| Underweight | |
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| The underweight range according to the body mass index (BMI) is the white area on the chart. | |
| Specialty | Endocrinology |
| Part of a series on |
| Human body weight |
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An underweight person is a person whose body weight is considered too low to be healthy. A person who is underweight is malnourished.
| Category [1] | BMI (kgm−2) |
|---|---|
| Underweight (severe) | < 16.0 |
| Underweight (moderate) | 16.0 – 16.9 |
| Underweight (mild) | 17.0 – 18.4 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | ≥ 30.0 |
The body mass index, a ratio of a person's weight to their height, has traditionally been used to assess the health of a person as it pertains to weight: under the cut-off point at a BMI of 18.5, a person is considered underweight. [2] The calculation is either weight in kilograms divided by height in meters, squared, or weight in pounds times 703, divided by height in inches, squared. Another measure of underweight is through comparison to the average weight of a cohort of people of a similar age and height: people who are at least 15% to 20% below the average weight for the group are considered underweight. [3]
Body fat percentage has been suggested as another way to assess whether a person is underweight. Unlike the body mass index, which is a proxy measurement, the body fat percentage takes into account the difference in composition between adipose tissue (fat cells) and muscle tissue and their different roles in the body. [4] The American Council on Exercise defines the amount of essential fat, below which a person is underweight, as 10–13% for women and 2–5% for men. [5] The greater amount of essential body fat in women supports reproductive function.[ citation needed ]
Using the body mass index as a measure of weight-related health, with data from 2014, age-standardised global prevalence of underweight in women and men were 9.7% and 8.8%, respectively. These values were lower than what was reported for 1975 as 14.6% and 13.8%, respectively, indicating a worldwide reduction in the extent of undernutrition. [6]
A person may be underweight due to genetics, [7] [8] poor absorption of nutrients, increased metabolic rate or energy expenditure, lack of food (frequently due to poverty), drugs that affect appetite, illness (physical or mental) or the eating disorder anorexia nervosa. [9] [10]
Being underweight is associated with certain medical conditions, including type 1 diabetes, [11] hyperthyroidism, [12] cancer, [13] and tuberculosis. [14] People with gastrointestinal or liver problems may be unable to absorb nutrients adequately. People with certain eating disorders can also be underweight due to one or more nutrient deficiencies or excessive exercise, which exacerbates nutrient deficiencies. [15] [16]
A common belief is that healthy underweight individuals can ‘eat what they want’ and then burn it off either by high levels of activity or elevated metabolism. It has been shown, however, that individuals with BMI < 18.5 eat about 12% less calories than individuals with normal BMI (21.5 to 25) and they are 23% less physically active (by accelerometry). [17]
Being underweight can be a symptom of an underlying condition, in which case it is secondary. Unexplained weight loss may require a professional medical diagnosis by a physician. [18]
Being underweight can also cause other conditions, in which case it is primary. Severely underweight individuals may have poor physical stamina and a weak immune system, leaving them open to infection. According to Robert E. Black of the Johns Hopkins School of Public Health (JHSPH), "Underweight status ... and micronutrient deficiencies also cause decreases in immune and non-immune host defenses, and should be classified as underlying causes of death if followed by infectious diseases that are the terminal associated causes." [19] People who are malnourished raise special concerns, as not only gross caloric intake may be inadequate, but also intake and absorption of other vital nutrients, especially essential amino acids and micronutrients such as vitamins and minerals.[ citation needed ]
In women, being severely underweight, as a result of an eating disorder or due to excessive strenuous exercise, can result in amenorrhea (absence of menstruation), [20] infertility or complications during pregnancy if gestational weight gain is too low.[ citation needed ]
Malnourishment can also cause anemia and hair loss.
Being underweight is an established [21] risk factor for osteoporosis, even for young people. This is seen in individuals suffering from relative energy deficiency in sport, formerly known as female athlete triad: when disordered eating or excessive exercise cause amenorrhea, hormone changes during ovulation leads to loss of bone mineral density. [22] [23] After this low bone mineral density causes the first spontaneous fractures, the damage is often irreversible.
Although being underweight has been reported to increase mortality at rates comparable to that seen in morbidly obese people, [24] the effect is much less drastic when restricted to non-smokers with no history of disease, [25] suggesting that smoking and disease-related weight loss are the leading causes of the observed effect.
Underweight individuals may be advised to gain weight by increasing calorie intake. This can be done by eating a sufficient volume of sufficiently calorie-dense foods. [26] [27] [28] Body weight may also be increased through the consumption of liquid nutritional supplements. [29]
Another way for underweight people to gain weight is by exercising, since muscle hypertrophy increases body mass. Weight lifting exercises are effective in helping to improve muscle tone as well as helping with weight gain. [30] Weight lifting has also been shown to improve bone mineral density, [31] which underweight people are more likely to lack. [32]
Exercise is catabolic, which results in a brief reduction in mass. However, during recovery, anabolic overcompensation causes the muscles to grow, which results in an overall increase in mass. This can happen through an increase in muscle proteins, or through enhanced storage of glycogen in muscles.[ citation needed ] Exercise can also help stimulate the appetite of a person who is not inclined to eat.
