Being underweight is defined as having a body mass index (BMI) below 18.5. This is estimated to be less than the body mass needed to sustain optimal health.
Conversely, over 25 is considered overweight and over 30 is considered obese.
Use this calculatorTrusted Source to see where you fit on the BMI scale (opens in a new tab).
However, keep in mind that there are many problems with the BMI scale, which only looks at weight and height. It does not take muscle mass into account.
What Are the Health Consequences of Being Underweight?
Obesity is currently one of the world’s biggest health problems.
However, being underweight may be just as bad for your health. According to one study, being underweight was associated with a 140% greater risk of early death in men, and 100% in women (3Trusted Source).
In comparison, obesity was associated with a 50% greater risk of early death, indicating that being underweight may be even worse for your heal
Several Things Can Cause Someone to Become Underweight
There are several medical conditions that can cause unhealthy weight loss, including:
- Eating disorders: This includes anorexia nervosa, a serious mental disorder.
- Thyroid problems: Having an overactive thyroid (hyperthyroidism) can boost metabolism and cause unhealthy weight loss.
- Celiac disease: The most severe form of gluten intolerance. Most people with celiac disease don’t know that they have it (10Trusted Source).
- Diabetes: Having uncontrolled diabetes (mainly type 1) can lead to severe weight loss.
- Cancer: Cancerous tumors often burn large amounts of calories and can cause someone to lose a lot of weight.
How to Gain Weight the Healthy Way
If you want to gain weight, it’s very important to do it right.
Binging on soda and donuts may help you gain weight, but it can destroy your health at the same time.
If you’re underweight, you want to gain a balanced amount of muscle mass and subcutaneous fat rather than a lot of unhealthy belly fat.
Eat More Calories Than Your Body Burns
The most important thing you can do to gain weight is to create a calorie surplus, meaning you eat more calories than your body needs.
You can determine your calorie needs using this calorie calculator.
If you want to gain weight slowly and steadily, aim for 300–500 calories more than you burn each day according to the calculator.
If you want to gain weight fast, aim for around 700–1,000 calories above your maintenance level.
Eat Plenty of Protein
The single most important nutrient for gaining healthy weight is protein.
Muscle is made of protein and without it most of those extra calories may end up as body fat.
Studies show that during periods of overfeeding, a high-protein diet causes many of the extra calories to be turned into muscle (12Trusted Source).
Fill up on Plenty of Carbs and Fat and Eat at Least 3 Times per Day
Many people try restricting either carbs or fat when trying to lose weight.
This is a bad idea if your goal is to gain weight, as it will make it harder to get in enough calories.
Eat plenty of high-carb and high-fat foods if weight gain is a priority for you. It is best to eat plenty of protein, fat and carbs at each meal.
Eat Energy-Dense Foods and Use Sauces, Spices and Condiments
Again, it’s very important to eat mostly whole, single-ingredient foods.
The problem is that these foods tend to be more filling than processed junk foods, making it harder to get in enough calories.
Using plenty of spices, sauces and condiments can help with this. The tastier your food is, the easier it is to eat a lot of it.
- Nuts: Almonds, walnuts, macadamia nuts, peanuts, etc.
- Dried fruit: Raisins, dates, prunes and others.
- High-fat dairy: Whole milk, full-fat yogurt, cheese, cream.
- Fats and oils: Extra virgin olive oil and avocado oil.
- Grains: Whole grains like oats and brown rice.
- Meat: Chicken, beef, pork, lamb, etc. Choose fattier cuts.
- Tubers: Potatoes, sweet potatoes and yams.
- Dark chocolate, avocados, peanut butter, coconut milk, granola, trail mixes.
Lift Heavy Weights and Improve Your Strength
To make sure that the excess calories go to your muscles instead of just your fat cells, it’s absolutely crucial to lift weights.
Go to a gym and lift 2–4 times per week. Lift heavy and try to increase the weights and volume over time.
If you’re completely out of shape or new to training, consider hiring a qualified personal trainer to help you get started.
10 More Tips to Gain Weight
- Don’t drink water before meals. This can fill your stomach and make it harder to get in enough calories.
- Eat more often. Squeeze in an additional meal or snack whenever you can, such as before bed.
- Drink milk. Drinking whole milk to quench thirst is a simple way to get in more high-quality protein and calories.
- Try weight gainer shakes. If you’re really struggling then you can try weight gainer shakes. These are