Published: 12 February, 2004

Nutrients in food form in organic and inorganic ways

How do minerals and nutrients form? Why do some foods have metals in them?

Nutrients can be divided into two groups. The first group is those that can be used in inorganic form. Inorganic means they do not need to come from living sources like plants or animals. These inorganic nutrients are usually called minerals. All forms of life require some inorganic nutrients. Minerals are present in the earth's crust and are taken up from soil or water by plants and microorganisms, thus making their way into the food chain. The amount of some minerals in foods can vary substantially depending on the concentration of that mineral in the soil or water in which the food was grown.

Human beings require over a dozen different minerals in their diets. These include calcium and phosphorous that we need to make bones and teeth, iodine that we need to make thyroid hormone, and iron that we need as part of certain proteins including the hemoglobin in red blood cells. Much of our mineral intake comes from the foods we eat, but we also obtain minerals from water sources, salts, and food additives.

The second group is the carbon-containing or organic nutrients that make up the bulk of our diets and provide us with energy. Organic nutrients include proteins, carbohydrates (sugars and starches), fats, and vitamins and are synthesized by living cells from simpler compounds. Green plants on land and photoplankton that live in water (like algae and a special group of photosynthetic bacteria) form the base of the organic nutrient chain. These chlorophyll-containing forms of life use energy from sunlight to combine carbon dioxide (CO₂) from the atmosphere and water (H₂O) to make carbohydrates (C_nH_2nO_n) by a process we call photosynthesis. Biologists call plants and photoplankton "producers" because of this ability to make organic compounds (like sugars and starches) from inorganic compounds (CO₂ and H₂O) in the environment.

Animals and most microorganisms cannot carry out photosynthesis and must have pre-formed organic material in their diets. Biologists call bacteria and animals "consumers" because they obtain food by eating other organisms. Bacteria generally have simple nutrient needs. Most bacteria need a simple organic carbon source, usually from decaying plant or animal life. Animals and humans, on the other hand, have complex nutritional needs and require a number of different organic compounds in their diets. We obtain organic nutrients - proteins, carbohydrates, fats including some essential fatty acids, and 13 essential vitamins - by consuming a variety of plant and animal foods.

Why do some foods have metals in them? Many chemical elements or minerals are also called metals because of their properties. Some of the minerals (like sodium and potassium) required in our diets are metals. Although we need a certain amount of each of the essential minerals in our diets, too much can be harmful or toxic. There is also concern about the pollution of our food supply with toxic compounds formed from some minerals that we do not need. The best-known example is the industrial pollution of some rivers and lakes with waste mercury. Bacteria convert the mercury to organic forms, and the mercury makes its way into marine organisms and fish, resulting in the need to limit our consumption of fish from these bodies of water.

How do minerals form? We know elements are formed by a complex process called atomic fusion that occurs inside the centers of stars, but this nutritional biochemist will leave the question of solar system formation for the astrophysicists and theologians!