Summary Nutrition An Applied Approach

Recall that the macronutrients carbohy- drates, fats, and proteins provide energy; thus, we need to consume them in relatively large amounts. In contrast, the micronutrients, vitamins and minerals, are needed in very small amounts. They are nev- ertheless essential to our survival, assisting critical body functions such as energy metabolism and the formation and maintenance of healthy cells and tissues. Much of our knowledge of vitamins and minerals comes from accidental observations of animals and humans. For instance, in the 1890s, a Dutch physician named C. Eijkman noticed that chickens fed polished rice developed paralysis, which could be reversed by feed- ing them whole-grain rice. Noting the high incidence of beriberi—a disease that results in extensive nerve damage—among hospital patients fed polished rice, Eijkman hypothesized that a highly refined diet was the primary cause of beriberi. We now know that whole-grain rice, with its nutrient-rich bran layer, contains the vitamin thiamin and that thiamin deficiency results in beriberi. Similarly, in the early 1900s, it was observed that Japanese children living in fishing villages rarely developed a type of blindness that was common among Japanese children who did not eat fish. Experiments soon showed that cod liver oil, chicken liver, and eel fat prevented the disorder. We now know that each of these foods contains vitamin A, which is essential for healthy vision. Such observations were followed by years of labora- tory research before nutritionists came to fully accept the idea that very small amounts of substances present in food are critical to good health. In 1906, English scientist F. G. Hopkins coined the term accessory factors for those sub- stances; we now call them vitamins and minerals. How are vitamins classified? Vitamins are organic compounds that regulate a wide range of body processes. Of the 13 vitamins recognized as essential, humans can synthesize only small amounts of vitamins D and K and niacin (a B vitamin), so we must consume virtually all of the vitamins in our diet. Most people who eat a varied and healthful diet can readily meet their vitamin needs from foods alone. The exceptions to this will be discussed shortly. Fat-Soluble Vitamins Vitamins A, D, E, and K are fat-soluble vitamins (TABLE 1). They are found in the fatty portions of foods (butterfat, cod liver oil, corn oil, etc.) and are absorbed along with dietary fat. Fat-containing meats, dairy products, nuts, seeds, vegetable oils, and avocados are all sources of one or more fat-soluble vitamins. In general, the fat-soluble vitamins are readily stored in the body’s adipose tissue; thus, we don’t need to con- sume them every day. While this may simplify day-to-day menu planning, there is also a disadvantage to our ability to store these nutrients. When we consume more of them than we can use, they build up in the adipose tissue, liver, and other tissues and can reach toxic levels. Symptoms of fat-soluble vitamin toxicity, described in Table 1, include damage to our hair, skin, bones, eyes, and nervous sys- tem. Overconsumption of vitamin supplements is the most common cause of vitamin toxicity in the United States; rarely do our dietary choices lead to toxicity. Of the four fat-soluble vitamins, vitamins A and D are the most toxic; megadosing with 10 or more times the recommended intake of either can result in irreversible organ damage and even death. Even though we can store the fat-soluble vitamins, deficiencies can occur, especially in people who have a malabsorption disorder, such as celiac disease, that reduces their ability to absorb dietary fat. In addition, people who eat very little dietary fat are at risk for a defi- ciency due to low intake and poor absorption. The conse- quences of fat-soluble vitamin deficiencies, described in Table 1, include osteoporosis, the loss of night vision, and even death in the most severe cases. Water-Soluble Vitamins Vitamin C (ascorbic acid) and the B-vitamins (thiamin, riboflavin, niacin, vitamin B 6 , vitamin B 12 , folate, pan- tothenic acid, and biotin) are all water-soluble vitamins LO 2 Distinguish between fat-soluble and water-soluble vitamins. megadosing Taking a dose of a nutrient that is 10 or more times greater than the recommended amount. LO 1 Identify some observations that led to the discovery of micronutrients. Avocados are a source of fat-soluble vitamins. 