Why are some people underweight?

1. They could be short. If a person is not too tall, there's literally less of that person - at least vertically. That equals fewer pounds when he or she steps on the scale.
2. They're small-framed or small-boned as some people like to call it. It just means that a person's skeleton and muscles might be smaller or thinner. One way to compare frames is to look at your wrist.
3. If we are talking about kids, they often feel thin compared with friends who've gone through puberty. During puberty, it's normal for kids to grow a lot and gain weight, too.  
4. The big part of weight perspective is inherited. This means that parents pass along their genes to their children - including the genes that help determine your height and body frame. If close family members are on the small or thin side, there's a good chance you will be too.

Eating Strategies to Gain Weight

It is proven that about the intake of about 3500 calories is needed to gain one pound. That means, in order to gain one pound a week, you have to consume 500 extra calories every day.

Here are some tips for getting those extra calories into your daily meal plan.

• Eat frequently! - Make time for 3 large meals and 2-3 hefty snacks every day.
• Eat portions that are larger than norma at meals.
• Eat high-calorie foods. Choose dried fruit, starchy vegetables, dense whole grain breads and cereals, hearty bean soups, nuts.
• Add lots of “extras” to food. Don’t eat anything plain.
• Add healthy unsaturated fats: olive and canola oil, nuts, seeds, peanut butter, avocados.
• Add healthy carbs and protein: honey, jam, dried fruit, wheat germ, nonfat dried milk powder, soy protein powder.
• Make beverages count. - Drink shakes, milk, juice, etc. instead of water, coffee, tea, and diet sodas.
• Do resistance exercises. - Weight training helps convert the extra calories into muscle rather than flab. Aim for 2-3 times per week.