Carbohydrates and Fats in Diet

Carbohydrates and Fat

• An energy source is needed by the body, any source will do
• There's no dietary requirement for carbohydrates or fats, except for essential fatty acids
• Carbohydrates and fats are a good energy source, provide fat-soluble vitamins, flavor, and fat lubricates food
• Diets with 35-40% energy from fat have been linked to an increased risk of heart disease and certain cancers
• Diets with >20% energy from protein have also been linked to chronic diseases
• A consensus for a healthy diet includes 55% energy from carbohydrates, 30% from fat, and 15% from protein

Functions of Carbohydrates

• Carbohydrates serve as a source of metabolic fuel and energy stores
• Carbohydrates are a component of DNA and RNA
• Carbohydrates are a component of glycoproteins and glycolipids, the cell membranes for cell-cell recognition and targeting

Energy from Carbohydrates

• ATP production comes from cellular respiration

Breaking Down Fat

• Carbohydrates are needed to break down fat
• Fat burns in a carbohydrate flame

Carbohydrate Absence

• A body requires energy during the starvation or absence of carbohydrates, thus breaking down fat
• FAO leads to the generation of acetyl CoA
• Acetyl CoA from TAGs is directed to TCA, ETC, and ox phos which generate energy
• Elevated acetyl CoA inhibits PDH which results in less pyruvate formation
• OAA, produced by pyruvate carboxylase, is used by the liver for gluconeogenesis, needing carbohydrates for the CNS
• FAO also decreases the NAD+/NADH ratio, thus the rise in NADH favors the conversion of OAA to malate
• Decreased availability of OAA for condensation with acetyl-CoA means the use of acetyl CoA for ketone body formation
• Thus, fat burns in an oxaloacetate flame

Dietary Carbohydrate Classification

• Monosaccharides
• Disaccharides
• Polysaccharides, including starch and non-starch polysaccharides
• Dietary fiber, including soluble and insoluble fiber

Nutritional Classification of Carbohydrates

• Polysaccharides, which include starch and non-starch polysaccharides
• Oligosaccharides, which include dextrins
• Sugar alcohols
• Sugars, which include monosaccharides and disaccharides
• Sugars are further classified into intrinsic (contained within plant cell walls in foods) and extrinsic (in free solution)
• Lactose in milk is a type of extrinsic sugar
• Non-milk extrinsic sugars are also classified as extrinsic sugars in free solution

Simple Sugars

• Monosaccharides are the simplest form of carbohydrate, including Glucose, Fructose, Galactose and Xylose
• Disaccharides contain 2 monosaccharide units, including Sucrose, Lactose, Maltose and Trehalose

Complex Carbohydrates/Polysaccharides

• Starch are polymers of glucose, also classified as storage carbohydrate
• Non-starch polysaccharides are classified as insoluble components like cellulose, and soluble like Pectin, B-glucan, Arabinoxylans, Xyloglucans, Glucomannans, Galactomannans
• Resistant starch (RS) are non-digestible and include physically protected starch (RS1), ungelatinised resistant granules (RS2), retrograded starch (RS3), chemically modified starch (RS4) and amylose-lipid complex (RS5)

Monosaccharides and Disaccharides

• Can be found contained within plant cell walls in foods
• Can be found in free solution in foods

Intrinsic Sugars

• Are sugars contained within plant cell walls in foods

Extrinsic Sugars

• Provide a substrate for oral bacteria in free solution, which leads to the formation of dental plaque and caries
• consumption should be minimized because of its role in dental decay and potential for over consumption
• Lactose is an exception

Sugar Alcohols

• They are formed by reducing the aldehyde group of a monosaccharide to a hydroxyl (-OH) group
• Sorbitol, derived from glucose, is quantitatively the most important
• Absorbed in the GI tract and metabolized slowly, resulting in a lower glycemic index compared to other carbohydrates
• Has a minor effect on glucose concentration in the blood
• Used in foods suitable for diabetics
• Is a metabolic fuel, yielding approximately ½ the energy of glucose
• Not suitable for weight-reducing diets

Xylitol

• Formed by reduction of the 5-carbon sugar xylose, an isomer of ribose
• Carries anti cariogenic action
• “tooth-friendly” sweets

Classification by Glycemic Index

• Glycemic include glucose containing carbohydrates
• Non-glycemic include many fibers

Glycemic Index

• A way of comparing blood glucose responses quantitatively after ingesting equivalent amounts of digestible carbohydrates from different foods

Glycemic Index and Insulin Secretion

• High glycemic index carbohydrates lead to greater insulin secretion after a meal
• Increased synthesis of fatty acids and TAGs
• High glycemic index carbohydrates may contribute to obesity
• High glycemic index carbohydrates may be a factor in the development of Type 11 diabetes

Glycemic Load

• Defined as the effect of 50g of CHO in a particular food on blood glucose levels compared to 50g of glucose
• Represents the index times the amount of carbohydrate in a standard serving size of the food

Glycemic Response

• Glycemic response measures the rate, magnitude, and duration of the rise in blood glucose after consuming a food or meal
• Glycemic index: Ranking of how much a food affects blood glucose compared to a reference food
• Glycemic load: An index of glycemic response

