A lot of people ask me if a ketogenic diet is good for your gut. It depends, I say. It depends on what’s going on down there, and what specific foods you're eating.
If your gut ecosystem is damaged, removing inflammatory foods and starving bad bacteria with a low-carb diet is a solid plan. But it’s not the best plan for all people, since eliminating carbs may come with long-term downsides. Good bacteria like carbs, too.
We’ll go deep on this topic shortly. First, let me tell you the story of my gut. (Riveting, I know!)
My gut problems started young. I (likely) inherited a compromised gut microbiome from my mother, and was exposed to inflammatory foods like soy and grains too early. I had countless cases of strep throat. I popped antibiotics like they were candy.
In adolescence, cow’s milk gave me such bad acne that I felt self-conscious just breathing. Nobody knew about food intolerances or sensitivities at the time, so I mostly ignored my diet. In retrospect, that was a bummer.
In my 20’s, I had another misguided idea: I became a vegan. I plummeted to a skeletal 135 pounds and was diagnosed with ulcerative colitis, a form of inflammatory bowel disease. My doctors and I considered a bowel resection, a procedure for cutting out a piece of my intestines. I wondered what future first dates would say when they noticed my colostomy bag. Check, please?
If you’ve read my books, you know the rest of the story. In a moment of clarity (desperation), I realized my inflammatory diet was keeping my gut on fire. If I wanted to get better, I needed to cut out the foods—grains, sugar, legumes, and dairy—that had infiltrated the modern diet. I needed to eat like a caveman would eat—only this time, with utensils.
Today, I follow a low-carb Paleo diet, and my gut is super happy. Let’s talk about the low-carb part, now.
Keto for Gut Health
I don’t like to throw around terms like “keto” without defining what they mean. In one sentence, the ketogenic diet is a very low-carb diet that promotes a unique metabolic state called ketosis.
Think of ketosis as your backup energy system. Normally your body runs primarily on carbs (glucose), but when carbs are scarce, your liver starts burning body fat and producing molecules called ketones to meet your fuel requirements.
The keto diet is a popular and effective weight loss diet—mostly due to appetite control, in my view—but weight loss is just one of keto’s many applications.
Therapeutic Applications of the Keto Diet
- Helping reverse type 2 diabetes (needs to be medically supervised).
- Adjuvant for certain cancers
- Potential treatment for neurodegenerative disorders, including Alzheimer’s disease
- Reducing inflammation, especially in the gut
I want to zoom in on the last bullet. What the heck is inflammation, anyway?
Inflammation is a term to describe your immune system’s response to perceived dangers. There are two main flavors:
- Acute inflammation
- Chronic inflammation
Acute inflammation is an immune response to specific illness or injury. When you cut yourself, cytokines and other immune cells rush to the site to promote wound healing and prevent infection. When the problem resolves, the immune activity should subside. But when the immune response persists, you cross into the ghoulish territory of chronic inflammation.
Chronic inflammation is most obvious in autoimmune disorders like multiple sclerosis and IBD, but it also underlies chronic diseases like Alzheimer’s, heart disease, and cancer. Where does all this inflammation come from? It’s multifactorial, but the gut—which houses 70% of your immune cells—is a good place to start looking.
Gut inflammation usually comes along with a condition called intestinal permeability, or leaky gut. When the gut is leaky, food particles slip through the gut barrier and into the bloodstream, creating an immune storm that worsens intestinal permeability. As we consume more inflammatory foods, the cycle continues. To break the cycle, we look first to diet.
Before we get to that, the gut is an interesting model to look at for both acute and chronic inflammation. A bout of food poisoning or giardia can severely damage the gut lining and leave us in a state of profound acute inflammation. For most people, a week of gut discomfort gives way to normal functions. But for some people, this infection can lead to chronic gut problems.
Keto Restricts Inflammatory Foods
Our Paleolithic ancestors didn’t eat grains, legumes, or sugar. Looking at their remains, archaeologists find scant evidence of the diseases of modernity. Coincidence? I don’t think so.
The keto diet I recommend (and follow) is simply a low-carb Paleo diet. When you eat Paleo, you avoid grains, legumes, sugar, and dairy. These also happen to be the foods most inimical to gut health.
#1: Grains and legumes
Grains and legumes are plant seeds. Over the millenia, these seeds have evolved defense mechanisms to make them less agreeable to hungry animals.
