Are Low Carb or Keto Diets Bad for Your Gut Health?

Why there’s confusion and what to consider.

Some articles circulate online claiming that low-carb or ketogenic diets starve your gut bacteria and are thus unhealthy. But these diets are not bad for your gut health. The claims are misleading: while they may starve some bacterial populations, they may promote the growth of others. These diets may not work for everyone. If you feel fatigued or irritable on a low-carb or keto diet, a moderate to higher-carb diet might be more ideal for your body. A diet low in fermentable carbs (called the low FODMAP diet) is worth considering if you suffer gas, bloating, diarrhea, constipation, or other digestive challenges.


Dr. Michael Ruscio, DC: Are low-carbohydrate or ketogenic diets bad for your gut health? Hi, this is Dr. Ruscio, and let’s discuss this question: if low-carb or ketogenic diets are bad for or could be damaging your gut health. In short, the answer is no. Low-carb or ketogenic diets are not bad for your gut health. But there’s confusion around this. Allow me to dispel briefly why there’s confusion and what this means for you.

[Continue reading below]

Dr. R’s Fast Facts Summary

Are low carbohydrate or ketogenic diets bad for or damaging to your gut health?

  • No
  • A low carb diet does not starve your gut bacteria

Low carb diet is good for:

  • Weight loss
  • Metabolism
  • Cholesterol levels (good for increasing HDL)

Keto diet is good for:

  • Weight loss
  • Inflammation
  • Can be helpful as a part of treatment for certain medical conditions

Discontinue low carb or ketogenic diet if you feel:

  • Fatigued
  • Irritable
  • Develop insomnia

Low FODMAP diet

  • Reduces the amount of fermentable carbohydrates

Helpful for those with digestive issues like gas, bloating, diarrhea, loose stools, abdominal pain.

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DrMR: Again, in short, if you’re doing a lower-carb or a ketogenic diet and deriving benefit from it, continue with it. Now, do not continue with that dietary approach if you’re feeling fatigued or irritable or having insomnia. A lower-carb or ketogenic dietary approach is not going to be the best approach for everyone, but for some, it will be helpful. Unfortunately, you may come across information on the internet that tells you a number of things. One of which could be that a low-carb diet can starve your gut bacteria and be bad for your gut bacterial health. And this is really misleading because while, yes, a lower-carb or ketogenic diet may starve certain populations, or you may see a dwindling of certain populations of bacteria, other populations of bacteria may actually bloom on a lower-carb diet.

There’s a debate in terms of what population of bacteria are better than the others. That is so littered with speculation that you as the healthcare consumer should not bother wading in that confusion.

What’s the Impact of a Low-Carb Diet?

Rather, we can look to outcome studies—meaning, what happens when people eat a certain way—for the answer to the question of what kind of impact a lower carb diet could have.

paleo dietI’m going to extrapolate a little bit from research on the paleo diet. Research has been published showing that a paleo-type diet—which is oftentimes, but not always, lower in carb—reduces colorectal cancer risk to a similar degree as the Mediterranean diet. So some good evidence there. Now there are a number of trials showing that a lower-carb diet, oftentimes looking at this through the context of either a paleo diet or an overtly low-carb diet, can be beneficial for weight loss, metabolism, and cholesterol levels. So more good news there. It can improve your metabolism.

Now, how this ties in with gut bacteria… some studies have actually looked at a moderate, low, and very low-carb grouping of patients, and tracked what happened in their microbiotas and how that correlated with weight change. And ironically, in one study, in particular, found that the very low-carb diet group saw the most weight loss and had a measurable shift in their intestinal bacteria. And the higher the carb intake went, the less the change on the intestinal bacteria, and the less the weight loss.

So this thinking—that if a diet impacts or causes a dwindling of certain bacterial populations, it’s going to automatically be bad for you—is really an erroneous premise that doesn’t have good evidence to support it.

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Low FODMAPFurther yet—and I review this evidence extensively in Healthy Gut, Healthy You—when you look at fiber content in the diet, as compared to what’s known as all-cause mortality or morbidity (so, your chances of dying from any disease or having any disease), there is no general trend showing that eating more fiber is better for your health.

There are about as much data showing that higher fiber intake is good for you as there are data showing higher fiber intake has no impact on your health. So there’s no need to subject yourself to a higher fiber diet if you don’t feel good on that diet. Now, fiber and carb intake in the diet don’t share this direct relationship. But oftentimes what you’ll see is, when someone is doing a ketogenic diet, their fiber intake may become a little bit lower. If that ends up being you, that’s nothing to necessarily worry about. I do think it’s a good idea to make sure you’re not eating an unhealthy version of a low-carb or ketogenic diet and making sure that you get an ample amount of vegetables in your diet and some fruits. When we look at the data comparatively, vegetarian diets do tend to have a higher fiber intake than lower-carb diets, but what that means, I think, is up for debate.

