We speak of underweight when someone weighs less than is good for his or her health. Being underweight entails risks, such as fatigue and reduced mental and physical fitness. Someone who is underweight feels tired and lethargic more quickly. Underweight people are more likely to develop osteoporosis and, as a result, bone fractures. Being underweight can have many causes. In the treatment of underweight, the cause must first be removed, which can be physical or psychological, for example. Together with a dietician, a suitable way can then be found to (re)build a healthy and nutritious diet.

• What is underweight?

• Definition
• BMI

• Underweight calculation
• Symptoms and signs of being underweight
• Causes of being underweight

• Starvation
• Physical ailments
• Frequent exercise
• Mental illnesses
• Family history
• A high metabolism

• Consequences of being underweight

• Osteoporosis
• Skin, hair or dental problems
• Getting sick regularly
• Constantly feeling tired
• Anemia
• Irregular menstruation
• Premature birth
• Slow or reduced growth
• Increased risk of death

• When to consult a doctor?
• Underweight treatment

• Treat underlying cause
• Nutrition plan
• Eating regularly
• Tube feeding

• Prognosis
• Underweight in children

 What is underweight? / Source: Istock.com/VladimirFLoyd

What is underweight?

Definition

One speaks of underweight when a body weight is less than can be considered healthy based on body height. That sounds quite subjective, but there is a generally accepted standard for determining whether someone’s weight is healthy: your BMI.

BMI

The Body Mass Index (BMI), also called the Quetelet index (QI), is an index for weight in relation to height and provides an estimate of the health risk of body weight. The weight in kilos must be divided by the squared height in meters. If the result is below 18.5, it is said to be underweight. In that case, a person weighs less than is healthy for him given his height.

Underweight calculation

Body weight is – as noted above – calculated using the Quetelet index, where body weight (e.g. 90 kg) is divided by the square of the body height (e.g. 1.90 x 1.90 m). The Quetelet index in this case is 90 divided by 3.61 is 24.9. A Quetelet index of 18.5 to 25 is considered normal for both women and men. The BMI is divided into the categories underweight, overweight and seriously overweight:

 Underweight according to BMI (white part indicates underweight) / Source: Created by InvictaHOG using gnuplot and Adobe Illustrator 92306, released into public domain, Wikimedia Commons (Public domain)

Symptoms and signs of being underweight

Someone who is underweight will have difficulty functioning properly. His physical and mental condition and stamina deteriorate and he may become dizzy. There is also destruction of the body’s own tissues. First the body consumes its fat reserves and then the other tissues, such as muscles, liver, kidneys, heart and nervous tissue. Slimming occurs and the skin becomes thin, dry and cold to the touch. The hair also feels dry and may fall out. Heart palpitations and sleep problems can also occur if you are underweight. Furthermore, sexual desires disappear. In addition, the intestines become ‘lazy’, making bowel movements difficult and slow. The person has protruding bones and if he or she is very overweight, organ functions are affected. Someone can even die from it.In young people, being underweight can cause osteoporosis (bone decalcification). In women it can lead to amenorrhea (absence of at least 3 menstrual periods during childbearing age) and complications during pregnancy.

Causes of being underweight

Possible causes of being underweight include:

Starvation

Malnutrition due to ingestion of insufficient food (starvation).

Physical ailments

lPhysical conditions, such as gastrointestinal infections, COPD, exhausting chronic infectious diseases, metastatic cancer, stroke, severe burns, chronic diarrhea, hyperthyroidism (overactive thyroid gland).Underweight due to intensive exercise / Source: Istock.com/Martinan

Frequent exercise

Athletes or people who exercise a lot, such as runners, can burn significant amounts of calories resulting in a low body weight.

Mental illnesses

mental disorders, including the eating disorder Anorexia nervosa, dementia, personality disorders in which someone feels neglectful.

Family history

Some people have a naturally low BMI due to physical characteristics that run in their family.

A high metabolism

If you have a high metabolism, you often have difficulty gaining weight, even when eating energy-rich foods.

Consequences of being underweight

Being underweight can cause health problems, just as being overweight can. Not all underweight people experience adverse effects. However, some people experience one or more of the following complaints associated with being underweight:Process of osteoporosis / Source: Blausen.com, Wikimedia Commons (CC BY-3.0)

Osteoporosis

Being underweight increases a woman’s risk of osteoporosis, which makes bones brittle and more prone to fractures.

Skin, hair or dental problems

If you don’t get enough nutrients in your daily diet, you may experience thinning skin, hair loss, dry skin or poor dental health.

