The relationship between metformin and weight is unclear, but several theories provide possible explanations for weight fluctuations.
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It Reduces Appetite, Possibly by Increasing Appetite-Suppressing Hormones
Research suggests that patients on metformin may have higher levels of an “anti-hunger” molecule called lac-phe in their bodies. It causes appetite loss and, in turn, weight loss from eating less at mealtimes.
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Metformin also boosts levels of the appetite-suppressing molecules GLP-1 and PYY, which signal fullness.
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It Limits Liver Glucose Production and Improves Insulin Sensitivity
Metformin is the most common treatment for type 2 diabetes because it mainly acts by lowering the amount of glucose released by the liver, according to Minisha Sood, MD, a board-certified endocrinologist in New York City.
Dr. Sood adds that this helps insulin to work more efficiently.
“When insulin works better — and insulin sensitivity improves — a person’s insulin levels are lower than they would be otherwise,” she says, adding that this is key for weight loss and weight management.
It May Trigger Changes in the Gut Microbiome
Research suggests metformin may also lead to weight loss as a result of shifts in the gut microbiome and reversal of metabolic changes that usually happen with age. Its effects on the microbiome are still being explored, but it may boost dozens of bacteria that regulate levels of inflammation, metabolism, and glucose production.
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Side Effects Like Nausea and Diarrhea May Curb Food Intake
The gastrointestinal side effects of metformin may directly or indirectly affect appetite.
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