Overview of Undernutrition

Infants and children are particularly susceptible to undernutrition because of their high demand for energy and essential nutrients. According to the World Health Organization (WHO), in 2020, 149 million children > 5 years were estimated to be stunted (too short for age) and 45 million were estimated to be wasted (too thin for height [ 1 Risk factor references Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition.) Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss... read more ]). The mortality rate for children < 5 years is the probability that a neonate will die before reaching 5 years of age and is expressed as deaths per 1000 live births. Worldwide, this rate decreased by 59%: from 93/1000 deaths per live births in 1990 to 38% in 2021 (2 Risk factor references Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition.) Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss... read more ). Despite this progress, lowering the mortality rate for children < 5 years remains a major public health concern.

Because vitamin K does not readily cross the placenta, neonates may be deficient, so they are given a single injection of vitamin K within 1 hour of birth to prevent hemorrhagic disease of the newborn Blood loss , a life-threatening disorder. Infants fed only breast milk, which is typically low in vitamin D, are given supplemental vitamin D; they can develop vitamin B12 deficiency Vitamin B12 Deficiency Dietary vitamin B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements. Deficiency causes megaloblastic anemia, damage... read more if the mother is vegan.

Inadequately fed infants and children are at risk of protein-energy undernutrition Protein-Energy Undernutrition (PEU) Protein-energy undernutrition (PEU), previously called protein-energy malnutrition, is an energy deficit due to deficiency of all macronutrients, but primarily protein. It commonly includes... read more (PEU—previously called protein-energy malnutrition) and deficiencies of iron Iron Deficiency Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron is contained mainly in animal products. It is absorbed much better than nonheme iron (eg, in plants... read more , folate Folate Deficiency Folate deficiency is common. It may result from inadequate intake, malabsorption, or use of various drugs. Deficiency causes megaloblastic anemia (indistinguishable from that due to vitamin... read more (folic acid), vitamins A Vitamin A Deficiency Vitamin A deficiency can result from inadequate intake, fat malabsorption, or liver disorders. Deficiency impairs immunity and hematopoiesis and causes rashes and typical ocular effects (eg... read more and C Vitamin C Deficiency In countries with low rates of food insecurity, vitamin C deficiency can occur as part of general undernutrition, but severe deficiency (causing scurvy) is uncommon. Symptoms include fatigue... read more , copper Acquired Copper Deficiency Copper is a component of many body proteins; almost all of the body’s copper is bound to copper proteins. Copper deficiency may be acquired or inherited. (See also Overview of Mineral Deficiency... read more , and zinc Zinc Deficiency Zinc (Zn) is contained mainly in bones, teeth, hair, skin, liver, muscle, leukocytes, and testes. Zinc is a component of several hundred enzymes, including many nicotinamide adenine dinucleotide... read more .

During adolescence, nutritional requirements increase because the growth rate accelerates. Anorexia nervosa Anorexia Nervosa Anorexia nervosa is characterized by a relentless pursuit of thinness, a morbid fear of obesity, a distorted body image, and restriction of intake relative to requirements, leading to a significantly... read more may affect adolescent girls in particular.

Requirements for nutrients increase during pregnancy (to support the metabolic demands of pregnancy and fetal growth) and breastfeeding. Aberrations of diet, including pica Pica Pica is persistent eating of nonnutritive, nonfood material for ≥1 month when it is developmentally inappropriate (eg, pica is not diagnosed in children < 2 years) and when it is not part... read more (consumption of nonnutritive substances, such as clay and charcoal), may occur during pregnancy. Anemia due to iron deficiency Iron Deficiency Anemia in Pregnancy Normally during pregnancy, erythroid hyperplasia of the marrow occurs, and red blood cell (RBC) mass increases. However, a disproportionate increase in plasma volume results in hemodilution... read more is common, as is anemia due to folate deficiency Folate Deficiency Anemia in Pregnancy Normally during pregnancy, erythroid hyperplasia of the marrow occurs, and red blood cell (RBC) mass increases. However, a disproportionate increase in plasma volume results in hemodilution... read more , especially among women who have taken oral contraceptives. Vitamin D deficiency Vitamin D Deficiency and Dependency Inadequate exposure to sunlight predisposes to vitamin D deficiency. Deficiency impairs bone mineralization, causing rickets in children and osteomalacia in adults and possibly contributing... read more is common during late pregnancy, predisposing the child to decreased bone mass. For women who are pregnant or breastfeeding, clinicians may need to recommend diet plans or dietary supplements, especially if nutritional status is compromised.

Older adults are at high risk of undernutrition because their nutritional needs increase but energy requirements decrease. This disparity requires consumption of nutrient-dense foods.

Aging—even when disease or dietary deficiency is absent—leads to sarcopenia (progressive loss of lean body mass), starting after age 40 and eventually amounting to a muscle loss of about 10 kg (22 lb) in men and 5 kg (11 lb) in women. Undernutrition contributes to sarcopenia, and sarcopenia accounts for many of the complications of undernutrition (eg, decreased nitrogen balance, increased susceptibility to infections).

