Underweight: Symptoms, Types, Causes and Treatment

Underweight is a condition that's often overshadowed by the global focus on overweight and obesity, yet it carries significant health risks and impacts millions worldwide. Whether due to chronic disease, socioeconomic factors, or nutritional deficiencies, being underweight can lead to serious complications affecting both body and mind. In this article, we'll explore the symptoms, types, causes, and treatment strategies for underweight, drawing on the latest research to provide a comprehensive, evidence-based overview.

Symptoms of Underweight

Being underweight isn't just about numbers on a scale. It can have far-reaching effects on physical health, mental wellbeing, and overall quality of life. Recognizing the symptoms early is crucial for timely intervention and preventing complications.

Symptom	Physical/Mental	Description	Source(s)
Fatigue	Physical	Persistent tiredness, low energy	1,3
Depressed Mood	Mental	Feelings of sadness, low mood	1
Infertility	Physical	Reproductive health issues, especially in women	4
Muscle Wasting	Physical	Loss of muscle mass, weakness	3,5
Recurrent Illness	Physical	Increased susceptibility to infections	3
Psychomotor Issues	Physical/Mental	Slowed movements, coordination difficulties	1

Table 1: Key Symptoms

Physical Symptoms

Underweight individuals may notice a variety of physical symptoms:

• Fatigue and Low Energy: Chronic tiredness is common, often due to insufficient caloric and nutrient intake, leading to a lack of energy for daily activities 1,3.
• Muscle Wasting: Inadequate nutrition can cause the body to break down muscle tissue for energy, resulting in visible weakness and muscle loss 3,5.
• Recurrent Illness: Weak immune function, due to lack of essential vitamins and minerals, increases vulnerability to infections 3.
• Infertility and Menstrual Issues: In women, underweight status can disrupt hormonal balance, leading to missed periods or infertility 4.
• Delayed Healing: Wounds and infections may take longer to resolve due to impaired tissue repair mechanisms 3.

Mental and Emotional Symptoms

• Depressed Mood: Studies have found that underweight adults are more likely to experience depressive symptoms, such as persistent sadness and loss of interest 1.
• Psychomotor Difficulties: Slowed movements, restlessness, or coordination problems can also be present, sometimes linked to underlying neurological or nutritional issues 1.

How Symptoms Manifest

Symptoms can vary by age, gender, and underlying cause. For example:

• Children: Growth retardation, stunted development, and frequent illness are prominent 2,3.
• Adults: Fatigue, mood changes, and decreased productivity are common 1,3.
• Elderly: Increased frailty, risk of falls, and poor healing 3.

Recognizing these signs early aids in diagnosis and guides appropriate intervention.

Types of Underweight

Underweight isn't a one-size-fits-all diagnosis. It presents in various forms, depending on the underlying cause, duration, and population affected.

Type	Description	Population Most Affected	Source(s)
Wasting	Rapid weight loss, muscle and fat depletion	Children, elderly, ill	3
Stunting	Chronic low weight and height for age	Children (esp. <5 yrs)	2,3
Emaciation	Severe thinness with visible bone structure	All ages, critical illness	3,6
Anorexia Nervosa	Psychiatric eating disorder, extreme thinness	Adolescents, young adults	4

Table 2: Types of Underweight

Wasting

Wasting refers to acute malnutrition, where there's a rapid loss of weight and muscle mass. It’s especially common in children and the elderly during periods of illness, famine, or neglect 3.

Stunting

Stunting is characterized by low height and weight for age, reflecting chronic malnutrition over a prolonged period. It's a major issue in low- and middle-income countries, particularly affecting children under five 2,3.

Emaciation

Emaciation involves severe loss of both fat and muscle, leading to a skeletal appearance. It often results from prolonged starvation, chronic illness, or severe eating disorders, and can be life-threatening 3,6.

Anorexia Nervosa and Related Disorders

Anorexia nervosa is a psychiatric condition marked by an intense fear of weight gain and self-imposed starvation. It is the most common cause of underweight in adolescent girls and young women, but can affect all genders 4.

Other Forms

• Relative Energy Deficiency in Sport (RED-S): Seen in athletes who do not consume enough calories for their level of physical activity, resulting in underweight and hormonal disturbances 4.
• Disease-Related Underweight: Chronic diseases like cancer, Parkinson’s disease, and gastrointestinal disorders can cause unintentional weight loss and underweight status 5,6.

Understanding these types is crucial for tailored treatment and prevention strategies.

Causes of Underweight

The reasons why someone may become underweight are diverse and often interconnected. They range from medical conditions to socioeconomic and environmental factors.

