Eric Westman MD – Low Carb, Health & the Microbiome

This entry is part 5 of 5 in the series Microbes & Health
Eric Westman Duke University

Eric Westman Duke University

In this interview, Dr. Eric Westman of Duke University will talk about how a low-carb, high fat, ketogenic diet affects health, including the health of our digestion and the trillions of microbes that live inside our guts.   Eric is currently the president of the American Society of Bariatric Physicians. He’s co-editor of the medical textbook, Obesity: Evaluation and Treatment Essentials.  He’s co-author of The New Atkins for a New You, Cholesterol Clarity and Keto Clarity.  As for the human microbiome – it’s increasingly clear that our gut microbes  may influence many aspects of our health, and there’s plenty to learn about this.  Little research has looked at how a ketogenic diet affects our microbes, and most microbiome scientists urge that we need more data before jumping to conclusions about the “best” way to eat.  Eric Westman sees so many people discover better health on a ketogenic diet, he suspect their “microbes” are doing fine.  As for some clinicians and bloggers who warn that a ketogenic diet does not provide enough fiber to make a “healthy” microbiome, Eric has a different point of view.  Here’s a transcript of this conversation with Eric Westman.

“Different” Isn’t Always “Bad”  



ERIC WESTMAN – You know, there’s a knee jerk reaction to claim that if something’s different than what we’ve seen before, that it must necessarily be bad.  And that reaction, we’ve seen in the low carb, high fat diet world quite a bit.   For instance, the findings, when the studies were finally done on low carb high fat diets (15 years ago), the data showed a ketogenic diet actually reduced cardiometabolic risk, but just by a different mechanism than how a low fat diet affects heart health.   Everyone assumed a high-fat, ketogenic diet would be bad for heart health, and it turns out, it’s not bad.


Regarding the microbiome, I do recall one study published about low fat high carb diets in humans where the gut flora changed quite a bit, and there was concern because the bacteria that produced the butyrate, which is the fatty acid similar to ketone bodies, butyrate went down on the low carb diet.  Classically, it’s taught that the colon cells, the cells of the large intestine, have to have the fuel, or basically ketones, from inside the lumen, meaning from inside the intestine itself.  But those teaching this concept had basically forgotten that on a low carb high fat diet, the ketones go up in the bloodstream, which is another way to feed the cells of the colon.  If you only looked at it in one way, that the ketone production went down inside the intestine itself, therefore it’s bad, well they forgot to look a little further and understand that actually the ketone levels go up in the blood and probably can nourish the cells just as well, if not better, than from the bacteria in the gut itself  But I have to say, there are very few studies looking in detail at the gut microbiome of people on a truly high fat, low carb diet.  On the other hand, we’ve had a lot of experience talking to people who’ve been on low carbohydrate high fat diets for health reasons.

SHELLEY – Can you say more about the studies looking at how gut health is maintained, even when microbes in the gut are not making butyrate?

ERIC WESTMAN – One study was out of England.  There’s another one out of Australia to look at the flora or the gut micro biome of people on low carb high fat diets.   But clinically, we do see changes that probably involve shifts of microbes.  When you talk to people who follow the low carb high fat diets, certainly there’s a reduction in the amount of stool, the amount of bowel movements, and also the reduction in how often they go to have a bowel movement.  Now some people are so fixated in having a regular bowel movement, these changes concern them.  There’s quite a wide variation in how frequently people have bowel movements, when they switch to a low carb, high fat diet.  Some people do get diarrhea or loose stools, but most people, if anything, about 90% of people have harder to pass stools and less flatulence, less bowel gas.  I’m taught that it’s the large intestinal bacteria that actually produce the gas.   So when people shift to a low-carb, high fat diet, there’s a change in the production of bacteria in the colon, no question about it.  If I can infer that having less bowel movement and then having less gas is what I see clinically, then I’m pretty confident there’s a big change in the colonic bacteria.  Not that it’s bad, but there’s just going to be a change.  So it doesn’t surprise me.

