Wardlaw's Perspectives in Nutrition: Chapter 5

Three common monosaccharides

Glucose, fructose and galactose; Hexose, each is a 6 carbon sugar. Classified as nutritive sweeteners

Disaccharides

Carbohydrates containing 2 monosaccharides. Sucrose, lactose, maltose; classified as nutritive sweeteners; duodenum border cells have enzymes to digest these (maltase, sucrase, lactase)

Sugar Alcohols

Derivatives of monosaccharides. Sorbitol, mannitol, xylitol; nutritive sweeteners. Not readily metabolized by bacteria in mouth. More slowly metabolised to glucose than other sugars.

Non-nutritive Sweeteners

Saccharin, Aspartame, Neotame, Acesulfame-K, Sucralose, Tagatose, Stevia

Good sources of starch

Legumes, tubers, grains like wheat, rye, corn, oats, barley and rice.

Soluble fiber

Dissolve in water. Pectins, gums, mucilages. Fruit, oat bran, legumes, seaweed and psyllium.

Insoluble fiber

Does not disolve in water. Skins of fruits, legumes, whole grains, cereal fibers, some vegies, seeds if fruits, bran layer of whole grains.

Recommended daily intake of Carbohydrates

RDA: 130g/day of digestible carbohydrates for adequate glucose supply for brain and central nervous system and energy. FNB: says should be higher; 45-65% of energy intake

3 functions of digestible carbohydrates

Provide energy, spare protein from use as energy source, preventing ketosis.

Main function of glucose

Source of energy for body cells. Red cells and cells of the nervous system drive most energy from glucose. Also fuels, with fatty acids, muscle cells and other cells.

Gluconeogenesis

When body is forced to break down amino acids in muscle tissue and other organs to synthesize glucose due to insufficient carb intake.

Ketosis

The breakdown of fatty acids in the liver due to insufficient carb intake, resulting in the formation of acidic compounds called keto-acids. Important adaptive mechanism for survival in starvation to protect breakdown of organs for glucogenesis.

Function of Indigestible carbohydrates

Fiber prevents constipation, diverticular disease, decreases intestinal transit timement

Goal of carbohydrate digestion

To break down starch and sugars into mono saccharides units small enough to be absorbed.

Carbohydrate digestion: mouth

Some starch is broken down to polysaccharide and disaccharide units by salivary amylase.

Carbohydrate digestion: Stomach

Salivary amylase is inactivated by the acidity in the stomach. No further digestion occurs in the stomach.

Carbohydrate digestion: Pancreas

Pancreatic amylase and dextrinase are secreted into the small intestines to break polysaccharides from starch into disaccharides.

Carbohydrate digestion: Small intestine

Enzymes in the wall of the small intestine break down the disaccharides into monosaccharides.

Carbohydrate digestion: Liver

The absorbed monosaccharides are transported to the liver by the portal vein.

Carbohydrate digestion: Large intestine

Some soluble fiber is metabolized into acids and gases by bacteria in the large intestine.

Absorption of monosaccharides

Glucose and galactose are pumped into the absorptive cells along with sodium. ATP energy pumps sodium back out of cell. Transported to liver then through blood for use by cells.

Absorption of fructose

Taken up by absorptive cells through facilitated diffusion. Carrier used, no energy input needed. Some fructose then converted to glucose in the intestinal cells. Transported to liver via portal vein.

Glucose storage

If blood glucose levels adequate for cell needs, excess is stored in the liver as reserve. When liver storage capacity is exceeded, extra glucose converted to fast for storage in the adipose tissue.

Primary vs Secondary lactose intolerance

Primary: insufficiency of lactase in intestines, Secondary: when conditions such as Crohn's and severe diarrhea damage the cells that produce lactase.

Simple form of Carbohydrates

Monosaccharides; single sugars (CH2O)6. Disaccharides; double sugars (CH2O)12.

Complex Carbohydrates

Polysaccharides, contain many glucose molecules together. Glycogen, starch and fiber.

Glucose

Most abundant monosaccharide. Much in or foetus is linked with other sugars to form disaccharides or polysaccharides.

Fructose

Monosaccharide found in fruits, vegetables, honey and HFCS. Most common sugar in diet.

Galactose

Third major monosaccharide of nutritional importance. Almost identical to glucose. When combined with glucose forms a disaccharide called lactose.

