As you have likely heard a number of times, obesity and diabetes are on the rise. Currently, 1 of every 3 Americans is obese and 1 in every 10 Americans has type 2 diabetes. The two diseases are closely related and are often seen together in the same person. Obesity is most simply caused by an excessive intake of food and a lack of physical activity to burn off the calories of that food. People who are obese suffer from a host of other health problems including: heart disease, high blood pressure, stroke, diabetes, gout, infertility, cancer, and liver disease. There have been genetic factors identified that predispose someone to becoming obese but what is unknown currently is if or how obesity is transferred between parents who are obese and their children. In order to answer this question a group of researchers performed an elegant study in mice.
The group from Germany and publishing in Nature, fed mice a high fat diet to induce weight gain and glucose intolerance (diabetes). As a control, mice fed a normal diet and mice fed a special low in fat diet were used. In order to see if the offspring were susceptible to gaining weight or developing diabetes, the researchers bred different combinations of mice to get offspring where both, one or neither of the parents were obese. However, it was not as simple as letting the mice breed as they wish. There are many things in the environment that could have influenced how these offspring would gain weight. Things like breast feeding from an obese mother, the eating habits of the obese mice, and even the bacteria present in the womb of the obese mother could impact the eventual weight gain and development of diabetes in these mice. To get around this, the researchers isolated sperm and egg cells from the parents, performed in vitro fertilization, and then raised the resulting embryo in a surrogate non-obese mother mouse. This surrogate mother would be of normal weight and fed a normal diet. By doing the experiment in this way, the researchers could be sure that any effect of parental obesity on the baby mice would be the result of some change to the genetics and not due to something in their environment. The offspring from this special mating were then fed a high fat diet and their weight gain and insulin resistance was tracked.
The results of this study were striking. Mice whose parents were both obese (fed the high fat diet) gained more weight when fed a high-fat diet and were more likely to develop insulin resistance, a first step in developing type-2 diabetes. When only one of the parents was obese (high fat diet), the resulting offspring gained less weight than the mouse with two obese parents but still gained more weight than the mouse with no obese parents. To summarize:
- Obese mom and obese dad = 20% weight gain (Ex. 30 pounds on a 150 pound person)
- Obese mom or obese dad = 8-14% weight gain (Ex. 12-21 pounds on a 150 pound person).
Interestingly, daughter mice were more prone to gaining weight if both parents were obese while sons were more prone to developing glucose intolerance (pre-diabetes). Also, the mothers diet (high-fat or not) seemed to have a larger effect on the offspring’s eventual weight gain compared to the father’s diet. This mirrors evidence in humans, moms diet is more important than dads diet, although dads diet still has an impact. There are some questions that the research leaves unanswered:
- Do the offspring of these obese mice spontaneously gain weight when fed a normal diet? Or do they only gain weight more rapidly when fed a special high-fat diet? This information would tell us whether sticking to a healthy diet will help the kids of obese parents keep the weight off.
- How is the trait (obesity) being passed from parents to children? The thought is that it involves subtle modifications to the DNA. These subtle changes are called epigenetic changes (explanation here) and are not the result of mutations in the genes but instead changes in the on/off or dimmer switches in the cell.
The results of the research are important in furthering our understanding of how the obesity epidemic is accelerating at such a fast rate. If obesity can be passed onto offspring, then more care may be needed to educate parents trying to get pregnant on the importance of remaining healthy before and during pregnancy.
Image credit: Flickr Tony Alter