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Overview of Undernutrition

By

John E. Morley

, MB, BCh, Saint Louis University School of Medicine

Last full review/revision Jul 2021| Content last modified Jul 2021
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Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition.) Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss of nutrients due to diarrhea, or increased nutritional requirements (as occurs in cancer or infection). Undernutrition progresses in stages; it may develop slowly when it is due to anorexia or very rapidly, as sometimes occurs when it is due to rapidly progressive cancer-related cachexia. First, nutrient levels in blood and tissues change, followed by intracellular changes in biochemical functions and structure. Ultimately, symptoms and signs appear. Diagnosis is by history, physical examination, body composition analysis, and sometimes laboratory tests (eg, albumin).

The number of undernourished people in the world has been increasing since 2014. In The State of Food Security and Nutrition in the World 2020, the United Nations Food and Agriculture Organization (FAO) reported that almost 690 million people, or 8.9 percent of the global population, were undernourished in 2019, which is 60 million more people than in 2014. Most live in countries with high rates of food insecurity. The FAO report anticipates that the COVID-19 pandemic COVID-19 Coronaviruses are enveloped RNA viruses that cause respiratory illnesses of varying severity from the common cold to fatal pneumonia. Numerous coronaviruses, first discovered in domestic poultry... read more may increase the number of people who are undernourished by an additional 83 to 132 million in 2020.

Risk Factors for Undernutrition

Undernutrition is associated with many disorders and circumstances, including poverty and social deprivation.

Risk is also greater at certain times (ie, during infancy, early childhood, adolescence, pregnancy, breastfeeding, and old age).

Infancy and childhood

Infants and children are particularly susceptible to undernutrition because of their high demand for energy and essential nutrients. 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 Anemia is a reduction in red cell mass or hemoglobin and is usually defined as hemoglobin or hematocrit > 2 standard deviations below the mean for age. Some authorities also consider a relative... read more , 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. It commonly includes deficiencies of many micronutrients... 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, contained mainly in animal products, is absorbed much better than nonheme iron (eg, in plants and... 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 Vitamin A Deficiency and C Vitamin C Deficiency In developed countries, vitamin C deficiency can occur as part of general undernutrition, but severe deficiency (causing scurvy) is uncommon. Symptoms include fatigue, depression, and connective... 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 Zinc Deficiency .

Pregnancy and breastfeeding

Old age

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:

  • Decreased physical activity

  • Decreased food intake

  • Increased levels of cytokines (particularly interleukin-6)

  • Decreased levels of growth hormone and mechano growth factor (insulin-like growth factor-3)

  • In men, decreasing androgen levels

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 (sometimes called anorexia tardive in older patients), paranoia, or mania interferes with eating. Dental problems limit the ability to chew and subsequently to digest foods. Swallowing difficulties (eg, due to strokes, other neurologic disorders, esophageal candidiasis, or xerostomia) 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. It commonly includes deficiencies of many micronutrients... 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.

Disorders and medical procedures

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.

Vegetarian diets

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

Fad diets

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.

Drugs and nutritional supplements

Many drugs (eg, appetite suppressants, digoxin) decrease appetite; others impair nutrient absorption or metabolism. Some drugs (eg, stimulants) have catabolic effects. Certain drugs can impair absorption of many nutrients; eg, anticonvulsants can impair absorption of vitamins.

Alcohol or drug dependency

Patients with alcohol or drug dependency may neglect their nutritional needs. Absorption and metabolism of nutrients may also be impaired. IV drug addicts typically become undernourished, as do people with alcohol use disorder who consume 1 quart of hard liquor/day. Alcohol use disorder can cause deficiencies of magnesium, zinc, and certain vitamins, including thiamin.

Symptoms and Signs of Undernutrition

Evaluation of Undernutrition

History

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 whether money is available for food and whether the patient can shop and cook.

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Physical examination

Physical examination should include

  • Measurement of height and weight

  • Inspection of body fat distribution

  • Anthropometric measurements of lean body mass

Body mass index Body Mass Index (BMI) Obesity is excess body weight, defined as a body mass index (BMI) of ≥ 30 kg/m2. Complications include cardiovascular disorders (particularly in people with excess abdominal fat), diabetes mellitus... read more (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 (3 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:

equation

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 Mid Upper Arm Muscle Area in Adults Mid Upper Arm Muscle Area in Adults Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition.) Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss... read more ). This measurement may be affected by physical activity, genetic factors, and age-related muscle loss.

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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. It commonly includes deficiencies of many micronutrients... 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 patient’s attention span is assessed first; an inattentive patient cannot cooperate fully and hinders testing. Any hint of cognitive decline requires examination of mental status (see Examination... read more should be assessed because depression and cognitive impairment can lead to weight loss.

The following assessment tools may be useful:

Simplified nutrition assessment questionnaire (SNAQ)

Simplified nutrition assessment questionnaire (SNAQ)

Testing

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. It commonly includes deficiencies of many micronutrients... 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.

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

Evaluation references

  • 1. Cederholm T, Jensen GL, Correia MITD, et al: GLIM [Global Leadership Initiative on Malnutrition] criteria for the diagnosis of malnutrition: a consensus report from the global clinical nutrition community. Clin Nutr 38(1):1-9, 2019. doi: 10.1016/j.clnu.2018.08.002

  • 2. Guigoz Y, Vellas B: Nutritional assessment in older adults: MNA® 25 years of a screening tool and a reference standard for care and research; What next? J Nutr Health Aging 25(4):528-583, 2021. doi: 10.1007/s12603-021-1601-y

  • 3. Fryar CD, Gu Q, Ogden CL, Flegal KM: Anthropometric reference data for children and adults: United States, 2011–2014. National Center for Health Statistics. Vital Health Stat 3 (39), 2016.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Drugs Mentioned In This Article

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LANOXIN
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