69 terms

Ch 5 Carbohydrates

carbs: general
-major source of energy
-made by plants from CO2 & H2O using energy from the sun
-ratio = CnH2nOn
- "carbon and water"
-ideal nutrient to meet your body's needs
how carbs are made
plants use the sun's energy to combine carbon, oxygen, and hydrogen to form carbohydrates.
photosynthesis function & definition
energy process
is the main biological energy storage process.
• Energy from sunlight is stored in the chemical bonds of glucose.
photosynthesis formula
6CO2 + 6H20 + Sunlight --> C6H12O6 + 6O2
carbon dioxide + water + sunlight glucose + oxygen
what happens to glucose (in plants)?
- used for energy by the plant itself or
- stored in a fruit or vegetable or seed or other plant
cellular respiration definition
is the biological energy releasing process.
• Energy stored in the bonds of glucose (and many other molecules) is released to do work in living cells
aerobic respiration formula
C6H12O6 + 6O2 --> 6CO2 + 6H20 + energy
glucose + oxygen --> carbon dioxide + water + energy
- reverse of photosynthesis
simple carbohydrates
mono and disaccharides
-included in soft drinks
complex carbohydrates (3)
starch, fiber, glycogen
monosaccharides function & shape
-are the main fuel that cells use for cellular work
- in aqueous solution they form rings
3 monosaccharides
1. glucose: primary energy for cells, aka dextrose. not abundant in food (fruits, vegetables, berries, grapes, honey, corn & carrots)
2. fructose: "fruit sugar/levulose" has to be broken down to glucose (fruit, honey HFCS)
3. galactose: part of "milk sugar" lactose, rarely free in foods
disaccharides - definition & by what process
-constructed from 2 monosaccharides
-Disaccharides are joined by the process of dehydration synthesis
3 disaccharides
Maltose = glucose + glucose "malt sugar", found in germinating seeds & wherever starch is being digested
Sucrose = glucose + fructose "table sugar"
Lactose = glucose + galactose "milk sugar"
sucrose - definition, how is it made & where found
- almost 100% carbs
- made from sugar cane or sugar beets
- refinement strips away vitamins & minerals
-occurs naturally in honey, maple syrup, carrots, sweet fruits such as pineapple
Nutritive sugars
- Contribute energy to foods • Provide 4 kcal/g
added sugars
-Nutritive sweeteners added during processing or preparation
» e.g., sucrose and high fructose corn syrup
-avoid these
alternative sweeteners
Substances added to a food to sweeten it but provide no or few calories
alternative sweeteners: sugar alcohols
• Alternative sweeteners:
- Sorbitol, xylitol, and mannitol
• Poorly absorbed and may cause diarrhea • Supply 2 kcal/g
• Do not contribute to dental cavities
nonnutritive sweeteners
• Intensely-sweet synthetic compounds that sweeten foods without providing kcal
• FDA approved nonnutritives:
- Saccharin, aspartame, acesulfame-K, sucralose, neotame, and "stevia"
•Saccharin used for >100 yrs
- Most scientific evidence supports its safety
• Cyclamates banned in the U.S. since 1970
- Despite being determined as safe by panel of experts from FDA and NAS
nonnutritive sweeteners: aspartame
- Brand names include Nutrasweet and Equal
- Consists of two amino acids: Phenylalanine + Aspartic acid
- People with phenylketonuria (PKU) must avoid aspartame.
nonnutritive sweeteners: Stevia
• From leaves of South American shrub Stevia rebaudiana Bertoni
• Rebiana - sweet chemical in stevia leaves
• Considered safe by FDA
complex carbs defnintion
• Contain >10 monosaccharides bonded together
• Storage form of carbohydrate in plants and animals
• Structural component of plants in stems and leaves (cellulose)
polysaccharides definition
• Complex carbohydrates are called polysaccharides
- They are long chain sugar units
- They are polymers of monosaccharides
polysaccharides: where are they found? (3)
1. - Starch - storage form of glucose in plants
2. - Glycogen - short-term storage form of glucose in animals, "muscle sugar"
• Muscles and liver where it is stored
3. - Cellulose of plant cells or Fiber - cell walls
• Wood and dietary fiber are both mostly cellulose
• Indigestible by most organisms
polysaccharide: starch
Storage form of carbohydrate in plants, plants use for energy
Mainly in seeds, roots, and tubers
- similar in structure to glycogen but fewer branches
- potatoes and grains are major sources of starch
polysaccharide: glycogen
- Storage form of carbohydrate (glucose) in humans and other animals
- Stored primarily in liver and muscles
- similar in structure to starch but more branches
- can break off a glucose easily with branches b/c enzymes start at the outside
- undetectable in meats b/c glycogen breaks down as soon as animal is slaughtered
carbs: fiber definition & 2 types
Most forms of fiber are complex carbohydrates that the human body cannot digest.
