It may not just be your diet and exercise habits that are making it difficult for you to shed pounds. The problem could also be in the type of foods you eat. A study of mice published in the journal Science Translational Medicine found that a diet high in fat and sugar does more than just supply the body with calories. It also changes the composition of bacteria in the intestines, making it easier to gain weight and more difficult to lose it.  (Bacteria are necessary to convert indigestible foods into a digestible form.)

While many reasons factor into why an individual gains weight (including genetics, amount of physical exercise, and food choices), a growing amount of evidence is showing that bacteria in the digestive system also plays a key role. The research, conducted at Washington University School of Medicine in St. Louis, was based on transplants of human intestinal microbes into germ-free mice. In the weeks leading up to the transplant, the mice were given a plant-rich, low-fat diet. After a month on the diet, half the mice were switched to a high-fat, high-sugar "Western"-style diet. Within 24 hours, the composition of the gut microbes changed and the mice on the Western diet became obese.

According to the lead author of the study, Jeffrey I. Gordon, M.D., director, Center for Genome Sciences at Washington University, there appears to be a link between obesity and the type of bugs in the gut. Obese people seem to have more of the type of digestive microbes that are especially good at extracting calories from food.

While these research findings may help shed new light on how to overcome the obesity epidemic in this country-two-thirds of Americans are overweight or obese, according to the Centers for Disease Control and Prevention-experts say that lifestyle choices are still the major factors in the obesity epidemic.

Tips to Lose Weight

  • Eat a variety of lower-fat foods to get all the nutrients you need
  • Keep track of your calorie intake by reading product labels. Remember, "low fat" doesn't always mean "low calorie"
  • Eat mostly plant-based foods, such as whole grain products, fruits and vegetables, and only moderate amounts of animal-based foods such as meat and dairy products
  • Increase your level of exercise each day to lose excess body fat