Feeding Bacteria Isn’t Everything

And finally, if you’re someone looking for digestive relief by employing a low-carb or ketogenic diet, (if we look at a low FODMAP diet as a proxy) we see that those on a low FODMAP diet—a diet that by design reduces the amount of fermentable carbohydrates, so many forms of fruits and vegetables are reduced—we actually see that that can be very helpful for many people with digestive maladies like gas, bloating, constipation, heartburn, diarrhea, loose stools, abdominal pain, and what have you.

More evidence showing that a diet that, by design, restricts foods that feed healthy bacteria can actually cause you to be healthier. That tells us there’s quite an ample amount of evidence showing you do not need to directly feed gut bacteria in order to be healthy. The posit that I put forth in Healthy Gut, Healthy You is that it’s not about just feeding gut bacteria and hoping that those gut bacteria make you healthy, but rather eating in such a way that makes you the host as healthy as you can be. And when you are healthy as the host that houses the microbiota—your bacteria—a healthier host means a healthier environment, means healthier bacteria can grow. That is what you should be focusing on. Whether it be feeling better on a lower-carb or ketogenic type diet, or on the other end of the spectrum, someone who feels better on a moderate to higher carbohydrate diet.

Are low carbohydrate or ketogenic diets bad for or damaging to your gut health? No … but these diets aren’t for everyone, watch the video to learn why. Click To Tweet

The carbohydrate diet needs to be personalized to the individual. If you as an individual are feeling better on a lower-carb diet, and that’s creating a healthier you and healthier environment, then ostensibly you will see healthier bacteria grow. Conversely, if you’re someone who feels better on a higher carb diet, then you will likely have a healthier internal ecosystem that will harbor healthier bacteria, and that will work well for you.

In short, there is no good evidence to my knowledge—and this is after a fairly extensive review of the literature—showing that a lower-carb or ketogenic diet is bad for your gut health. In fact, there’s more evidence showing that it could be quite good for your gut health. But remember not to be dogmatic regarding diet. If you try that type of diet and don’t feel well, then you may want to try a moderate to higher-carb diet and see how you feel. So the answer: No, a low carb or ketogenic diet is not bad for your gut health.

This is Dr. Ruscio, and hopefully, this information helps you get healthy and get back to your life.

Links & References
What do you think? I would like to hear your thoughts or experience with this.

Discussion

I care about answering your questions and sharing my knowledge with you. Leave a comment or connect with me on social media asking any health question you may have and I just might incorporate it into our next listener questions podcast episode just for you!

18 thoughts on “Are Low Carb or Keto Diets Bad for Your Gut Health?

    1. Hi Denise,

      Yes, Dr Ruscio definitely sees people with gastritis. I’m sorry to hear you didn’t receive a response. You may want to try calling the clinic at (800) 335-7009 or (925) 705-7454. Hope this helps!

  1. I did a 30-day keto experiment, testing my microbiome before, after 30 days on keto (monitoring macros, getting greens daily, small amounts of berries, salmon, grass-fed meats/dairy, organic coconut oil, low-carb veg), then again 30 days later (back on my normal higher carb diet). Before keto, my mood and general health were great, my F. prausnitzii and Akkermansia levels were fantastic, my butyrate production was good, as were my GABA and serotonin production. By the end of 30 days of keto, I was experiencing depression, anxiety, moodiness, fatigue, and felt generally crappy. My gut tests were abysmal after keto – my Akkermansia levels dropped to 0.32%, my butyrate production dropped significantly, as did my GABA and serotonin levels (not surprising, as how I felt perfectly reflected this). My test results at 30-days back on my regular diet were much better – my gut was recovering – but it still another month or two until I felt back to normal. I have to wonder how many people are unknowingly harming their microbiomes on low carb or keto (or carnivore for that matter). Some people just don’t tolerate low carb. It seems to me that regularly monitoring the microbiome would make sense for anyone doing low carb. Just because the effect on the microbiome hasn’t been extensively researched doesn’t mean there isn’t reason to proceed with caution.

    1. Hi Sandi,

      Thanks for sharing your experience! If you haven’t read Dr Ruscio’s book, “Healthy Gut, Healthy You” yet, you may want to check it out. He dedicates an entire chapter to carbs, including how different people do better on different amounts and how to determine what’s best for you.

  2. I’ve heard it mentioned a few times in your podcasts though perhaps not directly from you but from your guests, that long low fodmap is “bad” due to deficiencies. I can mostly see how to get most all micronutrient RDIs even on low FODMAP, low carb, keto diets, but some seem more problematic, at least for me with IBS. In particular it seems like Potassium is tough to get the full RDI of 4700 mg for me as a lot of the things that are high in potassium seem to be problematic (currently) for symptoms. And to be honest I don’t even know that I was getting that much potassium regardless of symptoms as that’s a ton of foods required to get that amount. That said, even though I seem to be deficient according to nutrition calculators it doesn’t seem like blood tests ever seem to show it low at all.