213 With the exception of vitamin B 12 , we do not store large amounts of water-soluble vitamins. Instead, our kidneys filter from our bloodstream any excess, which is excreted in urine. Because our tissues don’t store these vitamins, toxicity is rare. When it does occur, however, it is often from the overuse of high-potency vitamin supple- ments. Toxicity can cause nerve damage and skin lesions. Because most water-soluble vitamins are not stored in large amounts, they need to be consumed on a daily or weekly basis. Deficiency symptoms, including seri- ous disorders, can arise fairly quickly, especially during fetal development and in growing infants and children. The signs of water-soluble vitamin deficiency vary widely and are identified in Table 2. Same Vitamin, Different Names and Forms Food and supplement labels, magazine articles, and even nutrition textbooks often use simple, alphabetic (A, D, E, K, etc.) names for the fat-soluble vitamins. The letters reflect their order of discovery: vitamin A was discovered in 1916, (TABLE 2) (see page 215). They are found in a wide variety of foods, including whole grains, fruits, vegetables, meats, and dairy products. In general, they are easily absorbed through the intestinal tract directly into the bloodstream, where they then travel to target cells. Water-soluble vitamins can be found in a variety of foods. TABLE 1 Fat-Soluble Vitamins Vitamin Name Primary Functions Recommended Intake* Reliable Food Sources Toxicity/Deficiency Symptoms A (retinol, retinal, retinoic acid) Required for ability of eyes to adjust to changes in light Protects color vision Assists cell differentiation Required for sperm production in men and fertilization in women Contributes to healthy bone Contributes to healthy immune system RDA: Men: 900 μg/day Women: 700 μg/day UL: 3,000 μg/day Preformed retinol: beef and chicken liver, egg yolks, milk Carotenoid precursors: spinach, carrots, mango, apricots, cantaloupe, pumpkin, yams Toxicity: Fatigue, bone and joint pain, spontaneous abortion and birth defects of fetuses in pregnant women, nausea and diarrhea, liver damage, nervous system damage, blurred vision, hair loss, skin disorders Deficiency: Night blindness and xerophthalmia; impaired growth, immunity, and reproductive function D (cholecalciferol) Regulates blood calcium levels Maintains bone health Assists cell differentiation RDA: Adults aged 19–70: 15μg/day Adults aged 770: 20 μg/day UL 100 μg/day Canned salmon and mackerel, milk, fortified cereals Toxicity: Hypercalcemia Deficiency: Rickets in children, osteomalacia and/or osteoporosis in adults E (tocopherol) As a powerful antioxidant, protects cell membranes, polyunsaturated fatty acids, and vitamin A from oxidation Protects white blood cells Enhances immune function Improves absorption of vitamin A RDA: Men: 15 mg/day Women: 15 mg/day UL: 1,000 mg/day Sunflower seeds, almonds, vegetable oils, fortified cereals Toxicity: Rare Deficiency: Hemolytic anemia; impairment of nerve, muscle, and immune function K (phylloquinone, menaquinone, menadione) Serves as a coenzyme during production of specific proteins that assist in blood coagulation and bone metabolism AI: Men: 120 μg/day Women: 90 μg/day Kale, spinach, turnip greens, brussels sprouts Toxicity: None known Deficiency: Impaired blood clotting, possible effect on bone health *RDA: Recommended Dietary Allowance; UL: upper limit; AI: Adequate Intake. 214 such as vitamin C and ascorbic acid, you may be familiar with both terms. But few people would recognize cobalamin as vitamin B12 . Some of the water-soluble vitamins, such as niacin and vitamin B 6 , mimic the “umbrella” clustering seen with vitamins A, E, D, and K: the term vitamin B6 includes pyridoxal, pyridox- ine, and pyridoxamine. If you read any of these three terms on a supplement label, you’ll know it refers to vitamin B 6 . The vitamins pantothenic acid and biotin exist in only one form. There are no other related chemical compounds linked to either vitamin. Table 2 lists both the alphabetic and chemical terms for the water-soluble vitamins. Since all vitamins are organic com- pounds, they are all more or less vulner- able to degradation from exposure to heat, oxygen, or other factors. For tips on preserving the vitamins in the foods you eat, see the nearby Quick Tips. How are minerals classified? Minerals—such as calcium, iron, and zinc—are crystal- line elements; that is, you’ll find them on the periodic table. Because they are already in the simplest chemical form possible, the body does not digest or break them down prior to absorption. For the same reason, they cannot be degraded on exposure to heat or any other natural process, so the minerals in foods remain intact during storage and cooking. Furthermore, unlike vita- mins, they cannot