How are B12 and weight loss related?

Vitamin B12 is essential for energy metabolism and red blood cell formation, but the claim that B12 supplements directly cause weight loss is weakly supported by evidence. Some observational studies show an association between low B12 levels and higher BMI, but this may be due to confounding factors like poor diet or lack of exercise. B12 injections are often marketed as 'energy boosters' for weight loss, yet in people with adequate B12 levels, there is no robust evidence for weight reduction. Deficiency can cause fatigue, which might be mistaken for a slow metabolism; correcting a deficiency merely restores normal energy. Genetic variants like MTHFR C677T can affect B12 metabolism, but their impact on weight is indirect and individual. The evidence is mixed: plausible mechanisms exist, but no strong randomized trials prove causal weight loss. Those seeking weight loss should focus on balanced diet and exercise, not B12 supplements. Safety note: high-dose B12 is generally safe but unnecessary.