Causes of sarcopenia include the following:

Aging decreases basal metabolic rate (due mainly to decreased fat-free mass), total body weight, height, and skeletal mass; from about age 40 to age 65, mean body fat (as a percentage of body weight) increases to about 30% (from 20%) in men and to 40% (from 27%) in women.

From age 20 to 80, food intake decreases, especially in men.

Anorexia due to aging itself has many causes, including

Occasionally, anorexia nervosa Anorexia Nervosa Anorexia nervosa is characterized by a relentless pursuit of thinness, a morbid fear of obesity, a distorted body image, and restriction of intake relative to requirements, leading to a significantly... read more (sometimes called anorexia tardive in older patients), paranoia, or mania Mania Bipolar disorders are characterized by alternating episodes of mania and depression, although many patients have a predominance of one or the other. Exact cause is unknown, but heredity, changes... read more interferes with eating. Dental problems limit the ability to chew and subsequently to digest foods. Swallowing difficulties (eg, due to stroke Overview of Stroke Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be Ischemic (80%), typically resulting... read more , other neurologic disorders, esophageal candidiasis Candidiasis Candidiasis is infection by Candida species (most often C. albicans), manifested by mucocutaneous lesions, fungemia, and sometimes focal infection of multiple sites. Symptoms depend... read more , or xerostomia Xerostomia Xerostomia is dry mouth caused by reduced or absent flow of saliva. This condition can result in discomfort, interfere with speech and swallowing, make wearing dentures difficult, cause halitosis... read more ) are common. Poverty or functional impairment limits access to nutrients.

Institutionalized older patients are at particular risk of protein-energy undernutrition Protein-Energy Undernutrition (PEU) Protein-energy undernutrition (PEU), previously called protein-energy malnutrition, is an energy deficit due to deficiency of all macronutrients, but primarily protein. It commonly includes... read more . They are often confused and may be unable to express hunger or preferences for foods. They may be physically unable to feed themselves. Chewing or swallowing may be very slow, making it tedious for another person to feed them enough food.

In older patients, particularly those who are institutionalized, inadequate intake and often decreased absorption or synthesis of vitamin D, increased demand for vitamin D, and inadequate exposure to sunshine contribute to vitamin D deficiency Vitamin D Deficiency and Dependency Inadequate exposure to sunlight predisposes to vitamin D deficiency. Deficiency impairs bone mineralization, causing rickets in children and osteomalacia in adults and possibly contributing... read more and osteomalacia.

Diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more , some chronic disorders that affect the gastrointestinal tract, intestinal resection, and certain other gastrointestinal surgical procedures tend to impair absorption of fat-soluble vitamins, vitamin B12, calcium, and iron. Gluten enteropathy, pancreatic insufficiency, or other disorders can result in malabsorption Overview of Malabsorption Malabsorption is inadequate assimilation of dietary substances due to defects in digestion, absorption, or transport. Malabsorption can affect macronutrients (eg, proteins, carbohydrates, fats)... read more . Decreased absorption possibly contributes to iron deficiency Iron Deficiency Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron is contained mainly in animal products. It is absorbed much better than nonheme iron (eg, in plants... read more and osteoporosis Osteoporosis Osteoporosis is a progressive metabolic bone disease that decreases bone mineral density (bone mass per unit volume), with deterioration of bone structure. Skeletal weakness leads to fractures... read more .

Liver disorders impair storage of vitamins A and B12 and interfere with metabolism of protein and energy sources. Renal insufficiency predisposes to protein, iron, and vitamin D deficiencies.

Anorexia causes some patients with cancer or depression and many with AIDS to consume inadequate amounts of food.

Infections, trauma, hyperthyroidism, extensive burns, and prolonged fever increase metabolic demands. Any condition that increases cytokines may be accompanied by muscle loss, lipolysis, low albumin levels, and anorexia.

Iron deficiency Iron Deficiency Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron is contained mainly in animal products. It is absorbed much better than nonheme iron (eg, in plants... read more can occur in people who follow an ovo-lacto diet (although such a diet can be compatible with good health). People who follow a vegan diet may develop vitamin B12 deficiency Vitamin B12 Deficiency Dietary vitamin B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements. Deficiency causes megaloblastic anemia, damage... read more unless they consume yeast extracts or Asian-style fermented foods. Their intake of calcium, iron, and zinc also tends to be low.

Some fad diets result in vitamin, mineral, and protein deficiencies; cardiac, renal, and metabolic disorders; and sometimes death. Very low calorie diets (< 400 kcal/day) cannot sustain health for long.

A fruit-only diet is not recommended because it is deficient in protein, sodium, and many micronutrients.

Many medications (eg, appetite suppressants, digoxin, glucagon-like peptide-1 [GLP-1] receptor agonists) decrease appetite; others impair nutrient absorption or metabolism. Some medications and other substances (eg, stimulants) have catabolic effects. Certain medications can impair absorption of many nutrients; eg, antiseizure medications can impair absorption of vitamins.