be synthesized in the laboratory or by any plant or animal, including humans. Minerals are the same wherever they are found—in soil, a car part, or the human body. The minerals in our foods ultimately come from the environment; for example, the selenium in soil and water is taken up into plants and then incorporated into the animals that eat the plants. Whether we eat the plant foods directly or the animal products, we consume the minerals. Minerals are classified according to the intake required and the amount present in the body. The three groups include major, trace, and ultra-trace minerals. Major Minerals Major minerals are those the body requires in amounts of at least 100 mg per day. In addition, these minerals are found in the body in amounts of 5 g (5,000 mg) or higher. There are seven major minerals: sodium, potassium, phosphorus, chloride, calcium, magnesium, and sulfur. whereas vitamin K was not isolated until 1939. These lay terms, however, are more appropriately viewed as “umbrellas” that unify a small cluster of chemi- cally related compounds. For example, the term vita- min A refers to the specific compounds retinol, retinal, and retinoic acid. Simi- larly, vitamin E occurs naturally in eight forms, known as tocopherols, of which the primary form is alpha-tocopherol. Com- pounds with vitamin D activity include cholecalciferol and ergocalciferol, and the vitamin K “umbrella” includes phylloqui- none and menaquinone. As you can see, most of the individual compounds making up a fat-soluble vitamin cluster have simi- lar chemical designations (tocopherols, calciferols, and so on). Table 1 lists both the alphabetic and the chemical terms for the fat-soluble vitamins. Similarly, there are both alphabetic and chemical designations for water-soluble vitamins. In some cases, QuickTips Retaining the Vitamins in Foods Watch the water. Use as little as possible when storing or cooking foods to minimize the loss of water-soluble vitamins. For maximal retention of these vitamins, steam or microwave vegetables. Lower the heat. Avoid high temperatures for long periods of time to maximize retention of vitamin C, thiamin, and riboflavin. Avoid air. Store foods in tightly sealed containers. Exposure to air dramatically reduces the amount of vitamins A, C, E, and K, as well as B-vitamins. Whenever possible, eat raw fruits and vegetables as soon as they are prepared. Limit the light. Keep milk and other dairy foods out of direct light. When exposed to light, the riboflavin in these foods is rapidly destroyed. Using coated cardboard cartons or opaque plastic bottles protects the riboflavin in milk. Don’t play with pH. Although the addition of baking soda to certain vegetables enhances their color, it also increases the pH of the cooking water (makes it more alkaline), destroying thiamin, riboflavin, vitamin K, and vitamin C. LO 3 Describe the differences between major, trace, and ultra- trace minerals. Plants absorb minerals from soil and water. 215 TABLE 2 Water-Soluble Vitamins Vitamin Name Primary Functions Recommended Intake* Reliable Food Sources Toxicity/Deficiency Symptoms Thiamin (vitamin B 1 ) Required as enzyme cofactor for carbohydrate and amino acid metabolism RDA: Men: 1.2 mg/day Women: 1.1 mg/day Pork, fortified cereals, enriched rice and pasta, peas, tuna, legumes Toxicity: None known Deficiency: Beriberi; fatigue, apathy, decreased memory, confusion, irritability, muscle weakness Riboflavin (vitamin B 2) Required as enzyme cofactor for carbohydrate and fat metabolism RDA: Men: 1.3 mg/day Women: 1.1 mg/day Beef liver, shrimp, milk and other dairy foods, fortified cereals, enriched breads and grains Toxicity: None known Deficiency: Ariboflavinosis; swollen mouth and throat; seborrheic dermatitis; anemia Niacin, nicotinamide, nicotinic acid Required for carbohydrate and fat metabolism Plays a role in DNA replication and repair and cell differentiation RDA: Men: 16 mg/day Women: 14 mg/day UL: 35 mg/day Beef liver, most cuts of meat/fish/poultry, fortified cereals, enriched breads and grains, canned tomato products Toxicity: Flushing, liver damage, glucose intolerance, blurred vision Deficiency: Pellagra; vomiting, constipation, or diarrhea; apathy Pyridoxine, pyridoxal, pyridoxamine (vitamin B 6 ) Required as enzyme cofactor for carbohydrate and amino acid metabolism Assists synthesis of blood cells RDA: Men and women aged 19–50: 1.3 mg/day Men aged 750: 1.7 mg/day Women aged 750: 1.5 mg/day UL: 100 mg/day Chickpeas (garbanzo beans), most cuts of meat/fish/poultry, fortified cereals, white potatoes Toxicity: Nerve damage, skin lesions Deficiency: Anemia; seborrheic dermatitis; depression, confusion, and convulsions Folate (folic acid) Required as enzyme cofactor for amino acid metabolism Required for DNA synthesis Involved in metabolism of homocysteine RDA: Men: 400 μg/day Women: 400 μg/day UL: 1,000 μg/day Fortified cereals, enriched breads and grains, spinach, legumes (lentils, chickpeas, pinto beans), greens (spinach, romaine lettuce), liver Toxicity: Masks symptoms of vitamin B 12 deficiency, specifically signs of nerve damage Deficiency: Macrocytic anemia, neural tube defects in a developing fetus, elevated homocysteine levels Cobalamin (vitamin B 12) Assists with formation of blood cells Required for healthy nervous system function Involved as enzyme cofactor in metabolism of homocysteine RDA: Men: 2.4 μg/day Women: 2.4 μg/day Shellfish, all cuts of meat/fish/poultry, milk and other dairy foods, fortified cereals Toxicity: None known Deficiency: Pernicious anemia; tingling and numbness of extremities; nerve damage; memory loss, disorientation, and dementia Pantothenic acid Assists with fat metabolism AI: Men: 5 mg/day Women: 5 mg/day Meat/fish/poultry, shiitake mushrooms, fortified cereals, egg yolk Toxicity: None known Deficiency: Rare Biotin Involved as enzyme cofactor in carbohydrate, fat, and protein metabolism RDA: Men: 30 μg/day Women: 30 μg/day Nuts, egg yolk Toxicity: None known Deficiency: Rare Ascorbic acid (vitamin C) Antioxidant in extracellular fluid and lungs Regenerates oxidized vitamin E Assists with collagen synthesis Enhances immune function Assists in synthesis of hor- mones, neurotransmitters, and DNA Enhances iron absorption RDA: Men: 90 mg/day Women: 75 mg/day Smokers: 35 mg more per day than RDA UL: 2,000 mg Sweet peppers, citrus fruits and juices, broccoli, strawberries, kiwi Toxicity: Nausea and diarrhea, nosebleeds, increased oxidative damage, increased formation of kidney stones in people with kidney disease Deficiency: Scurvy, bone pain and fractures, depression, anemia *RDA: Recommended Dietary Allowance; UL: upper limit; AI: Adequate Intake. 216 amounts of less than 5 g (5,000 mg). Four trace minerals have an established RDA or AI: fluoride, iron, manga- nese, and zinc. 1 TABLE 4 identifies the primary functions, recommended intakes, food sources, and toxicity/defi- ciency symptoms of these minerals. A subset of trace minerals is a group known as ultra- trace minerals because they are required in amounts less than 1 mg per day. The DRI Committee has established an RDA or AI guideline for five ultra-trace minerals: chromium, copper, iodine, molybdenum, and selenium.1 TABLE 3 summarizes the primary functions, recommended intakes, food sources, and tox- icity/deficiency symptoms of these minerals. Trace and Ultra-Trace Minerals Trace minerals are those we need to con- sume in amounts of less than 100 mg per day. They are found in the human body in TABLE 3 Major Minerals Mineral Name Primary Functions Recommended Intake* Reliable Food Sources Toxicity/Deficiency Symptoms Sodium Fluid balance Acid–base balance Transmission of nerve impulses Muscle contraction AI: Adults: 1.5 g/day (1,500 mg/day) Table salt, pickles, most canned soups, snack foods, cured luncheon meats, canned tomato products Toxicity: Water retention, high blood pressure in some populations, loss of calcium in urine Deficiency: Muscle cramps, dizziness, fatigue, nausea, vomiting, mental confusion Potassium Fluid balance Transmission of nerve impulses Muscle contraction AI: Adults: 4.7 g/day (4,700 mg/day) Most fresh fruits and vegetables: potatoes, bananas, tomato juice, orange juice, melons Toxicity: Muscle weakness, vomiting, irregular heartbeat Deficiency: Muscle weakness, paralysis, mental confusion, irregular heartbeat Phosphorus Fluid balance Bone formation Component of ATP, which provides energy for our body RDA: Adults: 700 mg/day Milk/cheese/yogurt, soy milk and tofu, legumes (lentils, black beans), nuts (almonds, peanuts and peanut butter), poultry Toxicity: Muscle spasms, convulsions, low blood calcium Deficiency: Muscle weakness, muscle damage, bone pain, dizziness Chloride Fluid balance Transmission of nerve impulses Component of stomach acid (HCl) Antibacterial AI: Adults: 2.3 g/day (2,300 mg/day) Table salt Toxicity: None known Deficiency: dangerous blood acid–base imbalances, irregular heartbeat Calcium Primary component of bone Acid–base balance Transmission of nerve impulses Muscle contraction RDA: Adults aged 19–50 and men aged 51–70: 1,000 mg/day Women aged 51–70 and adults aged 770: 1,200 mg/day UL for adults 19–50: 2,500 mg/day UL for adults aged 51 and above: 2,000 mg/day Milk/yogurt/cheese (best-absorbed form of calcium), sardines, collard greens and spinach, calcium- fortified juices Toxicity: Mineral imbalances, shock, kidney failure, fatigue, mental confusion Deficiency: Osteoporosis, convulsions, heart failure Magnesium Component of bone Muscle contraction Assists more than 300 enzyme systems RDA: Men aged 19–30: 400 mg/day Men aged 730: 420 mg/day Women aged 19–30: 310 mg/day Women aged 730: 320 mg/day UL: 350 mg/day Greens (spinach, kale, collard greens), whole grains, seeds, nuts, legumes (navy and black beans) Toxicity: None known Deficiency: Low blood calcium, muscle spasms or seizures, nausea, weakness, increased risk for chronic diseases (such as heart disease, hypertension, osteoporosis, and type 2 diabetes) Sulfur Component of certain B-vitamins and amino acids Acid–base balance Detoxification in liver No DRI Protein-rich foods Toxicity: None known Deficiency: None known *RDA: Recommended Dietary Allowance; UL: upper limit; AI: Adequate Intake; DRI: Dietary Reference Intake. 217 TABLE 4 Trace and Ultra-Trace Minerals Mineral Name Primary Functions Recommended Intake* Reliable Food Sources Toxicity/Deficiency Symptoms Trace Minerals Fluoride Development and maintenance of healthy teeth and bones RDA: Men: 4 mg/day Women: 3 mg/day UL: 2.2 mg/day for chil- dren aged 4–8; 10 mg/day for children aged 78 Fish, seafood, legumes, whole grains, drinking water (variable) Toxicity: Fluorosis of teeth and bones Deficiency: Dental caries, low bone density Iron Component of hemo- globin in blood cells Component of myo- globin in muscle cells Assists many enzyme systems RDA: Adult men: 8 mg/day Women aged 19–50: 18 mg/day Women aged 750: 8 mg/day Meat/fish/poultry (best-absorbed form of iron), fortified cereals, legumes, spinach Toxicity: Nausea, vomiting, and diarrhea; dizziness and confu- sion; rapid heartbeat; organ damage; death Deficiency: Iron-deficiency micro- cytic anemia (small red blood cells), hypochromic anemia Manganese Assists many enzyme systems Synthesis of protein found in bone and cartilage AI: Men: 2.3 mg/day Women: 1.8 mg/day UL: 11 mg/day for adults Whole grains, nuts, leafy vegetables, tea Toxicity: Impairment of neuro- muscular system Deficiency: Impaired growth and reproductive function, reduced bone density, impaired glucose and lipid metabolism, skin rash Zinc Assists more than 100 enzyme systems Immune system function Growth and sexual maturation Gene regulation RDA: Men: 11 mg/day Women: 8 mg/day UL: 40 mg/day Meat/fish/poultry (best-absorbed form of zinc), fortified cereals, legumes Toxicity: Nausea, vomiting, and diarrhea; headaches; depressed immune function; reduced absorption of copper Deficiency: Growth retarda- tion, delayed sexual maturation, eye and skin lesions, hair loss, increased incidence of illness and infection Ultra-Trace Minerals Chromium Glucose transport Metabolism of DNA and RNA Immune function and growth AI: Men aged 19–50: 35 μg/day Men aged 750: 30 μg/day Women aged 19–50: 25 μg/day Women aged 750: 20 μg/day Whole grains, brewers yeast Toxicity: None known Deficiency: Elevated blood glu- cose and blood lipids, damage to brain and nervous system Copper Assists many enzyme systems Iron transport RDA: Adults: 900 μg/day UL: 10 mg/day Shellfish, organ meats, nuts, legumes Toxicity: Nausea, vomiting, and diarrhea; liver damage Deficiency: Anemia, reduced levels of white blood cells, osteo- porosis in infants and growing children Iodine Synthesis of thyroid hormones Temperature regulation Reproduction and growth RDA: Adults: 150 μg/day UL: 1,100 μg/day Iodized salt, saltwater seafood Toxicity: Goiter Deficiency: Goiter, hypothyroid- ism, cretinism in infant of mother who is iodine deficient Molybdenum Assists many enzyme systems RDA: Adults: 45 μg/day UL: 2 mg/day Legumes, nuts, grains Toxicity: Symptoms not well defined in humans Deficiency: Abnormal metabolism of sulfur containing compounds Selenium Required for car- bohydrate and fat metabolism RDA: Adults: 55 μg/day UL: 400 μg/day Nuts, shellfish, meat/ fish/poultry, whole grains Toxicity: Brittle hair and nails, skin rashes, nausea and vomiting, weakness, liver disease Deficiency: Specific forms of heart disease and arthritis, impaired immune function, mus- cle pain and wasting, depression, hostility *RDA: Recommended Dietary Allowance; UL: upper limit; AI: Adequate Intake. 