SIBO and weight

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SIBO and weight

Medically reviewed by:
Dr James Freeman

SIBO can lead to weight gain and weight loss for varying reasons. It really comes down to how the bacteria you have impact your body.

Weight gain

Fermentation in the small intestine instead of the large

The fermentation of carbohydrates you consume should take place in your large intestine. To support this, the large intestine has a tremendously diverse bacterial load to facilitate standard process and gas production. SIBO leads to gas in the small intestine that has a harder time leaving your stomach. This can make you look “larger” than you are.

SIBO and weight gain due to more calories being extracted

With SIBO there is an overgrowth of bacteria in the small intestine that can break down and use energy from carbohydrates (including fiber). The fermentation process can cause you to extract energy from foods usually unavailable to humans and lead to weight gain. That is most common with methane or Hydrogen sulfide SIBO, but this isn’t always the case.

To put this concept in very basic terms, your small intestine has an abnormal ability to digest carbohydrates and extract energy from fiber that would not usually occur. Cows can get energy from grass; humans can’t. Sometimes, with SIBO, bacteria in the gut can extract energy from food not usually available.

Methane SIBO and weight gain

Methane in the GI tract has proven to slow down gut transit which may have implications that result in weight gain or make it harder to lose weight. Slow transit time, which refers to the retention of food in the gut for a longer period than clinically normal or required, is often associated with symptoms of constipation.

The slow transit increases methane gas production but also allows excessive calories to get absorbed because the contents stay longer in the gut, giving the bacteria more time to extract energy.

Studies have found that SIBO is associated with high VFA/SFA ratio measured from cross-sectional CT image. This type of fat is considered the most dangerous as it often stores on the stomach area, increasing this risk of heart disease and diabetes.[1]


SIBO and energy levels

SIBO can make you deficient in nutrients required for energy production. Iron is one of the most common deficiencies seen with SIBO. You need iron to feel well and energized. Without it, you’re likely to spend more time feeling exhausted, which doesn’t help your daily energy expenditure. The chronic inflammation caused by the SIBO bacteria and constant bloating can leave you feeling exhausted too. When you feel exhausted, you are more likely to reach for a quick “pick me up” snack. These tend to be high in sugars and fat.

Decreased metabolism

Those with SIBO maybe be more prone to a decrease in metabolism due to a variety of metabolic factors. Decreases in metabolism often lead to weight gain when diet and exercise isn’t adjusted accordingly. SIBO can affect your insulin and leptin, which impact your weight and fat storage.

SIBO and sleep

SIBO can impact restful sleep. Bloating is usually at its worst by the end of the day, which can make you very uncomfortable. Science shows, in women, the fewer hours of sleep we get, the more we eat, and the less energy we spend.[2] This can lead to weight gain.

SIBO and weight loss

SIBO can also cause weight loss. The SIBO can take the energy from your food (along with other vital vitamins and nutrients) and cause weight loss and malnutrition. It depends on how SIBO manifests itself in the individual body.

Premature fullness

The feeling of premature fullness and pressure on the stomach bag also might cause some people to eat less. It also might cause painful reflux that can result to eating less or fear food, and as a result, lose weight.

SIBO bacteria consume nutrients

In some people, the type of bacteria living in the small intestine can use the energy from the food we consume, not allowing the body to extract this energy.


The pressure created by the small intestine in those with SIBO may cause them to vomit, resulting in the loss of energy. Feelings of nausea may also lead to vomiting.

Take away

Individual cases can vary substantially, and not everyone with SIBO has the same microorganisms living in the small intestine. Not everyone’s SIBO will manifest in the same way as no two people are the same. The bacteria present with SIBO can cause different issues, and you can have more than one at a time.

1 Fialho et al., 2016
2 Sharma and Kavuru, 2010