A man, who does not know when to stop eating, is suffering from

Bulimia nervosa is an eating disorder marked by recurrent binge eating, where the person feels unable to stop eating, followed by compensatory behaviour such as self-induced vomiting, laxative misuse, fasting or excessive exercise. The core idea is loss of control over food intake, which is exactly what the stem describes.

• Bulimia (correct): a psychiatric condition defined by binge episodes and purging, not a digestive or metabolic complaint.
• Diabetes: a metabolic disorder of blood glucose regulation caused by insulin deficiency or resistance. Overeating is a risk factor, but the condition itself is not defined by eating behaviour.
• Anorexia nervosa: the opposite pattern. The person severely restricts food and fears weight gain, so the problem is refusing to eat, not failing to stop.
• Hyperacidity: excess stomach acid causing heartburn. It is a digestive symptom with no link to compulsive eating.

Mains angle: eating disorders sit at the intersection of mental health and public health, relevant to GS Paper II (health) and to the psychology of behaviour in GS Paper IV.

Trap: candidates pick diabetes because overeating is linked to it. Check what the stem defines, which is the eating behaviour itself, and that points to bulimia.