Nutrition II Lect 3 PDF

NUTRITION II Nikita Sahadeo, Ph.D. Biochemistry Unit Department Of Preclinical Sciences Faculty of Medical Sciences University of the West Indies January 2024 NUTRITION II: LEARNING OBJECTIVES Discuss the role of micronutrients in human and animal nutrition Discuss the results of inadequate dietary...

NUTRITION II Nikita Sahadeo, Ph.D. Biochemistry Unit Department Of Preclinical Sciences Faculty of Medical Sciences University of the West Indies January 2024 NUTRITION II: LEARNING OBJECTIVES Discuss the role of micronutrients in human and animal nutrition Discuss the results of inadequate dietary intake of micronutrients (vitamins) Discuss the absorption and metabolism of vitamins and trace minerals and their roles as coenzymes and cofactors in metabolic pathways Discuss the role of dietary fibre as part of a healthy diet Outline the dietary goals that are consistent with a healthy diet Discuss the special nutritional needs at various stages of the life cycle (infancy, childhood, adolescence, elderly), during pregnancy and lactation, and following major surgery MICRONUTRIENTS Required by the body in lesser quantities (micrograms to milligrams) Central role in metabolism and maintenance of tissue function THE ROLE OF MICRONUTRIENTS Cofactors in metabolism Coenzymes in metabolism Genetic control Antioxidants Damage is limited by mechanisms that include direct quenching of oxidant activity by tocopherols (vitamin E) or carotenoids (vitamin A), or enzyme systems to dispose of the products of oxidation— superoxide dismutase (either zinc/copper or manganese dependent) and glutathione peroxidase (selenium dependent) WHAT ARE VITAMINS? Complex, essential organic substances Perform a variety of metabolic functions Perform the same functions in different forms of life With the exception of vitamin D, micronutrients are not produced in the body and must be derived from the diet Though people only need small amounts of micronutrients, consuming the recommended amount is important At least half of children worldwide younger than 5 years of age suffer from vitamin and mineral deficiencies. THE B-COMPLEX VITAMINS THE “OTHER” VITAMINS VITAMINS & COENZYMES THIAMINE (VITAMIN B1) Only small amounts are stored in the liver, so a daily intake of thiamin-rich foods is needed The Recommended Dietary Allowance (RDA) for men ages 19 and older is 1.2 mg daily, and for women in the same age range 1.1 mg daily. For pregnancy and lactation, the amount increases to 1.4 mg daily. Is a cofactor (TPP) for multiple enzymes, including pyruvate dehydrogenase, alpha-ketoglutarate, transketolase, and branched-chain ketoacid dehydrogenase, all of which are involved in glucose breakdown. Deficiency can result in ATP depletion and often affects highly aerobic tissues such as the brain, nerves, and heart first. THIAMINE DEFICIENCY With heart involvement, it is called wet beriberi and is characterized by high-output heart failure, edema, and dyspnea on exertion. When the nervous system is involved, it is called dry beriberi, characterized by polyneuritis and symmetrical muscle wasting. Damage to the medial dorsal nucleus of the thalamus and the mammillary bodies in the brain can result in a condition called Wernicke encephalopathy, recognized by the classic triad of confusion, ophthalmoplegia, and ataxia, or Wernicke-Korsakoff syndrome when accompanying confabulation, personality change, and memory loss is present. Thiamine deficiency often is part of the presentation in patients with alcohol use disorder secondary to malnutrition and malabsorption, in addition to patients suffering from malnutrition. RIBOFLAVIN (VITAMIN B2) Naturally present in foods, added to foods, and available as a supplement Bacteria in the gut can produce small amounts of riboflavin, but not enough to meet dietary needs A key component of coenzymes involved with the growth of cells, energy production, and the breakdown of fats, steroids, and medications. Most riboflavin is used immediately and not stored in the body, so excess amounts are excreted in the urine The Recommended Dietary Allowance (RDA) for men and women ages 19+ years is 1.3 mg and 1.1 mg daily, respectively. For pregnancy and lactation, the amount increases to 1.4 mg and 1.6 mg daily, respectively. Is a cofactor in redox reactions (FAD and FMN) RIBOFLAVIN AND COENZYMES FMN is required for: l-amino acid oxidase cytochrome C reductase FAD is required as a coenzyme for: pyruvate dehydrogenase complex succinate dehydrogenase α-ketoglutarate dehydrogenase complex xanthine oxidase. RIBOFLAVIN DEFICIENCY Deficiency leads to cheilosis (inflammation of lips and fissures of the mouth) and corneal vascularization Because riboflavin assists many enzymes with various daily functions throughout the body, a deficiency can lead to health problems Animal studies show that the brain and heart disorders and some cancers can develop from long-term riboflavin deficiency. Disorders of the thyroid can increase the risk of a deficiency. A riboflavin