Stress can make a bad diet more fattening

The combination of chronic stress and a junk-food diet causes more weight gain than the diet would on its own, according to a new study on mice.

The study, published online in the journal Nature Medicine, identified the biochemistry responsible for the effect, suggesting a possible target for future weight-loss drugs.

Such a drug could offer both cosmetic and medical benefits, said Zofia Zukowska of Georgetown University Medical Center in Washington, D.C., who co-led a team of scientists from the United States, Australia and Slovakia.

Zukowska and her colleagues focused on a brain chemical called neuropeptide-Y. Researchers knew that high levels of NPY can stimulate appetite and contribute to weight gain, but they didn't know whether it directly affected the growth of fat tissue.

The new study shows that the combination of chronic stress and a high-calorie diet increases the amounts of NPY in abdominal fat and promotes the growth of new fat cells. An injection that blocked NPY's activity in the mice prevented the growth of the extra fat cells, proving that NPY was the linchpin in the process.

The new research explains how stress and bad diet can work together to increase people's weight, says Mary Dallman, a professor of neuroscience at the University of California-San Francisco who wrote a commentary accompanying the new study. "It's a big step forward," she said.

However, crafting a practical treatment from the research is still a distant dream. "In a best-case scenario, it would be at least two years before it's tested in humans but many more years before any drug can be (approved)," Zukowska said.

Even then, it might not work, because the forces driving humans toward obesity may be more complex than those that fatten lab mice. "Our brains are hard wired to seek fat when we're stressed," says Elissa Epel, an obesity researcher at the University of California-San Francisco, who was not affiliated with the study.

In the study, the combination of psychological stress and a "junk-food diet" -- a rodent-pleasing chow that was rich in fat, carbs and calories -- led mice to put on fat, particularly around the waist and lower abdomen. The mice developed problems similar to those that arise in abdominally obese people, including high blood pressure and a prediabetic condition known as impaired glucose tolerance.

While developing a drug that targets NPY could take years, simple lifestyle changes -- reducing either emotional stress or consumption of fat and sugar -- might help people in much the way that the hoped-for drug would. "Eat for pleasure, not as a way to cope with stress," Zukowska advises. "If you are stressed and hungry, try to eat something healthy."