The modest multivitamin might be helping you stay lean. While it often gets beaten up by the mainstream media, an animal study conducted at two French research institutes points to new evidence that vitamin deficiencies can lead to unwanted weight gain. Scientists found that mice who were given the same number of calories over 12 weeks, but who were shortchanged on their vitamins, added more body fat than animals who received the same amount of calories but more vitamins. It seems the vitamin shortage made cells less sensitive to insulin and thus reduced fat-burning abilities in the deficient mice. A multivitamin may not seem like a sexy supplement, but there is good reason to keep it as part of your daily routine.