Nutrition is that the science that interprets the nutrients and other substances in food in reference to maintenance, growth, reproduction, health and disease of an organism. It includes ingestion, absorption, assimilation, biosynthesis, catabolism and excretion. The diet of an organism is what it eats, which is essentially determined by the supply and palatability of foods. For humans, a healthy diet includes preparation of food and storage methods that preserve nutrients from oxidation, heat or leaching, which reduces risk of foodborne illnesses. The seven major classes of human nutrients are carbohydrates, fats, fiber, minerals, proteins, vitamins, and water. Nutrients are often grouped as either macronutrients or micronutrients (needed in small quantities). In humans, an unhealthy diet can cause deficiency-related diseases like blindness, anemia, scurvy, preterm birth, stillbirth and cretinism, or nutrient excess health-threatening conditions like obesity and metabolic syndrome; and such common chronic systemic diseases as disorder , diabetes, and osteoporosis. Undernutrition can cause wasting in acute cases, and therefore the stunting of marasmus in chronic cases of malnutrition.