Short Chain Fatty Acids and Low-Carb
"Why does my stomach feel so good?"
It had been a long week of moving from Brooklyn to Queens and having no kitchen, I had eaten out every single day. Queens is probably one of the ethnic food capitals of the US. I had thrown caution to the wind and hadn't bothered trying to be paleo beyond avoiding gluten and junk food. Chris and I ate a large variety of Filipino, Thai, and Mexican food. Rice was the dominant food, but there was plenty of coconut milk and offal to be had. I expected to pay in cramps, but instead my stomach felt better than ever.
I suppose it's a waste of time to coat a talk about digestive problems with euphemisms. So I'll give it to you straight. Before "paleo" I had struggled with IBS (constipation, gas, and diarrhea) and GERD (chronic acid reflux). When I started paleo, I found low-carbing did an amazing job eliminating the worst IBS symptoms and my GERD disappeared. But two years into it, I started having different stomach problems, particularly intermittent severe diarrhea. There were some IBS symptoms I never eliminated as well, such as the "never feeling done" issue after going to the bathroom.
I found that the diarrhea would actually respond quite well to a high-carb diet of "gentle" foods like pumpkin, apple-sauce, and broth. It kept coming back though. I stocked my pantry with canned pumpkin and apple sauce.
I was because these foods seemed to have a positive effect and the Queens experience that I've shifted away from low-carb paleo and actually pretty much shifted away from the typical conception of paleo. I'm not sure why low-carb seemed to destabilize my stomach, but I'm not alone. I know a lot of LC paleo folks who have intermittent diarrhea.
Luckily, at the same time I've been studying gut bacteria and their byproducts. I'm hoping my AHS presentation will be up soon because I talk a lot about gut bacteria and a particular metabolic known as butyrate. Since I've been studying it, I've started to wonder if it and other short chain fatty acids are very much involved with digestive difficulties like mine.
The short story on butyrate is that it is made in the colon by fermentation of carbohydrates. Butyrate has many important roles, but I would sum up its main roles as promoting satiety, reducing inflammation, and protecting the colon. Currently it is mainly being studied as having a role in obesity, inflammatory bowel disorders, and colon cancer. Does lack of it cause these conditions? We don't know yet, but it seems promising. IBD patients have low levels of it in the colon and administering it reduces symptoms significantly. A caveat is that everyone produces butyrate differently. The gut microbiome is individual for each person. Another caveat is that butyrate is present in certain foods, but this has been poorly studied, which is unfortunate. If you want to read more on this subject, I suggest this free dissertation.
When you think of low-carb foragers, you probably think of the Inuit. However, to describe them as just low-carb is a disservice to the diversity of their diet. In a previous post I discussed the many plants they eat. They ferment some of these plants and they also ferment the guts of certain animals. Some of these foods seem to violate optimal foraging theory. Gathering teeny tiny roots from mouse nests? Not efficient! But I would suspect that these fermented foods might be high in butyrate and/or the Inuit gut flora is adapted to make butyrate with very little fiber.
Otherwise, conventional low-carb diets generally do a very poor job of generating butryate in the populations studied. There are several papers on this, the most recent being High-protein, reduced-carbohydrate weight-loss diets promote metabolite profiles likely to be detrimental to colonic health. This one is interesting because the low-carb diet studied reminds me a bit of what I've seen some low-carb paleos eat.
It was pretty fatty, but I am personally a bit more interested in the high-protein part since contrary to popular belief, protein is fermented in the colon. There is a control diet (M), a high-protein low-carb diet (HPLC), and a high-protein medium-carb diet (HPMC).
In the HPLC diet, SCFA production decreased quite a lot. Butyrate concentration in particular was halved. On the HPMC diet it didn't decrease much. In the high-protein diets branched-chain fatty acids (BCFAs) isovalerate and isobutyrate were increased. N-nitroso compounds (NOC) were also increased (5.4 fold in HPLC and 3.6 fold in HPMC- carbs seem to have a modulating effect). These are produced by the fermentation of protein. In vitro NOCs have shown carcinogenic effects, but there haven't been many in vitro studies. Plant-derived phenolic compounds (such as ferulic acid) were reduced in the HPLC diet, but increased in the HPMC diet compared to M. These may have anti-inflammatory effects. On HPLC the proportion of Roseburia/Eubacterium rectale bacteria, which produce butyrate, decreased and Bacteroides increased.
Overall this paper and many others on the effect of low-carb on gut bacteria seem to paint a bleak picture. What about all the success people have with low-carb diets and diets that focus on controlling carbs like the Specific Carbohydrate Diet? I think low-carb can play a role in fighting disease, but I think it's a mistake to carry on this kind of diet long term. The SCD doesn't advocate low-carb forever, but healing and then adding in carbs cautiouly to figure out which ones are benign. Perhaps low-carb can work in the long-term if small amounts of certain carbohydrates or foods with SCFA are consumed (fermented foods or butter, which is high in butyrate), but there is little research into this. A recent animal study did find that oral administration of butyrate supplements could help people with IBD, which is promising and great since most other studies relied on enemas, but there is very little research (if any) on the effects on butyrate in actual foods.
UC mouse model
In the meantime I continue to enjoy success from diet that includes ample amounts of carbohydrates that work for me, like rice and buckwheat, and keeping my protein low. Fat I eat ad libetum. I actually had more success with these then with root vegetables, some of which seem to make my symptoms worse (sweet potatoes...I'm looking at you...).
Another facinating paper sheds some light on why some fiber studies are disappointing. It may be because they aren't thinking about fat. Linoleic acid and butyrate synergize to increase Bcl‐2 levels in colonocytes implies that the colon-cancer preventing effects of butyrate may be muted by excess linoleic acid and enhanced by added DHA. Meanwhile nutritionism(ist) Marion Nestle says...replace your saturated fat with heart-healthy PUFA! If it's DHA that might be OK, but if you are adding more linoleic acid into your diet...that's just dumb.