Two types: Soluble and Insoluble
carbs: fiber - soluble
- Dissolve in water
- Form viscous gels
- Easily fermented by bacteria in gut
- Barley, legumes, fruits (bananas, apples, citrus fruits), oats, vegetables (carrots)
carbs: fiber - insoluble
- Don't dissolve in water
- Only parts fermentable, if at all
- all plants, Bran of whole grains, hulls of seeds, skins of corn, "strings" in celery
- most abundant organic compound on earth
- It forms cable- like fibrils in the tough walls that enclose plant cells
- It is a major component of wood
-It is also known as dietary fiber
Cellulose is similar to starch
- Polysaccharide of glucose, but alternate monosaccharides are "flipped" (gives a different shape to the bond)
• Our digestive enzymes cannot (hydrolyses) this bond because of its shape, but those of some bacteria, fungi, and protists can
fiber other (3)
1. Structural: form of glucose in plant leaves, stems, and seeds.
2. Other fibers play other roles, for example, to retain water and protect the seeds from drying out.
3. Human digestive enzymes cannot break the chemical bonds holding the sugar units together, i.e. indigestible in human beings.
why have fiber-rich foods? (5)
Reduced risk of heart disease
Reduced risk of hypertension
Reduced risk of diabetes
Reduced risk of bowel disease
Promotion of healthy body weight
what is a whole grain?
• The intact, ground, cracked, or flaked seeds of cereal grains
• Must contain all of the "fruit":
- Fiber-rich bran (outer covering of seed)
- Starchy endosperm
- Oily germ
Carbs to glucose: sugar digestion
Sugars - and maltose from starch digestion
- Split to yield free monosaccharides
- Enzymes on small intestine lining
- Absorbed into blood and travel to the liver
- Livers converts them all to glucose or other products
- Circulatory system transports glucose and other products to cells
- Liver & muscle may store some glucose as glycogen
- All body cells may split glucose for energy
Carbs to glucose: fiber digestion
-fermented by bacteria in the colon
- odorous gas
- gradually increase fiber intake
carbs: what happens in your body (6 steps)
1. Mouth — salivary amylase digests some starch
2. Stomach — inactivates salivary amylase
- unravels proteins
3. Small intestine — main site for carbohydrate digestion (di to mono) and absorption (& protein & fat)
4. Liver — absorbed monosaccharides (glucose, galactose, and fructose) travels to liver
5. Large Intestine — some soluble fiber fermented
6. Rectum — very little dietary carbohydrate excreted in feces
1. secreted = when increase in blood glucose.
2. Action= uptake by cells
3. removes excess glucose from blood to become glycogen or fat
1. secreted = when decrease in blood glucose levels
2. Action = glycogen breakdown--> synthesis of glucose
3. Glucagon - triggers the breakdown of liver glycogen to free glucose.
* epinephrine also breaks down liver glycogen during emergencies (fight or flight)
-must be in starvation for muscles to give up glycogen
storing glucose as glycogen
After a meal, as blood glucose rises, the pancreas releases insulin, which signals the body's tissues to take up the surplus glucose.
- Muscle and liver cells can convert the glucose to glycogen
- Brain stores a little glycogen
releasing glycogen
When blood glucose concentrations drop, a pancreatic hormone, glucagon, is released.
Glucagon liberates stored glucose from liver glycogen.
- When blood is low on glucose the liver readily converts glycogen to glucose
- The muscles hoard their glycogen for themselves, and only give it up to the blood under extreme conditions
what happens after eating carbs?
Insulin is released from pancreas:
1. Enables glucose to enter cells
2. Enhances production/storage of:
- Fat, glycogen & protein
3. Decreases hunger
what happens when you don't eat?
When blood glucose decreases, pancreas releases glucagon stimulating:
1. - Glycogenolysis
Glycogen breakdown-- releasing
glucose into the blood -
2. Lypolysis
Breakdown of triglycerides (fat) for energy
Glycogen breakdown-- releasing
glucose into the blood -
Breakdown of triglycerides (fat) for energy
glucose for energy: what's used & formed
• Cells use oxygen energy stored in glucose's chemical bonds.
• energy and water are formed in the process.
glucose + Oxygen --> CO2 + H2O + energy
ketone bodies: definition & how you can get it
1. form as a result of incomplete fat breakdown
- Poorly controlled diabetes
- Fasting or starving
- Low-carbohydrate, high-protein diet (e.g.,Atkins)
• Used by certain cells for energy
• Condition that occurs with very high blood ketone bodies
• Unconsciousness and death may occur
carb consumption
• Average American ~23% kcal (~30 tsp) from added sugars
• Dietary Guidelines recommend limiting added sugar intake to 8 tsp/day for a 2000 kcal diet.
are carbs fattening?
It may depend on the type of carbohydrate...
