Final answer:
Hyperthyroidism, fat malabsorption, and cancer can cause a person to become malnourished due to various effects on metabolism, nutrient absorption, and appetite which lead to weight loss and nutrient deficiencies.
Step-by-step explanation:
Hyperthyroidism, fat malabsorption, and cancer are some medical reasons a person may become malnourished. Conditions like hyperthyroidism can lead to an increased metabolic rate, which may result in weight loss rather than weight gain. Fat malabsorption issues prevent the body from properly absorbing necessary fats, which can also contribute to malnutrition. Cancer and its treatments can significantly affect appetite and the body's ability to use nutrients, leading to malnutrition as well. This contrasts with conditions such as overnutrition which typically contributes to obesity, a condition marked by excessive body fat leading to health issues like metabolic syndrome and cardiovascular diseases.