Even if you normally eat nothing but salads, one junk food binge may cause a serious shift in your body making it easier to pack on the pounds.

A new research study found that the type of food you eat can affect the type of bacteria in your stomach in as little as 24 hours, which can make gaining weight easier and losing it harder.

Researchers at the Washington University in St. Louis examined two types of stomach bacteria: Bacteroidetes and Firmicutes. It's this bacteria that determines if the food you eat is stored as fat or burned as calories. While some bacteria in the stomach is good to help safeguard against disease, the amount of Bacteroidetes and Firmicutes can make a difference in your waistline. And a major contributor to which type of bacteria people have is food.

The researchers discovered that obese people tend to have high levels of Firmicutes in their stomach and intestines, while thinner people have more Bacteroidetes bacteria. They also discovered that one splurge of high-fat, high-calorie food can alter these levels.

In the study, human stomach bacteria from fat mice was injected into thin mice. The lean mice quickly gained weight despite being fed low-fat foods. Interestingly enough, the weight was also much harder to lose once the Firmicutes -- or fat-causing bacteria -- was in the stomach.

What does all of this mean? It further substantiates the importance of a healthy diet every day. It also raises questions about the possibility of eating more probiotic foods. "Probiotics could have an exciting role in changing the flora in the gut," states registered dietitian and nutrition consultant, Tara Gidus. "We already know they benefit gastrointestinal disorders like irritable bowel syndrome. There is also some research that shows they may boost the immune system." While Gidus believes it is too early to start recommending probiotics for weight loss, the key to staying thin seems to be avoiding the junk.

In addition to diet, fat-causing stomach bacteria can also be increased by stress and lack of sleep. All the more reason to ditch the in-laws this holiday season and take that trip to the Keys instead.