“Starving Our Microbial Self” – maybe in mice, not in ketogenic people

The Colon, AKA large intestine, AKA the gut

The Colon, AKA large intestine, AKA the gut

SHELLEY – I talked with Justin Sonnenburg, who recently wrote an essay in Cell titled, “Starving Our Microbial Self,” based in part on some of the remarkable studies he’s doing in mice. He cautioned that if the microbes in the gut don’t get adequate food for themselves, they not only stop creating the butyric acid the intestinal cells like, but the microbes may start to devour the mucus gel that protects the intestinal lining, and they may even start digging into the  intestinal lining itself, as food.  That might explain why, in Justin’s words, he says that many studies indicate more colitis and inflammatory bowel disease in people on a high fat diet.

ERIC WESTMAN – Well, there are a couple of things I would call into question with those comments.  Not having talked with him directly.  Just because something is different from what we see doesn’t mean it’s bad.  In fact the gut micro biome of people on a low-carb, high fat, ketogenic diet may be healthier than what we see in the typical American Diet.  We don’t know if different means bad.  The second thing is I’m not convinced that higher fat diets cause colitis.  The studies that report digestive problems in that way are almost always done in the context of high carb, high fat diets, which are not the same as a very low carb, very high fat diet.

NOT a ketogenic diet (courtesy Krispy Kreme wiki)

NOT a ketogenic diet (courtesy Krispy Kreme wiki)

SHELLEY – Justin did say he doesn’t get to talk with clinicians very much.  He’s a basic researcher.  He said he would love to talk with clinicians about what they see in the clinical world.  And when I’ve looked myself at research studies that are identified as “high fat/colitis” studies, for instance, usually a high fat diet means basically the typical American diet, which more like “the donut diet.”  Meaning people or mice are fed a standard american diet that is high carbohydrate and high sugar along with moderate fat.  But in the title of the research and in its summary, often the sugar isn’t mentioned.  It’s simply labeled as a high fat diet.

Cutting carbs heals human digestion

Ketogenic anti-epilepsy diet (courtesy wiki - epilepsyu)

Ketogenic anti-epilepsy diet (courtesy wiki – epilepsyu)

ERIC WESTMAN – That’s often the case.  That’s in fact what they’re trying to do in many of these high-sugar/moderate fat studies, is to cause the colitis, and they’re not trying to fix it by changing the diet away from the Standard American diet.  They’re trying to create the model where the animal they’re studying actually gets the colitis.  So, when you take away the carbohydrate in the human, and they’re eating high fat diets, to the extent that their body is burning fat, their metabolism shifts substantially from before, and lots of things change that weren’t predicted.  And if anything, by taking away the carbohydrate in the food, I can pretty much fix every gastrointestinal problem that affects people today.

SHELLEY – Can you say more?

ERIC WESTMAN – So we’ve done studies on diarrhea predominate irritable bowel syndrome, That was done by Greg Austin, who we collaborated with when he was a fellow at UNC Chapel Hill. Austin also did a study on GERD, where heartburn went away, which was totally unpredicted in the research world, although, in the clinic, using a low-carb, high fat diet, I see that all the time.  NASH or fatty liver which is a pretty common cause of cirrhosis today, actually goes away when you cut away the carbohydrates.  The bowel gas or flatulence is greatly reduced or almost entirely resolves when you take away carbohydrate from the diet.  Gluten which is found in carbohydrate containing foods is a well known cause of gastrointestinal problems including celiac disease or gluten intolerance.  The signals that we get clinically are if someone has gastrointestinal disturbance you want to reduce or eliminate the carbohydrate, not the fat, so it’s almost the exact opposite of what is being discussed in the animal research.

Microbes as Mafia

Microbes as Mafia? (courtesy wiki-mafiagame)

Microbes as Mafia? (courtesy wiki-mafiagame)

SHELLEY – The difference between clinical results in people and research results in animals is sometimes an indication that mice are not men.  But with regard to Justin Sonnenburg, this idea that you need to feed your gut microbes carbohydrates so that they do good for you . . . or else.  One way I find myself thinking about it is, with microbes adapted to high carb, you need to feed them lots of fiber to produce the kind of nutrients your own intestinal lining needs.  Because if you don’t feed the microbes, they’ll start eating you.  I keep thinking, that makes the carb-adapted microbes sound sort of like the mafia.

