How to gain weight healthily?

To gain weight, your body has to be in a calorie surplus. To do that, you have to consume 300-500 calories over your maintenance calorie level. 300 is generally the accepted amount to properly gain .5lb/week, and 500 for 1lb/week.

How that works is, eating 500 calories over maintenance every day, creates a surplus of 3,500 calories at the end of the week. Scientifically, one pound of fat is 3,500 calories, and a pound of muscle is 2,500 calories. Combined with exercise, you can still gain muscle, but be aware that the weight you gain will be a combination of muscle, fat, and water weight.

Easy way of gaining weight: 1-1.5g of protein/lb. - Protein provides nutrients for the body to maintain muscle and also to grow it. 1-3g of carbs/lb. - Provides really efficient and easily digested energy. 0.3-1g of fat/lb. - Sustains proper insulin levels, hormone function, and sex drive. 300-500+ calories over your maintenance.

You can eat pizzas, ice cream, sodas and whatnot, if they somehow fit into your macronutrient (protein/fat/carb) and calorie goal. Also, the body doesn’t care if you ate 2 meals or 20 meals, as long as you reach your calorie and nutrient goal at the end of the day, you will gain weight. Generally, I’d suggest 3-8 meals a day because smaller meals feel more satiating than larger ones, but if you can only eat 3-4 meals in your schedule, then build your diet based around eating 3-4 meals. Meal frequency only makes a small difference, and that difference is only aimed towards elite athletes who have trained for more than 10 years.