Hello, 

While I am not familiar with the details of nutrition policy in the Philippines, I do know that most countries lack guidance on undernutrition in teenagers and adults. From what I can see online, it looks like Philippines policy focuses on reducing overweight and obesity, and micronutrient deficiencies in adults, not underweight. However, they do have some good dietary guidelines - such as those mentioned here - https://www.fnri.dost.gov.ph/index.php/publications/writers-pool-corner/57-food-and-nutrition/204-nutritional-guidelines-for-filipinos-a-prescription-to-good-nutrition  -although I think there is a further updated version... 

If you are trying to support weight gain in underweight adolescents/adults, you could advise them to increase their consumption of healthy-high-fat foods, using small but regular meals, such as eating more avocado, milk, milk powder, yogurt, cheese, and nuts. I understand that the costs of these foods may be prohibitive to students, so maybe there is a social protection program they can access, or food supplementation program.