There are many causes that can lead to weight gain
Eat more but not properly, not enough and do not balance the components of energy, lack of nutrients.
There may be a lack of energy due to insufficient fat in the diet, this is the most concentrated energy supply, 1g of fat provides 9kcal, while 1g of protein or starch provides only 4kcal, so eat a lot. Sweets can not gain weight yet.
Some cases of eating foods that are energy rich but are poorly-hugely nutritious (such as candy snacks, poorly processed foods).
In addition, due to poor absorption, poor digestion. Common in people suffering from gastrointestinal diseases, disorders of absorption due to lack of enzymes, allergies ...; Due to helminth; Some people have high basic metabolism, so their energy needs are higher. While the current diet is only sufficient for the body to survive and for activities, not enough to gain weight.
To gain weight, you need to check and overcome the above causes (if any) and pay attention to proper nutrition and exercise.
Nutrition helps to gain weight:
Need to eat enough. One day there are 3 main meals (morning, afternoon, afternoon) with 4 food groups (sugar powder, protein, fat, vegetables and fruits).
Need to eat more than half the present - 1 cup of rice each meal. Should add 2 - 3 snacks in a day with milk, yogurt, potatoes, tea, beans ...
Keep drinking 2 cups of high-calorie milk every day.
Motor:
Should be active for 60 minutes in a day, at least 5 days a week. It's best to play your favorite sport often. Exercise will help improve health, help eat more delicious, develop lean muscle and healthy weight gain.
Limit alcohol, beer, cigarettes, keep spirit relaxed, get enough sleep (7 - 8 hours a day), do not stay up late. Remember to worm out every 6 months.