ERIC WESTMAN – (LAUGHS)  Just stepping way back, a carnivore, a mammal that just eats other mammals, has a very different gut microbiome than an herbivore – a mammal that just eats vegetable matter.  It doesn’t surprise me that the gut flora will be different.  But an herbivore has to have those bacteria changing the plants into fats.  So if you’re a gorilla, for example, you eat mainly leaves.  What happens inside the gut, though, is that the carbohydrate in the leaves get changed into fat.  So the gorilla has a cecum that’s equivalent to the large intestine, but it’s full of bacteria changing plant matter into short chain fatty acids.  So if you are eating mostly plants, this could be explained by an adaptation of an omnivore, meaning if humans are omnivores, we could eat meat or we could eat plants, it’s a good adaptation that if we’re eating mostly vegetable matter and plants, it’s a good adaptation that if we’re eating mostly vegetable matter and plants, we develop the bacteria that digests the and gives us nutrients from the plants.  But It’s equally plausible that when you eliminate all the plants, and all the micro biome that’s good at eating plants and turning them into fats and other things, that we’ll be just fine and we’ll be a micro biome that’s adapted to mainly eating meat.

SHELLEY – I know some people here in Boulder who are planning to get samples of their poo while being ketogenic, as part of participating in the American Gut project.  For some who’ve gone back and forth between more regular eating and more ketogenic eating, they’re predicting that after two weeks, they’ll bonk.  They’re wondering whether it’s just because the body in general is not producing ketones yet and is not yet adapted hormonally to burning fat, or if there’s a micro biome connection.  What if there’s a gap between when their gut microbes are not producing butyrate any longer, and when the old regime of carb-adapted microbes isn’t gone yet, and might even be “eating” the gut lining . . . and when the microbes settle into a “meat eating” community that doesn’t require so much fiber, plus when the body’s own production of ketones in the bloodstream kicks in.  A couple of people are wondering about this, and with all that in mind, two who are doing this micro biome check plan to get one sample of micro biome two weeks in.

ERIC WESTMAN – I don’t have an answer.  But . . .  As a clinical researcher myself, I wait until something is powerful and has clinical relevance, rather than just seeing something that’s interesting.  I haven’t seen much in terms of the micro biome and low carb high carb discussions going on among the microbiome animal researchers, that really knocks me in the head and says, I need to pay attention to this.  I guess the classic low carb high fat teaching of Dr. Atkins did have a strong emphasis on yeast.  I don’t know if the micro biome people are not considering yeast.

SHELLEY – No.  Most of these researchers are not studying yeasts.  At this point, the technologies they’ve developed make it possible only to study gut bacteria and archaea in an efficient way, rather than cells such as yeast cells.  So there’s not any measure of what happens to yeast, and yeast die-off, and rebalancing after getting rid of yeast infections, and so on.

ERIC WESTMAN – That’s interesting and just points out again that if you just focus on one element of the whole system, you may not see the whole picture.  One change could lead to another regulatory reaction.  I mean, I want to be supportive of the new research.  I think it’s great and I hope we learn a lot from it.  But I think we need to be cautious to not be too alarmist about any changes that are found.

SHELLEY – Well, there’s still the indication that it takes a lot of fiber to keep a carb-adapted microbe happy and helping you.  I did talk with another clinician, Ron Rosedale, who mentioned that IF fiber’s critical, it could be obtained without adding carbs to the diet. And then, there’s the issue of colon cancer.  Ron also mentioned a recent study by Alberto Martin.  Martin used mice prone to colon cancer, and in his study feeding their gut microbes plenty of fiber actually increased the rate of the colon cancer.  Ron’s suspicion was that all that fiber was too much of a good thing and encouraged too rapid multiplication and division of gut cells that were prone to colon cancer.

ERIC WESTMAN – Interesting idea, and (Alberto Martin’s study) just points out again that if you just focus on one point of the whole system (such as people who argue that microbiome research “proves” that a high fiber diet is the key to health) then you may not see the whole picture.  I want to be supportive of the new research into the microbiome.  I think it’s great and we’ll learn a lot from it, but I want to be cautious and not too alarmist about any new observations about the microbiome that are being found at this point.

