Nutrition Evaluation and Support

Introduction

• Malnutrition is a consequence of nutrient imbalance resulting from inadequate intake, absorption, or utilization of protein and energy. Undernutrition can result in changes in subcellular, cellular, or organ function that increase the individual’s risks of morbidity and mortality
• Nutrition screening provides a systematic way to identify individuals in any care environment who need a detailed nutrition assessment.
• Nutrition assessment is the first step in developing a nutrition care plan. Goals of nutrition assessment are to identify the presence of factors associated with an increased risk of developing undernutrition and complications, estimate nutrition needs, and establish baseline parameters for assessing the outcome of therapy.
• This assessment should include a nutrition-focused history, a physical exam including anthropometrics, and laboratory measurements.

Clinical Evaluation

Medical and dietary history should include weight changes within 6 months, dietary intake changes, gastrointestinal (GI) symptoms, functional capacity, and disease states.

• Physical examination should focus on assessment of lean body mass (LBM) and physical findings of vitamin, trace element, and essential fatty acid deficiencies.

Anthropometric Measurements

Anthropometric measurements are physical measurements of the size, weight, and proportions of the human body used to compare an individual with normative population standards. The most common measurements are weight, stature, head circumference (for children younger than 3 years of age) waist circumference, and measurements of limb size ( e.g., skinfold thickness and midarm muscle and wrist circumferences), along with bioelectrical impedance analysis (BIA).

• Interpretation of actual body weight (ABW) should consider ideal weight (IBW) for height, usual body weight (UBW), fluid status, and age. Change over time can be calculated as the percentage of UBW. Unintentional weight loss >10% in 6 months increases risk of poor clinical outcome in adults.
• The best indicator of adequate nutrition in children is appropriate growth. Weight, stature, and head circumference should be plotted on the appropriate growth curve and compared with usual growth velocities. Average weight gain for newborns is 10 to 20 g/kg/day (24 to 35 g/day for term infants and 10 to 25 g/day for preterm infants).
• Body mass index (BMI) is another index of weight-for-height that is highly correlated with body fat. Interpretation of BMI should include consideration of gender, frame size, and age. BMI values greater than 25 kg/m2 are indicative of overweight, and values less than 18.5 kg/m2 are indicative of undernutrition. BMI is calculated as follows: Body weight (kg)/[height (m)]2
• Measurements of skinfold thickness estimate subcutaneous fat, midarm muscle circumference estimates skeletal muscle mass, and waist circumference estimates abdominal fat content.
• BIA is a simple, noninvasive, and relatively inexpensive way to measure LBM. It is based on differences between fat tissue and lean tissue’s resistance to conductivity. Fluid status should be considered in interpretation of BIA results.

Specific Nutrient Deficiencies

Biochemical assessment of trace element, vitamin, and essential fatty acid deficiencies should be based on the nutrient’s function, but few practical methods are available. Therefore, most assays measure serum concentrations of the individual nutrient.

• Clinical syndromes are associated with deficiencies of the following trace elements: zinc, copper, manganese, selenium, chromium, iodine, fluoride, molybdenum, and iron.
• Single vitamin deficiencies are uncommon; multiple vitamin deficiencies more commonly occur with undernutrition.

Assessment Of Nutrient Requirements

Assessment of nutrient requirements must be made in the context of patient-specific factors (eg, age, gender, size, disease state, clinical condition, nutrition status, and physical activity).

• To replace recommended dietary allowances, the Food and Nutrition Board created the dietary reference intakes made up of seven nutrient groups.

Energy Requirements

Adults should consume 45% to 65% of total calories from carbohydrates, 20% to 35% from fat, and 10% to 35% from protein. Recommendations are similar for children, except that infants should consume 40% to 50% of total calories from fat.

• Energy requirements of individuals can be estimated using published, validated equations or directly measured, depending on factors including severity of illness and resources available. The simplest method is to use population estimates of calories required per kilogram of body weight.
• Healthy adults with normal nutrition status and minimal illness severity require an estimated 20 to 25 kcal ABW/kg/day (84–105 kJ ABW/kg/day). Daily energy requirements for children are approximately 150% of basal metabolic rate with additional calories to support activity and growth. Consult references for equations used to estimate energy expenditure in adults and children.
• Energy requirements for all ages increase with fever, sepsis, major surgery, trauma, burns, long-term growth failure, and chronic conditions (e.g., bronchopulmonary dysplasia, congenital heart disease, and cystic fibrosis).