Could Your Gut Bacteria be Making you Fat? - Kristie Lebeau, Registered Dietitian Nutritionist
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How Your Gut Bacteria Could be Putting You at Risk for Obesity and Diabetes

Your gut is home to many bacteria – intestinal bacteria make up 10 times the number of cells as those in the human body. You’re probably already aware that bacteria can affect your gastrointestinal health. But research also suggests that these bacteria – known as the gut microbiota – can affect our metabolism and influence whether we become obese, get diabetes, or have other metabolic problems.

The gut microbiota influences our health in a number of ways. One of the ways it works is that good bacteria (probiotics) ferment dietary fibers in our intestines into short chain fatty acids (SCFA). These SCFAs can modestly improve blood sugar levels, improve insulin resistance and reduce inflammation by acting on glucagon-like hormone.

Short chain fatty acids produced by good bacteria can help us to reduce food intake by increasing hormones that decrease appetite and food intake, and by lowering ghrelin, the hormone that makes us hungry. They can also reduce the amount of energy obtained from the diet by speeding up transit time in the intestinal tract. Gut bacteria can also suppress fat storage by inhibiting lipoprotein lipase. So, bottom line, good bacteria can help us to eat less, extract less energy from our food, and store less fat.

Of course, not all gut bacteria are equal. There are two main phyla of gut bacteria that are prevalent in our intestinal tract: Firmicutes and Bacteroidetes. Some studies show that the obese are more likely to have a higher ratio of Firmicutes, whereas those who are lean are more likely to have higher amount of Bacteroidetes. When individuals lose weight through decreased food intake, their levels of Bacteriodetes increase. Similar changes occur with gastric bypass weight loss surgeries.

However, some studies have not shown an association with these two phyla, rather showing that other differences take place in the microbiota. But when individuals with metabolic syndrome are given a transplant of bacteria from a lean individual, their insulin sensitivity and other metabolic measurements improve.

Some probiotic strains, particularly Lactobacillus and Bifidobacterium, have been shown to improve obesity and metabolic disorders, at least in mice. More studies will need to be done to prove that it would actually help in humans, but given other benefits of a healthy gut microbiota, it seems worthwhile to improve your gut bacteria. 

What you can do to improve your gut microbiota:

  1. Consume good bacteria in the form of probiotics: yogurt, kefir (a fermented milk drink pronounced keh-FEAR), fermented vegetables such as sauerkraut, kimchi, and fermented soy products, such as tempeh and miso.
  1. If you don’t consume much of these foods, consider taking a probiotic in the form of a pill. Look for strains in the lactobacillus or bifidobacterium species with at least 10 billion CFUs (colony forming units) for adults or 5 billion CFUs for children. Well-researched brands include Align, Culturelle, which you can find at most drug stores. There is also VSL #3, a medical grade probiotic which you can ask your pharmacist to order, it should be refrigerated, and it costs about $50 per bottle (though insurance may cover it for those with GI conditions such as ulcerative colitis).
  1. Eat adequate fiber. Eat at least 25-35 grams of fiber per day, or 14 grams per 1000 calories. This should be a mix of insoluble fiber (“roughage”) and soluble fiber (the fiber that attracts water to form a gel, and is found in foods like oat bran, beans/legumes and psyllium). Remember, fiber is found only in plants, so eat plenty of vegetables, fruits, beans, nuts, seeds and whole grains; the less processed, the better. If your fiber intake is low, you might want to gradually increase your intake to reduce unwanted side effects like excessive gas.
  1. Consume prebiotics. Prebiotics are food for good bacteria, and are found in whole grains, bananas, onions, garlic and artichokes. They also may be added to probiotic supplements.
  1. Don’t use antibiotics unless you need them. They kill both bad and good bacteria. I’m not saying antibiotics are bad – they are one of the most important medical discoveries and have saved countless lives.   However, they only treat bacterial infections, so if you have a common cold, flu, or other virus, an antibiotic won’t help.  Also, over 80% of the antibiotics sold in the U.S. are used in food animal production to help animals grow larger more quickly (which leads one to wonder – if it makes animals grow larger, why not humans?). Reducing or eliminating intake of meat and poultry, or choosing meat products that are labeled “certified organic,” “raised without antibiotics,” or “no antibiotics administered” are some ways to reduce the exposure to antibiotics in your foods and reduce the risks of antibiotic resistance and “superbugs” in the environment.


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