Considering that (i) obesity is a known chronic low-grade inflammatory condition (48) and (ii) our results show proinflammatory adipocytokines, such as TNF-α and IL-6, are significantly increased as early as 4 weeks of feeding vitamin B12 deficient diet, suggesting that severe vitamin B12 deficiency in early life may increase the animal’s vulnerability to obesity. Here, TNF is linked to obesity due to melanocortin 4 receptor deficiency.