Final answer:
The condition causing extreme energy deficit and tissue wasting is known as cachexia. Unlike severe acute malnutrition, anorexia nervosa, kwashiorkor, or marasmus, cachexia is a complex metabolic syndrome associated with underlying illness and involves loss of muscle and potentially fat mass.
Step-by-step explanation:
The condition of extreme energy deficit causing tissue wasting is known as cachexia.
Cachexia is a complex metabolic syndrome associated with underlying illness and characterized by loss of muscle with or without loss of fat mass. The prominent clinical feature of cachexia is weight loss in adults (or growth failure in children). While similar in some aspects, it is important not to confuse cachexia with other forms of malnutrition such as severe acute malnutrition, anorexia nervosa, kwashiorkor, or marasmus, though these can also be associated with severe weight loss and muscle wasting.
Marasmus and kwashiorkor are both considered forms of protein-energy malnutrition, with marasmus resulting from inadequate protein and energy intake and kwashiorkor primarily due to inadequate protein intake, often with adequate calorie consumption. Anorexia nervosa is an eating disorder defined by an irrational fear of weight gain leading individuals to starve themselves, potentially leading to severe malnutrition.