Turns out dads are also eating for two. A study published in Cell Metabolism reveals that a man's weight affects the heritable information contained in sperm. The sperm cells of lean and obese men possess different epigenetic marks, notable at gene regions associated with the control of appetite.

The comparisons, which included 13 lean men and 10 obese men, offer one biological explanation for why children of obese fathers are themselves more predisposed to obesity.

The investigators tracked 6 men undergoing weight-loss surgery to see how it affected their sperm. An average of 5,000 structural changes to sperm cell DNA were observed from the time before the surgery, directly after, and one year later. More needs to be learned about what these differences mean and their effects on offspring, but it is early evidence that sperm carries information about a man's health.

Researcher salso compared specific epigenetic marks in the ejaculate of lean and obese men (men were the focus because sperm is much easier to obtain than eggs). While no differences were seen in the proteins that wrap up DNA, there were variations between the participants' small RNAs (for which the function is not yet determined) as well as methylation of genes associated with brain development and appetite. The next question was whether these differences were byproducts of obesity or lifestyle, which yielded the look at how bariatric surgery affects sperm epigenetics and discovery that weight is the main factor.

There are likely evolutionary reasons why information about a father's weight would be valuable to offspring. Authors theory is that in times of abundance, it's an instinctual way to encourage children to eat more and grow bigger. "It's only recently that obesity is not an advantage," author says. "Only decades ago, the ability to store energy was an advantage to resist infections and famines."

http://www.cell.com/cell-metabolism/home