Carbohydrates

Carbohydrates

I Functions
A. main source of kcalories
1. 4 kcal/gram
B. necessary for the formation of nerve tissue
C. necessary for the formation of RNA/DNA
D. necessary for the structure of cells
II Composition
A. carbon
B. hydrogen
C. oxygen
III Simple Carbohydrates
A. Monosaccharides
1. glucose: blood sugar
2. fructose: fruit sugar
3. galactose: part of milk sugar
B. Disaccharides
1. maltose (malt sugar): glucose + glucose
2. sucrose (table sugar): glucose + fructose
3. lactose (milk sugar): glucose + galactose
IV Complex Carbohydrates
A. Oligosaccharides
1. oligo: scant
2. short chains of monosaccharides (3-10) units
3. virtually tasteless
B. Polysaccharides
1. glycogen: animal storage form
a. storage form of glucose in the body
b. provides a rapid release of energy when needed
2. starches: plant storage form
a. storage form of sugar in plants
b. found in grains, tubers and legumes
3. fiber
a. cannot be digested by humans (chemical)
b. provides form and structure to plants
c. insoluble fiber (visual plant fibers)
i. adds bulk, aids in elimination
d. soluble fiber ( clear, gel like)
i. prebiotics (digested by bacteria. Ex: Activa)
ii. functional fibers: lowers risk of certain chronic diseases. (heart disease, diabetes, obesity)
e. health benefits of fiber
i. heart disease: lowers risk, lowers cholesterol
ii. diabetes: slows glucose absorption
iii. GI health: decrease transit time of food through colon, holds moisture/softens stools, prevents diverticulosis
iv. cancer: helps prevent colon cancer, decreased transit time = less carcinogens.
v. weight management: displaces energy dense foods
V Glucose in the body
A. A preview of carbohydrate metabolism
1. the body stores glucose as glycogen in liver and muscle cells
2. the body uses glucose for energy if glycogen stores are available
3. if glycogen stores are depleted, the body makes glucose from protein.
a. gluconeogenesis: the conversion of protein to glucose (“new glucose creation”)
b. protein-sparing action is having adequate carbohydrate in the diet to prevent the breakdown of protein for energy.
B. primary function of glucose is to provide energy to the cells
C. glucose homeostasis: maintenance of normal blood sugar levels
D. regulating hormones (pancreatic)
1. insulin: decreases blood sugar
a. blood glucose “into” cells
2. glucagon: increases blood sugar
a. release glucose from liver glycogen (makes glucose gone from the liver, and into blood)
E. Diabetes Mellitus
1. diabetes: to pass through
2. mellitus: honey
3. a metabolic disorder characterized by high blood sugar levels resulting from insufficient insulin, ineffective insulin, or a combination of both.
F. When blood sugar rises, insulin is secreted by the pancreas and it lowers the blood sugar. If you don’t eat lunch and the blood sugar drops, glucagon stimulates the liver to release glucose which raises blood sugar levels. (homeostasis) If no insulin is available, blood sugar (glucose) remains high.
VI Carbohydrate-related disorders (Diabetes)
A. Insulin dependent diabetes (juvenile diabetes/ type 1 diabetes)
1. pancreas produces little or no insulin
2. only 10% of all diabetics
3. cause:
a. genetic susceptibility
b. viral infection
B. Non-insulin dependent diabetes (type 2 diabetes)
1. aka: adult onset
2. most common type
3. the cells fail to respond to insulin
4. cause: unknown
5. associated with:
a. obesity (central)
b. heredity
c. ethnicity: Native Americans, Hispanics, African Americans, Asians.
C. Symptoms
1. polydipsia: excessive thirst
2. polyphagia: excessive hunger
3. polyuria: excessive urination
4. hyperglycemia: high blood glucose
5. unexplained weight loss
D. Chronic complications
1. neuropathy: degeneration of nerve tissue
2. nephropathy: degeneration of kidneys
3. retinopathy: degeneration of retina
4. metabolic syndrome aka: syndrome X
a. high cholesterol
b. high triglycerides
c. hypertension
E. Consequences
1. atherosclerosis, heart disease, hypertension, stroke
2. kidney failure
3. loss of limb
4. blindness
F. Management (3 fold management system)
1. diet
2. medication
a. insulin: injection, pump, powder
b. oral hypoglycemic agents
3. physical activity (exercise)
G. Medical nutrition therapy
1. carbohydrate
a. controlled, consistent
b. high fiber
2. dietary fat
a. low fat, low cholesterol
3. protein
a. 15-20% of total calories (relatively low)
4. weight loss (NIDDM)
VI Health effects and recommended intakes of sugars
A. sugar poses no major health problem except dental caries
B. excessive intakes may displace nutrients and contribute to obesity
C. consuming foods with added sugars should be limited
D. naturally occurring sugars from fruits, vegetables, and milk are acceptable sources.
E. Controversies surrounding sugars
1. excessive sugar intake can contribute to the development of body fat
2. sugar may be able to alter blood lipid levels and contribute to heart disease in some.
3. there is no scientific evidence that sugar causes misbehavior in children and criminal behavior in adults.
4. there is a theory that sugar increases serotonin levels, which can lead to cravings and addictions
F. recommended intakes of sugars
1. the USDA food guide states that added sugars can be included in the diet as part of discretionary kcalories
2. dietary guidelines state to limit intake of foods and beverages that are high in added sugars
3. DRI suggest added sugars should contribute no more than 25% of a day’s total energy intake
VII Health Effects and recommended intakes of starch and fibers
A. May be some protection from heart disease and stroke
1. soluble fibers bind with bile and thereby lower blood cholesterol levels
2. fiber may also displace fat in the diet
B. reduce the risk of type 2 diabetes by decreasing glucose absorption
C. Enhance the health of the GI tract which can then block the absorption of unwanted particles
D. may protect against colon cancer by removing potential cancer-causing agents from the body.
E. Promote weight control because complex carbohydrates provide less fat and added sugar.
F. Harmful effects of excessive fiber intake
1. displaces energy and nutrient-dense foods
2. abdominal discomfort and distension
3. may interfere with nutrient absorption
G. recommended intakes of starch and fibers
1. RDA for carbohydrate is 130 g/day, or 45-65% of energy intake
2. daily value is 300 g/day
3. dietary guidelines encourage a variety of whole grains, vegetables, fruits and legumes daily.
4. healthy people 2010 recommends six servings of grains and 5 servings of fruits and vegetables
5. FDA recommends 25 grams of fiber for a 2,000 kcalorie diet
VIII Alternatives to sugar
A. Artificial sweeteners aka: nonnutritive sweeteners
1. saccharin
a. used primarily in soft drinks and as a tabletop sweetener
b. rapidly excreted in urine
c. does not accumulate in the body
d. has been removed from list of cancer-causing substances
2. aspartame (Nutra-sweet, Equal)
a. general purpose sweetener
b. warning about phenylalanine for those with PKU
c. controversial finding that aspartame may have caused cancer in rats
d. excessive intake should be avoided by those with epilepsy
3. Acesulfame-K (acesulfame potassium, aka: ACK)
a. research confirms safety
4. sucralose (Splenda)
a. made from sugar
b. passes through digestive tract
c. only one you can sprinkle on food
5. neotame (acts like equal)
a. most recent on the market
b. very sweet
c. phenylalanine not an issue
B. Sugar replacers
1. also called nutritive sweeteners, sugar alcohols, and polyols
2. malitol, mannitol, sorbitol, xylitol, isomalt, and lactitol
3. absorbed more slowly and metabolized differently in the body. (most not absorbed)
4. low glycemic response
5. side effects include GI discomfort