What types of foods are the best source of calories?

The answer to this question is

Healthy high-calorie foods include nuts, seeds, dark chocolate, dried fruit, avocados, whole grains, milk, dairy, eggs, fish, and meats. The amount of calories a person needs depends on their age, gender, activity level, and muscle mass.

Hope It Helps

You would modify how often you work out in reps and sets and also modify calorie intake