Men genetically predisposed to obesity may be more likely to become infertile compared to those who become obese owing to a high-fat diet, suggests a new study from a city-based research institute. The study was published in the Endocrinology Journal this year.

Researchers from the National Institute for Research in Reproductive Health (NIRRH), Mumbai, and Hyderabad’s National Institute of Nutrition, compared two groups of 10 male rats each to understand the effects of obesity on male fertility. The first group was made up of rats that became obese, even on a low-fat diet (genetically predisposed), while the other group was of rats that became obese as a result of a high-fat diet.

“To the first group, we gave balanced amounts of carbohydrate, protein, fats, minerals, and vitamins. To the other group we fed high-fat food that contained coconut fat and lard [pig fat],” said Sharvari Deshpande, PhD student at NIRRH and first author of the study.

Findings revealed that obese rats with genetic links to the disease were unable to mate with female rats. “These rats had a loss of sexual potency or what we popularly refer to as loss of libido,” said Dr Nafisa Balasinor, scientist at the NIRRH, who led the study.

Further, researchers found that impotent rats in the genetically obese group also had a nearly 55%-less sperm count than ones who were obese due consumption of fatty food. “In the first group, we saw a higher disruption of levels of the hormones testosterone and estradiol, which are essential for sperm formation,” Deshpande said. “The second group wasn’t completely free of reproductive problems either. While they could mate and had normal sperm counts, they were able to produce a lesser number of offspring compared to lean male rats.”

However, in rats which had obesity written in their DNA, infertility could be reversed through a “calorie-restricted diet”. “[After changing the diet] we saw the hormonal levels were partially reversed and they were able to mate with the females and produce offspring,” said Dr Balasinor.

The researchers chose to use male rats for the study as the genomes are similar to those of humans and have parallel reactions to conditions.

According to the research team, the study could have similar implications for genetically-obese men as well. In these cases, interventions such as dietary restriction, physical activity or surgery-induced weight loss could reverse the effects of obesity on male reproductive health. “Doctors can advise men, couples attending assisted reproductive technology ([ART] and in-vitro fertilisation [IVF] clinics, that a healthy diet could, in fact, help resolve the problem,” said Deshpande.

The World Health Organization states that issues with being overweight and obesity represent a rapidly growing threat to the health of populations around the world. They are now replacing more traditional problems such as undernutrition and infectious diseases as significant causes of ill-health.