Final answer:
Pregnant women and young children are especially vulnerable to undernutrition due to their higher nutritional requirements and susceptibility to the negative effects of undernutrition.
Step-by-step explanation:
Especially vulnerable groups to undernutrition include pregnant women and young children. According to the World Health Organization, there are 47 million children under 5 years of age who are underweight for their height and 144 million children who are stunted due to undernutrition. Pregnant women and young children have higher nutritional requirements and are more susceptible to the negative effects of undernutrition.