Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Gut Bacteria Believed to Affect Numerous Aspects of Health

Dear Doctor: I can't seem to lose weight and am wondering if my gut bacteria could be to blame. How can I change it?

Dear Reader: In recent years, it has become increasingly clear that the bacteria that live in our gastrointestinal tract, also known as the gut microbiome, play a significant and far-reaching role in our health. Researchers now believe that these bacteria, which number in the trillions, have an effect on immunity, inflammation, allergies, asthma, diabetes, weight issues, and even depression and anxiety. In fact, the metabolic activity of these microorganisms, also known as probiotics, is so complex that the gut microbiome has been referred to as the "forgotten organ."

So how does the gut microbiome develop?

Just before birth, a baby's intestinal tract is sterile. The first major infusion of bacteria comes from your mother, both in the birth canal and through breastfeeding. Next come microorganisms from the physical world around you. Throughout your life, your gut microbiome will continue to evolve. Research shows that contact with pets, farm animals, soil, dust and the outdoors contribute to its diversity. Exposure to antibiotics, overuse of antibacterial products and excessive use of alcohol have been shown to damage the gut microbiome.

Although studies have linked the presence of certain strains of gut bacteria to a tendency to be lean, and the absence of other types of bacteria to obesity, the science is still in its infancy. At this time, there is no reliable information on how exactly to harness the power of the gut microbiome to address weight issues. However, considering how important a diverse array of bacteria is to good health, making some lifestyle and behavioral changes to bolster the gut microbiome is a good idea.

Eat more fiber: With what we know about the gut microbiome, the fact is you're not just eating for one; you're eating for trillions. According to new research, fiber not only provides nourishment for gut bacteria, it also helps with diversity. So skip the processed foods and snacks. Instead, choose fruit, vegetables and whole grains. New attention is now focused on prebiotics, which are indigestible fiber that are believed to nourish gut bacteria. Natural sources of prebiotics include asparagus, Jerusalem artichokes, leeks, bananas and jicama.

Choose healthy oils: Replace refined omega-6 rich vegetable oils with a good-quality extra-virgin olive oil. Amp up your omega-3 intake with salmon, halibut, sardines, kale, Brussels sprouts, flax seeds and walnuts.

Skip the sweets: According to the USDA, we Americans consume 94 grams of sugar per day, which is about half a cup. But your gut bacteria crave complex carbohydrates, so try reaching for an orange or a handful of walnuts when that afternoon snack attack hits.

Pick probiotic foods: Fermented foods like yogurt, kefir, miso, kimchi, sauerkraut, kombucha, brine-cured olives and tempeh provide a variety of friendly bacteria. No need to go overboard -- using them in moderation is all it takes.

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)