Your small intestine is designed to be relatively low in bacteria — most of your gut bacteria are supposed to live further down in the large intestine.

With SIBO, bacteria migrate upward or simply overgrow in the small intestine, where they don't belong in large numbers.

Once they set up camp there, they start fermenting food before your body has a chance to properly absorb the nutrients.

That fermentation produces excess hydrogen or methane gas, which is what causes the bloating, cramping, and discomfort that makes SIBO so frustrating.

Over time, this overgrowth can damage the lining of the small intestine, making it harder for your body to absorb key nutrients like iron, B12, and fat-soluble vitamins.

This is why people with SIBO often deal with fatigue, brain fog, and deficiencies even when they're eating well.