Certain drugs may increase appetite either as their primary effect or as a side effect. Antidepressants, such as mirtazapine or amitriptyline, and antipsychotics, particularly chlorpromazine and haloperidol, as well as tetrahydrocannabinol (found in cannabis), all present an increase in appetite as a side effect. In states where it is approved, medicinal cannabis may be prescribed for severe appetite loss, such as that caused by cancer, AIDS, or severe levels of persistent anxiety. Other drugs or supplements which may increase appetite include antihistamines (such as diphenhydramine, promethazine or cyproheptadine). [33]
Dieting is the practice of eating food in a regulated way to decrease, maintain, or increase body weight, or to prevent and treat diseases such as diabetes and obesity. As weight loss depends on calorie intake, different kinds of calorie-reduced diets, such as those emphasising particular macronutrients, have been shown to be no more effective than one another. As weight regain is common, diet success is best predicted by long-term adherence. Regardless, the outcome of a diet can vary widely depending on the individual.
Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone sterility, and consequent increase in fracture risk. It is the most common reason for a broken bone among the elderly. Bones that commonly break include the vertebrae in the spine, the bones of the forearm, the wrist, and the hip. Until a broken bone occurs there are typically no symptoms. Bones may weaken to such a degree that a break may occur with minor stress or spontaneously. After the broken bone heals, the person may have chronic pain and a decreased ability to carry out normal activities.
The human skeleton is the internal framework of the human body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton makes up about 14% of the total body weight and reaches maximum mass between the ages of 25 and 30. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.
Amenorrhea is the absence of a menstrual period in a female who has reached reproductive age. Physiological states of amenorrhoea are seen, most commonly, during pregnancy and lactation (breastfeeding). Outside the reproductive years, there is absence of menses during childhood and after menopause.
Cachexia is a complex syndrome associated with an underlying illness, causing ongoing muscle loss that is not entirely reversed with nutritional supplementation. A range of diseases can cause cachexia, most commonly cancer, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease, and AIDS. Systemic inflammation from these conditions can cause detrimental changes to metabolism and body composition. In contrast to weight loss from inadequate caloric intake, cachexia causes mostly muscle loss instead of fat loss. Diagnosis of cachexia can be difficult due to the lack of well-established diagnostic criteria. Cachexia can improve with treatment of the underlying illness but other treatment approaches have limited benefit. Cachexia is associated with increased mortality and poor quality of life.
Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, by a mean loss of fluid, body fat, or lean mass. Weight loss can either occur unintentionally because of malnourishment or an underlying disease, or from a conscious effort to improve an actual or perceived overweight or obese state. "Unexplained" weight loss that is not caused by reduction in calorific intake or increase in exercise is called cachexia and may be a symptom of a serious medical condition.
In nutrition, diet is the sum of food consumed by a person or other organism. The word diet often implies the use of specific intake of nutrition for health or weight-management reasons. Although humans are omnivores, each culture and each person holds some food preferences or some food taboos. This may be due to personal tastes or ethical reasons. Individual dietary choices may be more or less healthy.
Weight gain is an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water or other factors. Weight gain can be a symptom of a serious medical condition.
Calorie restriction is a dietary regimen that reduces the energy intake from foods and beverages without incurring malnutrition. The possible effect of calorie restriction on body weight management, longevity, and aging-associated diseases has been an active area of research.
Osteopenia, known as "low bone mass" or "low bone density", is a condition in which bone mineral density is low. Because their bones are weaker, people with osteopenia may have a higher risk of fractures, and some people may go on to develop osteoporosis. In 2010, 43 million older adults in the US had osteopenia. Unlike osteoporosis, osteopenia does not usually cause symptoms, and losing bone density in itself does not cause pain.
Relative energy deficiency in sport (RED-S) is a syndrome in which disordered eating, amenorrhoea/oligomenorrhoea, and decreased bone mineral density are present. It is caused by eating too little food to support the amount of energy being expended by an athlete, often at the urging of a coach or other authority figure who believes that athletes are more likely to win competitions when they have an extremely lean body type. RED-S is a serious illness with lifelong health consequences and can potentially be fatal.
Senile osteoporosis has been recently recognized as a geriatric syndrome with a particular pathophysiology. There are different classification of osteoporosis: primary, in which bone loss is a result of aging and secondary, in which bone loss occurs from various clinical and lifestyle factors. Primary, or involuntary osteoporosis, can further be classified into Type I or Type II. Type I refers to postmenopausal osteoporosis and is caused by the deficiency of estrogen. While senile osteoporosis is categorized as an involuntary, Type II, and primary osteoporosis, which affects both men and women over the age of 70 years. It is accompanied by vitamin D deficiency, body's failure to absorb calcium, and increased parathyroid hormone.
