If you want to gain weight, you need to build an appetite; and while this might be a tad non-traditional, you can rely on wine as a hunger stimulant. A small glass of wine before your evening meal will help you appreciate your food a whole lot more. Also, avoid drinking water before meals and in between meals, you don't want to ruin your appetite.

Gradual weight gain is always advisable. An increase in 500 kcal per day can result in increasing the body weight by 0.5 kgs per week. Objective should be to restore a desirable weight/ ideal body weight according to one's age, gender and height. To rebuild body tissues, to maintain a good nutritional status and to maintain ideal body weight are a few reasons why healthy weight gain is important.

Inadequate feeding habits, prolonged meal time gaps, poor selection of foods, increased physical activity without increasing the food intake can lead to energy deficit, are a few of the major reasons for being underweight. Other reasons can be malabsorption due to prolonged illness, diseases such as tuberculosis, cancer, hormonal imbalances (hyperthyroidism) and eating disorders such as anorexia nervosa or bulimia.