Here’s some bad news for health conscious people. If their parents and grandparents gorged on unhealthy food, they may face an exaggerated risk of weight gain. That’s the finding of a new mouse study. It’s not yet been confirmed that the same is true in people. But it was a concern over human risks that prompted the new study.
Too little exercise and eating too many calories are root causes of obesity. However, in the past few years, scientists have begun to explore the role of our DNA. Some genes may play a role in making people fat. For instance, studies have shown that some genes can make a person’s body burn calories less efficiently. People with these “fat” genes could find it hard to lose weight.
The latest study, conducted in Australia, adds to those depressing data. It shows that the tendency of some people to become overweight may trace to what their parents or even grandparents ate long before they were born.
That new experiment was conducted in two parts. First, the researchers bred a group of obese male mice with lean females. They also bred a control group with each other. Here, both males and females had a healthy weight.
When male mice that had an obese father were given junk food to eat, they developed a lot of problems. They had higher-than-normal levels of blood sugar, or glucose. They also had an excess of the hormone insulin in their blood. Perhaps worst of all, their livers accumulated too much fat. All of these conditions are generally found in people who are obese, have metabolic syndrome or have diabetes.
Female mice born to obese fathers were not affected. The male mice that had a lean father also showed no problems.
The DNA in the two sets of offspring were the same. This meant that the genes of those obese fathers were not the problem, says Jennifer Cropley. She works at the Victor Chang Cardiac Research Institute in Darlinghurst, Australia. The animals’ genes had not been directly to blame, her team found. Their symptoms of metabolic syndrome instead traced to how or when certain genes were allowed to operate.
Cropley studies epigenetics. It’s the branch of science that looks at how things in the environment, including diet, can affect little “tags” on genes. These tags work like switches to turn genes on and off. And it was those external switches that were somehow altered, Cropley’s group discovered.
What’s more, it wasn’t just the sons of the obese dads that showed this metabolic problem. The grandsons, too, developed the same problems after they ate junk food for a while. And this held even for mice whose fathers had eaten well and maintained a healthy weight.
These findings will be published soon in the journal Molecular Metabolism.
Why was this just a male thing?
When the scientists realized it wasn’t genes themselves that were making the next generation of mice fat, they wondered what was going on. What might be happening during mating that made sons and the grandsons of obese male mice so vulnerable?
They decided to look at the sperm of the male mice. RNA is a type of genetic material. It acts like a watchdog, deciding whether or not its gene gets turned on. The RNA in sperm was different in the sons with obese fathers than in sons with lean dads. “It was always thought that sperm just have DNA,” says Cropley. “But in fact, they have RNA molecules,” she says.
This study will change people’s attitudes toward pregnant women, Cropley predicts. “If you’re pregnant, you’re told you should eat well and not drink or smoke,” says Cropley. “Our results prove that contributions of dads might be just as important.”
Laura Dearden is a researcher at the University of Cambridge in England. There, she studies how early-life factors can affect someone’s appetite. Dearden says the study sends out a warning message: “If you are aware of a history of obesity in your family tree, even if your parents aren’t obese, you should be careful what you eat.”
Michelle Holland is a researcher at Blizard Institute in London, England. Like Cropley, she studies epigenetics. Holland says scientists always thought this kind of “non-genetic inheritance” did not occur in mammals. But studies such as this have begun to prove that the previous “assumption was wrong.”