Definition

Being underweight is a condition where the ratio of body weight to height is disproportionate. This can be assessed using the Body Mass Index (BMI), which is calculated by dividing a person's weight (in kilograms) by the square of their height (in meters), or using an online BMI calculator.

For Asians, BMI categories are:

BMI measurement is an estimate of body composition, so that in some groups, such as athletes who have large muscle mass will have a large BMI value that does not really indicate their body mass. In addition, BMI measurements may also be less accurate in older people because over time they will experience muscle loss so that BMI may fall into the low category. 

It should be noted that BMI can be used as an initial screening tool but cannot be used as a diagnosis to measure an individual's body fat.

Causes

In addition to daily food intake, factors influencing body weight include:

• Genetics or family history

Some people have a genetically low BMI due to family history.

• High metabolism

Individuals with a high metabolism may struggle to gain weight despite consuming high-calorie foods.

• Physical activity

Athletes or people with high activity levels may burn many calories, leading to lower body weight.

• Chronic diseases

Conditions like nausea, vomiting, diarrhea, and appetite loss due to cancer, diabetes, thyroid disorders, or digestive issues (e.g., Crohn's disease) can lead to weight loss.

• Medications

Certain drugs can cause side effects like nausea and reduced appetite. Chemotherapy, for example, can lead to weight loss.

• Malnutrition

Inadequate consumption of balanced, nutritious foods or conditions that impair nutrient absorption can result in being underweight.

• Mental disorders

Disorders such as depression, anxiety, obsessive-compulsive disorder, and eating disorders like anorexia (obsession with thinness) and bulimia (purging food) can affect eating habits and weight.

Risk Factor

Risk factors for being underweight may include gender, age, birth weight, maternal BMI, and education level. Women are more prone to being underweight. Low maternal BMI can affect birth weight and childhood weight. Education level influences nutritional knowledge and dietary choices.

Symptoms

Symptoms associated with being underweight often correlate with causes such as malnutrition, manifesting as fatigue, frequent illness, irregular or absent menstrual cycles, hair thinning, dry skin, and dental issues. In addition, you may experience anemia and a decrease in immune function.

Other symptoms that may be measured through BMI calculations. Eating disorders can also cause thinness due to mental and dietary influences. The symptoms of eating disorders include suspicious behavior, sudden weight loss, unwillingness to attend family or social events, looking tired, and unwillingness to eat in front of others. If someone experiences these symptoms, friends or family should support them in seeking professional help from a doctor or therapist.

Diagnosis

The doctor will perform a physical examination, such as measuring your weight and height, to see your condition through BMI. The Centers for Disease Control and Prevention (CDC) recommends measuring a person's body mass index to categorize whether the patient is underweight, ideal or overweight.

BMI is considered a good measurement of a person's weight because it compares it to their height. More accurate measurements can use special tools that can measure body composition.

Management

If someone is underweight, some methods that can be suggested to gain weight are by eating a healthy diet that combines nutrients and dense calories. Your doctor may recommend that you consult a dietitian or nutritionist to help you manage your diet. Some key components to a weight gain diet include:

• Adding snacks

Small meals high in protein and whole carbohydrates, such as peanut butter crackers, protein bars, pita chips and hummus, or almonds.

• Eating smaller meals more often

Sometimes thin patients are unable to eat large meals, so an alternative is to eat smaller meals more frequently throughout the day.

• Adding extras

Additions to foods such as almonds in yogurt or sunflower seeds or chia seeds in salads or soups.

• Avoiding empty calories

High-calorie foods can cause weight gain, but they can also lead to excess fat, which can affect heart and blood vessel health. You should also avoid foods high in sugar and salt.

Complications

Not everyone experiences side effects or symptoms of being thin, but some people experience complications such as:

• In women with thin conditions have an increased risk of osteoporosis, where bones become more fragile and prone to fracture
• Disorders of the skin, hair or teeth. If someone does not get enough nutrition in their daily needs, the patient can experience physical symptoms such as thinning skin, hair loss, dry skin or poor dental health
• Immune system disorders so that they are more susceptible to illness
• Feeling tired all day
• Easily experiencing low blood pressure or anemia, which can cause dizziness, headaches and fatigue
• Irregular menstruation in women
• Premature birth
• Slow or impaired growth in children

Prevention

Maintaining a balanced, nutritious diet and regular exercise can help prevent being underweight. If there is a family history of being underweight, consult with a nutritionist for dietary recommendations.

When to See a Doctor?

Consult a doctor if you struggle to gain weight despite efforts or if you experience health issues such as missed menstrual cycles or infertility. Seek professional help if facing difficulties related to health or eating disorders.

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