You can take supplements, however, you would benefit more from the foods you eat. Suggest eating a moderate fat
diet to gain weight slowly,
protein (amino acids) and eat healthy. Moderate fat diet means = use polyunsaturated (omega 3, corn oil, nuts, etc) fats and monounsaturated (olive oil, canola oil, peanut oil, etc) fats, no saturated fats (high fat snack foods, butter, fat spreads) and no trans fats.