All oils and fats have fatty acids and that is why they are called oils or fats, but perhaps you are asking if mustard oil will make you fat in comparison to other oils?

If that is the question then, the answer is NO! Mustard oil does not make a person gain weight unless you are consuming fried foods made with mustard oil. Weight gain primarily is due to over-consumption of sugar and carbohydrates (example samosa, biscuits, Kachori, pasta, Noodles, ice creams, rice, bakery items, bread etc) and refined carbohydrates deep fried in oil is twice as bad for weight.