SHELLEY – And in general, the microbiome scientists are being more circumspect and saying they don’t know yet what their findings indicate yet about what the “best” way is to eat.     But there’s a pretty strong energy from the popularizers to take what microbiome data is there and say that the date is proving that people should eat a high plant based diet, and a high carbohydrate diet, and avoid fats.

ERIC WESTMAN – That’s probably true if  your goal sustain the current state of the American microbiome, if that’s the intent then it’s probably true.  But I learned from Ron Rosedale that we can probably do better than what we currently see.  I guess clinically it looks as if the carbohydrate is the culprit for many digestive problems.  Now colon cancer, if there’s a link between the cancer and insulin levels, then we have to consider that what raises insulin levels the most, and that’s dietary carbohydrate, and insulin resistance and obesity also increase the risk of cancer.  But there are very few signals that I have seen that say that fat in the diet is harmful.  Other than if people have other reasons for not eating fat, be it religious or social or economic.

typical ratio of "high fat" to surge used in "high fat" research studies. (donut courtesy wiki)

typical ratio of “high fat” to surge used in “high fat” research studies. (donut courtesy wiki)

SHELLEY – Well, it’s too bad that the main studies of “high fat” diets in mice and people is the “donut diet” variety, moderate in fat and pretty high in starches and sugars.  It’d be nice if more researchers would study truly high fat, low carb diets.

ERIC WESTMAN – You know, it’s possible they never will, because low carb diets don’t create the outcome they want . . . they’re trying to create the model of the disease.  This was explained to me by a monkey colony researcher who used moderate fat, high sugar diets typical of the American diet.  He said, we’ve never changed the diet because we already have the diet that creates the disease of atherosclerosis.  High sugar, high fat.  He wanted to induce atherosclerosis and then study it and try to fix it with a drug, rather than create a diet that fixed atherosclerosis.  So I saw him many years later and I asked him, have you studied different diets to change and reduce atherosclerosis, and he said no.  Because he’s basically paid to create the disease of atherosclerosis and just try to modify it.  So a lot of these researchers are interested in the mechanism of the disease rather than the prevention of the disease.

SHELLEY – What does all this mean for you as a researcher and a clinician?

ERIC WESTMAN – My world has become mainly clinical at this point, so four out of five days, I’m in the clinic learning and teach other doctors what I do.  People come in for two days, and they follow me and see how I work with patients.  There’s no substitute for actually seeing it in action.  I finally stepped back and realized that’s how I learned to encourage people in a ketogenic diet.  You see, when I give talks about this, most of the doctors go away not knowing exactly how strict you have to be, so they end up doing a moderately low carb diet with medication.  While I’ve been successful in getting many doctors to lower their patient’s carbs, the majority aren’t really low carb, ketogenic doctors because they just say, well, I can’t keep people on it.

SHELLEY – Those doctors don’t believe in trying a truly low carb, high fat, adequate protein, ketogenic diet, and so neither do their patients?

ERIC WESTMAN – Exactly.  But the ones that come to the clinic and see it are the ones who do the true conversion, and believe it.  I was just going to mention there’s a lot of interest in ketogenic diets in the treatment and prevention of cancer.  And, do you know about our latest book, Keto Clarity?   It came out last month.  Jimmy Moore, the internet blogger, has talked me into doi  ng a series.  We did Cholesterol Clarity last year, and Keto Clarity now.  The book is doing really well.  We’ve interviewed multiple experts, many who have been on Jimmy’s podcast, giving their opinions and how to do a ketogenic diet and there are recipes in the back.  Check out Keto Clarity.

Series NavigationAlberto Martin – Carbohydrates and Colon Cancer

  20 comments for “Eric Westman MD – Low Carb, Health & the Microbiome

  1. February 11, 2017 at 9:52 pm

    Hi, Ty,

    I’ve moved the audio player up to the top of the page where it’s easier to see. Let me know if you can download the audio from here.

