Metformin timing and food intake
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Metformin Timing, Food Intake, and Appetite Suppression
Metformin Reduces Food Intake and Appetite
Multiple studies show that metformin can reduce food intake and suppress appetite in both humans and animal models. In women with obesity and type 2 diabetes, metformin given in the morning (either 850 mg or 1700 mg at 8:00 AM) led to a dose-dependent reduction in calorie intake and subjective hunger later in the day, with the higher dose having the strongest effect. This reduction in food intake was associated with significant weight loss over 24 weeks of treatment compared to placebo . Similar effects were observed in animal studies, where metformin treatment decreased food intake and body weight in mice and rats with obesity or diabetes Derkach2019Lv2012.
Mechanisms: Hypothalamic and Gut-Brain Pathways
Metformin’s appetite-suppressing effects are linked to changes in the brain and gut. In animal models, metformin was found in the cerebrospinal fluid after oral administration, indicating it can reach the brain. It reduced the expression of appetite-stimulating neuropeptides (like neuropeptide Y and agouti-related protein) in the hypothalamus, while increasing the activity of signaling pathways (such as STAT3) that are known to suppress appetite Derkach2019Lv2012. Metformin also increased the expression of genes related to satiety and improved leptin and insulin signaling in the hypothalamus, further contributing to reduced food intake .
Role of GDF15 and Lac-Phe in Food Intake Regulation
Recent research highlights the role of specific molecules in mediating metformin’s effects on appetite. Metformin increases levels of growth differentiation factor 15 (GDF15), a hormone that acts on the brainstem to reduce food intake and body weight. This effect has been confirmed in both humans and animals, and blocking GDF15 or its receptor prevents metformin’s impact on appetite and weight Zhang2023Coll2019. Additionally, metformin induces the production of N-lactoyl-phenylalanine (Lac-Phe), a metabolite that also suppresses appetite. Mice unable to produce Lac-Phe do not experience the appetite- and weight-lowering effects of metformin, and human studies support Lac-Phe’s role in mediating these effects .
Timing and Food Intake: Acute vs. Long-Term Effects
The timing of metformin administration can influence its effects on food intake. Acute administration (such as a single morning dose) can reduce appetite and calorie intake later in the day . However, long-term studies in people with type 2 diabetes found that while metformin prevented weight gain over several years, this effect was not explained by a sustained reduction in energy intake, suggesting other mechanisms may also contribute to weight control .
Gut Sensing and GDF15-Independent Pathways
Metformin also enhances the gut’s ability to sense nutrients, particularly lipids, which can suppress food intake through gut-brain signaling. In high-fat-fed rats, metformin improved the gut’s lipid sensing and reduced food intake independently of GDF15, indicating that multiple pathways are involved in metformin’s regulation of appetite .
Conclusion
Metformin reduces food intake and suppresses appetite through a combination of central (brain) and peripheral (gut and kidney) mechanisms. These include changes in hypothalamic signaling, increased production of appetite-suppressing molecules like GDF15 and Lac-Phe, and enhanced gut nutrient sensing. The timing of metformin administration can acutely reduce appetite, but long-term weight control may involve additional factors beyond reduced food intake. Overall, metformin’s effects on appetite and food intake are multifactorial and involve both direct and indirect pathways Lee1998Derkach2019Lv2012+6 MORE.
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