What does smoking do to your gut and gut microbiome?
Smoking disrupts your gut microbiome and increases the risk of intestinal inflammation, gastrointestinal complaints and certain forms of cancer. Quitting smoking is the most direct way to reduce these risks.
Smoking is associated with changes in the composition of the gut microbiome. In a large Dutch study of more than a thousand people, smoking was one of 126 factors that were measurably linked to how the gut microbiome looked. Which specific bacterial species increase or decrease was not made clear by this study. The effect has therefore been demonstrated, but the details have not yet been fully mapped out.
A more concrete consequence is the increased risk of inflammatory bowel diseases. Smoking raises the likelihood of inflammatory bowel diseases such as ulcerative colitis and Crohn's disease, probably in part because it disrupts the gut microbiome. This is considered probably causal, not merely an association. In addition, smoking is a risk factor for functional dyspepsia: a condition in which you experience pain or a feeling of fullness in the upper abdomen without any physical cause being found.
Smoking also increases the risk of a rare autoimmune disease of the bile ducts in the liver, called primary biliary cholangitis. In people with this condition, the gut microbiome is less diverse. Smoking is one of the environmental factors that can trigger the disease in people who are genetically susceptible to it. Whether smoking directly reduces the diversity of the gut microbiome, or whether this occurs through the disease itself, cannot be stated with certainty on the basis of the available research.
Finally, there is strong evidence that smoking increases the risk of a specific form of oesophageal cancer, particularly in combination with excessive alcohol use. While this does not directly involve the gut microbiome, it shows that the damage caused by smoking affects the entire digestive tract, from the oesophagus to the large intestine.
Based on several large population studies and reviews (Lancet 2020, Lancet 2024, and others). The causal relationship between smoking and IBD is probable, but for the direct effects on microbiome diversity the associations are associative in nature. No randomised studies are available (not ethically feasible).
What does alcohol do to your gut microbiome?
Chronic heavy drinking demonstrably disrupts the gut microbiome, with consequences for the heart and liver. Moderate drinking was not examined in these studies, but the mechanisms identified provide a clear picture of how harm arises.
Can your gut microbiome influence inflammation in your body?
Your gut microbiome can influence inflammatory processes throughout your body via the gut wall. Eating more fibre and exercising regularly are the most well-supported ways to influence this favourably.
Can your gut microbiome influence your risk of heart disease?
Your gut microbiome influences your heart health through metabolic by-products that can promote arterial hardening, high blood pressure and blood clots. The association is plausible, but how best to modify the gut microbiome to protect your heart has not yet been sufficiently proven: always discuss major interventions with your doctor.
Can your gut microbiome influence how long you live?
There are clear indications that the composition of your gut microbiome is associated with how long and how healthily you age, but whether modifying your microbiome extends your life has not yet been demonstrated in humans.
Can exercise improve your gut microbiome?
Moderate regular exercise demonstrably improves your gut microbiome, but you need to keep exercising because the effect disappears when you stop. Do not overdo it: very intensive training can actually put gut health under pressure.
Can your gut microbiome affect your memory and concentration?
Your gut microbiome can influence your memory and concentration through several routes, but most of the evidence still comes from animal and laboratory research. What you can concretely do right now is support your gut health through diet, as direct supplementation or probiotics for cognition have not yet been sufficiently proven in humans.