What does eating red meat do to your gut over the long term?

Eating a lot of red meat is associated with a less favourable composition of the gut microbiome. A review of 106 studies classifies red meat as one of the dietary components that negatively affects the diversity and balance of gut bacteria, alongside processed meat and heavily refined products. Lower diversity in the gut microbiome is in turn linked to a wide range of health complaints.

The most concrete risk lies with colorectal cancer. People who consistently eat large amounts of red and processed meat have a demonstrably higher risk of colorectal cancer; review literature estimates that dietary and lifestyle changes could prevent up to half of all cases. That is a rough estimate, not a fixed figure, but the association itself is reasonably consistent and runs in part through the gut bacteria: certain bacterial species that increase strongly with red meat consumption are also linked to worse blood sugar and lipid values, as shown by a study in more than 21,000 people.

In people with a predisposition to intestinal inflammation, such as Crohn's disease or ulcerative colitis, there is additional reason for restraint. A review of multiple systematic reviews concludes that high consumption of red and processed meat increases the likelihood of both the onset and the worsening of such inflammatory conditions. The strength of the evidence is not equally strong for everyone, but the trend is clearly negative.

There are also preliminary indications that red meat plays a role, via the gut microbiome, in early-onset colorectal cancer, meaning cancer in people under fifty. This follows from one study in Chinese patients and has not yet been confirmed in other populations. The link with skin conditions such as psoriasis or joint conditions such as rheumatoid arthritis also runs partly through the gut microbiome, but those associations have been studied to a limited extent and are largely based on mechanistic studies.

All of these findings are associative: causal evidence in humans is largely absent. But the signals consistently point in the same direction. If you regularly eat red meat, moderation, and more frequently choosing fish, legumes or plant-based protein sources, is the most concrete step you can take on the basis of these studies.