Macronutrients 1_Carbohydrates 23_24.pdf

Carbohydrates MD140 23-24 Jan , 2024 LOConnor Carbohydrates and Fat Why do we need them? We need an energy source – any source will do No requirement for dietary CHO or Fat (except essential FAs) – caution! Good source of energy /fat soluble vitamins/flavour /fat lubricates food Diets (35-40% energy...

Carbohydrates MD140 23-24 Jan , 2024 LOConnor Carbohydrates and Fat Why do we need them? We need an energy source – any source will do No requirement for dietary CHO or Fat (except essential FAs) – caution! Good source of energy /fat soluble vitamins/flavour /fat lubricates food Diets (35-40% energy from fat) associated with increased risk of heart disease and some cancers Diets (> 20% energy from protein) – also associated with chronic diseases So consensus – 55% energy CHO, 30% fat and 15% protein Carbohydrates Functions Source of metabolic fuel and energy stores Component of DNA and RNA Component of glycoproteins and glycolipids – cell membranes for cell-cell recognition and molecular targeting Carbohydrates Provide Energy ATP production – cellular respiration 4-22 Carbohydrates are Needed to Break Down Fat “fat burns in a CHO flame”M Recall from Sem 1 During Starvation/absence of CHO in the diet – body needs energy so breaks down fat 1. FAO – leads to generation of acetyl CoA 2. Acetyl CoA from TAGs can be directed to TCA , ETC and ox phos to generate energy 3. Elevated acetyl CoA inhibits PDH (less pyruvate formed) 4. OAA produced by pyruvate carboxylase is used by the liver for gluconeogenesis (needs CHO for CNS) 5. FAO also decreases NAD+/NADH ratio and the rise in NADH will favour the conversion of OAA to malate 6. Decreased availability of OAA for condensation with acetyl-CoA - acetyl CoA used for ketone body formation -So Fat burns in an oxaloacetate flame Classification of Dietary CHO Monosaccharides Disaccharides Polysaccharides i) ii) Starch polysaccharides Non-starch polysaccharides Dietary Fiber i) ii) Soluble fiber Insoluble fiber Nutritional classification of carbohydrates polysaccharides starch oligosaccharides dextrins sugar alcohols sugars: monosaccharides disaccharides intrinsic sugars extrinsic sugars in free solution non-starch polysaccharides trisaccharides tetrasaccharides lactose in milk non-milk extrinsic examples Monosaccharides + Disaccharides Sugars contained with Sugars in free solution in Plant cell walls in foods Foods INTRINSIC SUGARS: Sugars contained within plant cell walls in foods EXTRINSIC SUGARS: In free solution, provide substrate for oral bacteria, lead to formation of dental plaque and caries Consumption should be minimized due to a) Role in dental decay b) So easy (nice!) to eat and so potential for overconsumption -obesity Note: Lactose exception Sugar Alcohols Formed by the reduction of the aldehyde grp of a monosaccharide to a hydroxyl (-OH) grp Quantitatively the most important – Sorbitol from glucose Absorbed in GIT and metabolized slowly- lower glycemic index that other CHOs Minor effect of conc of glucose in blood Widely used in foods suitable for diabetics Is a metabolic fuel –energy yield approx ½ of glucose Not suitable in weight-reducing diets Xylitol Sugar alcohol formed by reduction of the 5C sugar xylose, an isomer of ribose Anti cariogenic action “tooth-friendly” sweets GLYCEMIC CHO NONGLYCEMIC CHO Classification of dietary CHOs by their glycemic index Glycemic polysaccharides starch oligosaccharides dextrins sugar alcohols sugars monosaccharides disaccharides intrinsic sugars extrinsic sugars in free solution Non-glycemic non-starch polysaccharides trisaccharides tetrasaccharides RED –non-glycemic CHOs lactose in milk non-milk extrinsic BLUE –Glycemic CHOs Dietary CHO & Blood Glucose Glycemic Index -A Means of comparing quantitatively the blood glucose responses following ingestion of equivalent amounts of digestible CHO from different foods CHO with high glycemic index – greater insulin secretion after a meal Increased synthesis of FAs and TAGs contributes to obesity? Factor in development of Type 11 diabetes? Glycemic Index /Load Index: Defined as the effect of 50g of CHO in a particular food on blood glucose levels compared to 50g of glucose Glycemic Load: The index times the amount of CHO in a standard serving size of that food. Glycemic Response The rate, magnitude, and duration of the rise in blood glucose that occurs after a food or meal is consumed. Glycemic index: a ranking of how a food affects blood glucose compared to the response of a reference food Glycemic load: an index of glycemic response 4-25 Fiber Cannot be digested by the human body All can be fermented to some extent by intestinal bacteria The products of bacterial fermentation may be absorbed and metabolized as metabolic fuel Beneficial health effects Terms related to fiber: Dietary fiber: A mixture of indigestible CHO and lignin that is found intact in plants Functional fiber: Isolated indigestible CHO that has been shown to have beneficial effects in humans Total fiber: The sum of dietary and functional Soluble fiber: Dissolves in water to form viscous solutions that can be broken down by the intestinal micro flora e.g. pectins, gums Insoluble fiber: Mostly does not dissolve in water and cannot be broken down by bacteria in the large intestine e.g. cellulose, lignin Soluble Fiber—Healthy Heart Dissolves in water or absorbs water Can be broken down by the intestinal microflora Includes: pectins, gums, semicelluloses Food sources: oats, apples, beans, seaweeds Health benefits: lower blood cholesterol Insoluble Fiber—Happy GI Tract Does not dissolve in water, can absorb water Cannot be broken down by bacteria in the large intestine Includes: cellulose, hemicellulose, and lignin