How a Healthy Gut Affects Your Weight

What's Happening in Your Gut

Roughly 100 trillion bacteria—anywhere from 300 to 1,500 different types—live in and on your body, Meyer says. Three to four pounds’ worth dwell within your digestive tract alone. Two families, Firmicutes and Bacteroides, make up about 90 percent of the bacteria in the colon.

These tiny organisms eat what you eat, and different types thrive on different foods, says Meyer. While Bacteroides prefer fiber-rich, whole foods, Firmicutes love refined carbohydrates and added sugars. So a diet heavy on pizza, pasta, bread and sugary sodas gives Firmicutes ample fuel to multiply—and potentially ransack your health.

It’s not that Firmicutes are inherently bad. Rather, “the ratio of these two groups can influence your health,” Meyere says. “In the Western world, most people have many more Firmicutes than Bacteroides. This is a problem because Firmicutes are tied to so many diseases, including type 1 and type 2 diabetes, heart disease, certain cancers, Alzheimer’s—and even obesity.”

Along with gobbling empty carbs, Firmicutes also increase carbohydrate cravings, Meyer says. In other words, the more nutrient-void foods you eat, the more these bacteria will scream for seconds. This kicks off a vicious cycle: You continually eat empty carbs to satisfy your (and your gut bacteria’s) cravings. The common consequence is weight gain.

Starve the Bad, Feed the Good

To stop these bacteria from sabotaging your waistline, eliminate empty carbs, Meyer advises. Then give Bacteroides and other friendly organisms more of what they like: fiber, abundant in fruits, vegetables, whole grains, nuts, seeds and legumes.

At breakfast, swap out your Frosted Flakes for whole-grain cereal or oatmeal topped with sliced strawberries or bananas. Or enjoy eggs with sliced avocadoes, Meyer suggests. For lunch, pack a hearty salad of spinach, diced veggies and dried beans or seeds instead of grabbing fast food. Snack on a pear or handful of raisins and walnuts midday. Prioritize vegetables, whole grains and other fibrous foods at dinner.

Eat Prebiotics and Probiotics

While all fiber helps feed good bacteria, prebiotic fibers such as inulin and pectin especially benefit gut health. According to Meyer, prebiotic fibers not only give Bacteroides sufficient food, but they also get converted into short-chain fatty acids, which may help reduce inflammation and control blood sugar and insulin. They also may reduce your risk of high cholesterol, obesity and even cancer. Meyer lists onions, garlic, sweet potatoes, plantains, miso, jicama and artichokes as excellent prebiotic fiber sources.

Also seek out foods and drinks rich in probiotics, live organisms that stimulate the growth of good bacteria. Many traditionally fermented foods such as sauerkraut, kimchi, pickled vegetables, yogurt, kefir and kombucha contain probiotics.

But be wary of the flurry of probiotic-infused packaged items now hitting the market. Meyer says many are just junk with some probiotics thrown in—“a total marketing gimmick.” If it’s not a healthy food to begin with—say, a burrito or a candy bar—it’s probably worth skipping.

Try Probiotic Supplements

To enhance (not replace) a healthy diet and promote bacterial diversity, consider a daily probiotic supplement. “I don’t know anyone whose gut is not out of balance, so a daily probiotic supplement can really help rebalance the ratio of Firmicutes and Bacteroides,” Meyer says.

Probiotic science is still relatively young, but Meyer says researchers are actively looking at specific strains for specific health issues, including weight. “For example, Bididobacterium lactis has been found to reduce obesity and inflammation,” she says. “These single-strain probiotics are still in their infancy, but to aid weight loss or manage sugar and carb cravings, look for a product that contains a high amount of B. Lactis.”

Whether or not a probiotic will benefit you really depends on its viability, Meyer says. To impact your health, the organisms must be alive when you consume them and also make it all the way to your colon where they can populate. “Probiotics need to be able to bypass many systems in your body—your acidic saliva, the harsh stomach environment—to have any effect,” Meyer says. The best way to find viable probiotics is to buy reputable, quality products versus bargain brands.