Uses of Sugar Alcohol

Sweeteners in diaries him and dietetic foods.

Condensation reaction

Chemical reaction in which two molecules bond to form a larger molecule by releasing water.

Digestibility difference between alpha and beta bonds.

Beta bonds can not be easily broken down by digestive enzymes for absorption in the small intestines.

Carbohydrates containing alpha bonds

Maltose (2 glucose molecules) and sucrose (glucose and fructose).

Carbohydrates containing beta bonds

Lactose (glucose joined to galactose by a beta bonds)

Raffinose and Stachyose

Oligosaccharides (complex carbs with 3 to 10 single sugar units) found in onions, broccoli, cabbage, whole wheat, and legumes.

Oligosaccharides

Complex Carbohydrates with 3 to 10 single sugar units. Cannot be broken down by our digestive enzymes. Special enzyme preparations like Beano are helpful.

Form of glucose storage in plants

Starch

Polysaccharides

Simple sugar units bonded together

Two forms of digestible starch

Amylopectin (branched chain), amylose (straight chain)

Foods good for glucose management

Oatmeal, apples, kidney beans

Beneficial for controlling hypoglycemia

Snacks containing protein. Meals with a mix of macro nutrients.

High fiber benefits of cholesterol

Binds to cholesterol fatty acids during fermentation of soluble fiber in the large intestines reducing cholesterol synthesis in the liver

Soluble fiber

Decreases the absorption of cholesterol if there is cholesterol rich bile in the blood.

Polysaccharides with branched structures

Amylopectin and glycogen

Maltose

2 glucose molecules connected by an alpha bond

Sucrose

A glucose and fructose molecule connected by an alpha bond

Lactose

A glucose and a galactose molecule connected by a beta bond.

Glycogen

Storage form of glucose in the human body, Liver glycogen (90g) converts to blood sugar, Muscle glycogen (300g) is glucose for muscle use.

Saccharin

Sweet n low

Oldest alternative sweetener: 300x sweeter than sucrose

Aspartame/

Equal

180 - 200x sweeter than sucrose. Contains phenlyalanine.

Neotame

7000 - 13,000 x sweeter than sucrose.similar to aspartame though not digested

Acesulfame k

200x sweeter. Can be used in cooking

Sucralose

Splenda

600x sweeter. Made from sucrose, substitutes 3 chlorines for 3 hydroxyl groups on sugar. Can not be digested or absorbed

Stevia

Comes from Amazon rain forest. 100-300 times sweeter. Recently approved by FDA.

Function of soluble fiber

Lowers blood cholesterol levels, delays gastric emptying, decreases blood glucose levels, reduces obesity risk (fullness and satiety)

Hydrolisis

Breaking of disaccharides into to molecules

Hormones that decreases blood glucose

Insulin, from pancreas. Increases glucose uptake by muscle and adipose tissue. Facilitates transfer of glucose from blood to cells

Hormones that increase blood glucose

Glucagon, from pancreas; epinephrine from adrenal glands, cortsol from adrenal glands, growth hormones from adrenal glands,

Glucagon

Hormone made in pancreas, increases glycogen breakdown and release of glucose by the liver. Increases gluconeogenesis.

Epinephrine, norepinephrine

Hormone made in Adrenal Glands. Increases glycogen breakdown and release of glucose by the liver. Increases gluconeogenesis.

Cortisol

Hormone made in Adrenal glands. Increases gluconeogenesis by the liver, decreases glucose use by muscles and other organs.

Growth hormone

Hormone made in the pituitary gland. Decreases glucose uptake by muscles, increases fat mobilization and utilization, increases glucose output by the liver.

Factors of Metabolic Syndrome

Insulin resistance/ glucose intolerance, abdominal obesity, high blood triglycerides and LDL, low hdl, elevated blood pressure, increases inflammatory blood proteins, higher concentrations of oxidized ldl. Is associated with overall obesity, physical inactivity, generic predisposition, and aging.

Glycemic Index (GI)

Ratio of blood glucose response top a given good, compared with a standard (glucose or white bread). Based on 50g carbohydrate serving.

Factors of glycemic index

Foods starch structure (amylose or amylopectin), fiber content, food processing, physical structure (small vs large surface area), temperature, amount of protein and fat in the meal.