The Short Answer: Regular exercise increases the diversity and function of beneficial gut bacteria independently of diet. This happens through changes in short-chain fatty acids (SCFAs) that reduce inflammation and support immune regulation — benefits that matter for anyone managing autoimmune conditions, including Hashimoto’s low thyroid.

Why gut bacteria matter for autoimmune health

Science has shown that healthy gut bacteria are essential to immunity, brain function, mood, digestive health, and management of autoimmune diseases. Your gut hosts about three to four pounds of bacteria comprising roughly 1,000 different species and 5,000 strains. Your body needs these gut bacteria to:

Maintain the health of the digestive tract

Protect the intestinal wall

Prevent inflammation

Metabolize nutrients

Produce vitamin K and short-chain fatty acids (SCFA), which support immune health

Regulate immunity, including in autoimmune conditions

Promote good brain health and function

We’ve long known that fermented foods, probiotics, and a diet rich in diverse vegetables and fruits cultivate healthy gut bacteria. Researchers have now discovered that regular exercise does something equally important: it changes your bacterial composition independent of what you eat.

How exercise reshapes your microbiome

In a landmark mouse study, scientists transplanted fecal material from both exercised and sedentary mice into sterile mice. The activity levels of the mice receiving transplants clearly mirrored those of their donors, demonstrating that gut bacteria influence physical activity levels.

The mice receiving bacteria from exercised animals showed significantly more bacteria that produce butyrate, a short-chain fatty acid (SCFA) that promotes healthy intestinal cells, reduces inflammation, and increases energy. These mice were also more resistant to ulcerative colitis.

Exercise increases protective fatty acids in humans

A human study tracked 18 lean and 14 obese adults as they transitioned from sedentary to active and back to sedentary. Their exercise routine consisted of 30 to 60 minutes of cardiovascular exercise three times a week for six weeks, while diets remained unchanged.

Results showed that exercise raised SCFA levels, and when activity stopped, levels declined again. Lean subjects demonstrated a more dramatic rise in SCFAs than obese ones, but increases occurred in both groups. This proves the effect happens through movement itself, not through dietary change.

Exercise and autoimmune management

For autoimmune patients managing chronic fatigue, whether from Hashimoto’s low thyroid, lupus, rheumatoid arthritis, or other conditions, the message is encouraging: you don’t need intense training to shift your microbiome. Regular, moderate movement that you enjoy creates measurable changes in the bacteria that regulate inflammation and energy production.

The combination remains age-old wisdom: eat your vegetables, cultivate a diverse diet, and move your body regularly. When managing autoimmune flares that limit your activity, use your better days to engage in exercise you genuinely enjoy.