A person can gain weight fast by adding 500 calories to a daily diet, eating 180 grams of protein each day, consuming high quality carbohydrates and ensuring that 20 percent of calorie intake comes from healthy fats. Junk food can account for anywhere from 10 to 25 percent of a person's diet.
The average calorie intake for protein is 150 grams a day, but consuming 180 grams each day or more may be necessary for people who are underweight. Protein-based foods also decrease heavy reliance on carbs. A 20 percent fat intake is a minimum recommendation, but increasing that amount to 40 percent is a better route for people who want faster results.
Dieters should see results in two weeks, but the weight gained during that period is most likely water weight. During the next three or four weeks, adding 750 calories to a diet is the best way to gain more weight if weight loss occurs. The addition of 500 calories each day is reserved for those whose weight gain is going steady. Adding 250 calories is for people who are gaining weight slowly. For example, people gaining 2 pounds each month should stick with the 250-calorie plan. Steady weight gain does not require additional calories, and those who gain weight too fast should cut their daily calorie levels by 250.