The gut microbiota is a hot topic because of how it may influence our health in multiple ways — including our bone health. A large body of research suggests that the gut microbiota may affect bone density and the absorption of calcium and other minerals needed for healthy bones. This could be significant, given that about 54 million Americans have low bone mass, placing them at increased risk for osteoporosis, according to the National Osteoporosis Foundation (NOF).
The NOF estimates that 1 in 2 women and up to 1 in 4 men age 50 or older will break a bone due to osteoporosis, which happens when the body loses too much bone, makes too little bone or both. Getting insufficient calcium in your diet can contribute to low bone mass, but so can poor absorption of the dietary calcium you do get. That’s why intestinal disorders that can interfere with nutrient absorption, such as celiac disease and inflammatory bowel disease, increase osteoporosis risk. So do surgeries that remove part of the stomach or intestines.
The gut microbiota is the diverse community of bacteria and other microbes living in your gastrointestinal tract, primarily your large intestine. One byproduct of bacterial fermentation of food in your large intestine is short-chain fatty acids (SCFAs), which affect distant sites in the body, including the bones. SCFAs can increase absorption of calcium, magnesium and other minerals, and may indirectly stimulate osteoblasts (cells that build bone) and inhibit osteoclasts (cells that break down bone), helping to prevent bone loss.
So how do you get more SCFAs? Eat more foods that contain prebiotic fiber, the preferred “food” of your gut microbes. Prebiotics are ingredients, including certain fibers and carbohydrates, that when fermented by our gut microbes, result in specific changes that benefit our health. Research suggests that eating more foods rich in prebiotic fiber — such as the onion family, dandelion greens, bananas, asparagus, artichokes, barley, wheat bran, oats, apples and jicama — may be a smart strategy during times of peak bone growth during adolescence as well as in times of greater bone loss as older adults. Different prebiotics may have different benefits for bone health, so aim to eat a variety of these foods. Not surprisingly, people who eat plant-rich diets have higher levels of SCFAs, and research has shown that these diets are beneficial for bone health.
What about taking probiotics — live microorganisms which provide health benefits when we consume them in adequate amounts — through food or supplements? A 2020 review concluded the evidence is compelling that probiotics may improve bone health, although response is stronger in women and is more easily observable during times of peak bone growth or loss.
The research is currently strongest for certain probiotic strains. For example, there is robust evidence that Lactobacillus rhamnosus GG, and possibly all lactobacilli-containing probiotics, can improve skeletal development. Lactobacillus strains are often added to fermented foods, including yogurt and kefir, and can be found in supplements. A 2018 randomized controlled trial of older women with low bone mineral density found that daily oral doses of Lactobacillus reuteri 6475 resulted in significantly reduced loss of total bone mineral density after 12 months. A randomized clinical trial of patients with osteoporosis showed that drinking kefir (fermented milk) for six months increased bone mineral density in men.
Because many factors affect risk of developing osteoporosis — including heredity, hormone levels, medications, nutrition and lifestyle — it’s important to discuss this with your doctor and to find out if you need a bone mineral density test.