The deficiency of b12 leads to little bumps over the tongue, a few of which contain taste buds. This is why B12 deficient people experience a decreased appetite and hence weight loss. However, when you take supplements of this vitamin, the levels normalize, and the appetite returns. Vitamin B12 can be received from many natural food items but even if you take enough of it and your body does not absorb it, it is of no use. Conditions like digestive disorders and old age restrict absorption. So, go for supplements as per your doctor’s suggestions.