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I like this part:

Quote:

But what about gut health? Shouldn’t fiber help with idiopathic constipation (i.e. constipation with no known cause)? Apparently not. Singaporean researchers found that “patients who stopped or reduced dietary fiber had significant improvement in their symptoms while those who continued on a high fiber diet had no change”. They conclude that “ Idiopathic constipation and its associated symptoms can be effectively reduced by stopping or even lowering the intake of dietary fiber” [55]. It seems like the carnivore diet’s lack of plant fiber isn’t obviously harmful – although this doesn’t entail that any amount of fiber more than zero is bad.

In recent years, claims have shifted toward ideas about colon health. The idea is that because fibre is fermented into short chain fatty acids (SCFAs), and because SCFAs are readily used for energy by the colon, and because one SCFA, butyrate, has positive effects on colon health when it’s metabolised, that therefore we need fibre to keep our colons healthy. There are many issues with this chain of reasoning.

One is that fibre isn’t the only source of SCFAs. We can, and do, make them out of proteins as well [56]. Second, just because a cell uses something for energy doesn’t mean it’s necessarily the best source of energy. Alcohol is readily used in the bloodstream, above other sources. That doesn’t make it good. Third, the most important metabolite of butyrate is a ketone body, D-beta-hydroxybutyrate, and it’s not clear how much of the positive effects of butyrate would be met just as well by a ketogenic diet (see my in-depth blog post on this).

Another relevant observation is that one specific type of bacteria, Akkermansia Muciniphila, is increased on ketogenic diets [57] and when fasting [58] (suggesting it isn’t from any plant foods consumed on ketogenic diets). This bacteria is widely held to be beneficial, because it correlates inversely with metabolic syndrome. Giving it to mice even delays the development of obesity and insulin resistance [59]. These bacteria live right in the mucosal layer of the colon feeding on the mucous and in turn producing butyrate. So it’s quite plausible that a ketogenic diet increases the availability of butyrate to the colon due to bacteria, but not the ones that make it out of plant fibre.

It makes very little sense to develop a theory of what a healthy gut biome looks like by suggesting it should match the biome of healthy people, and then to turn around and reject a diet that improves someone’s health because the biome doesn’t match your previous data. Until we know a lot more, a healthy gut biome should be defined as the gut biome of a healthy person.

While none of these points prove that we wouldn’t benefit from more fibre, they point out weaknesses in the pro-fiber arguments. The fibre-for-the-colon arguments are largely speculative. This is another area where some basic research on outcomes in carnivorous diets would be very helpful. Certainly many of the people currently enjoying a carnivore diet are doing it specifically because the lack of fibre reduces inflammation in the colon.