Sperm don’t just deliver DNA to an ovum; they also carry information about the pending father’s weight, according to a new report. When a team led by Romain Barrès at the University of Copenhagen compared methylation patterns on the DNA of obese men with those of lean men, they found differences on genes involved in the regulation of appetite (Cell Metab. 2015, DOI: 10.1016/j.cmet.2015.11.004). Furthermore, obese men who underwent bariatric surgery to reduce their weight had changes in their sperm DNA’s methylation patterns that trended toward the configurations of lean men. The work suggests—but does not yet prove—that obese men might unwittingly alter the appetite and increase the risk of obesity in their children and that obese men may want to lose weight before helping conceive a child. Barrès and his colleagues are currently investigating those possibilities. They think sperm weight imprinting might have once served a useful evolutionary function by encouraging large appetites during eras of food abundance. However, studies nowadays have shown that “children of obese fathers are at a higher risk of developing metabolic disease later in life, independent of the body weight of their mother,” the researchers note.