Class website… kind of

• http://bio200-nutrition.wikispaces.com/• Has all of the past lectures, syllabus, disease

list, important reminders etc.• We will be using this for the time being.• Eventually will be replaced with professors

online

Carbohydrates: Part 2

Will BrownLecture 5

1/127/2012

Outline and Content

• Objective – To identify basic structure, sources, and digestion of carbohydrates. Also to identify the role of carbs and some of the issues associated with to little or to much

• Content– Finish up with alternative sweeteners– Making carbs available– Role of carbohydrates in the body– Glycemic index and glycemic load

Tagatose

• Brand name = Naturlose®• Altered form of fructose• Poorly absorbed • Yields 1.5 kcal/g• Eventually fermented in LI so thought to act as

prebiotic

Stevia

• Brand name = Sweet Leaf®• Derived from South American shrub• 100-300 times sweeter than sucrose• Provides no energy• Available in Japan since ‘70s but not approved

in US till 2008

Digestion and absorption of carbs

Digestion of Carbs

• Where does the breakdown of carbohydrates begin?– Begins with cooking– Heat will break down some of the connective

structure• Food is easier to chew

– Starch molecules will absorb water causing them to swell• Easier to digest

Digestion of Carbs: quick review

• Mouth– mechanical breakdown by

chewing– Chemical breakdown by

salivary amylase-short lived• Stomach– Salivary amylase inactivated

by acid– No further digestion of carbs

occurs in the stomach

Digestion of Carbs: quick review

• Pancreas– Enzymes released into SI– Enzymes (more amylase)

breakdown starch to maltose• Small Intestine– Enzymes in lining breakdown

disaccharides into monosaccharides• Maltase, sucrase, and lactase

– Absorption of monos heads to the liver for processing

Digestion of Carbs: quick review

• Large Intestine– Viscous fiber is fermented into

acids and gases by bacteria• Rectum and Anus– Nonfermentable fiber

excreted– Little other dietary carbs

remain

Absorption of Carbs• Disaccharides are broken

down by absorptive cells• Glucose and Galactose

are taken up by active transport

• Fructose is taken up by facilitated diffusion– Not absorbed as fast– Large amounts of fructose

can result in diarrhea

Absorption of Carbs• Once in the absorptive cells, some fructose is converted to

glucose– Small fraction

• All monosaccharides transported to the liver via the portal vein

• What are the functions of the liver in carbohydrate availability to the body?– Metabolize fructose and galactose to glucose– Release glucose into blood stream– Store glucose by producing glycogen– May produce fat – only if extreme caloric excess

Lactose Maldigestion and Intolerance

• Reduced ability or complete inability to digest lactose– Results in reduced lactase production by absorptive cells– Symptoms are caused by excess gas produced by the

fermentation of lactose by bacteria in the gut– When symptoms are severe then called “intolerance”

• Affects ~25% of adults• Begins in early childhood and progresses through

adulthood• More predominant in those from Asian, African, or

Latino descent

Lactose Maldigestion and Intolerance

• Most people can handle some amounts of lactose - ~1/2 to 1 cup with a meal

• What are some health impacts of lactose maldigestion and intolerance?– ↓milk comsuption = ↓ Ca+ and Vit. D– ↑ discomfort caused by excess gas

• What are some ways to handle it?– Eat foods with Lactase in them– Drink milk with fatty meal– Eat foods with bacteria in them; i.e: yogurt– Lactase pills

The role of carbs in the body

Digestible carbs in the body

• Remember from previous lecture the difference between digestible and indigestible carbs?

• What is the main monosaccharide in the body?– Glucose

• What is the primary role of glucose in the body?– Provide fuel/energy to the body

Digestible carbs in the body

• What happens when not enough carbs are present in the diet?– The body breaks down fat – process known as Ketosis

• Produces ketone bodies• Can disrupt acid-base balance in the blood• Debate about health issues - argument against low-carb diets

– The body can also breakdown protein – usually only in extreme cases like extreme starvation• Results in protein being catabolized from tissues; i.e; muscle,

kidney, liver and heart• Can lead to system failure• Primary cause of death in eating disorders? Heart failure due to

breakdown of cardiac tissue

Regulating glucose

Elevated blood glucose

Normal Glucose Levels

100 mg/dL

70 mg/dL

Hyperglycemia

125 mg/dLPancreas releases

insulin

Glucose uptake by cells

Glucose converted to Glycogen

Hypoglycemia

50 mg/dLLow blood glucose

Pancreas releases Glucagon

Increased gluconeogenesis

Glycogen broken down to Glucose

Concentration of Glucose in blood (milligram

s/deciliter)

Regulating Glucose

• Under tight regulation by liver and pancreas– Liver controls glucose ↔ gylcogen conversion– Pancreas secretes hormones

• Insulin• Glucagon

• When is insulin released and what are insulin’s effects on blood glucose?– Released after a meal– On liver-causes conversion of glucose to glycogen– On cells-causes uptake of glucose

Regulating Glucose

• When is glucagon released and what are glucagon’s effects on blood glucose levels?– Released when blood glucose levels fall below 70

mg/dL– Caused liver to convert glycogen to glucose

• Epinephrine also elevates blood glucose levels– Released by adrenal glands due to perceived

threat– Causes liver to increase glycogen breakdown

Hyperglycemia/Hypoglycemia:The two extremes

• Hyperglycemia-severely elevated blood glucose levels; >125 mg/dL

• Hypoglycemia-severely low blood glucose levels; < 50 mg/dL

• Usually caused by hormone imbalance; i.e: reduced insulin production in type 1 diabetics

Glycemic Index and Glycemic Load

Glycemic index

• Different foods increase blood glucose levels differently– Kraft Mac N’ Cheese vs. Chili

• Why care about the impacts of different carbohydrate sources on blood glucose?– Sources that cause quick elevations cause big spikes in

insulin– Chronically high insulin results in a host of problems

• Increased fat deposition• Resistance of insulin’s effects on muscle tissues

Glycemic Index

• Ratio of blood glucose response of a food compared to a standard – usually glucose or white bread

• Examples of high GI foods – baked potatos, short grain white rice, and mashed potatos

• Examples of low GI foods – Carrots, skim milk and bread

• Problem – based on the serving of food that would deliver 50 g of carbs– May not reflect the typical serving of food

Glycemic Load

• Takes into account the glycemic index and the amount of carbs consumed

• Considered more reflective of the effects on blood glucose levels

• How to calculate:Glycemic Load = (Glycemic Index) x (Grams of carbs consumed)

100Example: Baked Potato (1 cup)

GI=85Carbs (g) = 57

(85*57)/100=48

What to do with GI and GL…

• Try to reduce the amount of high GI or GL foods

• Don’t eat too many high GI foods at one meal– Substitute one High GI food for Low GI foods at

every meal• Eat a combination of high GI with low GI• Increase physical activity