Food sources: wheat bran, rye bran, and vegetables Health benefits: soften stools and decrease transit time Diverticula form at weak points due to pressure exerted when the colon contracts – inflammed – diverticulosis - diverticulitis Note: fiber without water consumption can cause constipation – the more fiber in the diet the more water is needed. Severe cases can result in intestinal blockages Indigestible CarbohydratesFiber-rich meal Low-fiber meal Fiber, some oligosaccharides, and resistant starch Health implications Stimulate GI motility Promote a healthy microflora Slow nutrient absorption Increase intestinal gas Bulk and vol – dilute the GI contents – slows digestion and absorption Dietary fibres reduce the risk of colorectal cancer by: High bile acid concentrations are associated with a high risk of colon cancer. Fibers -by adsorbing bile acids serve a protective effect. Fiber fermentation to short-chain fatty acids decreases the luminal pH, thereby decreasing synthesis of secondary bile acids Fibers reduce exposure of colonic enterocytes to carcinogens Fibers by increasing fecal bulk decrease the intraluminal concentrations of carcinogens Insoluble fibers such as lignin that resist degradation bind carcinogens, thereby minimizing the chances of interactions with colonic mucosal cells. A shortened colonic fecal transit time decreases the time during which toxins can be synthesized and in contact with the colon. Soluble fibers can be fermented into short chain fatty acids. The SCFA, butyric acid slows the proliferation and enhance differentiation of colon cancer cells. Fibres are digested by colon microflora Dietary fibres and undigested starch are substrates for degradation by the bacteria of the large intestine that produce short chain fatty acids (SCFAs) These short chain fatty acids are: acetate, propionate, and butyrate. SCFAs are readily absorbed by enterocytes of the colon and released in the blood stream. Butyrate is the major energy source for colonocytes. Propionate is largely taken up by the liver. Acetate enters the peripheral circulation to be metabolized by peripheral tissues. Butyrate also promotes differentiation, cell-cycle arrest and apoptosis of transformed colonocytes; inhibiting the enzyme histone deacetylase (an enzyme involved in gene inactivation and often aberrantly active in cancers) and decreasing the transformation of primary to secondary bile acids as a result of colonic acidification. http://journals.lww.com/jcge/pages/articleviewer.aspx?year=2006&issue=03000&article=00015&type =abstract Nutrition Research Volume 83, November 2020, Pages 63-72 Superior inhibitory efficacy of butyrate over propionate and acetate against human colon cancer cell proliferation via cell cycle arrest and apoptosis: linking dietary fiber to cancer prevention☆ K.HamlinaBryan D.SafratowichaWen-HsingChengbLuAnn K.Johnsona Optional Reading – Carbohydrates in Nutrition Food for the human infant“Breast is best” Many valuable components in breast milk Human milk rich in prebiotic oligosaccharides that enhance the infant’s ability to develop a desirable intestinal bacterial flora Breast Milk Protein, fats, CHO, vits and minerals Wide range of immune cells Bioactive components with i) anti-inflammatory ii) Anti-infective iii) Probiotic action Evidence it contains its own microbiota Factors that influence the composition of the intestinal microbiota Major insoluble non-starch polysaccharides CELLULOSE: (insoluble) Polymer of glucose (b1-4 ) bonds – cannot be hydrolysed by human enzymes Hemicelluloses (insoluble) Branched polymer of pentose and hexose INULIN (insoluble) Polymer of fructose – storage CHO of many root veg (Jerusalem artichoke) Pectin (soluble) A complex polymer of a variety of monosaccharides, including some methylated sugars Plant Gums (soluble) e.g. gum Arabic, gum tragacanth etc – complex polymers of mixed monosaccharides Mucilages (soluble) E.g. alginates, agar and carrageen; complex polymers of mixed monosaccharides found in seaweeds and other algae Good sources of soluble fiber Legumes Prunes Apricots Raisins Oranges Bananas Oats Apples eggplant Good sources in insoluble fiber Wheat bran Whole-wheat bread Broccoli Corn Eggplant Apple skins Nuts and seeds Alternative Sweeteners Acceptable Daily Intakes (ADIs) set by FDA Cut down on kcalories in, but do not add whole grains, fruits, and vegetables to the diet Have been shown to reduce the incidence of dental caries Usefulness for weight loss controversial Types of Alternative Sweeteners Saccharin 200–700 times sweeter than sugar No warning labels required since May 2000 Aspartame Made of aspartic acid and phenylalanine Can be dangerous to people with phenylketonuria (PKU) Sucralose (Trichlorogalactosucrose) Sold under the name “Splenda” Derived from sugar 4-46 Acesulfame K (Sunette or Sweet One) 200 times as sweet as sugar Heat stable Neotame Similar to aspartame, with stronger chemical bond (cannot be broken down easily) 7000–13,000 times sweeter than sugar! Sugar alcohols Chemical derivatives of sugar Low-calorie: 0.2–3 kcalories/gram Can be described as “sugar free” on food labels 4-47 HFCS (high fructose corn syrup) Cheaper and more stable during storage than other sweeteners Link with obesity Omnipresent in food Biochem: fructose enters glycolysis after the main regulatory step – results in increased synthesis of FAs and TAG in liver and adipose tissue Pharmacol Biochem Behav 97: 101-106, 2010 – rats fed diet supplemented with water sweetened with either HFCS or sucrose. HFCS ones got fatter, had higher TAG levels –despite consuming less calories Proteins and Amino Acids That May Harm Certain Individuals Aspartame and phenylketonuria (PKU) Monosodium glutamate (MSG) sensitivity