Patients with alcohol or substance dependency may neglect their nutritional needs. Absorption and metabolism of nutrients may also be impaired. People with IV drug use disorders typically become undernourished, as do people with alcohol use disorder Alcohol Use Disorder and Rehabilitation Alcohol use disorder involves a pattern of alcohol use that typically includes craving and manifestations of tolerance and/or withdrawal along with adverse psychosocial consequences. Alcoholism... read more who consume ≥ 1 quart of hard liquor/day. Alcohol use disorder can cause deficiencies of magnesium, zinc, and certain vitamins, including thiamine.

History should include questions about

Unintentional loss of ≥ 10% of usual body weight during a 3-month period indicates a high probability of undernutrition. Social history should include questions about food security and the patient's ability to shop and cook.

Review of systems should focus on symptoms of nutritional deficiencies (see table ). For example, impaired night vision may indicate vitamin A deficiency Vitamin A Deficiency Vitamin A deficiency can result from inadequate intake, fat malabsorption, or liver disorders. Deficiency impairs immunity and hematopoiesis and causes rashes and typical ocular effects (eg... read more .

Physical examination should include

Body mass index Body Mass Index (BMI) (BMI = weight[kg]/height[m]²) adjusts weight for height. If weight is < 80% of what is predicted for the patient’s height or if BMI is ≤ 18, undernutrition should be suspected. Although these findings are useful in diagnosing undernutrition and are acceptably sensitive, they lack specificity.

The mid upper arm muscle area estimates lean body mass. This area is derived from the triceps skinfold thickness (TSF) and mid upper arm circumference. Both are measured at the same site, with the patient’s right arm in a relaxed position. The average mid upper arm circumference is about 34.1 cm for men and 31.9 cm for women (4 Evaluation references Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition.) Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss... read more ). The formula for calculating the mid upper arm muscle area in cm² is as follows:

This formula corrects the upper arm area for fat and bone. Average values for the mid upper arm muscle area are 54 ± 11 cm² for men and 30 ± 7 cm² for women. A value < 75% of this standard (depending on age) indicates depletion of lean body mass (see table ). This measurement may be affected by physical activity, genetic factors, and age-related muscle loss.

Physical examination should focus on signs of specific nutritional deficiencies. Signs of protein-energy undernutrition Protein-Energy Undernutrition (PEU) Protein-energy undernutrition (PEU), previously called protein-energy malnutrition, is an energy deficit due to deficiency of all macronutrients, but primarily protein. It commonly includes... read more (eg, edema, muscle wasting, skin changes) should be sought. Examination should also focus on signs of conditions that could predispose to nutritional deficiencies, such as dental problems. Mental status How to Assess Mental Status The mental status examination is used to evaluate the patient’s level of consciousness and the content of consciousness. Patients are considered alert if they are actively perceiving the world... read more should be assessed because depression and cognitive impairment can lead to weight loss.

The following assessment tools may be useful:

The extent of laboratory testing needed is unclear and may depend on the patient’s circumstances. If the cause is obvious and correctable (eg, a wilderness survival situation), testing is probably of little benefit. Other patients may require more detailed evaluation.

Serum albumin measurement is the laboratory test most often used. Decreases in albumin and other proteins (eg, prealbumin [transthyretin], transferrin, retinol-binding protein) may indicate protein deficiency or protein-energy undernutrition Protein-Energy Undernutrition (PEU) Protein-energy undernutrition (PEU), previously called protein-energy malnutrition, is an energy deficit due to deficiency of all macronutrients, but primarily protein. It commonly includes... read more (PEU). As undernutrition progresses, albumin decreases slowly; prealbumin, transferrin, and retinol-binding protein decrease rapidly. Albumin measurement is inexpensive and predicts morbidity and mortality better than measurement of the other proteins. However, the correlation of albumin with morbidity and mortality may be related to nonnutritional as well as nutritional factors. Inflammation produces cytokines that cause albumin and other nutritional protein markers to extravasate, decreasing serum levels. Because prealbumin, transferrin, and retinol-binding protein decrease more rapidly during starvation than does albumin, their measurements are sometimes used to diagnose or assess the severity of acute starvation. However, whether they are more sensitive or specific than albumin is unclear.

Total lymphocyte count, which often decreases as undernutrition progresses, may be determined. Undernutrition causes a marked decline in CD4+ T lymphocytes, so this count may not be useful in patients who have AIDS.

Urinary creatinine is related to muscle mass. Urinary creatinine excretion over a 24-hour period can be used to compute the creatinine height index (CHI [%]), which reflects lean muscle mass. The CHI is calculated as (24-hour urine creatinine x 100)/ideal creatinine excretion for height (obtained from standard tables). The CHI indicates extent of muscle depletion:as follows:> 30% is severe, 15 to 30% is moderate, and 5 to 15% is mild (9 Evaluation references Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition.) Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss... read more ).

Skin tests Initial testing using antigens can detect impaired cell-mediated immunity in PEU and in some other disorders of undernutrition.

Other laboratory tests, such as measuring vitamin and mineral levels, are used selectively to diagnose specific deficiencies.