Colonic Health: How Fermentation and Short-Chain Fatty Acids Protect the Gut

This 2006 review helped renew scientific interest in short-chain fatty acids (SCFAs) at a time when prebiotics and probiotics were rising in popularity. Written by a respected clinical nutrition group in Toronto, it lays out clearly why the products of fiber fermentation are so central to gut health.

What fermentation produces

When gut bacteria ferment fiber and resistant starch, they make three main SCFAs that together account for 90–95% of the total:

• Acetate — over half the total.
• Propionate — about a quarter; it travels to the liver and contributes to glucose production.
• Butyrate — around 15%, but outsized in importance: it supplies roughly 70% of the energy used by the cells lining the colon.

In the colon these acids reach high concentrations (70–130 mmol/L in the early colon), and by lowering the local pH they help hold pathogenic bacteria in check.

Why SCFAs protect the gut

The review summarizes the protective roles of these molecules. Butyrate, in particular, influences gene activity by inhibiting enzymes called histone deacetylases (HDACs), which underlies its anti-inflammatory and anti-cancer effects. Notably, the authors point to evidence that people with colorectal cancer tend to have reduced fecal butyrate, tying SCFA depletion to disease risk.

“Interest has been rekindled in short chain fatty acids (SCFAs) with the emergence of prebiotics and probiotics aimed at improving colonic and systemic health.”

The practical message is consistent with the rest of the SCFA literature: high-fiber, lower-fat diets produce more of these protective acids, while low-fiber diets produce less — making fiber intake one of the most direct ways to support a healthy colon.