Being underweight can happen for a variety of reasons. Many factors play a role in determining a healthy weight, including age, gender, height, metabolism, and genetics. While some people are naturally skinny and struggle to gain weight, being underweight can also be the result of an underlying medical issue or eating disorder. Understanding the potential causes and health risks of being underweight is important. With the right support and treatment plan, many underweight individuals can reach and maintain a healthy weight.
What causes someone to be underweight?
There are several factors that may lead someone to be underweight:
Fast metabolism
Some people simply have a faster metabolism that burns calories at a quicker rate. This can make it difficult to keep weight on. Teenagers and young adults often have faster metabolisms as their bodies are still developing. Metabolism tends to slow down with age.
Small appetite or eating habits
Lack of appetite or small portion sizes at meals can result in low calorie intake. Some underweight people get full quickly and don’t feel the need to eat more. Eating disorders like anorexia nervosa severely restrict food intake and lead to dangerous weight loss.
Hyperthyroidism
An overactive thyroid gland (hyperthyroidism) can raise metabolism and cause unintended weight loss. Other symptoms include racing heartbeat, anxiety, tremors, and frequent bowel movements. Hyperthyroidism should be diagnosed and treated by a medical professional.
Celiac disease
Inability to absorb nutrients from food due to celiac disease can lead to malnutrition and weight loss. Following a strict gluten-free diet is the main treatment.
Diabetes
Poorly managed diabetes can interfere with the body’s ability to regulate blood sugar levels and utilize energy from food. Unexplained weight loss may be a warning sign of diabetes.
Genetics
Some people are simply predisposed to being thin. Having a naturally fast metabolism and slender build runs in families. As long as their weight is stable and growth/development is normal, genetically slender individuals are likely healthy.
Other medical conditions
Digestive disorders, cancer, autoimmune diseases like HIV/AIDS, kidney or liver disease, and other chronic illnesses can sometimes cause weight loss and being underweight. Treatment plans should be customized for the individual’s medical needs.
What are the health risks of being underweight?
Being underweight comes with the following health risks:
Weakened immune system
Not getting adequate calories and nutrients can weaken the immune system and make underweight people more prone to infections.
Anemia
Lack of iron, folate, vitamin B12 can lead to anemia, a condition characterized by fewer red blood cells transporting oxygen through the body. Symptoms of anemia include fatigue, pale skin, dizziness, and shortness of breath.
Osteoporosis
Low body weight often correlates with lower bone mineral density. Weak and brittle bones (osteoporosis) are more susceptible to fractures.
Organ failure
Heart, lung, kidney and other major organ problems can occur when the body lacks sufficient nutrients for prolonged periods of time.
Fertility issues
Women who are underweight may stop ovulating and have irregular periods, leading to reduced fertility. Restoring a healthy weight can help some women conceive.
Mood disorders
Anxiety, depression, and other mental health conditions occur more often in people who are underweight, especially those with eating disorders. Getting mental health treatment is important.
Higher mortality risk
Being underweight raises the risk of dying prematurely, especially when caused by disease. Carrying extra weight as muscle or fat reserves helps the body endure illness and trauma.
Determining if you are underweight
Body mass index (BMI) is a common screening tool for determining if a person’s weight is in a healthy range. It measures weight in relation to height.
For adults 20 years and older:
| BMI | Weight status |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Normal weight |
| 25.0–29.9 | Overweight |
| 30.0 and above | Obese |
However, BMI is not a perfect measure. Very muscular athletes may have BMIs in the overweight or obese range without added health risks. Older adults tend to have more body fat at a given BMI compared to younger people. A medical provider can evaluate your growth charts, weight history, diet, symptoms, and family medical history to determine if your weight is unhealthy.
Gaining weight in a healthy way
If you have unintentionally lost weight or are underweight, your doctor can help figure out the cause and advise you on a treatment plan. Here are some tips for gaining weight safely:
Eat more frequently
Eat larger portions by adding extra servings at meals. Also eat calorie-dense healthy snacks between meals, like nuts, seeds, dried fruit, peanut butter, hummus, avocado and cheese.
Drink high-calorie beverages
In addition to water, drink milk, fortified plant milks, juices, smoothies and protein shakes to boost calorie intake. Avoid excessive soda and sweetened coffee drinks high in sugar.
Choose calorie-rich foods
Select foods higher in healthy fats and protein like fatty fish, beans, eggs, nuts, seeds, avocados, and yogurt. Go for whole grains over refined carbs when possible.
Exercise and build muscle
Strength training helps build muscle mass which supports metabolism and burns calories. However, don’t over-exercise as this can hinder weight gain.
Keep a food diary
Writing down meals and snacks can help identify gaps where you can add more calories. Share this info with your doctor or dietitian.
Consider supplements
Your doctor may recommend supplements like protein powder, vitamins, zinc or iron if blood tests indicate nutritional deficiencies contributing to weight loss.
Get support
An eating disorder, depression or other illness may require therapy, medication or inpatient treatment. Having social support makes the process easier.
Gaining weight steadily through balanced nutrition and some strength training is ideal. Aim to gain 1-2 pounds per week. Stay in touch with your medical team to ensure you are improving any underlying conditions.
When to see a doctor
Consult a doctor or dietitian if:
– Your BMI is under 18.5
– You have experienced rapid unintentional weight loss
– Weight loss is impacting your daily function
– You miss or avoid meals and restrict food intake
– You exercise excessively as a means of losing weight
– You have symptoms of anemia, thyroid issues, diabetes or other illnesses
– You have a history of eating disorders
– You feel anxious, depressed or dissatisfied with your body shape
Medical supervision ensures weight is restored safely and healthfully. Don’t try quick fixes like crash dieting or overeating junk foods to gain weight back. Get personalized advice tailored to your needs.
Conclusion
Being underweight can happen due to genetics, illness or problematic eating habits. The health consequences range from fatigue and fragile bones to organ damage in severe cases. Restoring a healthy weight minimizes these risks and improves wellbeing. Work with your healthcare providers to set reasonable weight goals through a nutritious diet, and medical or mental health support if needed. Consistency is key – pace yourself by making gradual lifestyle changes that can be maintained long-term.