Probably "fattening" :
• Added sugars
• Refined starches
• High-fructose corn syrup
Healthier choices are: fruits, vegetables, and unrefined grains)
handling excess glucose
converted in the liver to:
- glycogen = liver and muscles hold a limited amount, 4 to 6 hours worth
- Fat = fat cells may also make fat from excess glucose unlimited potential!
diabetes mellitus
• Group of serious chronic diseases characterized by abnormal glucose, fat, and protein metabolism
- Type 1 diabetes
• Autoimmune disease • Beta cells stop making insulin
- Type 2 diabetes
• Most common type
• Insulin resistant cells
controlling diabetes
1. Maintenance of normal or near normal blood glucose levels
- Daily self-testing of blood glucose
- Periodic measurement of glycosylated hemoglobin
2. Maintain healthy body weight
3. Follow special diet
4. Obtain regular physical activity
what is glycemic index & load?
Glycemic index (GI) and Glycemic Load (GL)
- Standard values that indicate the body's insulin response to a carbohydrate-containing food
• Low GI foods may promote satiety
• High GI foods may contribute to hyperinsulinemia.
glycemic index
-method of classifying carbohydrate-rich food by comparing the rise in blood glucose after eating a portion of food that contains 50 g digestible
carbohydrate to the rise that occurs after eating 50 g of a standard source of glucose
-Some carbohydrate-rich foods raise blood glucose and insulin concentrations higher relative to others.
- Foods can be ranked on a scale known as the glycemic index.
glycemic load
- Grams of carbohydrate in a serving of food multiplied by the food's glycemic index; this figure is then divided by 100
criticism of GI & GL
• Some nutrition scientists do not think GIs and GLs are useful for menu planning.
• GI and GL values for a particular food may vary depending on:
- When food is grown
- Degree of ripeness
- Extent of processing
- Other components in the meal
glycemic index of food (3)
1. Elevation of blood glucose & insulin = Food score compared to standard food
2. Diabetes
- Glycemic load (GL)
a. Lower GL = less glucose guild up and less insulin needed
3. Limitations of glycemic index = Resist notion of "good" or "bad" foods
diabetes: ways to reduce the risk (3)
1. Avoid excess body fat
2. exercise daily
3. Follow a "prudent diet"
- Abnormallylowbloodglucoselevels
Fasting blood glucose < 70 mg/dl (healthy person)
- Blood glucose level is too low to provide cells adequate energy.
- True hypoglycemia is rare in non-diabetics.
reactive hypoglycemia: definition (2)
- In some people, blood glucose drops after eating highly refined carbohydrates.
- Pancreas responds to the carb intake by secreting excess insulin.
metabolic syndrome: definition & 5 signs
• Seen in ~47 million of adult Americans
• Characterized by having > 3 of these signs:
• Large waist circumference (40" for men, 35" for women)
• Hypertension
• increased blood triglycerides
• increased blood cholesterol
• increased fasting blood glucose
tooth decay
• Linked to high-carbohydrate diet, especially sticky simple sugars that remain on teeth (food residue)
•Bacteria in mouth-->
• Use carbohydrate reside on teeth for energy
• Produce acid by-product of metabolism
• Acid damages tooth enamel->Damaged enamel allows decay
lactose intolerance
• Inability to digest lactose
• Caused by inadequate lactase
- Affects ~30 to 50 million Americans
- Very common in people of African, Asian, or Eastern European descent
• Bacteria in the large intestine break down undigested lactose, resulting in:
- intestinal cramps, bloating, gas, and diarrhea
- Milk allergy is due to the immune system's reaction to milk protein.
alternatives=cheese, yogurt, lactose free products
low fiber & related health problems (2)
1. Low fiber intake is linked to constipation and straining to expel feces.
2. Pressure on large intestine (colon) may result in diverticula formation (abnormal tiny sacks that form in wall of colon)
high fiber & proper colon function (7)
- Cellulose enlarges and softens the stools
- Speeds up transit time
• Prevents constipation
• Lower risk of hemorrhoids
• Lower risk of appendicitis
• Lower risk of diverticula
- high fiber diets protects against colon cancer
evidence concerning fiber & cancer (4)
Some studies support a role for fiber in defending against cancers of the colon and rectum:
- Fiber attracts water, so may dilute potential cancer- causing agents and speed their removal from the colon.
- Fiber-rich foods supply folate which may be protective.
- Resident bacteria multiply rapidly in fiber-rich intestinal contents and may bind nitrogen, a possible cancer causer.
- A colon well supplied with butyrate from a diet high in soluble fibers may resist chemical injury that could otherwise lead to cancer formation
carb intake & heart disease
- saturate fat is the major culprit in heart disease susceptibility
However, high glycemic index carbohydrates are being investigated for causing undesirable shifts in blood lipids
Look for more research
why are fiber-rich foods recommended?
1. Lower cholesterol and heart disease risk
- Complex carbohydrates --> more than just fiber
a. Viscous fiber - soluble fiber
i. May lower cholesterol
- by binding with cholesterol-rich bile in digestive tract, carrying it out with the feces
- Bacterial fiber fermentation products reduce liver's cholesterol synthesis
how can fiber maintain a healthy weight? (3)
- Whole foods rich in complex carbohydrates tend to be low in fats and added sugars and therefore promote weight loss by delivering less energy per bite.
- Fiber provides a feeling of fullness .
- Fiber delays hunger because fibers swell as they absorb water.