🍽️nutrition assessment review
9.2 Protein-Energy Malnutrition Assessment
4 min read•Last Updated on July 30, 2024
Protein-energy malnutrition (PEM) is a serious form of undernutrition that can affect people of all ages, but especially young children. It's caused by not getting enough protein and calories, leading to wasting, stunted growth, and weakened immunity.
Assessing PEM involves measuring body size, composition, and biochemical markers. Key indicators include weight-for-age, height-for-age, and mid-upper arm circumference. Blood tests for proteins like albumin and prealbumin can also show nutritional status at the cellular level.
Protein-energy malnutrition: Pathophysiology
Definition and Causes
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- Protein-energy malnutrition (PEM) is a form of undernutrition resulting from chronic deficiency of protein and energy. It is most common in young children but can impact all age groups.
- Primary PEM is caused by inadequate intake of protein and calories (poverty, food insecurity, poor feeding practices)
- Secondary PEM occurs due to nutrient malabsorption (intestinal disorders), impaired utilization (metabolic diseases), or increased requirements (burns, infections, trauma)
Clinical Forms and Manifestations
- Marasmus is a severe form of PEM characterized by wasting and depletion of subcutaneous fat and muscle. It typically occurs in the first year of life.
- Kwashiorkor is a severe form of PEM characterized by edema, fatty liver, skin lesions (flaky paint dermatosis), and hair changes (sparse, thin, reddish). It typically manifests in older children.
- PEM impairs cellular growth and function, weakens the immune system, delays wound healing, and leads to loss of muscle mass and subcutaneous fat.
- Prolonged PEM can result in stunted growth (short stature), impaired cognitive development (lower IQ scores), increased risk of infections (pneumonia, diarrhea), and organ damage (liver, heart, kidneys).
Anthropometry for malnutrition identification
Body Size and Composition Measurements
- Anthropometry involves taking body measurements to assess nutritional status and identify PEM. Key measurements include weight, height/length, head circumference, mid-upper arm circumference (MUAC), and skinfold thickness.
- Low weight-for-age (underweight) is an indicator of acute and/or chronic PEM. It is defined as weight-for-age < -2 standard deviations (SD) of the WHO Child Growth Standards median.
- Low height/length-for-age (stunting) reflects chronic PEM. It is defined as height/length-for-age < -2 SD of the WHO Child Growth Standards median.
- Low weight-for-height/length (wasting) indicates acute PEM. It is defined as weight-for-height/length < -2 SD of the WHO Child Growth Standards median. Severe wasting is < -3 SD.
- MUAC is a simple screening tool for PEM. MUAC < 11.5 cm (severe), 11.5-12.5 cm (moderate), > 12.5 cm (mild/normal). It is useful for children aged 6-59 months.
Body Fat and Muscle Assessments
- Triceps skinfold thickness < 3rd percentile for age and sex suggests PEM and depletion of fat stores. Other skinfold sites (subscapular, suprailiac) may also be measured.
- BMI-for-age is used to screen for PEM in children and adolescents aged 5-19 years. BMI-for-age < -2 SD indicates thinness (PEM).
- Arm muscle area (AMA) estimates skeletal muscle mass using MUAC and triceps skinfold. AMA < 5th percentile indicates muscle wasting.
- Bioelectrical impedance analysis (BIA) measures body composition based on electrical conductivity of tissues. Low phase angle suggests cell membrane integrity loss and malnutrition.
Biochemical markers of protein-energy status
Serum Proteins
- Biochemical markers provide objective measures of protein and energy status at the cellular level. They are used in conjunction with anthropometric and dietary data.
- Serum albumin is the most abundant plasma protein and reflects protein status over the previous 14-20 days. Levels < 3.5 g/dL suggest protein depletion.
- Serum prealbumin (transthyretin) has a shorter half-life than albumin and is a more sensitive indicator of recent protein intake. Levels < 15 mg/dL indicate protein deficiency.
- Serum transferrin is a transport protein for iron. Levels < 200 mg/dL may indicate protein depletion, but it is also affected by iron status.
- Serum retinol-binding protein (RBP) transports vitamin A and has a short half-life. Levels < 2.6 mg/dL suggest protein deficiency.
Functional and Metabolic Indicators
- Total lymphocyte count (TLC) assesses immune function and protein status. TLC < 1200 cells/mm3 indicates protein depletion and impaired immunity.
- Nitrogen balance studies compare nitrogen intake (from protein) to nitrogen excretion (urine, feces, sweat). Negative nitrogen balance indicates protein catabolism and malnutrition.
- Creatinine-height index (CHI) estimates muscle mass based on 24-hour urinary creatinine excretion. CHI < 60% of standard suggests protein malnutrition.
- Insulin-like growth factor-1 (IGF-1) mediates growth hormone action. Low IGF-1 levels reflect chronic undernutrition and growth impairment.
Dietary adequacy for malnutrition prevention
Protein and Energy Requirements
- Dietary assessment methods such as 24-hour recalls, food frequency questionnaires, and food records are used to evaluate protein and energy intake.
- Protein requirements vary by age, sex, body size, and physiological state. The Recommended Dietary Allowance (RDA) for protein is 0.8 g/kg/day for adults, 1.2-2.0 g/kg/day for children, and up to 1.5 g/kg/day for pregnant/lactating women.
- Energy requirements depend on age, sex, body size, physical activity level, and health status. The Estimated Energy Requirement (EER) equations predict energy needs based on these factors.
- Inadequate energy intake leads to use of protein for energy, reducing its availability for growth and maintenance. Protein sparing occurs when sufficient calories are provided.
Protein Quality and Diet Diversity
- Protein quality is determined by digestibility and amino acid composition. High-quality, complete proteins (eggs, meat, fish, dairy, soy) contain all essential amino acids. Lower-quality, incomplete proteins (most plant proteins) are limited in one or more essential amino acids.
- Protein-energy ratio (P/E ratio) is the proportion of protein to total energy in the diet. A P/E ratio of 0.06-0.08 (6-8% of calories from protein) is considered adequate for most healthy individuals. Higher ratios may be needed for catch-up growth, wound healing, or other catabolic states.
- Dietary diversity scores and minimum acceptable diet indicators assess diet quality and micronutrient adequacy, which are important for preventing PEM in developing countries.
- Complementary feeding practices (timely introduction of solid foods, meal frequency, nutrient density) are critical for preventing PEM in infants and young children.