The best foods for weight gain usually contain plant and animal protein, fats and oils, complex carbohydrates, and dairy products made with whole milk. What you should eat, however, depends on your specific weight and health goals. <br>For some people, gaining weight or adding muscle can feel as difficult as losing weight is for others. <br>For weight gain, you need to try to take in more calories than you burn throughout the day by eating many frequent, smaller meals.