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Learn the basic components of weight assessment

This is an excerpt from Physical Activity and Obesity-2nd Edition by Claude Bouchard & Peter T. Katzmarzyk.

Clinical Evaluation of the Overweight Patient

The basic components involved in the evaluation of any overweight or obese patient are a medical examination and a laboratory assessment. These should include a record of the historical events associated with the patient’s weight problem, a physical examination for pertinent information, and appropriate laboratory evaluation. I will use the criteria recommended by the U.S. Preventive Services Task Force (1) and also take into account the reports from the National Heart, Lung, and Blood Institute (NLHBI) (2) and the World Health Organization (3). The importance of evaluating overweight individuals has increased as the epidemic of overweight has worsened and the number of potential patients needing treatment has increased.

Clinical History

Among the important elements of the clinical history to identify is whether there are specific events associated with the increase in body weight. Has there been a sudden increase in weight, or has body weight been rising steadily over a long period of time? Weight gain is associated with an increased risk to health. Three categories of weight gain are identified:10 kg (>22 lb). In addition to total weight gain, you need to consider the rate of weight gain after age 20 when deciding on the degree of risk for a given patient. The more rapidly the patient is gaining weight, the more concerned you should be.

Etiologic factors that cause overweight should be identified, if possible (4). If there are clear-cut factors, such as drugs that produce weight gain, or cessation of smoking, these should be noted during the clinical evaluation.

Successful and unsuccessful weight loss programs that the patient has undertaken should also be identified. For example, a sedentary lifestyle increases the risk of early death, and individuals with no regular physical activity are at higher risk than individuals with modest levels of physical activity. Thus, even in the absence of successful weight loss, patients should be encouraged to maintain adequate levels of physical activity.

Family History

It is important to determine whether the patient comes from a family in which overweight is common—the usual setting—or whether she or he has become overweight in a family where few people are overweight. The latter setting suggests a need to search for environmental factors that may be contributing to weight gain. Recent studies have shown that among children and adolescents with a BMI above 30 kg/m2, alteration in the melanocortin-4 receptor occurs in 2.5% to 5.5% of these individuals. Among genetic defects associated with any chronic disease, this is one of the most common; and evaluation of whether this defect is present may become important in the treatment of overweight people.


Physical Examination

A physical examination of the patient is important to determine the degree of overweight and obesity, and to immediately identify any overt health concerns. Minimally, a physical examination should consist of measurements of BMI, waist circumference, blood pressure, and other visible signs of obesity-related complications such as Acanthosis nigricans.

1. Determining BMI and waist circumference—the vital signs associated with overweight. I will use the algorithm in figure 6.1 from the NHLBI (2). The BMI provides the first assessment of risk. Individuals with a BMI below 25 kg/m2 are at very low risk, but nonetheless, nearly half of those in this category at ages 20 to 25 will become overweight by age 60 to 69. Thus, a large group of pre-overweight individuals need preventive strategies. Risk rises with a BMI above 25 kg/m2. The presence of complicating factors further increases this risk. Thus, an attempt at a quantitative estimate of these complicating factors is important.

The first step in clinical examination of the overweight patient (5) is to determine vital signs, which include BMI and waist circumference as well as pulse and blood pressure. Accurate measurement of height and weight is the initial step in the clinical assessment (6), since these are needed to determine the BMI. The BMI is calculated as the body weight (kg) divided by the stature (height [m]) squared): kg/ht2. Body mass index has a reasonable correlation with body fat and is relatively unaffected by height. The height, weight, BMI, and other relevant clinical and laboratory data should be recorded during this evaluation. This helps categorize the patient as pre-overweight or overweight, and with or without clinical complications. The BMI needs to be interpreted in an ethnically specific context. An Asian conference selected lower levels of BMI to define overweight (BMI >23 kg/m2) and obesity (BMI >25 kg/m2).

Body mass index has a curvilinear relationship to risk. Several levels of risk can be identified. These cut points are derived from data collected on Caucasians. It is now clear, however, that different ethnic groups have different percentages of body fat for the same BMI. Thus, the same BMI presumably carries a different level of risk in each of these populations. One needs to take these differences into consideration when making clinical judgments about the degree of risk for the individual patient. During treatment for weight loss, the body weight is more useful than the BMI, since the height is not changing, and the inclusion of the squared function of height makes the BMI more difficult for physician and patient to evaluate.

2. Waist circumference. Waist circumference is the second vital sign in the evaluation of the overweight individual. The waist circumference is the most appropriate measurement for calculating central adiposity. It is determined using a metal or a nondistensible plastic tape. The two most common locations for measurement are at the level of the umbilicus and at the midpoint between the lower rib and the suprailiac crest. Although visceral fat can be measured more precisely with computed tomography (CT) or magnetic resonance imaging (MRI), these are expensive procedures; and clinical studies show that the waist circumference is essentially as good an indicator of visceral fat and much less difficult to obtain.

Measuring the change in waist circumference is a good strategy for following the clinical progress of weight loss. It is particularly valuable when patients become more physically active. Physical activity may slow loss of muscle mass and thus slow weight loss, while fat continues to be mobilized. Waist circumference can help in making this distinction. The relationship of central fat to risk factors for health varies among populations as well as within them. Japanese Americans and Indians from South Asia have relatively more visceral fat and are thus at higher risk for a given BMI or total body fat than are Caucasians. Even though the BMI is below 25 kg/m2, central fat may be increased particularly in Asian populations. Thus central adiposity is important, especially with BMI between 22 and 29 kg/m2.

3. Blood pressure. Careful measurement of blood pressure is important. Hypertension is amenable to improvement with diet and is an important criterion for a diagnosis of the metabolic syndrome. Having the patient sit quietly for 5 min before measuring the blood pressure with a calibrated instrument will help stabilize it. The blood pressure criteria from the Seventh Joint National Commission recommendations should be followed.

4. Other items for the physical examination. Acanthosis nigricans deserves a comment. This is a clinical condition with increased pigmentation in the folds of the neck, along the exterior surface of the distal extremities, and over the knuckles. It may signify increased insulin resistance or malignancy and should be evaluated.

Laboratory Evaluation

One strategy for refining the meaning of the BMI and the waist circumference is with laboratory measurements of lipids, glucose, and C-reactive protein (CRP). An increased fasting glucose, low high-density lipoprotein (HDL) cholesterol, and high triacylglycerol values are atherogenic components of the metabolic syndrome. Along with elevated blood pressure, it is possible to categorize the patient as having metabolic syndrome by one of several sets of criteria. In the International Diabetes Foundation (IDF) criteria, presence of increased central adiposity is required with abnormalities in two of the other four categories needed for making the diagnosis of metabolic syndrome. I prefer the IDF criteria, since they focus on the importance of central adiposity. In addition to the lipids that are determined as part of the assessment of the metabolic syndrome, a patient should have a measurement of low-density lipoprotein (LDL) cholesterol, which is a key risk factor. Also important is a measurement of highly sensitive C-reactive protein (hs-CRP). It is now clear that risk for heart disease can be predicted from both the LDL-cholesterol and hs-CRP.

The final issue is the plateau in body weight. Although not part of the evaluation of the overweight individual, it needs to be discussed with patients before they begin any program. After a period of time, weight loss slows and then stops. A value of 10% below starting weight would be a reasonable estimate of where most people will stop. Patients need to recognize this and need to know that when they maintain this lower weight for a time, they can then resume weight loss before another plateau occurs.