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, BMI of greater than 25 is considered overweight and greater than 30 is considered obese.
BMI scale only looks at weight and height. It does not take muscle mass into account. Some people are naturally very skinny but still healthy. Being underweight according to this scale does not necessarily mean that you have a health problem.
Being underweight is about 2–3 times more common among girls and women, compared to men. In the US for example, 1% of men and 2.4% of women 20 years and older are underweight.
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.
In comparison, obesity was associated with a 50% greater risk of early death, indicating that being underweight may be even worse for your health. Another study found an increased risk of early death in underweight men, but not women, suggesting that being underweight may be worse for men.
In addition, people who are underweight are much more likely to get sarcopenia (age-related muscle wasting) and may be at greater risk of dementia.
Conditions That 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.
- 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.
Infections: Certain infections can cause someone to become severely underweight. This includes parasites, tuberculosis and HIV/AIDS.
If you’re underweight, you may want to see a doctor to rule out any serious medical conditions. This is particularly important if you have recently started losing large amounts of weight without even trying.
How to Gain Weight the Healthy Way
There are plenty of normal-weight people who get type 2 diabetes, heart disease and other health problems often associated with obesity. Therefore, it’s absolutely essential to eat healthy foods and live an overall healthy lifestyle.
If you want to gain weight, it’s very important to do it right. You would want to gain a balanced amount of muscle mass and subcutaneous fat rather than a lot of unhealthy belly fat.
1. 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. If you want to gain weight slowly and steadily, aim for 300–500 calories more than you burn each day.
If you want to gain weight fast, aim for around 700–1,000 calories above your maintenance level.
2. 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.
However, keep in mind that protein is a double-edged sword. It’s also highly filling, which may reduce your hunger and appetite significantly, making it harder to get in enough calories. If you’re trying to gain weight, aim for 0.7–1 grams of protein per pound of body weight (1.5–2.2 grams of protein per kilogram).
3. Eat Plenty of Carbs and Fat
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. It is also a bad idea to do intermittent fasting. This is useful for weight loss and health improvement but can make it much harder to eat enough calories to gain weight.
Make sure to eat at least three meals per day and try to add in energy-dense snacks whenever possible.
4. 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.
Also, try to emphasize energy-dense foods as much as possible. These are foods that contain many calories relative to their weight.
Some energy-dense foods that are perfect for gaining weight include:
- 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.
5. 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.
You may also want to consult with a doctor if you have skeletal problems or any medical issue. Doing some cardio is fine to improve fitness and well-being, but don’t do so much that you end up burning all the additional calories you’re eating.