Hi.... Remember , if you want to put on weight and look fit, you need to build muscles not flab. Eat - Eggs, lean meat, fish, pulses, sprouts, and dairy products that rich sources of proteins. Fish such as tuna and mackerel are rich in oil and are one of the best ways to increase weight..... Whey protein is an increasingly popular supplement that you can add to your milk or smoothies.... It has certain limits.....