Most dieting and health advice focuses on losing fat, not gaining it. Accordingly, you may be at a loss for information about how to properly put on fat. Whether you’re gaining fat for health reasons or are an actor preparing for a movie role, there are safer and healthier ways to gain fat than not exercising and eating junk food. By following the correct regimen, you can gain the fat you want while maintaining your health.

Part 1 : Preparation:

Certain medical conditions will require you to keep your weight up. Thyroid problems, digestive health issues, diabetes, and cancers can all lead to severe weight loss that will endanger your health. Being underweight can lead to health risks like a weakened immune system, anemia, hair loss, and decreased bone density. Hence, it is advisable that you meet with your doctor before you start.
Very high physical activity can also cause you to be underweight. If you’re an athlete, gaining some fat would be good for you because it can increase your energy levels and allow you to workout for longer periods.
Set your goal.

You must ask yourself certain question like how much weight do you want to gain.  By when? By figuring this out and drawing up a schedule, you’ll be able to gain weight more effectively.

Start by figuring out how much weight you want to gain. This can either be a personal goal, or one you’ve worked out with your doctor. Either way, you need a concrete number in mind to start your progress so you don’t stop half way through
Remember, the basic way the body gains weight is when you take in more calories than you burn. So when drawing up your plan, you should figure out how much you need to eat every day to offset the amount of calories you burn. There are various ways to calculate this. Click here for a tool to estimate your daily calorie burn.
Plan to start slowly. Flooding your body with hundreds of more calories than it’s used to is dangerous for your heart, blood pressure, digestion, and other body systems. Work your way up gradually to acclimate your body to the increased caloric intake. This will help you avoid an initial shock when you start your weight-gain regimen. Break your weight-gain down into stages. Determine how much you would like to gain per week or month. That way, you can ease your body into the weight increase instead of starting off too quickly.
Just like with losing weight, gaining weight should come gradually. Gaining about 1 pound per week is a healthy way to go.
Draw up a meal plan. Since you are working on something, it would be important you have a meal plan. Focus on nutrient and calorie dense foods instead of junk food. There are plenty of foods that will help you gain weight and also contain all of the nutrients you need to stay healthy.

Plan on eating more than 3 meals a day. Increase your meals to 5 or more per day, plus snacks throughout the day.
Make sure all your meals have a good balance. Each meal should contain carbohydrates, protein, and unsaturated fats. These three nutrients will help most with your weight gain.
Eating more often and including healthy foods in your diet will get expensive. It would also be helpful if you drew up a new budget to go along with your new diet. This implies that getting fat isn’t for the poor man.