Lectins are one such defense mechanism. These proteins are so difficult to digest, they can rupture the GI tract! Traditional cultures deactivated lectins with soaking and sprouting techniques, but few modern citizens soak and sprout.
Gluten is the most infamous plant-based digestive scourge. Most people know that folks with celiac disease (an autoimmune condition in which the immune system rebels against a component of gluten called gliadin) have trouble digesting this wheat-based protein. Less people are aware of a widespread phenomenon called non-celiac gluten sensitivity. Many, many people are sensitive to gluten. In fact, I’ve noticed that most people (celiac or not) feel better on gluten-free diets.
A keto diet is easy to make gluten-free, legume free, and grain free by design. For folks with gut problems, removing these foods can increase one’s quality of life overnight.
If you’re having digestive issues, dairy is a first-line food to eliminate. A large proportion of people, myself included, are reactive to milk products. My immune system has never been fond of dairy.
Grains, nuts, soy, and eggs also tend to be problem foods. Abolishing these foods (temporarily, at least) can give your gut time to cool off and heal.
#3: Refined sugar
The average American consumes about 17% of their calories from added sugar. Most of this sugar comes from sugar-infused beverages like soda, fruit juice, and sports drinks.
All that sugar is making us sick. Part of that is inflammation-related.
How Sugar Increases Inflammation
- By increasing blood sugar levels (hyperglycemia is inflammatory)
- By decreasing the production of anti-inflammatory ketones
- By promoting weight gain
- By feeding overgrowths of bacteria and yeast in the gut
The last point is most relevant to our discussion today. The gut microbiome is a delicate ecosystem, and sugar throws it out of balance. Specifically, sugar feeds bacteria in the small intestine while starving bacteria in the large intestine. That’s the opposite of what we want.
The resulting overgrowth in the small bowel, called small intestinal bacterial overgrowth (SIBO), is like a low-grade infection. It drives inflammation, liver damage, and even the metabolic issues underlying type 2 diabetes.
Low-Carb Diets For SIBO
SIBO is an underappreciated problem. Around 50% of those suffering with irritable bowel syndrome (IBS) test positive for this bacterial overgrowth. Some forward-thinking doctors, like Mark Pimentel, even believe SIBO is the primary cause of IBS. Check out his book The IBS Solution for more on this topic.
To treat SIBO, we ask: What’s feeding the overgrowth? Mostly it’s carbs like fiber, starch, and sugar. Bacteria love carbs.
By love carbs, I mean bacteria love to ferment carbs. In the healthy gut, this can be beneficial. But in the case of SIBO, it leads to excess gas, inflammation, and unpleasant symptoms.
Transitioning to a keto diet reduces bacterial fermentation in the gut, allowing the overgrowth to subside and the gut to heal. It’s no surprise that both low-carb and low-fiber diets have been shown to improve IBS symptoms.
Is Keto Sustainable For Gut Health?
The keto diet can be therapeutic for gut issues. By reducing the supply of fermentable carbohydrates, you starve inflammatory overgrowths and calibrate the gut towards healing. Eventually, you reintroduce healthy carbs to nurture a happy gut biome.
But what if you don’t reintroduce carbs? Can a very low-carb diet sustain gut health long-term?
The truth is, we don’t know. Long-term data on the keto diet is scarce, plus researchers are still debating what a “healthy” gut microbiome even looks like.
One concern is that low-carb diets reduce the production of short chain fatty acids (SCFAs) by gut bacteria. SCFAs like butyrate have anti-inflammatory effects, and appear to block colon cancer growth.
I also worry that, in the absence of carbs, gut bacteria get hungry for the mucous layer lining the intestine. You don’t want your gut bacteria eating this barrier. It’s your shield against microscopic terrors.
Yet keto doesn’t restrict all fermentable carbs. It doesn’t restrict onions, leeks, and garlic. If you don’t have SIBO, you should probably be eating these gut-nurturing foods daily. Just keep the breath mints handy.
And just to muddy the waters further, it appears carnivorous animals produce the short chain fats commonly attributable to fermentable fiber from… amino acids. There is some preliminary evidence that humans can do this as well, but it helps make my point:
The gut is complex. What works for one person may not work for another, so we might be best served tinkering to find the best clinical outcomes we can.