A disruption in normal metabolism can lead your body to store more fat as it attempts to develop energy reserves
Vegans, vegetarians, people over the age 50, anyone with stomach/bowel issues like chronic gastritis, leaky gut, IBS or celiac, and anyone who regularly takes medications such as Metformin, PPIs (used for GERD), H2 Receptor Antagonists (used for peptic ulcers), or anything that interferes with stomach acid production are actually at risk for vitamin B12 deficiency, and should supplement B12 regularly
They may help with injury recovery, immune function, soft tissue repair, nerve regeneration, brain tissue repair, heart health, and more
So, why then would it be surprising that people with low B12 tend to be more overweight
Zhong, Nanosuspension drug delivery system: preparation, characterization, postproduction processing, dosage form, and application, in Nanostructures for Drug Delivery, Elsevier, 2017, pp