There is no scientific evidence that any vitamins lead to weight gain, as reported by the Dana Farber Cancer Institute. However, taking a daily multivitamin can ensure that an individual gets balanced nutrients to support healthy weight gain, according to the Center for Young Women's Health.
To gain weight, an individual must consume more calories than he expends, explains WebMD. This should be achieved by eating foods that are high in both calories and nutrients. Each meal or snack should contain protein, starch, fruits or vegetables and fat. A turkey and tomato sandwich on whole grain bread with mayonnaise added for fat and a fruit smoothie is an example of a balanced, calorie-rich meal. Eating meals like this six times per day can encourage healthy weight gain of up to a pound per week.
The highest-calorie foods are fats. Foods rich in healthy fats include avocados, nuts, seeds, peanut butter and vegetable oils. Animal-based fats are calorie-rich as well, but they should be limited if high cholesterol is an issue, according to WebMD. To build muscle, strength training should be added and additional protein must be consumed. High-calorie protein shakes and nutritional bars are a good source of additional protein.