The Center For Disease Control website on colon Cancer prevention advises a "diet low in animal fats and high in fruits, vegetables, and whole grains to reduce the risk of other chronic diseases, such as coronary artery disease and diabetes. This diet also may reduce the risk of colorectal cancer." (1) I bet the advice sounds familiar. Their rationale does involve solid science, but as usual, there is more to the story. 

 Fiber, Healthy Colons, and Short-Chain Fatty Acids

Fiber is indigestible by humans, but it has an indirect effect on health. For many years, scientists have known that bacterial fermentation of dietary fiber in the colon produces the short-chain fatty acids butyrate, propionate, and acetate. Moreover, studies show that they play a critical role in the maintenance of intestinal health. For example, they tend to lower inflammation, and colon cancer starts as inflammation; thus, fiber reduces colon cancer risk.

No Fiber, Healthy Colons, and Short-Chain Fatty Acids

Many health-minded articles ignore that other compounds found in our diet ferment in the colon into short-chain fatty acids; however, a 1998 paper by Smith and MacFarlane found that the building blocks of protein (amino acids) also do. The same study found that up to 40% of gut bacteria can help ferment amino acids. Whatsmore, they discovered that carbohydrates decreased fermentation by up to 35%. Another mechanism that diminishes fermentation by 40% is lower PH (more acidity). The study demonstrated that in the absence of carbohydrates, as in someone on the carnivore diet, fermentation of short-chain fatty acids is accomplished by amino acid fermentation. (2) 

Good News For Low-Carb and Carnivore Dieters

These findings are significant since most of us eat carbs and never need to ferment amino acids. Remember, carbs interfere with amino acid fermentation. But for those of us who don't eat carbs, we can easily use amino acids to get the job done. 

According to a Finnish study done in 2019, high-protein diets lead to more undigested protein-derived constituents ending up in the large intestine than moderate or low-protein diets. Hence, more bacterial amino acid metabolism takes place in the colon. For this reason, the amino acids serve the bacteria to produce short-chain fatty acids. The primary protein fermenting bacteria in the colon are Clostridium, Desulfovibrio, Peptostreptococcus, Acidaminococcus, Veillonella, Propionibacterium, Bacillus, Bacteroides, Staphylococcus, and Proteobacteria. The amount of protein eaten, rather than the type, determines how much fermentation will occur. Because carbohydrates are the preferred carbon source for many gut microbes, protein fermentation happens when no fermentable fiber is available. (3)

My Situation

My body composition, mood, and performance are all optimized on the carnivore diet, and it's nice to know that my dietary choice is not leading me to colon cancer. I did a Genova Diagnostics stool analysis recently, and it shows that I am doing well. I have normal levels of protein breakdown products, which of course, should lead to fermentation. The expected level is 1.8 to 9.9 micromol/g, and I come in at 6.3. I also have a typical short-chain fatty acids level at 37.3 micromol/g, and the healthy level should be above 23.3.  

Hedonic Response to Foods

Highly tasty low-quality foods are hard to resist, but why? Food cravings involve a network of brain structures regulated by emotional and cognitive factors, sensory cues, and anticipated reward. (4) In other words, it's all in our heads. Since being on the carnivore diet, I have noticed that I don't care much about how food tastes at all. I also have zero cravings for delicious foods. Not only the hormones accountable for hunger have altered, but my brain has much to do with it.

High Colonic Propionate

My overall short-chain fatty acid profile is average; however, butyrate is normal, but my propionate is much higher than expected, and my acetate is slightly lower than expected. Unfortunately, I could find no literature on why this is happening, but I suspect the carnivore diet has much to do with it. 

Propionate Reduces Cravings

I did find this paper on how propionate makes you not crave high-reward, low-quality junk food, however. In the paper, the researchers state that propionate has a regulatory effect on our energy set-point. In other words, in humans, increased colonic production of propionate acutely reduces energy intake, leading to fat loss.

Propionate and the Gut-Brain Connection

In the paper I mentioned above, they studied normal-weight individuals' brains using functional MRI imaging. The reward center has two areas called the caudate and nucleus accumbens. When stimulated by looking at photos of tasty foods, they show up on MRI because more blood oxygen goes to the areas. The signal is called the blood oxygen level-dependent signal, or BOLD that is visible on an fMRI. And, amazingly, they found that higher propionate in the colon made the signals weaker. 

Our Friendly Germs

They give credit to the positive change to the bacteria that ferment the propionate because, without them, we could not produce propionate. In addition, gut bacteria affect behavior, stress, and stress-related diseases. Thus, gut microbes (microbiota) changes may influence disease risk, and manipulating microbiota may provide novel ways to intervene in clinical situations related to mood and anxiety disorders. (5) The famous author Michael Pollan has an excellent article called "Some of My Best Friends Are Germs" about this fascinating subject.

How to Increase Your Propionate

The good news is that you don't have to go on the carnivore diet if you don't want to. The dietary supplement inulin-propionate ester, or IPE, is widely available. It is considered a prebiotic. It is an indigestible starch that makes its way to our colons and is fermented selectively into propionate. The recommended dose is ten grams. You can search for and order it online. 

Studies On IPE Supplementation

In this study, IPE lowered the desire to eat. In addition, the authors found it affected the hormones that regulate hunger, proving that propionate has a central mechanism and a systemic mechanism of action.

Additionally,  this study demonstrated that the subjects on it burned more fat in overweight women. Finally, this study showed that insulin sensitivity improves with IPE, but also inflammation decreases. This makes sense because propionate reduces inflammation.

Conclusion

• Propionate in the gut is beneficial for us.

• Friendly germs make propionate in our gut.

• Propionate is the fermentation product of fiber or amino acids.

• Healthy Levels of Propionate are possible on the carnivore diet.

• IPE is a supplement that raises propionate.

• Weight loss is more effortless when you have good propionate levels.

• Propionate acts by decreasing food cravings in the brain.