TY - CHAP M1 - Book, Section TI - Toxic Effects of Calories A1 - Ronis, Martin J.J. A1 - Shankar, Kartik A1 - Badger, Thomas M. A2 - Klaassen, Curtis D. PY - 2019 T2 - Casarett & Doull’s Toxicology: The Basic Science of Poisons, 9th edition AB - All biotic organisms derive energy from food to sustain life and this energy “drives” various cellular functions, including digestion, metabolism, pumping blood, and muscle contractions. Nutrients can broadly be defined as chemical substances (typically found in foods or supplements) that are necessary for proper growth and development, reproduction, cellular function and maintenance, and repair following injury. Based on their chemical nature, nutrients can be grouped into organic (carbon-containing) and inorganic classifications. Carbohydrates, proteins, fats, and vitamins comprise the former, while minerals and water are inorganic nutrients essential for life (Stipanuk, 2006). Inorganic nutrients such as minerals can be absorbed into the body through food and are generally incorporated into the food chain through environmental sources (soil, water). Minerals comprise about 4% of the body weight in humans and in combination with water furnish a major part of the obligatory milieu necessary for cellular functioning (pH, osmolarity). Macrominerals are those whose abundance is generally 0.01% of body weight or daily required amounts exceed 100 mg/day. Calcium, phosphorous, sodium, and magnesium fall in this group. Other minerals that are not as abundant can be equally important for an organism. Trace minerals are defined as minerals whose concentration is less than 0.01% of total body weight. Other alternative definitions include nutrients whose requirements are below 1 ppm. Iron, zinc, copper, iodine, selenium, and molybdenum are six essential trace elements with established recommended dietary allowances. Overall, trace nutrients perform a variety of important functions, including transport of oxygen (iron as a part of hemoglobin), catalysis of biological reactions as component of enzymes (iron, zinc), and as part of other organic molecules (selenocysteine). While inorganic compounds serve important roles in physiology, the energy in food is derived from metabolism of organic substances. Organic compounds are generally synthesized by living cells from simpler molecules. For example, green plants and marine phytoplankton utilize photosynthesis to convert the very simple molecule carbon dioxide into more complex, energy-rich compounds such as carbohydrates using the energy from the sunlight. Because most bacteria and higher organisms cannot carry out photosynthesis, they derive their energy by metabolism of preformed organic molecules, such as carbohydrates. In general, bacteria utilize simpler organic molecules and animals and humans require more complex macronutrients (proteins, fats, and carbohydrates) to meet their energy needs. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/10/09 UR - accessbiomedicalscience.mhmedical.com/content.aspx?aid=1158503365 ER -