Fiber

• Humans cannot digest fiber
• All fiber can be fermented to some extent by intestinal bacteria
• The products of bacterial fermentation may be absorbed and metabolized as metabolic fuel
• Consumption of fiber has beneficial health effects

Fiber-related Terms

• Dietary fiber: A mixture of indigestible carbohydrates and lignin that is found intact in plants
• Functional fiber: Isolated indigestible carbohydrates shown to have beneficial effects in humans
• Total fiber: The sum of dietary and functional fiber
• Soluble fiber: Dissolves in water to form viscous solutions that can be broken down by the intestinal microflora 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

• Dissolves in water or absorbs water
• Can be broken down by the intestinal microflora
• Includes pectins, gums, semicelluloses
• Food sources include oats, apples, beans, seaweeds
• Soluble fibre provides health benefits and lowers blood cholesterol

Insoluble Fiber

• Does not dissolve in water, but can absorb water
• Cannot be broken down by bacteria in the large intestine
• Includes cellulose, hemicellulose, and lignin
• Food sources include wheat bran, rye bran, and vegetables
• Provides health benefits and softens stools and decreases transit time
• Diverticula form at weak points due to pressure exerted when the colon contracts, which causes diverticulosis and diverticulitis

Indigestible Carbohydrates

• Fiber, some oligosaccharides, and resistant starch
• Stimulate GI motility
• Promote a healthy microflora
• Slow nutrient absorption
• Increase intestinal gas

Dietary Fiber

• High bile acid concentrations are associated with a high risk of colon cancer
• Fibers that adsorb bile acids serve a protective effect.
• Fiber fermentation to short-chain fatty acids decreases the luminal pH, thereby decreasing the 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, resist degradation and 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 enhances the differentiation of colon cancer cells

Colon Microflora

• Dietary fibers and undigested starch are substrates for degradation by the bacteria of the large intestine which produce short chain fatty acids (SCFAs)
• The SCFAs that are produced include 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 and decreasing the transformation of primary to secondary bile acids as a result of colonic acidification

Benefits of Breast Milk

• Contains many valuable components
• Rich in prebiotic oligosaccharides which enhance the infant's ability to develop a desirable intestinal bacterial flora

Breast Milk Composition

• Protein, fats, CHO, vitamins, and minerals
• Contains a wide range of immune cells
• Bioactive components with anti-inflammatory, anti-infective and probiotic action
• Contains its own microbiota

Major Insoluble Non-Starch Polysaccharides:

• Cellulose: A polymer of glucose (ẞ1-4) bonds that cannot be hydrolyzed by human enzymes.
• Hemicelluloses: Branched polymers of pentose and hexose
• INULIN (soluble): A polymer of fructose and a storage carbohydrate of many root vegetables, such as the Jerusalem artichoke

Soluble non-starch Polysaccharides

• Pectin: A complex polymer of a variety of monosaccharides, including some methylated sugars
• Plant Gums: such as gum Arabic and gum tragacanth, are complex polymers of mixed monosaccharides
• Mucilages: such as alginates, agar, and carrageen, are complex polymers of mixed monosaccharides found in seaweeds and other algae

Soluble Fibre

• Legumes, Prunes, Apricots, Raisins, Oranges, Bananas, Oats, Apples and eggplant

Insoluble Fibre

• Wheat bran, whole-wheat bread, broccoli, corn, eggplant, apple skins and nuts and seeds

Alternative Sweeteners

• Acceptable Daily Intakes (ADIs) are set by the FDA
• Alternative sweeteners cut down on kcals but do not add whole grains, fruits, and vegetables to the diet
• They have been shown to reduce the incidence of dental caries
• Their usefulness for weight loss is controversial

Types of Artificial Sweeteners

• Saccharin is 200–700 times sweeter than sugar with no warning labels required since May 2000
• Aspartame is made of aspartic acid and phenylalanine, and can be dangerous to people with phenylketonuria (PKU)
• Sucralose (Trichlorogalactosucrose) is sold under the name "Splenda" and is derived from sugar

Other Types of Artifical Sweetners

• Acesulfame K (Sunette or Sweet One) is 200 times as sweet as sugar and heat stable
• Neotame, similar to aspartame but with a stronger chemical bond (cannot be broken down easily), is 7000–13,000 times sweeter than sugar
• Sugar alcohols are chemical derivatives of sugar, low-calorie (0.2–3 kcal/gram), and can be described as "sugar free" on food labels

HFCS

• High fructose corn syrup is cheaper and more stable during storage than other sweeteners
• It is linked to obesity and omnipresent in food
• Biochemically, fructose enters glycolysis after the main regulatory step, resulting in increased synthesis of fatty acids and TAG in the liver and adipose tissue
• Animal studies suggest that rats fed a diet supplemented with water sweetened with either HFCS or sucrose and those fed HFCS got fatter, had higher TAG levels, despite consuming less calories

Substances That May Harm Certain Individuals:

• Aspartame and phenylketonuria (PKU) due to impaired tyrosine production from phenylalanine
• Monosodium glutamate (MSG) sensitivity

Overview of carbohydrates and fats as energy sources in the diet. It highlights their roles, including providing fat-soluble vitamins and lubrication. The lesson also covers recommended energy percentages from carbohydrates, fats, and proteins for a healthy diet.