  2. December 19, 2016 at 10:13 pm

    If it was me, I guess I might ask your health care provider two things. 1. If your blood sugars are pretty normal when your C-Peptide is low, then why is your C-Peptide considered low? Maybe you’re just insulin sensitive, so the C-peptide (which is a hint of insulin response) being low which may well be a good thing! 2. As for abnormal hypoglycemia, according to Joseph Kraft, that’s often caused by an abnormally high insulin response to carbohydrate, where the insulin release is super strong and lasts too long, and drives blood sugars down much longer, and more powerfully, than is beneficial to the body. You might want to look for Kraft’s book on Diabetes and see if it resonates with you. If it does, there are ways to find out how your insulin responds to food challenge, compared with the standard fasting insulin, c-peptide, etc tests.

  3. jawaher
    December 16, 2016 at 12:53 pm

    I have a question, would low carb/keto diet have an effect on abnormal low c-peptide? well when going on low carb high fat diet I experienced documented hypoglycemia (40 mg/dI), when consulting with my doctor few test were done and found that my c-peptide was low, glucose level were normal, A1c was 5.1. Things were good except for my low peptide level!
    I have no idea what caused my abnormal hypoglycemia? and is it abnormal to have a low c-peptide level with a normal glucose level?
    what are your thought?

  4. Marilyn
    May 4, 2016 at 1:07 am

    If the cave man ate a ketogenic diet but average age span was 35yrs old then did he die of disease or animal attack because the average life span now is 80 yrs despite obesity and junk food as the norm for a lot of families ? Its so confusing but i know obesity and diabetes has skyrocked in the past 50 yrs that coincides with the low fat high carb way of eating and low carb has helped me loose weight that was impossible before following lchf diet

  5. Ty Cobb
    March 11, 2016 at 12:38 pm

    Is there a way to actually download the podcast? I listen on my mp3 player and need to be able to download the mp3. Thanks so much.

  6. Patricia Broderick
    October 12, 2015 at 12:47 pm

    My medical history: I nearly died when first put on solids. I had digestive problems all my childhood and into adulthood. I was painfully thin, I did not digest my food and now I understand it was fermenting inside me. I had a bloated stomach long after meals and sometimes terrible pain accompanied with bursts of diarrhoea. My Mother would give me toast without butter and marmite, when I was sick! I vomited frequently especially at children’s parties. At age around 50 my sister recommended cutting out gluten. I did that for around 20 years, but it helped only slightly. When I discovered LCHF I cut out all processed foods and all the gluten free flours. Within two weeks my bowel movements were normal and have remained so ever since. Other nagging problems have cleared up. I had painful breasts for years, that has gone. My teeth remain clean and my tongue is pink. I enjoy real food and cook with mostly beef fat. Dr Westman, you are one of the people to whom I am very grateful as I have listened to your podcasts along with many others. I live in Zimbabwe, Dr Austin Jeans is a good friend and doctor who you likely met at the conference in Cape town. He is making UTube videos of his lectures and we are trying to spread the word, here. My only problem is why did I have to live to the age of seventy two, to feel so healthy and full of energy!

  7. Drego
    September 4, 2015 at 2:55 pm

    Hi Shelley,

    There’s no audio on the page.


  8. June 22, 2015 at 5:43 am

    Hi, Drego,

    Not sure what you’re looking for here. Is it the audio that you can’t hear, or that you can’t specifically download and save it?

  9. June 18, 2015 at 10:27 am

    Hi, Michael,

    That’s an interesting perspective you have, though it does not jive with archeological evidence, nor with evidence from studying more modern hunter gatherers prior to them getting “Westernized” with white flour, white sugar and so on. On the other hand, it’s certainly true that for many people, being vegan and or vegetarian fits well with their beliefs and works well with their health. I’m curious. What’s your favorite way to eat?

  10. June 18, 2015 at 10:22 am

    Just checked, and the audio of the interview with Eric is there and works on my machine. Want to try again?

  11. Michael
    June 3, 2015 at 10:28 am

    I can say that from my personal experience, the high fat, no grain, low net carb diet has done harm to my gut biome. I also developed an auto-immune thyroid disorder.