    How do folks with IBS get the full nutrients they need and/or how important is it to get those RDIs? A lot are pretty easy, potassium and even magnesium seem to be a bit more of a challenge along with getting the full amount of some vitamins.

    1. Hi Mike,

      I added your question about low fodmap + deficiencies that you left on a different page to the list for an upcoming listener q+a episode. Hang tight, we have lots of questions to get through, but it’ll get answered 🙂

      1. Oops, sorry. Memory isn’t always what it used to be. LOL

        Thank you so much for all the work you do here answering us as best you can. 🙂

  3. Hi, I am working with an integrative nutritionist who is recommending against these diet plans like Element, GAPS, Low Fodmap! She explains to me based on patients experiences with them they don’t address root cause of the problem. Many times come back with the same problem months later or even a year later. Whats your take on that recommendation?

    1. Hi Michael,

      For some people, diet modifications will be enough (though I wouldn’t put elementel diet in that category). For others, there’s something deeper going on, as I think your nutritionist is alluding to, and futher treatments will be needed in addition to dietary modifications to fully resolve the underlying cause of the issue.

  4. I’ve heard it mentioned a few times in your podcasts though perhaps not directly from you but from your guests, that long low fodmap is “bad” due to deficiencies. I can mostly see how to get most all micronutrient RDIs even on low FODMAP, low carb, keto diets, but some seem more problematic, at least for me with IBS. In particular it seems like Potassium is tough to get the full RDI of 4700 mg for me as a lot of the things that are high in potassium seem to be problematic (currently) for symptoms. And to be honest I don’t even know that I was getting that much potassium regardless of symptoms as that’s a ton of foods required to get that amount. That said, even though I seem to be deficient according to nutrition calculators it doesn’t seem like blood tests ever seem to show it low at all.

    How do folks with IBS get the full nutrients they need and/or how important is it to get those RDIs? A lot are pretty easy, potassium and even magnesium seem to be a bit more of a challenge along with getting the full amount of some vitamins.

    1. Hi Mike,

      I added your question about low fodmap + deficiencies that you left on a different page to the list for an upcoming listener q+a episode. Hang tight, we have lots of questions to get through, but it’ll get answered 🙂

      1. Oops, sorry. Memory isn’t always what it used to be. LOL

        Thank you so much for all the work you do here answering us as best you can. 🙂

  5. I did a 30-day keto experiment, testing my microbiome before, after 30 days on keto (monitoring macros, getting greens daily, small amounts of berries, salmon, grass-fed meats/dairy, organic coconut oil, low-carb veg), then again 30 days later (back on my normal higher carb diet). Before keto, my mood and general health were great, my F. prausnitzii and Akkermansia levels were fantastic, my butyrate production was good, as were my GABA and serotonin production. By the end of 30 days of keto, I was experiencing depression, anxiety, moodiness, fatigue, and felt generally crappy. My gut tests were abysmal after keto – my Akkermansia levels dropped to 0.32%, my butyrate production dropped significantly, as did my GABA and serotonin levels (not surprising, as how I felt perfectly reflected this). My test results at 30-days back on my regular diet were much better – my gut was recovering – but it still another month or two until I felt back to normal. I have to wonder how many people are unknowingly harming their microbiomes on low carb or keto (or carnivore for that matter). Some people just don’t tolerate low carb. It seems to me that regularly monitoring the microbiome would make sense for anyone doing low carb. Just because the effect on the microbiome hasn’t been extensively researched doesn’t mean there isn’t reason to proceed with caution.

    1. Hi Sandi,

      Thanks for sharing your experience! If you haven’t read Dr Ruscio’s book, “Healthy Gut, Healthy You” yet, you may want to check it out. He dedicates an entire chapter to carbs, including how different people do better on different amounts and how to determine what’s best for you.

    1. Hi Denise,

      Yes, Dr Ruscio definitely sees people with gastritis. I’m sorry to hear you didn’t receive a response. You may want to try calling the clinic at (800) 335-7009 or (925) 705-7454. Hope this helps!

  6. Hi, I am working with an integrative nutritionist who is recommending against these diet plans like Element, GAPS, Low Fodmap! She explains to me based on patients experiences with them they don’t address root cause of the problem. Many times come back with the same problem months later or even a year later. Whats your take on that recommendation?

    1. Hi Michael,

      For some people, diet modifications will be enough (though I wouldn’t put elementel diet in that category). For others, there’s something deeper going on, as I think your nutritionist is alluding to, and futher treatments will be needed in addition to dietary modifications to fully resolve the underlying cause of the issue.

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