deficiency most often occurs with other nutrient deficiencies, such as in those who are malnourished. NIACIN (VITAMIN B3) Two most common forms (food and supplements) are nicotinic acid and nicotinamide The body can also convert tryptophan to nicotinamide. Works in the body as a coenzyme, with more than 400 enzymes dependent on it for various reactions Utilized in redox reactions (as NAD+ and NADP+) Helps to convert nutrients into energy, create cholesterol and fats, create and repair DNA, and exert antioxidant effects Niacin is measured in milligrams (mg) of niacin equivalents (NE). One NE equals 1 milligram of niacin or 60 mg of tryptophan. The Recommended Dietary Allowance (RDA) for adults 19+ years is 16 mg NE for men, 14 mg NE for women, 18 mg NE for pregnant women, and 17 mg NE for lactating women. Metabolic function is to form the nicotinamide ring of the coenzymes NAD and NADP Helps release energy from nutrients NAD is required as a coenzyme for: pyruvate dehydrogenase complex; α-ketoglutarate dehydrogenase complex. NADP is required for reactions involving: glucose-6-phosphate dehydrogenase; 6-phosphate gluconate dehydrogenase. Groups at risk for deficiency Limited diets Chronic alcoholism Carcinoid syndrome PANTOTHENIC ACID (VITAMIN B5) A component of coenzyme A and fatty acid synthase Necessary for energy production and the formation of hormones The Recommended Dietary Allowance (RDA) for men and women ages 19+ years is 5 mg daily. For pregnancy and lactation, the amount increases to 6 mg and 7 mg daily, respectively. Deficiency is characterized by dermatitis, enteritis, alopecia, and adrenal insufficiency PYRIDOXINE (VITAMIN B6) Includes three compounds: pyridoxine, pyridoxal, and pyridoxamine. There may also be other forms of pyridoxine Pyridoxine, pyridoxal, and pyridoxamine are equal in activity for animals under many conditions Converted to pyridoxal phosphate (PLP) and is part of reactions including transamination, decarboxylation, and glycogen phosphorylase Critical for the formation of red blood cells The Recommended Dietary Allowance (RDA) for men ages 14-50 years is 1.3 mg daily; 51+ years, 1.7 mg. The RDA for women ages 14-18 years is 1.2 mg; 19-50 years, 1.3 mg; and 51+ years, 1.5 mg. For pregnancy and lactation, the amount increases to 1.9 mg mcg and 2.0 mg, respectively. PYRIDOXINE DEFICIENCY Deficiency can result in sideroblastic anemia, hyperirritability, convulsions, peripheral neuropathy, and mental confusion. BIOTIN (VITAMIN B7) Necessary for the metabolism of protein, fats, and carbohydrates Helps to regulate signals sent by cells and the activity of genes Biotin functions as a coenzyme in reactions involving CO2 E.g. pyruvate carboxylase; propionyl CoA carboxylase; acetyl CoA carboxylase Deficiency is very rare BIOTIN DEFICIENCY Initial symptoms are: hair loss, dry skin, brittle hair, fungal infections, seborrheic dermatitis, and rashes. Other symptoms include: fatigue, anemia, nausea, appetite loss, conjunctivitis, depression, dandruff, psoriasis, eczema, and loss of muscular reflexes. Prolonged deficiency can lead to muscle pain, heart problems, anemia, and depression Alcoholism can increase the risk of biotin deficiency FOLIC ACID (VITAMIN B9) Helps to form DNA and RNA and is involved in protein metabolism Plays a key role in breaking down homocysteine (an amino acid that can exert harmful effects in the body if it is present in high amounts) Needed to produce healthy red blood cells and is critical during periods of rapid growth, such as during pregnancy and fetal development. The Recommended Dietary Allowance for folate is listed as micrograms (mcg) of dietary folate equivalents (DFE). Men and women ages 19 years and older should aim for 400 mcg DFE. Pregnant and lactating women require 600 mcg DFE and 500 mcg DFE, respectively. People who regularly drink alcohol should aim for at least 600 mcg DFE of folate daily since alcohol can impair its absorption. TETRAHYDROFOLATE Coenzyme form of folic acid is tetrahydrofolate Carrier of single carbon and involved in single carbon transfer reactions Tetrahydrofolate is also involved in the generation of dTMP from dUMP (pyrimidine synthesis) in a reaction is catalyzed by thymidylate synthase FOLIC ACID DEFICIENCY Deficiency is rare because it is found in a wide range of foods The following conditions may put people at increased risk: Alcoholism Pregnancy Intestinal surgeries or digestive disorders that cause malabsorption Genetic variants Signs of deficiency can include: megaloblastic anemia; weakness, fatigue; irregular heartbeat; shortness of breath; difficulty concentrating; hair loss; pale skin; mouth sores. COBALAMIN (VITAMIN B12) Essential for erythropoiesis and development and functioning of the nervous system Binds to the protein in the foods, in the stomach, hydrochloric acid and enzymes unbind vitamin B12 into its free form. From there, vitamin B12 combines with a protein called intrinsic factor so that it can be absorbed further down in the small