    What I find so strange about the ‘ancestral’ rationale for the high fat diet is that fat was absolutely NOT a readily available nutrient source for our ancestors. The most available source of food for ancient man was fruit. Apples, pears, berries, bananas, oranges, etc. Man also certainly at a lot of greens but he was not ever on a ‘diet’ or a ‘program.’ Ancient man wasn’t told by his doctor or nutritionist that greens were better for him than fruit. He just ate what was readily available first and if he had to choose between fruit and greens which one would he have selected? Now everyone be honest when you answer…..Of course the answer is FRUIT!

    In addition, it was VERY difficult for ancient man to catch a high-fat source of game. And even a successful hunter would not have had enough meat and fat on hand to be able to eat it as often and in the amounts that modern day proponents say we need to eat it in order to stay in a ketogenic state. I will go so far as to say that it was IMPOSSIBLE for ancient man to stay in a ketogenic state due to the low availability of fat from animal sources.

    So, again, to call this an ‘ancestral’ diet is ridiculous. Ancient man was not a scientist and did not have test strips to determine if he was in ketogenesis or not. He saw food on trees and bushes that was safe to retrieve and readily available and he ate it. A LOT of it. Ancient man was NOT low-carb. He was probably extremely high carb. So to say that we should be eating tons of butter and bacon and grass-fed beef because that’s what our ancestors ate is just untrue. The nutrient sources that ancient man ate most were fruits because they were safer & easier to retrieve, abundant, grew back quickly, stayed fresh longer, and tasted great.

    If you were in a tree or sleeping in a cave and you woke up hungry, what would you grab to eat….the BANANA sitting right there on the tree in front of you!!!! Not the giant sloth that had to be hunted down and killed. How often do you think that happened? Once every few days? At that kill rate, would enough fat and protein be maintained in the diet to keep a tribe of early humans in a ketogenic state? Obviously the answer is no.

    The high fat, low carb diet was undoubtedly NOT the way ancient man ate.

    – Mike

  12. D
    May 22, 2015 at 4:27 pm

    Will you be posting the audio of this interview?

  13. May 8, 2015 at 4:00 pm

    Good point, Jack, though keep in mind that Westman is explaining that even without these “safe starch” and high fiber foods, most of his patients do just fine on a ketogenic diet. Additionally, some caution might be in order for people with blood sugar handling problems and/or carb intolerance. Plenty of foods have been touted for their “safe” starches, without being tested by people who have sugar handling problems. The results may vary from person to person, but among the “low net carb” products that have been reputed to be safe, some have been taken off the market due either to class action lawsuits or FDA complaints. And then, there are citizen science groups, such as some of my friends who tested “low net carb” Quest Bars with their glucometers. Some saw those supposedly low carb bars shoot up their blood sugars! So if you’re not a diabetic yourself, brainstorming here . . . perhaps if you recruit a few people who are diagnosed diabetics but control the problem by eating normally low carb, and offer them glucometers for using as they eat something such as raw potato starch, then track their blood sugars over a couple of hours, plus the next morning. I’d be curious to learn the results!

  14. Jack Wild
    May 8, 2015 at 3:07 am

    We don’t need to eat loads of carbohydrates to feed our gut bacteria. There are many prebiotics that are not high in carbohydrates such as raw potato starch, leeks, garlic etc.

  15. Elderberrywine
    April 13, 2015 at 12:35 pm

    Thank you for this information. It explains why all the hullabaloo about “good gut flora” doesn’t help me. I first noticed it was harmful to me way back in the early 1980s when FOS was the new hot thing. It just made me sick and gave me back pain. Then probiotics just did the same or had no effect. I had some pain relief from kefir but that was the only one that ever helped since the 80’s ever. Sauerkraut was okay but only about 50% of the time did it help. I finally gave up and said okay maybe I don’t need all this starch eating bacteria and maybe I am better as a full keto no fiber person. I don’t have constipation with it, sorry that people do have that problem, but I don’t. This resistant starch theory is now the new hot thing, I think it’s equally bogus… probiotics again, gas and bloating again, and basically pain was the result of my experiment with it. Again, not all people need the same exact solutions. I’m not like everybody else and that’s just fine.

  16. Drego
    February 13, 2015 at 9:16 pm


    Are the gut series interviews with Westman and Sonnenburg going to be available for download?



Comments are closed.