Download Carbohydrates

Carbohydrates
•General formula CH2O
•Sugars, starches, sugar alcohols, and some dietary fiber
•__ Calories/gram
Plants make glucose via photosynthesis
•6CO2 + 6H2O
C6H12O6 + 6O2
•Requires energy in form of light
•Exact process still an “area of active research”
Monosaccharides
•Single sugar molecule
•Hexoses--glucose, galactose, fructose
–General formula C6H12O6
•Pentoses--ribose, deoxyribose
–General formula…
Disaccharides
•Two sugar molecules linked together
–Sucrose = glucose + fructose
–Lactose = glucose + galactose
–Maltose = glucose + glucose
•During condensation (bonding), water is released
•When disaccharides are digested, water is added across bond--hydrolysis
Oligosaccharides
•Fructooligosaccharides (FOS)
–A pr_biotic
•Raffinose and stachyose--found in legumes
–Also indigestible by humans, but very digestible by colonic bacteria
Polysaccharides
•Starches--storage form of carb in plants
–Amylose--straight chain
–Amylopectin--branched
•Glycogen--highly branched; storage form of carb in animals
•Dietary fiber--bonds cannot be broken by human digestive enzymes (more later)
The form of starch in a food influences its texture
•Rices
–Sticky rice is higher in amylopectin than long grain (“regular”) rice
•Potatoes
–Baking (russet) potatoes have a higher content of amylose than boiling (waxy) potatoes
Digestion & Absorption
•Where are carb-digesting enzymes made?
•Where do they work?
•What are the end products of digestion?
•Where are these end products absorbed?
•Where do they go after they leave the cell in the gut?
Meet the Liver
•The largest gland in the body, and the second largest organ (after the skin)
•Converts galactose and fructose to glucose
•Produces and stores glycogen
•Can produce glucose from amino acids via gluconeogenesis
How does the body utilize glucose?
•Primary energy source, especially for red blood cells and nervous system
–Spares protein
–Prevents ketosis
•Storage as glycogen in liver and muscles
•Storage as fat (with excess energy consumption)
•Component of glycoproteins (mucus)
Use of Glucose for Energy
•Some cells (red blood cells and cells in brain) require glucose and cannot use other
energy sources
•Other cells are adaptable
•Your body needs AT LEAST 50-100 grams of carbohydrate per day to keep red blood
cells and brain happy, spare use of protein to make glucose, and prevent ketosis
What is ketosis?
•Ketosis occurs when there is insufficient glucose for energy
•Fat is broken down in the liver to ketones, which can be used by some cells for energy
•Ketones increase water loss through urine
•Also disrupt acid-base balance of body
Introduction to Energy Metabolism
•Glycolysis--breakdown of 1 molecule of glucose to 2 molecules of pyruvate
•Occurs in cytoplasm
•Does not require oxygen
•Produces a net yield of 2 molecules of ATP (energy storage compound)
Energy Metabolism 2
•Krebs/Citric Acid/TCA cycle and oxidative phosphorylation
–Begins with pyruvate from glycolysis
–Occur only in mitochondria
–Require oxygen
–Net yield of about 28 ATP
Control of Glucose Metabolism
Insulin
•Secreted by pancreas in response to a meal (stimulated by which hormone?)
•Allows cells (e.g., muscle) to take up glucose from blood
•Also stimulates liver to store glucose as glycogen
•In cases of overeating, insulin can stimulate formation of fat from excess carbohydrate
Control of Glucose Metabolism
Glucagon
•Secreted in response to low blood glucose (hypoglycemia)
•Stimulates glycogen breakdown in liver
•Increased glucose release into blood
•Increased blood glucose
Diabetes Mellitus
Greek for sweet urine
•A disturbance of carbohydrate metabolism due to lack of insulin or lack of
responsiveness to insulin
Type 1 Diabetes
–Beta cells of pancreas are damaged, resulting in no insulin secretion
–No insulin
hyperglycemia
–BUT cells are starving for glucose
–Fat is broken down to ketones
–Ketones and glucose spill into the urine
Treatment of Type 1 Diabetes
•Lifelong insulin injections (or now inhaled)
•Control of diet to keep blood glucose levels constant
•Monitoring of blood glucose levels
•Exercise
Type 2 Diabetes
•Obesity and family history are major risk factors
•Pancreas produces plenty of insulin, but the target cells (muscles) lack enough insulin
receptors--resistance to insulin
•No ketosis
Treatment of Type 2 Diabetes
•Weight loss
•If weight loss does not bring glucose down, drugs may be added
•Diet to control blood glucose
•Exercise to control blood glucose and encourage weight loss
The Diabetes Prevention Program
•Overweight adults with high fasting blood glucose were assigned to no treatment, drug
treatment, or lifestyle intervention
•Lifestyle intervention--altered diet to achieve at least a 7% weight loss plus 2.5 hours
exercise per week
Incidence of Diabetes at End of Study (about 3 years)
•Control group had 11 cases of diabetes per 100 patient years
•Drug group had 7.8 cases/100 patient years
•Lifestyle group had 4.8 cases/100 patient years
•Diet and exercise were more effective at preventing type 2 diabetes than the drug
Consequences of uncontrolled diabetes (either type)
•Blindness
•Kidney failure
•Poor wound healing
•Nerve damage
•Premature heart disease, due to high blood pressure and hardening of the arteries
Diabetes Diagnosis
•Two fasting blood glucose values over 125 mg/dL
•Symptoms of diabetes plus nonfasting blood glucose > 200 mg/dL
•Oral glucose tolerance test--less commonly used except in pregnancy
The Glycemic Index
•How quickly the glucose in a food containing 50 g carbohydrate enters the blood after
eating
•Individual foods are charted on a scale that sets either white bread or table sugar as 100
Glycemic Index 2
•The more fat a food has, the lower its glycemic index is
•The more processed a food, the higher its glycemic index is
–White bread has GI > whole wheat
–Brown rice has GI < white rice
Problems with the GI
•We don’t eat a single food at a meal
•Some low-GI foods aren’t exactly low sugar
•GI’s were assessed on a limited number of people; “your mileage may vary”
Bottom Lines on GI
•It can help you be aware of fiber content of food (high fiber, low GI)
•Eating low GI may be helpful for people with diabetes who have limited food
preferences
Dental Caries (Cavities)
•A consequence of excess sugar intake and poor dental hygiene
•Sugar in the mouth is metabolized by bacteria, which produce acid, which erodes tooth
enamel
•“Baby bottle caries”
Added Sugars
•Sodas--a 12-ounce can contains, on average, 40 g carbohydrate
•Candy
•Sugar-coated cereal
–Over 1/2 the carb in a serving of Froot Loops is sugar
–Only 4% of carb in a serving of Cheerios is sugar