218 These are included in Table 4. Other ultra-trace minerals such as arsenic, nickel, and vanadium are thought to be important or essential for human health, but there is not yet enough research to establish an RDA or AI guideline.1 As research into these ultra- trace minerals continue, scientists may soon be able to define a DRI value. Same Mineral, Different Forms Unlike vitamins, most of which can be identified by either alphabetic designations or their chemical name, minerals are simply referred to by their chemical name. Minerals in foods and supplements are often bound to other chemicals in compounds called salts; for example, a supplement label might identify calcium as calcium lactate, calcium gluco- nate, or calcium citrate. As we will discuss shortly, these different salts, while all containing the same elemental min- eral, may differ in their ability to be absorbed by the body. How does our body use micronutrients? The micronutrients found in foods and supplements are not always in a chemical form that our cells can use. This discussion will highlight some of the ways in which our body modifies the food forms of vitamins and minerals to maximize their absorption and utilization. What We Eat Differs from What We Absorb The most healthful diet is of no value unless the body can absorb its nutrients and transport them to the cells that need them. Unlike carbohydrates, fats, and proteins, which are efficiently absorbed (85–99% of what is eaten makes it into the blood), some micronutrients are so poorly absorbed that only 3–10% of what is eaten ever enters the bloodstream. The absorption of many vitamins and minerals depends on their chemical form. Dietary iron, for example, can be in the form of heme iron (found only in meats, fish, and poultry) or non-heme iron (found in plant and animal foods, as well as iron-fortified foods and supple- ments). Healthy adults absorb heme iron more readily than non-heme iron. In addition, the presence of other factors within the same food influences mineral absorption. For example, approximately 30% to 45% of the calcium found in milk and dairy products is absorbed, but the calcium in spin- ach, Swiss chard, seeds, and nuts is absorbed at a much lower rate because factors in these foods bind the calcium and prevent its absorption. Some micronutrients actually compete with one another for absorption. Several minerals, for example, use the same protein carriers to move across the enterocytes for release into the bloodstream. Iron and zinc compete for intestinal absorption, as do iron and copper. The absorption of many vitamins and minerals is also influenced by other foods within the meal. For example, the fat-soluble vitamins are much better absorbed when the meal contains some dietary fat. Calcium absorption is increased by the presence of lactose, found in milk, and non-heme iron absorption can be doubled if the meal includes vitamin C–rich foods, such as red peppers, oranges, or tomatoes. On the other hand, high-fiber foods, such as whole grains, and foods high in oxalic acid, such as tea, spinach, and rhubarb, can decrease the absorption of zinc and iron. It may seem an impossible task to cor- rectly balance your food choices to optimize micronutrient absorption, but the best approach, as always, is to eat a variety of healthful foods every day. See an example in MEAL FOCUS FIGURE 1, which compares a day’s meals high and low in micronutrients. What We Eat Differs from What Our Cells Use Many vitamins undergo one or more chemical transforma- tions after they are eaten and absorbed into our body. For example, before they can go to work for our body, thiamin and vitamin B 6 must combine with phosphate groups, and vitamin D must have two hydroxyl (OH) groups added to its structure. These transformations activate the vitamin; because the reactions don’t occur randomly, but only when the active vitamin is needed, they help the body maintain control over its metabolic pathways. While the basic nature of minerals does not change, they can undergo minor modifications that change their atomic structure. Iron (Fe) may alternate between Fe 2+ (ferrous) and Fe 3+ (ferric); copper (Cu) may exist as Cu1+ or Cu2+. These are just two examples of many modifica- tions that help the body make the best use of dietary micronutrients. What are some controversies in micronutrient research? The science of nutrition continues to evolve, and our current understanding of vitamins and minerals will no doubt change over the next several years or decades. While some people interpret the term controversy as negative, nutrition controversies are exciting develop- ments, proof of new information, and a sign of continued growth in the field. LO 4 Explain why the amount of a micronutrient we consume differs from the amount our body absorbs and uses. LO 5 Discuss three controversial topics in micronutrient research.