Functional hypothalamic amenorrhea (FHA) is a form of amenorrhea and chronic anovulation and is one of the most common types of secondary amenorrhea. It is classified as hypogonadotropic hypogonadism. It was previously known as "juvenile hypothalamosis syndrome," prior to the discovery that sexually mature females are equally affected. FHA has multiple risk factors, with links to stress-related, weight-related, and exercise-related factors. FHA is caused by stress-induced suppression of the hypothalamic-pituitary-ovarian (HPO) axis, which results in inhibition of gonadotropin-releasing hormone (GnRH) secretion, and gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Severe and potentially prolonged hypoestrogenism is perhaps the most dangerous hormonal pathology associated with the disease, because consequences of this disturbance can influence bone health, cardiovascular health, mental health, and metabolic functioning in both the short and long-term. Because many of the symptoms overlap with those of organic hypothalamic, pituitary, or gonadal disease and therefore must be ruled out, FHA is a diagnosis of exclusion; "functional" is used to indicate a behavioral cause, in which no anatomical or organic disease is identified, and is reversible with correction of the underlying cause. Diagnostic workup includes a detailed history and physical, laboratory studies, such as a pregnancy test, and serum levels of FSH and LH, prolactin, and thyroid-stimulating hormone (TSH), and imaging. Additional tests may be indicated in order to distinguish FHA from organic hypothalamic or pituitary disorders. Patients present with a broad range of symptoms related to severe hypoestrogenism as well as hypercortisolemia, low serum insulin levels, low serum insulin-like growth factor 1 (IGF-1), and low total triiodothyronine (T3). Treatment is primarily managing the primary cause of the FHA with behavioral modifications. While hormonal-based therapies are potential treatment to restore menses, weight gain and behavioral modifications can have an even more potent impact on reversing neuroendocrine abnormalities, preventing further bone loss, and re-establishing menses, making this the recommended line of treatment. If this fails to work, secondary treatment is aimed at treating the effects of hypoestrogenism, hypercortisolism, and hypothyroidism.
Being overweight or fat is having more body fat than is optimally healthy. Being overweight is especially common where food supplies are plentiful and lifestyles are sedentary.
Anorexia nervosa (AN), often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin.
Weight management refers to behaviors, techniques, and physiological processes that contribute to a person's ability to attain and maintain a healthy weight. Most weight management techniques encompass long-term lifestyle strategies that promote healthy eating and daily physical activity. Moreover, weight management involves developing meaningful ways to track weight over time and to identify ideal body weights for different individuals.
Exercise addiction is a state characterized by a compulsive engagement in any form of physical exercise, despite negative consequences. While regular exercise is generally a healthy activity, exercise addiction generally involves performing excessive amounts of exercise to the detriment of physical health, spending too much time exercising to the detriment of personal and professional life, and exercising regardless of physical injury. It may also involve a state of dependence upon regular exercise which involves the occurrence of severe withdrawal symptoms when the individual is unable to exercise. Differentiating between addictive and healthy exercise behaviors is difficult but there are key factors in determining which category a person may fall into. Exercise addiction shows a high comorbidity with eating disorders.
Emotional eating, also known as stress eating and emotional overeating, is defined as the "propensity to eat in response to positive and negative emotions". While the term commonly refers to eating as a means of coping with negative emotions, it sometimes include eating for positive emotions, such as overeating when celebrating an event or to enhance an already good mood.
Nutrition is the intake of food, considered in relation to the body's dietary needs. Well-maintained nutrition includes a balanced diet as well as a regular exercise routine. Nutrition is an essential aspect of everyday life as it aids in supporting mental as well as physical body functioning. The National Health and Medical Research Council determines the Dietary Guidelines within Australia and it requires children to consume an adequate amount of food from each of the five food groups, which includes fruit, vegetables, meat and poultry, whole grains as well as dairy products. Nutrition is especially important for developing children as it influences every aspect of their growth and development. Nutrition allows children to maintain a stable BMI, reduces the risks of developing obesity, anemia and diabetes as well as minimises child susceptibility to mineral and vitamin deficiencies.
Locomotive syndrome is a medical condition of decreased mobility due to disorders of the locomotor system. The locomotor system comprises bones, joints, muscles and nerves. It is a concept put forward by three professional medical societies in Japan: the Japanese Society for Musculoskeletal Medicine, the Japanese Orthopaedic Association, and the Japanese Clinical Orthopaedic Association. Locomotive syndrome is generally found in the ageing population as locomotor functions deteriorate with age. Symptoms of locomotive syndrome include limitations in joint mobility, pain, balance disorder, malalignment and gait abnormality. Locomotive syndrome is commonly caused by chronic locomotive organ diseases. Diagnosis and assessment of locomotive syndrome is done using several tests such as the stand-up and two-step tests. The risk of having locomotive syndrome can be decreased via adequate nutrition, attainment of an exercise habit and being active.
