Carbohydrates Flashcards
photosynthesis
plants creating carbs from the sun and releasing O2 into atmosphere
how do we classify carbohydrates
by number of sugar units in molecule
simple carbs
1-2 sugar units
complex carbs
3 or more sugar units
monosaccharides
single sugar units
3 nutritionally important monosaccharides
glucose, fructose, and galactose
all C6 H12 O6
most abundant monosacccharide in foods and in body
glucose
fructose
5 sided ring
“fruit sugar”
double bond on C2
where is the double bond on both glucose and galactose?
C1
how do glucose and galactose differ structurally
4th carbon is mirrored
galactose
monosaccharide
rarely found along in nature
usually found bonded with glucose as part of lactose
disaccharides
2 sugar units
sucrose
table sugar
glucose+ fructose
lactose
milk sugar
galactose+glucose
maltose
malt sugar
glucose+glucose
not very common in nature; processed food is main source of maltose
maltose is formed during starch digestion
how are sugar units linked to each other?
condensation reaction, glycosidic bonds link them to each other
how does the type of glycosidic bond in a carbohydrate affect digestibility
alpha bonds are more easily digested
beta bonds can be more difficult to digest
what kind of glycosidic bonds is lactose made of?
beta
which are sweeter: complex or simple carbs
simple
oligosaccharides
3-10 sugar units
complex
make up part of plant cell walls
pass undigested into large intestine, bc humans do not have the enzymes to break oligosac. bonds
2 common oligosaccharides
raffinose and stachyose
foods that contain oligosaccharides
beans/legumes, cabbage, brussels sprouts, broccoli
polysaccharides
consist of many (>11) sugar units
long chains and branches of glucose linked together
includes starch, dietary fiber, glycogen
starch
storage form of glucose in plants
plants contain both forms: amylose and amylopectin
amylose
straight chain starch
more resistant than amylopectin; linear chains are harder to break down
amylopectin
branched chain starch
because it is branched, enzymes can reach bonds better –> easier to digest
resistant starch
not digested in GI tract, but has important benefits in large intestine
foods with high levels of resistant starch
unripe bananas
baked beans
plaintains
cooked then chilled pasta and potatoes
dietary fiber
food components that humans cannot digest
mostly non digestible polysaccharides in plant walls (cellulose)
passes through intestines intact; does not provide kcal but decreases hunger bc it adds bulk
cellulose
straight string of glucose units with beta glycosidic bonds
type of dietary fiber
soluble fiber
dissolves in H2O
easily fermented by GI flora
pectins, beta-glucans, and some gums are examples of which type of dietary fiber
soluble
insoluble fiber
does not dissolve in H2O
not easily fermented
still healthy and good!
cellulose, lignin, and hemicellulose are examples of which type of dietary fiber
insoluble
functional fiber
non digestible polysaccharides that are added to foods because of a specific desired effect on human health
glycogen
storage form of glucose in animals
long-branched chains stored in muscle and liver
able to break down quickly and easily
does eating meat provide glycogen?
