Fiber or Not: Short-Chain Fatty Acids and the Microbiome

A common viewpoint among both conventional and alternative health practitioners is that fiber is good for you. Not only good but necessary. Millie Barnes, as an example, identifies her expertise as a chef and nutrition coach. She apparently comes from a functional medicine approach, common among those advocating traditional foods diet that is plant-based and fiber-heavy (another example is Dr. Terry Wahls).

Barnes wrote a post about fiber and short-chain fatty acids (SCFAs), Why Short-Chain Fatty Acids Are Key To Gut & Overall Health, Plus How To Get More — her position is typical: “SCFAs are produced when bacteria—the good kind—ferment fiber in the gut, thereby providing your body with energy, keeping your metabolism humming, and even thwarting a wide range of digestive disorders.” There is nothing necessarily wrong about this position, although the scientific evidence is severely limited and highly contested. The problem is in treating the science as settled.

I’m not against fiber. I eat some high-fiber vegetables, especially fermented, along with other cultured foods. I used to eat even more fiber and vegetables, back when I was doing a paleo diet. And there was benefits to it, at least in comparison to my prior high-carb diet of processed foods. But I’ve also tried the carnivore diet and felt freaking awesome! I never realized how hard to digest are most plant foods (Like water fasts, meat fasts are good for health.).

I’m much more cautious about the plants and hence plant substances, including toxins and anti-nutrients, I allow into my body. Still, I have nothing against plants on general principle and I’m persuaded by Siim Land’s argument for hormesis and antifragility, that is to say beneficial stress (in case you’re interested, there is an intriguing scientific paper to check out: Hagen, Roulette & Sullivan, Explaining Human Recreational Use of ‘pesticides’). I now think of plants as more medicine than food, but nonetheless quite useful as medicine.

SCFAs are a complex topic, as is the microbiome of which we know little. As aside note, while some SCFAs (acetate and butyrate) are ketogenic, others (propionate) is glycogenic. They play an important role in health. That much we can agree on. What is less understood or at least less acknowledged is that SCFAs can come from other sources besides fiber. Butyrate, for example, is found in dairy fat. The cow eats the fiber and makes the butyrate for us.

So butyrate deficiency shouldn’t be a problem for anyone on a reasonably healthy diet, plant-based or animal-based. That is assuming they are getting plenty of high-fat dairy, pasture-raised all the better, and most Westerners tend to consume tons of dairy. As for myself, I get plenty of ghee (clarified butter) which means I’m probably fine on butyrate levels. By the way, my preferred mode of ghee delivery is through coffee and tea, what has been made famous as Dave Asprey’s Bulletproof Coffee, but he got the idea from a Tibetan woman who served him tea with yak butter. This maybe is not such a foreign practice. My mother recalls her Kentuckiana grandmother regularly pouring coffee over butter, although she also mixed in saltine crackers — that latter part probably less traditional and certainly not low-carb.

To get back to our discussion of SCFAs, I’m not as familiar with acetate, but apparently you can get it from apple cider vinegar (ACV), something I also take on a daily basis. I assume that the microbes in the ACV produced the acetate and so bypasses the need of the microbes in your own gut to do the work. No fiber is required, at least not in the diet. Furthermore, one can get acetate from ketosis as well and ketosis is my preferred state. Acetate/acetoacetate sometimes is what is measured for ketone levels. Some amino acids such as leucine and lysine can be converted into acetoacetate through fatty acid synthesis. Acetoacetate then is reduced to beta-hydroxybutyrate and the latter gets turned into acetone and acetate.

Now on to propionate, even more fascinating. It is a food additive that the modern person is getting overdosed on and appears to be a causal factor behind such conditions as autism (The Agricultural Mind). Those on the autistic level tend to have high levels of the bacteria that produce propionate and tend to crave foods that are high in it. Rodents injected with propionate express autistic-like behaviors. And those on the autistic spectrum show decreased behavioral problems when propionate is removed from their diet or when an antibiotic kills off some of their microbiome. SCFAs are a key part of a health diet, but they are powerful substances not to be taken lightly. They potentially can do harm as well.

