A doctor that specializes in GI health explains how the keto diet "decimates the gut."
high fat diet

The high-fat, very low-carb ketogenic diet first emerged in the 1920s as an epilepsy treatment and gained popularity as a weight-loss plan about 100 years later. While keto dieters tout promising benefits like quick weight loss and increased satiety—all while eating as much cheese and bacon as they want—there's one thing that's often overlooked: gut health.

You may have heard how important it is to maintain a healthy gut microbiome; the good bacteria in our gut can positively affect our weight and even keep chronic diseases at bay. And more research says that our gut health—and overall health—is largely tied to what we eat.

Will Bulsiewicz, M.D., aka "The Gut Health M.D.," is a board-certified physician in both internal medicine and gastroenterology. As a gut health expert, Dr. Bulsiewicz has very strong feelings about the keto diet.

"I get very frustrated when I see claims on the internet that the keto diet is good for your gut health. There's not one single study to support that. In fact, the studies that exist suggest that keto decimates the gut," says Dr. Bulsiewicz.

Here's why: Dr. Bulsiewicz says most people in the U.S. have somewhere between 300 to 1,000 different species of bacteria living in our guts, and that bacterial diversity is necessary for good health. "When people lose or reduce the number of bacteria species in their gut, they can develop diseases such as ulcerative colitis, Crohn's disease and inflammatory bowel disease," says Dr. Bulsiewicz.

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Dr. Bulsiewicz adds that by eating a ketogenic diet "you may not have IBS yet, but you're already laying the foundation for it."

When you eat a keto diet, you're eliminating nearly all carb-containing foods, including those good-for-you, fibrous foods like fruit, veggies and whole grains that support your microbiome. The largest gut health study to date, called the American Gut Project, surveyed over 11,000 people and found the number one predictor of a healthy microbiome was the variety of plant foods consumed in one's diet.

"When you restrict the diversity within your diet, you are also restricting the diversity of your gut microbiome, which causes disease," says Dr. Bulsiewicz.

According to the American Gut Project's findings, we should all be eating 30 or more different plant foods each week for optimal gut health (yep, you read that right!). While that would be one very expensive grocery trip, you can look for other opportunities to boost your plant-food intake by loading up on various fruits and veggies at the salad bar, making your own mix of nuts and seeds at the grocery store bulk bins, and opting for whole grains over refined whenever possible.

Not quite sold on reintroducing carbs to your diet? "Carbohydrates aren't bad; refined sugar, processed grains, and ultra-processed foods are bad. I support cutting those out 100 percent, but I don't support cutting out carbs," says Dr. Bulsiewicz.

As a reminder, you don't have to take an all-or-nothing approach when pursuing a healthy eating pattern. But we agree that limiting added sugar and ultra-processed foods while upping your intake of healthy carbs can improve your overall health.

Dr. Bulsiewicz also recommends that, for losing weight, the key is adding foods to your diet, not taking them away. He points to a 2017 study that showed a completely unrestricted plant-based diet (one where you can eat whenever you're hungry), helped participants lose 14 pounds on average.

Other studies, like a 2021 review in Advances in Nutrition, have shown similar results.

Bottom Line

If you want to lose weight, the key isn't going keto or cutting out an entire food group (unless your healthcare provider has specifically advised you to). To help support your efforts, aim to reduce your intake of ultra-processed and refined carbs, and try to add in more high-fiber foods like fruits, vegetables, and whole grains. Your gut will thank you!