Men play a much bigger role in the health of their babies than previously thought. Recently published studies — one on rats, the other on grown men — find that dads' weight and diet have a significant impact on babies' weight, appetite, and even mental health.

First, the rodent study: Six weeks prior to breeding, male rats were fed 25 percent less of the same food than rats in the control group. The results of this calorie restriction were significant — the babies of the calorie-restricted diets weighed less, ate less, and appeared less anxious than the offspring of the control group rats.

The body weights of the rats in the calorie-restricted group were around 10 percent lower, which might explain why they also tended to eat less, the researchers say, as smaller animals typically need less food.

A possible explanation for why this happens is that reduced calorie intake might sharpen survival instincts and make animals more up for adventure, says Antonio G. Paolini, a psychology professor at the RMIT University in Melbourne, Australia, and one of the study co-authors. "Our findings imply that it's important to consider the male diet prior to conception, as this [has] a direct effect on the programming of the sperm," Paolini says.

"Programming of the sperm" has to do with epigenetics, a growing area of research studying the modification of gene expression in our bodies, or what influences how genes turn on or off. A particular area of interest in epigenetics is how environment, such as exposure to everyday chemicals like bisphenol-A (BPA) and diet, can affect gene expression.

Paolini says their results support previous research that concluded high-fat diets of dad rats increased body weight and impaired glucose tolerance and insulin sensitivity in their offspring , but that this was the first study to examine transgenerational effects of paternal diet on anxiety in offspring.

In the other study, out this month, researchers at the University of Copenhagen studied the sperm of 10 obese men and 13 men of normal weight and found significant differences in gene expression. They also looked at six men before and after the men had undergone gastric bypass surgery for weight loss and noted 5,000 epigenetic changes, which means that it isn't necessarily a genetic predisposition to obesity affecting offspring but the current weight of a father at the time of conception that has an impact. These epigenetic changes could affect appetite signals in children, the researchers wrote, but they said more research is needed to determine what the actual epigenetic effects might be.

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