If you're underweight, it can compromise your immune system, energy and quality of life. People with a body mass index of less than 20 are considered underweight, while a measurement of below 18.5 indicates a severe underweight status. Being too thin can compromise your immune system, your sports performance, your self-esteem, and, if you're a woman, your fertility. Gaining weight can help you look and feel healthier. Discuss your weight gain goals with your doctor, however. Too much weight gain in the form of fat can actually be deleterious to your health.
Better Quality of Life
An underweight status can be a sign that you're purposefully, or inadvertently, eating a diet that doesn't contain all the nutrients you need for good health and the calories necessary to maintain a healthy weight. The lack of these nutrients can make you feel weak and tired, and prevent your body from adequately fighting off infection. A meta-analysis published in the Journal of Epidemiology and Community Health in 2014 showed that being severely underweight almost doubles your risk of dying early.
By gaining weight with a balanced diet and a greater quantity of protein, vegetables, fruits, whole grains, dairy and healthy fats, you supply your body with the nutrients it needs. This can help ward off osteoporosis, which often results from deprivation of calcium, and iron-deficient anemia, resulting from too little iron. Pale, dull complexions and thinning hair will likely respond to better nutrition, too. Weight gain can improve your skin tone and give your hair more body, so you look healthier.
More Energy at a Healthy Weight
When you don't get all the calories you need, your body conserves energy to maintain the operation of essential functions -- such as the action of your internal organs and blood flow. This means you may feel more tired and listless when you're underweight. Gaining weight boosts your energy by giving your body the fuel it needs to operate optimally.
Gaining weight doesn't just help you gain more physical energy, but mental energy too. When you're underweight, the lack of nutrients can lead to brain fog, which makes it hard to focus on tasks.
Weight Gain May Improve Body Composition
If you're purposefully holding back on your calorie intake and exercising more at the gym, you may be missing out on the strong, fit, muscular physique you desire. To put quality effort into a workout, you must have some fuel. If you're eating too little and hoping to sculpt your physique by putting on lean muscle, your efforts may backfire. When you eat too little, your body actually starts using lean muscle for fuel and increases body fat as it senses starvation and wants to hold onto energy reserves. If you're too thin, you also can't develop the muscle you want to look fit and strong; you need excess energy, in the form of calories, to put on muscle, so a very calorie-restricted diet won't help. Gaining weight in the form of muscle improves your fat to muscle ratio so you look and feel healthier. Muscle is a far healthier, and more aesthetically pleasing tissue as compared to fat.
Sports Performance and Weight Gain
Being too thin means you don't have the muscle mass or energy to do your best in sports. Weight gain particularly benefits athletes who need power and strength, such as football or hockey players. Add muscle by slightly increasing your calorie intake by 250 to 500 calories per day, primarily with added protein, and participating in a regular weight-training routine at the gym. Some body types aren't destined to look like linebackers, but you can still add muscle so you're the healthiest possible for your shape.
Benefits for Fertility
Being underweight signals to a woman's body that it isn't a good time to reproduce. Your system senses that you might be experiencing a famine or that your body just isn't strong enough to support another life. When you have irregular or no menstruation, it's a sign that your body isn't producing enough of the female hormone estrogen, which is important to bone and sexual health. By gaining weight, you can restore normal hormonal function, which will help your periods return to normal, so it's easier to get pregnant.