How Paleo and Ketogenic Lifestyles can Prevent Leaky Gut Syndrome


What prompted you to start Mark’s Daily Apple?

Two main reasons: I wanted in on this cool new thing called blogging. I could tell having that direct line to readers was the wave of the future, whether you wanted to make money, promote your business, or build new ideas or communities.

I’d been in the health, fitness, and nutrition game for so long and seen so much erroneous information spewed out that I wanted to help correct the record. I figured I’d write every day for a year, and after that, I would have said all there was to say on the subject. That turned out to be a miscalculation.

You mention that you were working in health and nutrition before starting the blog — what exactly were you doing?

I was on the anti-doping commission for the sport of triathlon, did a lot of personal coaching and training, coached some triathlon teams, and in 1997 started a supplement company called Primal Nutrition.

Can you explain what leaky gut syndrome is, what the main symptoms are, and why people need to know about it?

Leaky gut syndrome is a funny story. For years, the health authorities called it a myth or woo-woo pseudoscience — something that only quacks and snake oil salesmen discussed.


But at the same time, researchers were studying something called intestinal permeability. Hundreds of papers have been published on the subject. And it turns out that intestinal permeability — a legitimate medical phenomenon well- accepted by the experts in the field — is a synonym for leaky gut.

The lining of our gut has gateways called tight junctions. The tight junctions are like doormen at a nightclub: they open up to permit desired compounds through, like nutrients and water, and bar toxins, antigens, and pathogens. In leaky gut, the tight junctions are allowing unwanted compounds entrance to the rest of the body.

More than “symptoms” there are conditions linked to leaky gut. They include obesity, celiac disease, inflammatory bowel disease, irritable bowel syndrome, food allergies and intolerances, asthma, autism, autoimmune diseases, depression (about 35% of patients with clinical depression have leaky gut) That’s not to say that leaky gut causes these conditions, just that they often occur together.

How common do you think leaky gut is? Is it something everyone is susceptible to, or only people who have particular digestive issues?

Everyone is susceptible to leaky gut because it’s a physiological (normal) aspect of gut function that can become pathological.

What’s the best way to diagnose things like leaky gut and diet-induced autoimmunity issues? Can people go off of symptoms like diarrhea and constipation, or should they be getting lab tests?

For a true medical diagnosis of leaky gut, there’s the intestinal permeability test. You drink a solution containing a pre-measured amount of mannitol and lactulose, two indigestible sugars. You collect your urine over the next 6 hours and measure the amount of excreted mannitol and lactulose to determine how much permeated through your gut.

Diarrhea and constipation can be good signals, too, but beware of reading too much into short term symptoms. We’re all a little leaky sometimes. Lots of things can transiently increase intestinal permeability, like hard exercise. It’s when the diarrhea isn’t letting up, or you consistently get rashes and constipation after you eat a particular food that you have a good signal that something is wrong with your gut health.

Why does hard exercise temporarily increase intestinal permeability? Do you view it as a negative side effect of exercise, or is it actually an adaptive response to help us take up more nutrients post-workout?

It’s just “one of those things.” A good way to think of exercise is as a very powerful stressor. You’re essentially doing trauma to your entire body with the hope that you’ll be able to recover better-adapted to the trauma than before. Increased permeability is just a consequence of the full-body trauma.

John’s note: It sounds like the increase in intestinal permeability post-exercise is probably a side effect of the rise in inflammation that occurs after a hard workout. Unfortunately, that inflammation is part of the anabolic signaling that makes your body get stronger after exercise. In other words, you need it to happen.

Is the medical test for leaky gut usually covered by insurance? What’s the best way to raise the subject with one’s doctor?

Most conventional docs aren’t thinking about intestinal permeability as a cause of disease at all. The test is generally used in research settings rather than clinical. I’ve never heard of anyone getting their Kaiser doc to order one.

Alternative/functional medicine docs are more likely to order it, but that’s less likely to be covered by insurance.

I’ve seen a lot of mixed evidence around the supposed dangers of gluten, with some research showing wheat is safe, some suggesting it’s dangerous, and some suggesting that gluten isn’t an issue for most people, but that other chemicals in grain (like FODMAPs and physic acids) are. What’s your take on this?

Gluten increases expression of zonulin, a compound that makes the gut more permeable or “leaky.” This happens in everyone, though the zonulin response is exaggerated in people with celiac disease.

