UK surgeon explains why high-fibre diets cause gas and bloating?

People who begin eating more fiber often expect immediate digestive benefits, but health experts say the first phase can feel surprisingly uncomfortable.

Dr. Karan Rajan, a UK-based surgeon and medical content creator, recently explained that increasing fiber intake for the first time commonly leads to temporary gas and bloating — not because fiber is harmful, but because the gut microbiome needs time to adapt.

In an Instagram post shared on April 25, Rajan described what he calls the “fiber-microbiome interaction curve,” showing how the digestive system responds when daily fiber consumption rises.

According to him, people with low-fiber diets may notice very little gas, but that does not necessarily mean they have an ideal gut. 

Instead, it often reflects that their gut bacteria are relatively inactive because they do not have enough fiber to ferment.

Once fiber-rich foods are introduced in larger amounts, those bacteria suddenly begin working harder to break the nutrient down. 

This fermentation process produces extra gas, which can lead to bloating, abdominal discomfort, and increased flatulence during the early adjustment period.

Dr. Rajan said many people mistakenly assume this reaction means fiber is not suiting them, when in reality it is a sign that the gut is being challenged to become more efficient.

With steady and consistent fiber intake, however, gut bacteria gradually adapt. Over time they produce more of the enzymes needed to digest fiber effectively, which reduces gas production and increases beneficial short-chain fatty acids that support colon health.

Experts say this means the uncomfortable bloating phase is often temporary. Once the microbiome adjusts, the body is able to process fiber more smoothly, allowing individuals to enjoy its long-term digestive benefits with far less discomfort.