Cause	Category	Key Details	Source(s)
Inadequate Intake	Dietary	Poor appetite, dietary restrictions	3,4
Chronic Illness	Medical	Cancer, chronic infections, Parkinson’s	3,5
Socioeconomic Status	Environmental	Poverty, food insecurity, low education	2,3
Eating Disorders	Psychiatric	Anorexia nervosa, bulimia	4
Malabsorption	Medical	Digestive disorders, nutrient loss	3
Increased Needs	Physiological	Pregnancy, growth, high physical activity	3,4
Gut Microbiota	Biological	Altered gut bacteria, inflammation	5

Table 3: Common Causes of Underweight

Inadequate Nutritional Intake

A primary cause is simply not eating enough calories or essential nutrients. This can result from:

• Poor appetite (due to illness or medication)
• Restrictive diets (intentional or unintentional)
• Lack of access to nutritious food 3,4

Chronic and Acute Illnesses

Certain diseases increase the risk of underweight by:

• Raising metabolic needs (e.g., infections, cancer)
• Causing malabsorption (e.g., gastrointestinal diseases)
• Leading to unintentional weight loss (e.g., Parkinson’s disease, as up to half of PD patients experience underweight due in part to changes in the gut microbiome) 3,5

Socioeconomic and Environmental Factors

Underweight is strongly linked to poverty, low parental education, and food insecurity. In some countries, children in poorer households and those with less-educated parents are significantly more likely to be underweight or severely underweight 2. Other contributing factors include:

• Living in regions with high food insecurity
• Large household sizes
• Inadequate access to iodized salt and other micronutrients 2

Eating Disorders and Psychiatric Causes

Anorexia nervosa and other eating disorders are prominent causes of underweight in adolescents and young adults. These conditions often require specialized psychiatric care 4.

Physiological and Biological Factors

• Increased Needs: Pregnancy, lactation, growth spurts, or high physical activity can increase caloric requirements, and if these aren't met, underweight may result 3,4.
• Gut Microbiota: Alterations in the gut bacterial environment, particularly in diseases like Parkinson’s, can mediate up to 40% of the effect of disease on underweight by increasing inflammation and disrupting appetite regulation 5.

Malabsorption Syndromes

Conditions that impair the body’s ability to absorb nutrients, such as celiac disease or chronic diarrhea, can also lead to underweight status 3.

Treatment of Underweight

Effectively addressing underweight requires a personalized, multidisciplinary approach that targets the root cause and supports overall health.

Treatment Approach	Focus Area	Typical Interventions	Source(s)
Nutritional Therapy	Diet and Supplementation	Caloric/protein increase, supplements	3,6
Medical Management	Underlying Illness	Treat infections, hormone therapy	4,5
Psychiatric Support	Mental Health	Counseling, medication (e.g., antidepressants)	4
Socioeconomic Support	Food Security	Food programs, education, community support	2,3

Table 4: Major Treatment Strategies

Nutritional Therapy

Increasing caloric and protein intake is foundational. This may involve:

• High-calorie, nutrient-rich foods
• Oral nutritional supplements
• Enteral (tube feeding) or parenteral (IV) nutrition in severe cases 3,6

Critically ill underweight patients may benefit from early nutritional support, though its impact on survival may depend on the severity of their illness 6.

Medical Management

Treating underlying diseases (e.g., infections, endocrine disorders, gastrointestinal issues) is crucial. For women experiencing infertility due to underweight, restoring energy balance can help normalize reproductive hormones, while medications such as leptin or psychiatric drugs may be used if nutritional and lifestyle interventions are insufficient 4.

In Parkinson’s disease, interventions may include targeting gut microbiota through dietary changes or probiotics, though research is ongoing 5.

Psychiatric and Psychological Interventions

Patients with eating disorders or depression often require:

• Cognitive-behavioral therapy (CBT)
• Family-based therapy
• Medication (antidepressants, antipsychotics) 4

Psychiatric care is an integral aspect of restoring healthy weight, particularly in cases where emotional or behavioral issues underpin underweight status.

Socioeconomic and Community Support

Addressing poverty, food insecurity, and lack of education is essential. Approaches include:

• Food supplementation programs
• School feeding initiatives
• Education on nutrition and health 2,3

Community-based interventions are especially important in low- and middle-income countries, where underweight remains a public health crisis.

Multidisciplinary Care

Given the complexity of underweight, optimal care often involves:

• Physicians
• Nutritionists/dietitians
• Mental health professionals
• Social workers 3,4

This collaborative model ensures that both the physical and psychological aspects of underweight are addressed.

Conclusion

Underweight is a multifaceted health issue with significant physical, psychological, and social consequences. While less discussed than obesity, its impact can be just as severe—especially for vulnerable populations like children, the elderly, and those with chronic illness or socioeconomic disadvantage.

Key takeaways:

• Underweight manifests in diverse symptoms, including fatigue, depressive mood, infertility, and increased illness risk.
• Types of underweight include wasting, stunting, emaciation, and psychiatric conditions like anorexia nervosa.
• Causes are varied, encompassing inadequate intake, chronic illnesses, socioeconomic factors, eating disorders, biological influences, and malabsorption.
• Effective treatment requires a personalized, multidisciplinary approach, combining nutritional, medical, psychiatric, and community-based strategies.

Awareness, early detection, and comprehensive care are essential to tackling underweight and improving the lives of those affected.