Chapter 24 WEIGHT LOSS
INTRODUCTION
Definitions
In research studies, weight loss may be defined as a weight loss of >5% of usual body weight over a period of 6–12 months. Weight loss >10% is usually associated with protein–energy malnutrition while weight loss >20% implies severe protein–energy malnutrition and significant organ dysfunction. One quantitative measure of nutritional status is that of body mass index (BMI). This is defined as body weight in kg divided by height in metres squared (kg/m2). A BMI lower than 17 is consistent with undernutrition. Other anthropometric measures include arm circumference and triceps skin fold thickness, but these are affected, at least to some extent, by skin changes associated with ageing.
CAUSES OF WEIGHT LOSS
Potential causes of weight loss are strongly influenced by the age at presentation. For example, in young adults, unintentional weight loss is often due to psychiatric disorders such as depression, anorexia nervosa, bulimia, psychoses and substance abuse. In contrast, weight loss in the elderly is often due to multiple factors including social isolation, bereavement, dementia, depression, poor dentition and side effects from drugs. In middle age, there may be a greater contribution from cancer, alcoholism, endocrine disorders and chronic inflammatory disorders. Cancer is diagnosed in up to 25% of patients with weight loss over the age of 50 years. Some of the factors that contribute to weight loss are outlined below and are summarised in Figure 24.1.