As a last comment, no studies have been done on the microbiome of those on a carnivore diet or near-carnivore diet such as the Inuit. Heck, there has been no research even on a more general healthy omnivore diet including meat — the studies on the Standard American Diet (SAD) don’t count. But from what we do know about biology in general, it appears humans have multiple pathways of producing or obtaining SCFAs. The microbiome, in particular, is probably extremely adaptable to a wide variety of diets that were necessary during evolution (e.g., the microbiome of some hunter-gathers completely alters from season to season). Dr. Paul Saladino has talked a lot about this kind of thing — take what he had to say in an interview with Geoffrey Woo (Nose-to-Tail Carnivore Diet: Organ Meat, TMAO Implications, & Reaching Ketosis ft. Dr. Paul Saladino; & video):

“There are many bacteria which can metabolize fat, protein and animal-based collagen. That’s the thing I think that most people are missing. That our gut microbiome can shift. There’s a study where they put people on what I would consider to be a very poor version of a carnivorous diet and they compare it a plant-based diet. What they see is a divergence in the gut flora within a week. The animal-based eater, again, it’s not an ideal diet. The animal-based eaters had more bile acid tolerant organisms and more organisms to ferment fat and protein. They made isobutyrate and they made acetate and they made propionate as short chain fatty acids.

“The plant-based eaters made butyrate as a short chain fatty acid and had different colonic and small intestinal microflora. The investigators in that study jumped to the conclusion. Look, we know what’s going on with the gut because they have this organism. What’s worthy of biophilia or they don’t have this organism. They clearly have an unhealthy gut microbiome and I think that is an extrapolation. We do not know that. Clinically, nobody is assaying anything clinically in that study. They didn’t do inflammatory markers. They didn’t follow those people moving forward. It was almost like a setup. They were just trying to prove that these bile acid tolerant organisms would show up when they gave people a bunch of foods, which promote the formation of bile.”

Dr. Paul Saladino was on the paleo diet before trying carnivore, but Dr. Will Cole went from vegetarian to a more paleo-style diet. Dr. Cole wrote a book, Ketotarian, about how to do a plant-based keto and so he is right in line with the likes of Millie Barnes. That didn’t stop him, in an interview with Vanessa Spina, from pointing to evidence that a high-fiber diet may not be necessary, even going so far as to mention the carnivore diet:

“Because we have an epidemic of gut problems in the United States and around the world and Europe as well that this is going take time. Sometimes some people can have it right out of the gate. Some people can’t. It’s important to know what’s right for your body and what’s not right for your body. But as you heal, what you used to not be able to have the goal is to be able to reintroduce these things as your body heals.

“So the carnivore diet, for example, it’s the ultimate elimination die because it’s removing a lot of these fibers. But the goal isn’t to be carnivorous forever and ever, even though maybe some people would prefer that. But the goal is to use something like that to drive down this inflammatory cascade to bring things back in, as long as it’s nutrient-dense. And there are studies to show like the Hadza tribe in Tanzania they have good bacterial diversity during those months where they are eating less vegetables. But they’re eating more raw meat or getting like drinking blood and doing things that most people that are on the carnivore diet in the West are not doing today.

“So there are other there are other ways to get back to our diversity beyond fiber. I would just say it is the most common, most well researched way to get back to our diversity.”

Vanessa Spina, in that interview, then added an important point, not all prebiotics are fiber or necessarily come from plants at all: “I found this list of prebiotic foods that were non-carbohydrate that included cellulose, cartilage, collagen, fructooligosaccharides, glucosamine, rabbit bone, hair, skin, glucose. There’s a bunch of things that are all — there’s also casein. But these tend to be some of the foods that actually have some of the highest prebiotic content. So it’s interesting, I think, if someone has less tolerance for fiber, they can also explore some of these other product prebiotics.” That is something I never hear anyone talk about.

This might explain why so many people do so well on a carnivore diet. They are still getting prebiotics. And we know those on entirely or mostly meat diets retain functioning microbiomes. But there has been so few scientists looking into this.