intestine. The Recommended Dietary Allowance for men and women ages 14 years and older is 2.4 micrograms (mcg) daily. For pregnancy and lactation, the amount increases to 2.6 mcg and 2.8 mcg daily, respectively. B12 used as descriptor for the cobalamins: § contain cobalt and corrin ring; § posses biological vitamin activity. Some corrinoids have no vitamin B12 activity Methylcobalamin Deoxyadenosylcobalamin COBALAMIN DEFICIENCY Deficiency may lead to pernicious anemia and subacute combined degeneration of the spinal cord The macrocytic megaloblastic anemia from B12 deficiency presents similarly to folate deficiency, and to differentiate them, it is imperative to obtain serum homocysteine and methylmalonic acid levels. In folate deficiency, homocysteine will elevate, but methylmalonic acid levels will be normal. In vitamin B12 deficiency, both homocysteine and methylmalonic acid levels will present as elevated Additionally, B12 deficiency will present with neurologic symptoms, whereas folate deficiency will not COBALAMIN DEFICIENCY Factors that may cause vitamin B12 deficiency: Avoiding animal products Lack of intrinsic factor Medications that cause decreased stomach acid Intestinal surgeries or digestive disorders that cause malabsorption COBALAMIN DEFICIENCY & NERVE DAMAGE Nerve damage caused by cobalamin deficiency: § methylcobalamin required in conversion of homocysteine to methionine; § causes lack of methionine used to make myelin. Occurs over a long period of time (decades) and may cause: § confusion or change in mental status (dementia) in severe or advanced cases; § depression; § loss of balance, numbness and tingling of hands and feet. ENZYMES DEPENDENT ON COBALAMIN Three enzymes dependent on cobalamin: methylmalonyl CoA mutase: § converts methyl malonyl CoA into succinyl CoA; § B12 deficiency causes accumulation of methylmalonyl CoA and urinary excretion of methylmalonic acid, which provides a means of assessing vitamin B12 nutritional status. leucine aminomutase methionine synthase: synthesis of methionine (affects myelin production). A HEALTHY DIET (WHO, APRIL 2020) Energy intake (calories) should be in balance with energy expenditure. To avoid unhealthy weight gain, total fat should not exceed 30% of total energy intake. Intake of saturated fats should be less than 10% of total energy intake, and intake of trans-fats less than 1% of total energy intake, with a shift in fat consumption away from saturated fats and trans-fats to unsaturated fats, and towards the goal of eliminating industriallyproduced trans-fats. Limiting intake of free sugars to less than 10% of total energy intake is part of a healthy diet. A further reduction to less than 5% of total energy intake is suggested for additional health benefits. Keeping salt intake to less than 5 g per day (equivalent to sodium intake of less than 2 g per day) helps to prevent hypertension, and reduces the risk of heart disease and stroke in the adult population. A healthy diet includes the following: Fruit, vegetables, legumes (e.g. lentils and beans), nuts and whole grains (e.g. unprocessed maize, millet, oats, wheat and brown rice). At least 400 g (i.e. five portions) of fruit and vegetables per day, excluding potatoes, sweet potatoes, cassava and other starchy roots. Less than 10% of total energy intake from free sugars, which is equivalent to 50 g (or about 12 level teaspoons) for a person of healthy body weight consuming about 2000 calories per day, but ideally is less than 5% of total energy intake for additional health benefits. Free sugars are all sugars added to foods or drinks by the manufacturer, cook or consumer, as well as sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates. Less than 30% of total energy intake from fats. Unsaturated fats (found in fish, avocado and nuts, and in sunflower, soybean, canola and olive oils) are preferable to saturated fats (found in fatty meat, butter, palm and coconut oil, cream, cheese, ghee and lard) and trans-fats of all kinds, including both industrially-produced trans-fats (found in baked and fried foods, and pre-packaged snacks and foods, such as frozen pizza, pies, cookies, biscuits, wafers, and cooking oils and spreads) and ruminant trans-fats (found in meat and dairy foods from ruminant animals, such as cows, sheep, goats and camels). It is suggested that the intake of saturated fats be reduced to less than 10% of total energy intake and trans-fats to less than 1% of total energy intake. In particular, industrially-produced transfats are not part of a healthy diet and should be avoided. Less than 5 g of salt (equivalent to about one teaspoon) per day. Salt should be iodized. DIETARY FIBRE Form the bulk of the stool and help in clearing the bowel and in preventing constipation Slow absorption of glucose and cholesterol from the GI tract, thus are helpful in diabetes and heart disease Fruits, vegetables, pulses, and whole cereals are sources of dietary fibre Our daily diet should contain some fibre for good health and well being