D) anorexia nervosa
Anorexia nervosa is a serious eating disorder that is characterized by an abnormally low body weight, an intense fear of gaining weight, and a distorted perception of weight. People with anorexia nervosa often have a persistent desire to lose weight, even if they are already underweight. This desire to lose weight is often achieved by severely restricting the amount of food they eat, and in some cases, engaging in excessive exercise or purging behaviors. Despite losing significant amounts of weight, people with anorexia nervosa continue to fear weight gain, which can lead to a range of physical and psychological health problems.
In this context, Jack's behavior of reducing his calorie intake from 1000 to 750 calories per day is concerning, as it may indicate that he is at risk of developing or may already have anorexia nervosa. Severe calorie restriction can have serious consequences for physical and mental health, including malnutrition, dehydration, electrolyte imbalances, and depression. Therefore, it is important for Jack to seek professional help if he is struggling with disordered eating or body image issues. Treatment for anorexia nervosa typically involves a combination of therapy, nutritional counseling, and medical monitoring to address both the physical and psychological aspects of the disorder.