no
carb digestion in mouth
mastication
salivary amylase breaks amylose and amylopectin into smaller chains of carbs
carb digestion in stomach
very little; because HCl deactivates salivary amylase
carb digestion in small intestine
pancreatic amylase breaks down amylose, amylopectin, and smaller chains of carbs into maltose
brush border enzymes break down all disaccharides to monosacharides
monosaccharides are absorbed through the enterocytes into bloodstream
carb digestion in large intestine
only fiber is left after having gone through small intestine
bacteria in colon metabolizes some fiber- but most fiber is eliminated in stool
brush border enzymes of small intestine
maltase, sucrase, lactase
glucose and galactose absorption
absorbed by active transport
diffuse into capillaries –> portal vein –> liver
fructose absorption
absorbed by facilitated diffusion
glycogenesis
process of assembling excess glucose into glycogen in liver and muscle cells
carbs provide ___ the energy used by muscles and other tissues
1/2
RBCs only use ___ as their energy source
glucose
primary fuel source for brain
glucose
glycogenolysis
hydrolysis of glycogen to release glucose to body
happens if blood glucose level is too low
gluconeogenesis
creation of glucose from noncarbohydrate sources, predominately protein
how does body use protein for energy
it doesnt want to, and it doesnt store extra protein
so it has to pull protein from muscles and organs
ketone bodies
by products of incomplete fat breakdown
spill into blood is liver glycogen is depleted
lower pH of blood
ketosis
increase in ketone bodies in the blood
ideal blood glucose level
70-110 mg/dL
hormones from pancreas that maintain steady bgl
glucagon and insulin
insulin response
eating carbs –> bgl rises –> stimulates release of insulin from beta cells in pancreas –> insulin increases # of glucose receptors on cell membrane surfaces –> glucose goes into cells
which organs can use glucose without insulin
brain, liver, kidney
lipogenesis
when glycogen stores are full, excess glucose can be converted to fatty acids
insulin increases number of glucose receptors on fat cells
glucagon
stimulates release of glucose into blood, raising bgl
alpha cells of pancreas release glucagon if bgl too low
main target organ of glucagon
liver
how do epinephrine and norepinephrine affect glucose metabolism
they act on liver to stimulate glycogenolysis and gluconeogenesis to raise bgl
how do cortisol and GH regulate glucose metabolism
cortisol stimulates gluconeogensis and decreases uptake of glucose by muscle cells
GH stimulates fat breakdown for energy, decreases uptake of glucose by muscle cells, increases glucose production in liver
how does fiber prevent constipation and diverticulitis
fiber bulks feces –> stretches muscles in lg intestine –> lowers transit time in colon
less transit time in colon means less water to be absorbed
RDA for carb intake for adults and children
130g/day
AMDR for carbs
45-65%
AI for fiber (adults)
25-38 g/day
whole grains
grain foods made with entire edible grain kernel
abundant in complex carbs
refined carbs
grain foods that are made with only the endosperm of the kernel
some valuable nutrients removed
quicker spike in bgl
enriched grains
refined grain foods that have folic acid and thiamin and niacin and riboflavin and iron added
glycemic index
rating scale of likelihood of foods to increase levels of blood glucose and insulin; compared to pure glucose
doesn’t account for amount of carb consumed
glycemic load
amount of carb in a food multiplied by amount of glycemic index in that food
foods with natural sugars are generally (more/less) nutrient dense
more
common added sugars in foods
sucrose and fructose
1 source of added sugars in U.S.
sweetened drinks
fruit flesh is rich in:
simple sugars and pectin and cellulose
how does sugar contribute to dental caries
sugar is food for bacteria in the mouth –> bacteria eat the sugar and grow –> produce acid and erode enamel
types of sugar substitutes
polyols (sugar alcohols), saccharin, neotame, stevia, aspartame, acesulfame-K, sucralose, rebaudiose A
which sugar substitutes don’t decay teeth and don’t affect bgl
aspartame, ascesulfame K, sucralose
stevia
natural sweetener extracted from plant
0 carb, 0 cal, no bgl effect
250x sweeter than sugar
aspartame
one of most common sugar substitutes in world
made of modified aspartic acid and phenylalanine
mostly in diet sodas
what types of individuals cannot have aspartame
phenylketonuria people
why is aspartame low cal if it still has 4kcal/gram?
because it is 200x sweeter than sugar so you use less
diabetes mellitus
condition where person either doesn’t have enough insulin or is resistant to the insulin available, resulting in increased bgl
how does diabetes develop
when pancreas produces inadequate amount of insulin and/or body cells develop insulin resistance
type 1 diabetes
autoimmune form of diabetes; pancreas does not produce insulin; rarer form
usually begins at young age
immune system destroys insulin-producing beta cells in pancreas
type 2 diabetes
insulin-resistance diabetes; more common by a lot
metabolic syndrome
cluster of risk factors including high bgl, abnormal blood lipids, high blood pressure, abdominal obesity
increases risk of T2D and CVD
prediabetes
condition where fasting bgl is higher than normal, but not high enough to be diabetes
diabetes diagnosis
fasting blood glucose test 126+
prediabetes diagnosis
fasting blood glucose level 100-126
A1C test
measures average amount of hemoglobin attached to glucose in blood over past 3 months
better screening tool for diabetes
gestational diabetes
form of diabetes that may develop in pregnancy
caused by pregnancy hormones
how can diabetes damage body tissues?
constant high blood glucose damages tissues
increases likelihood of nerve damage, leg/foot amputation, eye disease, blindness, etc