However, not everyone experiences overt symptoms of leaky gut after eating gluten. Some people can clearly tolerate it just fine. If you insist on eating gluten on a regular basis, you’re probably better off with a fermented form, like sourdough.

Speaking of FODMAP’s, they’re present in high qualities in a lot of foods that are considered paleo, like artichokes, cashews, and pears. Should people be cutting back on “paleo” foods that are high in FODMAPs?

Only if they have FODMAP intolerance. Symptoms include horrible gas, stomach pain, constipation and/or diarrhea.

Ironically, the foods that you eliminate on a FODMAP program in addressing a gut dysbiosis are some of the same foods that can feed the “good bugs” when you have a healthy gut. Some foods that are beneficial in some instances can be problematic under other circumstances. No right answer here — just choices.

Are there any dietary supplements, over-the-counter drugs, or non-dietary lifestyle changes that help prevent or heal gut inflammation and leaky gut?

Stress and sleep deprivation are major stressors for the gut. Stress reduction and getting enough sleep are gut health fundamentals that most people don’t even consider.

Since intestinal permeability is a normal part of human gut function, is there a condition that’s the opposite of leaky gut — one where intestinal permeability is too low? If so, what are the symptoms and how would you diagnose it?

I’ve never come across or heard of it.

I’ve heard of people taking collagen supplements for their joints and skin before, but not for gut health. How does collagen help the gut?

Part of gut health is supporting and rebuilding the structural tissue the gut is made of. Most of that is collagen, and dietary or supplementary collagen provides the raw building blocks needed to make necessary repairs.

How do seed oils damage the gut lining?

It’s not that seed oils directly damage the gut lining — although that’s a distinct possibility, I haven’t seen any clinical evidence that it happens. The problem with seed oil consumption is that it creates an overall inflammatory environment in the body. You need a solid foundation of health to maintain gut health, and the constant drip-drip-drip of inflammation makes it hard to erect that foundation.

Leaky gut is highly correlated with inflammation. Would anti-inflammatories help to treat it? Do you think leaky gut causes inflammation, inflammation causes leaky gut, both, or neither?

Some anti-inflammatories, like aspirin and ibuprofen, can actually cause leaky gut.

Leaky gut is more likely to be a proximate cause of inflammation, but an inflammatory environment makes it harder for the body to support and maintain the integrity of the gut. More resources devoted to dealing with inflammation, fewer available to maintain gut health.

After cutting out grains, which carbohydrates do you primarily replace the with?

Fruit, winter squash, and starchy tubers like potatoes or sweet potatoes. I’m generally low carb myself, but those are healthy sources of carbohydrate.

John’s note: Cutting back on carbs is generally a good idea for most people, particularly those looking to lose weight. Your carbohydrate intake should depend on a few factors, including how active you are, how lean and muscular you are, and a few genes that regulate how the body processes carbohydrates and fats. More detail here.

What about legumes–most paleo experts recommend avoiding them because of the lectin content. Do you agree or think this is an exaggerated concern?

It’s exaggerated (and I got this wrong back in the day, too). The vast majority of legume lectins are degraded with sufficient heating.

John’s note: You can also remove most of the legumes from beans and lentils by soaking them in water. Just put your cooked legumes into a colander and run some cool water over them for a minute or two. Lectins are the chemical that causes beans to give people gas; if beans don’t make you gassy, they’re probably not causing any significant damage to your gut either.

For people looking to prevent gut inflammation and autoimmunity, which foods would you recommend completely avoiding, and which foods would you recommend eating less of, but not necessarily cutting out?

Avoid: Seed oils (corn, canola, soybean, grapeseed, sunflower, safflower), gluten-containing grains (wheat, barley, rye).

Reduce: Grains in general, sugar.

What do you personally do to avoid gut issues?

I drink bone broth and use collagen supplements.

I avoid grains and high omega-6 seed oils.

I’m very selective about my alcohol intake. A few years back, I gave up alcohol entirely for a few months and it fixed my lingering gut issues. These days, I pretty much only drink lower-alcohol (12%-ish) natural wines.

I get plenty of sun. Low levels of vitamin D (which we make in response to UVB) have been implicated in leaky gut. John’s note: Most people don’t get nearly as much sun as Mark does, and should take a vitamin D supplement.

I’m religious about my sleep. John’s note: if this is an issue for you, read my guide on sleep.

I’m working on my stress. Meditation doesn’t really work for me, but standup paddling is a kind of meditative practice that really calms my mind. I try to paddleboard as much as possible.

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