Weight and muscle loss can result from various conditions. Because they can result from serious health conditions, anyone experiencing sudden changes in weight or muscle mass should see their physician. Common causes for weight loss and muscle wasting, or sarcopenia, include changes in diet and activity level, disease and age. Some health conditions can be prevented with proper nutrition and exercise.
Weight loss that is a result of intentional undernourishment, such as anorexia, or extreme calorie reducing diets, causes the body's metabolic rate to slow down and conserve energy, in this case fat. Since muscle is metabolically active, meaning it requires energy to perform, breaking down muscle tissue for fuel helps to reduce the energy requirements and provide nourishment for the rest of the body. Simply put, the body may burn muscle for fuel while storing fat for emergency. This is called muscle catabolism. This is why proper nutrition and exercise plans should be implemented to prevent muscle loss as you lose weight, the 2008 text "Physiology of Sport and Exercise" notes.
Disease and Nerve Damage
The National Institutes of Health explains that muscle atrophy can result from disease or injury to nerve cells, called neurogenic atrophy, and states that contrary to muscle loss with aging, this type of muscle loss occurs quickly. Other diseases and conditions that can cause weight loss and/or muscle loss include diabetes, stroke, Lou Gehrig's disease, muscular dystrophy, HIV, thyroid disorders and polio.
Age-related Weight and Muscle Loss
With the natural aging process, the body's ability to maintain muscle mass lessens after the age of 30. Without strength training, the average adult will lose 10 percent of muscle mass each decade. This loss is difficult to detect since adults tend to gain fat weight simultaneously as they are losing lean muscle mass because their eating habits typically do not change with their energy requirements. Simple scales will not reveal a change in body composition. Body composition is measured with various techniques provided by a physician or trained athletic personnel. Weight and muscle loss is common in older adults and can result from loss of appetite, loss of the sense of smell or taste, medications or poor health, "Physiology of Sport and Exercise" notes.