There are different people with different needs. I know someone who used to take vitamins to gain weight. She has always been thin and in fact always been underweight ever since forever. She has problems eating not to the point of being anorexic though she sometimes eat so much and sometime eat nothing or shall I say not like normal people do because she loses her appetite fast. They say that she needs to take vitamins to be healthier. I think everyone needs vitamins not just to gain weight but to be healthier.