Nutrition refers to the interactions and balance between nutrients and other substances in food in relation to health and disease, and the processes by which the body ingests, digests, absorbs, transports, utilizes and excretes substances. Protein-energy malnutrition (PEM) occurs when the supply of protein and/or calories does not meet the needs of the organism to maintain normal physiological functions. Nutritional measurements include anthropometric indicators (e.g., body weight, body mass index, skinfold thickness, mid-arm muscle circumference, etc.), biochemical indicators (e.g., serum albumin, serum prealbumin, etc.), as well as dietary surveys and subjective comprehensive nutritional assessments.