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Nutrition and health: overnutrition Edx NUTR101x (Carbohydrates (Digestion…
Nutrition and health: overnutrition Edx NUTR101x
1.2
Study Designs
Observational
You can determine just
correlation
Cross-sectional
The measurements are done at the same moment: the exposure & outcome
You don't know which came first
Ecological
The measuring unit is a gruoup or country
You cannot extrapolate results to the individuals
Case-control
You study cases and control subjects
Is also used to study rare diseases
Retrospective
prone to subject selection
bias
: inherent differences that are not taken into account
prone to
confounding
issues: related side consequences of the measured traits that should be taken into aacount (
confounders
)
Cohort
They track the subjects over time
very powerful for epidemiology
restrctriction based on people's
accuracy of answers
in questionaries
we get dietay recomendations based on this
confounding
can be present also, deal with it in the analysis
Experimental
You can determine
causality
Intervention
You ask people to do something you think will affect
The control group gets a
placebo
you measure a baseline, then results over time
It can get expensive: manage many people along long time...
1.3 Alimentary tract
Functions
Digestion
Is mainly a
hydrolisis
process
Chemical breakdown
By:
digestive enzymes
Working as catalysts
Breaks
Carbohydrates > glucose
Fats > Fatty acids
Protein > aminoacids
Parts
Mouth
starch (carbhydrates)
Stomach
Proteins
Fats (small role)
small intestine
Most of digestion
Fiber
Enzymes produced by pancreas & intestine cells
Large intestine
Fiber (By
fermentation
thanks to bacteria)
Mechanical breakdown
Intestinal muscles
Thooth
Absortion
Nutrients go from intestines to the blood
Structure
Mouth
Salivary glands: Saliva
Lubricate food
Anti-microbial functions
Start of hydrolysis (digestion)
Thanks to amylase
stops at the stomach because of acidity
Tasting
Theeth
Thonge
Carbohydrates
Simple
("sugars")
mono-saccarides
Can be absorbed to the blood directly
Dont need digestion
Glucose
Only plants can produce it (photosyntesis)
Fructose
Galactosa
Di-saccarides
Need digestion to be absorbed
Composed of 2 mono-saccarides linked
Sucrose
= glucose + fructose
Lactose
= glucose + galactose
Maltose
= glucose + glucose
What do we mean when we say "Sugar"?
Table sugar = sucrose
sugar in the blood = glucose
some industrial sweetners, honey... = inverted sugar
High fructose corn syrup
Health effects of sugars
Controversial contribution to obesity
Contribution to cavities
Sweeteners
Non-nutritive
No evidence to be harmful
Are very sweet, so they are used in small amounts
Are artificial (except stevia)
Nutritive
Dont contribute to cavities
Complex
Poly-saccarides
Starch
Is a mixture of chains of glucose:
amylopectin (branched chains)
amylose (linear)
Glycogen
Fiber
Carbohydrates not digested by enzymes
Fermented in the colon by bacteria
Soluble groups
(viscous)
Pectin
Found on the wall of plant cells
Requently added to food to improve consistency
Hemicellulose
Fructans
eg. Inulins, nice pre-biotic (present in onion, leek, banana, asparagus...)
Non-soluble
(non viscous)
Cellulose
Human-undigestible glucose chains
lignins do not belong to the carbohydrates
Hemicellulose
diverse polysaccharides
Resistant starches
Not digested in the GI track, may be fermented in the colon
RS1: physically inaccessible starch (eg. whole kernel grains)
RS2: granular starch (eg. uncooked potato)
RS3: retrograded starch (cooked and cooled starchy foods)
RS4: chemically modified starches
Another category is:
Naturally present in food or added
Health effects of fibers
Protective and beneficial to deal with Diabetes Type 2
Soluble
Fibers reduce blood cholesterol levels (eg. pectines, psyllium, beta glucans and possibly inulin). Probably related to fermentation of fatty acids and related processes.
Slowers glucose absorption
Holds moisture on stools (easier evacuations)
In Food
Fiber
Fruits, vegetables, nuts, whole grains
Animal products have almost none
Carbs
Starchy food!
Grains, tubercules, fruit
Meat contains little carbohydrates (mostly glycogen)
Digestion
Need digestion:
Starch
maltose
lactose
Sucrose
Jouney of stach for digestion
Saliva's amylase
Pancreatic amylase in the duodenum
Results: maltose
Final enzimatic digestion in the small intestine
maltose <- by maltase
lactose <- by lactase
Sucrose <- by sucrase
Results: glucose, fructose, galactose
Go to liver and are distributed in the body
fiber
Gut Microbiota Ferments it in the large intestine
Results: (short chain fatty acids) acetate, propionate and butyrate... and gasses
Absortion
1. GLucose enters the blodstream
2. Pancreas produces "Insulin"
Stimulates:
Intake of glucose in the tissue
Glucose -> Glycogen
thus, blood sugar levels decrease
3. Pancreas produces Glucagon
Stimulates:
Glycogen -> Glucose
thus, blod sugar levels rise
Glycogen storage
Liver - can be returned to the blodstream
Muscles - Can only be used there (High intensity exersise)
Convert to fat
Diseases
Lactose intolerance
The body stops producing lactase to process lactose
because it kills the cells that produce it
Diabetes
Type 1
No production of insulin
Type 2
Tissue doesnt respond to insulin, body produces more to compensate
Linked to obesity and
controversially to high sugar intake
Fats
Chemistry
Triglycerides (95% intake): 3 fatty acids + 1 glycerol
** Fats: solid (room temp)
** Oils: liquid
Phospholipids
**Are part of cell membranes
**they are amphipathic (thus, good emulsifiers)
sterols
** Cholesterol (animal foods)
** the plant ones are mostly not absorbed
Liquid
+Unsaturated (cis configuration)
+shorter chains
Solid
+Saturated
+longer chains
More stable, less prone to spoilage
can be the product of Hidrogenation: Un to saturated fats
Fatty acid
Chain length 3 to 24+
Degree of Unsatration: # of double bond
Point of unsaturation: location of double bond
** (omega-6 is nomenclature for position of double bonds)
Most common:
Oleic ++ (Unsaturated C18:1)
Palmitic ++ (saturated C16:0)
stearic (saturated C18:0)
linoleic (Unsaturated C18:2)
linolenic (Unsaturated C18:3)
Essential (our body cant prodeuce and we need them and derivates):
linoleic (Unsaturated C18:2) n-6
linolenic (Unsaturated C18:3) n-3
Digestion and absoption
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Lipid metabolism
Cholesterol is used to make the
bile acids (digest the fatty acids)
Membranes
Syntheis of vitamin D
Hormones...
Lipoproteins carry the cholesterol in the blood
Our bodie can sintethize cholesterol
Fat tissue (adipocites)
Used to:
store energy
Isolate heat
endocrine function
Adipocites can increase-decrease size, or increase the number of cells(typically the first happens)
Ingested fat goes ether to muscle or fat tissue depending on th activity we do