Doctor’s Tip: Could the bacteria in your gut be making you fat? |

Doctor’s Tip: Could the bacteria in your gut be making you fat?

One of the new frontiers in medicine is the gut microbiome. This refers to the microorganisms that inhabit the human gut, which consist primarily of bacteria; but also includes viruses and fungi such as yeast. Today’s discussion is about gut bacteria, which are at least three times greater in number than all the cells in the human body.

Scientists are finding more and more links between the type of bacteria we have in our gastrointestinal tracts — particularly our colons — and various aspects of our health.

The September issue of the University of California, Berkeley, Wellness Letter contains an article by John Swartzberg, M.D., chair of the editorial board, about antibiotics and obesity. He points out that research “has found that the composition of the microbiome can influence energy metabolism as well as how carbohydrates and fats are digested, thus affecting the risk of obesity.”

One of the reasons livestock are treated with antibiotics is that they cause animals to gain weight. In humans, studies have shown that “impoverished, malnourished children who are treated with antibiotics gain weight.” A group of intestinal bacteria called Firmicules “cause us to absorb more calories from the same amount of food” compared with another group called Bacteroidetes. Therefore, a preponderance of Firmicules is associated with obesity, while a preponderance of Bacteroidetes is associated with being lean.

One factor that can affect our microbiome is what we eat. Our gut bacteria thrive on fiber and resistant (indigestible) starch. Fiber is found in plants, but not in animal products. People who eat a purely plant-based diet have gut bacteria that promote being lean. People on an animal-based diet have gut bacteria that promote obesity, and many chronic diseases including cardiovascular disease and diabetes.

The microbiome can also be affected by antibiotics. Although antibiotics can be life-saving when used to treat severe infectious diseases such as meningitis and bacterial pneumonia, they are overprescribed by doctors, and patients often demand them for minor illnesses.

According to Dr. Swartzberg, even a short course of antibiotics can affect the gut flora for up to a year. A study reported in the JAMA Pediatrics journal “found that children who took antibiotics — especially broad spectrum antibiotics — at least four times before age 2 had an elevated risk of becoming obese by age 5.” There is even a link between antibiotics given in the second and third trimester of pregnancy and having children who become obese.

In conclusion, you will be more apt to attain and maintain an ideal body weight if you have a health-promoting gut microbiome, and the way to achieve that is to eat a plant-based diet and avoid antibiotics unless absolutely necessary. If you continue to eat animal products, try to avoid meat that contains antibiotics.

Dr. Feinsinger, who retired from Glenwood Medical Associates after 42 years as a family physician, now has a nonprofit Center For Prevention and Treatment of Disease Through Nutrition. He is available for free consultations about heart attack prevention and any other medical concerns. Call 970-379-5718 for an appointment. For questions about his columns, email him at

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