waistline, it may harm the chances of conception.
Experts from the University of East Anglia in Norwich investigated how time-restricted fasting affected reproduction in zebrafish.
Hollywood A-listers like Jennifer Aniston (pictured above), Nicole Kidman, Cameron Diaz, and Mark Wahlberg have all jumped on the trend since it rose to prominence in the early 2010s
In this latest study, scientists at the University of East Anglia in Norwich examined how time-restricted fasting affected reproduction differently in male and female zebrafish. Pictured above, Mark Wahlberg, who is known to intermittent fast fast
The study looked at the impact of fasting on the fertility of zebrafish, an animal widely used in research on human health implications
Critically, the researchers found that both egg and sperm quality were negatively affected even after the fish returned to their normal levels of food consumption.
writing in the diary, Proceedings of the Royal Society B: Biological Sciencesresearchers said the findings “call for careful evaluation of the effects of intermittent fasting on fertilization.”
Scientists measured both sperm and egg production and the quality of the resulting offspring.
Q+A: Everything you need to know about intermittent fasting
How does it work?
Intermittent fasting means alternating between days of fasting and days of normal eating.
It generally falls into two categories: restricting eating times to 6-8 hours a day, known as the 16:8 diet, and 5:2 intermittent fasting.
The 16:8 diet is a form of intermittent fasting, also known as Time Restricted Eating.
What is the difference between time-restricted eating and 5:2 intermittent fasting?
Followers of the 16:8 eating plan fast for 16 hours a day and eat whatever they want in the remaining eight hours — usually between 10 a.m. and 6 p.m.
This may be more bearable than the well-known 5:2 diet – where followers limit their calories to 500 to 600 per day for two days a week and then eat normally for the remaining five days.
What are the benefits of time-restricted eating?
In addition to weight loss, 16:8 intermittent fasting is believed to improve blood sugar control, boost brain function and help us live longer.
Many prefer to eat between noon and 8 p.m., as this means they only have to fast overnight and skip breakfast, but can still have lunch and dinner along with a few snacks.
If you do eat, it’s best to choose healthy options such as fruits, vegetables, and whole grains, and drink water and unsweetened beverages.
What are the disadvantages?
Downsides of the fasting plan can be that people overeat in the hours they can eat, leading to weight gain.
It can also lead to digestive problems in the long run, as well as hunger, fatigue, and weakness.
They took 12 male and 12 female fish and put them on a fully fed diet.
While another group of 18 men and 18 women was put on a fasting group.
After 15 days, the fasted fish were allowed to eat normally again.
To test reproductive performance, the 30 male and 30 female fish were randomly mated on days seven, 15, 21, 28 and 35 of the experiment with fish of the opposite sex from the ‘general population’.
Fish were then given up to five hours to spawn.
Failing this, they got another partner and the process was repeated the next day.
Sperm from each of the 30 males was also collected on days seven, 15, 21 and 35, while eggs were assessed at two and 24 hours.
Scientists found that female fish on the fasted diet had, on average, “significantly lower” reproduction rates on days seven and 15.
“This resulted in a reduced total number of offspring for females,” she added, with 163 offspring among those who were fully fed compared to the 75 who fasted.
The reduction in the number of offspring continued even after the females were fed normally, with the fish simultaneously registering an increasing growth of their fins.
Researchers suggested this could be a sign that the female bodies prioritized their own post-fast health over their ability to reproduce.
Fasting male fish also showed a more rapid decrease in the rate of their sperm over time and a “significant decrease in sperm quality” compared to the fed group, the scientists said.
The study’s authors said the results “cannot be directly compared to a two-week period in a mammal,” due to differences in metabolism between us and fish.
However, they hope the findings highlight its importance taking into account not only the effect of fasting on weight and health, but also on fertility.
Dr. Edward Ivimey-Cook, an expert in biological sciences and author of a study, said: ‘These findings underscore the importance of considering not only the effect of fasting on body maintenance, but also on egg and egg production. semen.
‘Importantly, some of the negative effects on egg and sperm quality become visible after the animals return to their normal level of food consumption after time-restricted fasting.
“More research is needed to understand how long it takes for sperm and egg quality to return to normal after the fasting period.”
Professor Alexei Maklakov, an expert in evolutionary biology and an author of the study, said: ‘The way organisms respond to food shortages can affect egg and sperm quality, and such effects could potentially persist after the end of the fasting period.
In the journal Proceedings of the Royal Society B: Biological Sciences, the researchers write that the findings “call for careful evaluation of the effects of intermittent fasting on fertilization.” Pictured above, Nicole Kidman, who is known to intermittent fast fast
To test reproductive performance, the 30 male and 30 female fish were randomly mated on days seven, 15, 21, 28 and 35 of the experiment with fish of the opposite sex from the ‘general population’. Pictured above, Cameron Diaz, who is known to intermittent fast fast
Zebrafish are a common animal to use in such studies because their genetic structure is broadly similar to humans and they have a high reproductive rate.
While it’s a popular celebrity diet trend, experts are divided on the benefits of intermittent fasting.
Some argue that fasters usually consume a relatively large amount of food at one time, meaning they don’t cut back on their calories — a known way to beat the bulge.
And in recent years, a small amount of research has emerged linking the trend to a shorter lifespan and a higher risk of heart disease.
Experts suggest this may be because intermittent fasters eat more in one sitting, which they say could damage cells.