Section 10: Nutrients and their functions

1. Section 10: Nutrients and their functions • Nutritional requirements; inorganic nutrients 01/17/05

2. Introduction to Nutritional Requirements • Calories (typically 1900 to 2900 per day for adults). • Structural components for biosynthesis of macromolecules. • Inorganic compounds. • Structures needed in small amounts that cannot be synthesized. • Water. • Another way to group them is: carbohydrates, lipids, protein, inorganics (minerals and trace elements), vitamins and water. 1

3. Definitions of Essential Nutrients • Some nutrients are essential for life; humans cannot live without them. • Other nutrients are essential for optimal health; humans are not as healthy, or do not grow as much or as rapidly during childhood, or do not reproduce as well, without them. • Determined from experiments on humans, which are not easy to do. • volunteers • accidental deprivations • Or, extrapolated from animal experiments, which may not be applicable. 2

4. Essential Carbohydrate • None is absolutely essential. • A minimum of 250 g/day of digestible carbohydrate is recommended to obtain adequate energy. • Glucose is synthesized by humans, but is sometimes identified as essential. This is probably related to obtaining enough calories. • Cellulose has no caloric value for humans, but is essential for its role in accelerating peristalsis in the gut, which optimizes health. At least 12 gm/day is recommended. 3

5. Essential Protein • Protein is essential as a source of essential amino acids. • Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine cannot be synthesized by humans (S08L01). • Arginine can be synthesized, but not at adequate levels for optimal health and growth during childhood. • The recommended dietary allowance of protein is 63 g (males) and 50 g (females) for ages 25 - 50 years of age. 4

6. Essential Lipid • At least one fatty acid with double bonds beyond the 9-position (linoleic, linolenic, arachidonic or eicosapentaenoic) is required for the synthesis of eicosanoid hormones: thromboxanes, prostaglandins and prostacyclins (S07L02). • Lipids provide energy, but it is recommended that less than 30% of one’s total energy come from lipids. • It is recommended that diets contain less than 300 mg/day of cholesterol. 5

7. Intake Levels of Essential Nutrients • RDA = Recommended Dietary Allowance. • When RDA cannot be obtained, a range for “safe and adequate daily dietary intake” is estimated. • Amounts vary with age, sex and activity. • Uptake into cells can be as important as dietary intake. • Food Labeling Terms: • USRDA = United States RDA, which differs from RDA. • Daily Value or Daily Reference Value (for fat, carbohydrate, protein and electrolytes) & Reference Daily Intake (for vitamins and other minerals). • Older Terms • SDA = Safe Daily Allotment, which is no longer widely used. • MDR = Minimum Daily Requirement, obsolete. 6

8. RDA Definition • A Gaussian distribution (the bell-shaped curve) is typically “fitted” to one point , the average amount required to avoid a particular symptom. • RDA is defined as the amount that satisfies the requirement for 97.5% of population, i.e., everyone up to two standard deviations above the mean. 7

9. Inorganic Nutrients • Water and mostly ionic species. • Water is the solvent for most reactions. • It is also often a reactant or a product (about 250 ml per day produced by reduction of oxygen). • There are electrolytes, such as Na+. • Minerals, such as Ca2+. • And trace elements (< 100 mg per day required), such as F–. 8

10. Electrolytes and minerals have varied roles Na+ Water balance, nerve conduction, pacemaker activity. K+ Water balance, nerve conduction, pacemaker activity. Cl– Water balance, nerve conduction, pacemaker activity. Ca2+ Bone, teeth, intracellular messenger (~ 2% of body weight). Pi Bone, DNA, RNA, ATP, GTP, phosphoenzymes. Mg2+ Bone, nerve conduction, muscle activity, chelated by nucleotides. 9

11. Minerals - RDA Nutrient Men (mg) Women (mg) Ca2+ 800 800 Pi 800 800 Mg2+ 350 280 • Values for 25-50 year old 70 kg individuals. • The other minerals: sodium, potassium and chloride, are considered as major electrolytes. 10

12. Water and Major Electrolytes • Sodium (Na+) 500 mg • Potassium (K+) 2,000 mg • Chloride (Cl-) 750 mg • Water 2,500 g (2.5 liter) • These are estimated minimums for daily consumption. • There are no RDA values for these nutrients. • Only potassium is acutely toxic, in high doses. 11

13. Water and Electrolyte Balance • [+] = [-] in all compartments. • Water moves toward compartments with higher concentrations of solutes to equalize osmotic pressure. • Ionic solutes have the greatest effect. • Solutes are typically pumped across the membranes. 12

14. Major Ionic Species in Electrolyte Balance • Cationsoutside cellcytosol • Na+ 145 meq/L 10 meq/L • K+ 5 145 • Ca2+ ~2.5 0.0002 • Mg2+ 2 1 • Anions • Cl– 107 meq/L 2 meq/L • phosphates <2 92 • HCO3– 25 10 • organic acids 5 2 • proteins 15 50 • These are contributions of ionic species (meq = mM x charge). There are additional bound ions that contribute to total concentrations, but not to the electrolyte balance. 13

15. Essential Trace Elements, RDA and Roles Men Women Roles Fe(II) 10 mg 15 mg Hb, Mb, hemes, non-hemes I- 150 g 150 g thyroxine Zn(II) 15 mg 12 mg carboxypeptidase, carbonic anhydrase, DNA and RNA polymerases, super oxide dismutase Se 70 g 55 g glutathione peroxidase Values are for 25 - 50 year olds. • Selenium is hazardous above 200 g per day. • Notice there are mg and g units. • From Recommended Dietary Allowances, 10th Edition, National Research Council, 1989. 14

16. Essential Trace Elements Safe and Adequate Daily Dietary Intakes and Roles Cu(II) 1.5 - 3 mg Cyt oxidase, dopamine -hydrolase, ceruloplasmin, super oxide dismutase, factor VIII Cr(III) 50 - 200 g Glucose transport proteins (GLUTs), chromodulin-Cr(3+)4 Mn(II) 2 - 5 mg Arginase in the urea cycle Mo(II) 75 - 250 g Xanthine oxidase, ribonucleotide reductase Co(III) 2 g of B12 B12 F(-I) 1.5 - 4 mg Enamel strength, anti-osteoporosis (?) • Not enough data to determine RDA for this group. • Toxic levels are typically only several times the upper limit shown. • Values are for adults. • From Recommended Dietary Allowances, 10th Edition, National Research Council, 1989. 15

17. Biological Response to Intake • This schematic figure applies to most essential trace elements and to some vitamins. • The center of the abscissa is the RDA/body mass and varies depending on the nutrient. 16

18. Deficiency and Toxicity Example • Too little Zn2+: Enzymes such as RNA polymerase do not function. • Too much Zn2+: Zn2+ requiring enzymes function, but the excess Zn2+ competes with binding sites for other divalent cations and causes deficiencies in their functions. 17

19. Low Dietary Level  Low Tissue Level  Biochemical Lesion  Anatomical Lesion  Disease At each phase, the deficiency must persist over sufficient time to progress to the next phase. Not every deficiency has a named disease associated with it. Deficiency to Disease 18

20. Web links Nutritional analysis of foods: NAT Estimate caloric needs/use: Calculator Next topic: Iron, iodide, mercury