Getting sick regularly

If you don’t get enough energy from your diet to maintain a healthy body weight, you may not get enough nutrients to effectively fight infections. As a result, you may get sick more often, and common illnesses, such as colds, may last longer than normal.

Constantly feeling tired

If you don’t consume enough calories to maintain a healthy weight, you may feel constantly tired.Headache due to anemia and underweight / Source: Andresr/Shutterstock.com

Anemia

A person who is underweight is more likely to have a low blood cell count, known as anemia, which causes dizziness, headaches and fatigue.

Irregular menstruation

Underweight women may not have regular periods, menstruation may stop altogether, or a teenage girl’s first period may be delayed or absent altogether. Irregular or absent menstruation can cause infertility.

Premature birth

A woman who is pregnant and underweight is at a higher risk of preterm labor, meaning she delivers her baby before 37 weeks of pregnancy.

Slow or reduced growth

Young people need nutrients to grow and develop healthy bones. Being underweight and not consuming enough calories could mean that someone is not developing properly.

Increased risk of death

Being underweight is associated with an increased risk of mortality compared to people with an average BMI. Being underweight affects the healing processes after an accident or trauma.Call a doctor if you are underweight / Source: Syda Productions/Shutterstock.com

When to consult a doctor?

Consult your doctor if you have tried to gain weight but have not been successful. Anyone who experiences the negative consequences of being underweight to a greater or lesser extent because they are unable to gain weight, such as missed periods or infertility or other health problems, would be wise to visit their doctor.If you are struggling with a mental illness or an eating disorder, it is important that you get professional help. Unfortunately, a person does not always recognize that his behavior is a problem. Some of the symptoms associated with eating disorders include:

• secretive behavior
• sudden, unexplained weight loss
• refusal to attend family or social events
• always seem tired
• refusing to eat in the presence of others

If a person exhibits these symptoms, his or her friends or family members should encourage him or her to seek professional help from their doctor. This person can refer him or her to a mental health care institution.

Underweight treatment

Treat underlying cause

To adequately treat underweight, it is first important to find out what the cause is. If there is a physical or psychological cause, treatment will focus on that. Someone who is underweight can receive further assistance from a dietician.Preparing healthy food / Source: Gpointstudio/Shutterstock.com

Nutrition plan

An underweight person should try to maintain the daily recommended amounts of food. For women, a minimum calorie intake of 2300 Kcal applies. and for men 2500. Underweight people can increase their body weight by having a healthy snack more often between the three main meals. This could include a bowl of yoghurt with fruit, a sandwich with lean toppings or a fruit salad. Other healthy snacks include vegetable soup, a muesli bun, apple-raisin cakes and muesli bars.

Eating regularly

When managing and gaining weight, regularity is essential. Eat at regular times (three meals a day) and take your time to eat; don’t do this in a hurry. Eat and chew calmly and ensure sufficient rest and relaxation. Also, one should not eat fatty products to gain weight. It is important that someone who is underweight also gets the right nutrients. Make sure you get enough proteins, vitamins and minerals. It may help to have a cup of broth or tomato juice half an hour before meals, as this stimulates the appetite.

Tube feeding

If you are seriously underweight, it may be necessary to give someone a tube feeding. This is artificial food that is delivered directly into the stomach through a plastic tube via the nose and throat.

Prognosis

An underweight person may be at increased risk of developing complications, including bone, dental and fertility problems. You should aim to maintain a healthy BMI. If for some reason you are unable to do this, contact your doctor.

Underweight in children

There can be various causes when a child is underweight, both serious – an illness or an eating problem – and less serious, such as being a fussy or small eater, a lot of physical activity, not eating anything and/or growing very quickly. A child can sometimes eat a lot of healthy food and still be underweight. But a child can also eat poorly or unhealthy food or eat (a lot of) sweets.A child who does not consume enough food will be tired more quickly and have less energy. His condition deteriorates and his resistance deteriorates. If you are seriously underweight, the risk of osteoporosis and bone fractures also increases.Provide healthy and nutritious meals. Also make sure that the child eats regularly. For example, give an extra sandwich in between. If necessary, consult an expert (for example your GP) to see what options are available to help the child gain weight.TNO has developed a special BMI meter for children , the LukaRotor . Based on the age, height, weight and gender of the child, the LukaRotor calculates in which BMI class the child falls. There are 7 BMI classes: two for underweight, one for normal weight, one for overweight, and three for obesity. 

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