Men's obesity affects fertility and sperm quality

Effect of obesity on sperm quality in men:

Men, now you have more reason to watch your waistline. A man's weight seems to affect the activity of his sperm genes and may be passed on to his children.

"Our results suggest that the environment causes changes in sperm cells, which may reflect a mechanism that can pass on obesity to the next generation." said Romain Barrès of the University of Copenhagen in Denmark. He also believes his findings may have led some expectant parents to seriously consider changing their behavior before becoming pregnant. We already know that children's weight seems to have a strong correlation with their parents. So far, many studies studying the genetic mechanisms of obesity have focused on mothers and their pre-pregnancy eating habits. But this new finding suggests that a father's health also matters.

After comparing the sperm of 13 lean men and 10 moderately obese men, Barrès and his team found significant differences in the epigenomes of the subjects 'sperm (the epigenetic genome is a modification on DNA that affects gene activity). "We found that the epigenetic markers of about 9000 genes in the sperm of obese men had changed." Barrès said.

"Now this result provides us with more evidence that our body size depends not only on our mother's eating habits, but also on our father's eating habits," said Susan Ozanne of the University of Cambridge.

In the past, it was thought that epigenetic changes would not be passed down from generation to generation in humans because patterns of DNA methylation-an epigenetic change that lowers gene activity-would be cleared after fertilization.

However, a study earlier this year found that some genes seemed to be able to escape the cleanup. Moreover, there is evidence that short RNA fragments that determine which gene is methylated can be passed through sperm. Barrès's research found that obese men have higher levels of certain short-strand RNAs, and one of the RNA fragments targets the CART gene, a gene that controls appetite.

"We haven't studied the transfer of these epigenetic modifications to future generations, but we are beginning to embark on this study," Barrès said. "We suspect that several epigenetic markers act simultaneously after fertilization, changing the program of embryo development.

But these epigenetic changes are not permanent. Barrès's team analyzed the sperm epigenetic genomes of six abnormally obese men who had undergone bariatric surgery to help lose weight. It turned out that just one week later, the methylation of 1500 genes had changed. A year later, the methylation of about 4000 genes had changed.

But of these, only 2700 genes were identified in previous studies, and most of these genes did not match the pattern found this time in the thinner male group.

"I can only say that the changes in epigenetic patterns caused by surgery can somehow compensate obese patients," said Isabelle Mansuy of the University of Zurich.

But without control, we cannot rule out this apparent heritage difference because of the time span between the two tests, Barrès said.