Porth's Essentials of Pathophysiology, 4e

229

Disorders of Nutritional Status

C h a p t e r 1 0

TABLE 10-2 Classification of Overweight and Obesity by BMI,Waist Circumference, and Associated Disease Risk * Disease Risk * Relative to Normal Weight and Waist Circumference

Men ≤ 102 cm ( ≤ 40 in.) Women ≤ 88 cm ( ≤ 35 in.)

Men > 102 cm ( > 40 in.) Women > 88 cm ( > 35 in.)

BMI (kg/m 2 )

Obesity Class

Underweight

<18.5

— —

— —

Normal †

18.5–24.9 25.0–29.9 30.0–34.9 35.0–39.9

Overweight

Increased

High

Obesity

I

High

Very high Very high

II

Very high

≥ 40

Extreme obesity

III

Extremely high

Extremely high

BMI, body mass index. *Disease risk for type 2 diabetes, hypertension, and cardiovascular disease.

† Increased waist circumference also can be a marker for increased risk, even in persons of normal weight. Pi-Sunyer FX, DietzWH, Becker DM, et al., for the NHLBI Obesity Education Initiative Expert Panel on the Identification, Evaluation, andTreatment of Overweight and Obesity in Adults. Clinical Guidelines on the Identification, Evaluation, andTreatment of Overweight and Obesity in Adults. 1998. NIH Publication No. 98–4083. Available at: http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.pdf

multiple sites. They can provide information about the location of the fat and can be used together with equa- tions and tables to estimate the percentage of lean body mass and fat tissue. However, these measurements often are difficult to perform, are subject to considerable vari- ation between clinicians, and do not provide informa- tion about abdominal and intramuscular fat. Bioelectrical impedance involves the use of electrodes attached to the wrists and ankles to send a harmless cur- rent through the body. The flow of the current is affected by the amount of water in the body. Because fat-free tis- sue contains virtually all the water and current-conduct- ing electrolytes, measurements of the resistance (i.e., impedance) can be used to estimate the percentage of body fat present. Computed tomography and MRI can be used to pro- vide quantitative pictures from which the thickness of fat can be determined. Computed tomography scans also can be used to provide quantitative estimates of regional fat and give a ratio of intra-abdominal to extra-abdominal fat. Another novel way of measuring body composition is the BOD POD. The subject sits inside the device, and air displacement is measured to determine body compo- sition (i.e., fat vs. lean tissue). Because these methods are costly, they usually are reserved for research studies. Laboratory Studies Various laboratory tests can aid in evaluating nutritional status. Some of the most commonly performed tests are serum albumin and prealbumin to assess the protein sta- tus, total lymphocyte count and delayed hypersensitivity reaction to assess cellular immunity, and creatinine– height index to assess skeletal muscle protein. Vitamin and mineral deficiencies can be determined by measure- ments of their levels in blood, saliva, and other body tis- sues or by measuring nutrient-specific chemical reactions.

SUMMARY CONCEPTS

■■ Nutritional status describes the condition of the body related to the availability and use of nutrients, which provide the energy and materials necessary for performing the activities of daily living and for the growth and repair of body tissues. ■■ Metabolism is the organized process whereby nutrients such as carbohydrates, fats, and proteins are broken down, transformed, or otherwise converted to cellular energy, measured in kilocalories (kcal or C). Carbohydrates are the body’s primary source of immediate energy. They supply 4 kcal/g, are stored in limited quantities as glycogen and can be converted to fatty acids. Fats are a concentrated water-free energy source. They contain 9 kcal/g and are stored in fat cells as triglycerides. Proteins, which are broken down into amino acids, generate 4 kcal/g. However, their main role is in building functional and structural body proteins. Excesses of any of the macronutrients will be stored as triglycerides in adipose tissue. Water, vitamins, and minerals are other essential nutrients. ■■ Nutritional status can be assessed by evaluation of dietary intake; anthropometric measurements such as measurements of height and weight, body circumference, and skinfold thickness; and laboratory tests.