Lecture 2a - Review of Nutrients Flashcards
What are the 5 functions of nutrients?
Involved in all basic functions of the body
1. Act as structural components
2. Enhance (or involved in) chemical reactions of metabolism
3. Transport substances into, throughout or out of the body
4. Maintain body temperature
5. Supply energy
Define essential nutrients
Nutrient can not be synthesized by the animal, must be obtained in the food
Define conditionally essential nutrients
A non-essential nutrient that becomes an essential nutrient when certain physiologic conditions result in relative deficiency
Define non-essential nutrients
Nutrient can be synthesized in adequate quantities by animals and are not specifically required in the food
What is an example of a condition for conditionally essential nutrients?
lactation
What is digestibility and what is it influenced by?
- Percentage of food’s gross nutrient content released following mechanical and chemical digestive processes
- Is influenced by both food characteristics and the digestive efficiency of the host
What is bioavailability?
The degree to which a nutrient becomes available to support metabolism after digestion and absorption.
How is digestibility measured?
We measure the difference between what was ingested and what was in the fecal material.
Is age a factor in digestibility?
Yes; adult animals will have greater digestibility than a young animal.
What is an example of a nutrient that sometimes are digestible but not available?
Lysine! Under certain conditions it can be cross linked with a sugar (maillard rxn) and can no longer be used for protein synthesis.
What is apparent digestibility?
Nutrient intake minus nutrient excretion in feces.
* Note: nutrients in feces are from the diet and endogenous losses
What is true digestibility?
Nutrient intake minus nutrient excretion in feces corrected for all intestinal endogenous losses
What are intestinal endogenous losses?
Excretion of nutrients into gut due to cell turn over, intestinal secretions, sloughing of intestinal cells, etc.
What causes an increase in intestinal endogenous losses?
An increase in fiber or an increase in undigestible protein
What are simple carbohydrates?
- Monosaccharides
- Glucose, fructose, galactose - Disaccharides
- Maltose, sucrose, lactose
What are complex carbohydrates?
- Oligosaccharides [DP = 3-10]
- fructo-, galacto-oligosaccharides - Polysaccharides [DP = >10]
- starch, cellulose glycogen
- DP = degree of polymerization = number of glucose molecules
What type of bond determines whether the CHO is digestible by mammalian enzymes?
Glycosidic bond
- Alpha: starch
- Beta: fiber
*animal cannot digest beta bonds itself, needs bacteria to break them
What CHOs are digestible for mammalian enzymes?
- sucrose, maltose, lactose, starch, glycogen
*these CHOs only have alpha bonds
What types of CHOs are digestible for bacterial enzymes?
- oligosaccharides
- non-starch polysaccharides: cellulose, hemicellulose, pectin
How do NSP (non-starch polysaccharides) relate to dietary fiber?
Dietary fiber is NSP + lignin; you include lignin
What is the function, digestion site, and digestion products of STARCH and GLYCOGEN?
Fxn
- storage polysaccharide in plants and animals
DS
- SI (host enzymes)
DP
- Glucose, maltose
What is the function, digestion site, and digestion products for hemicellulose and cellulsoe?
Fxn
- structural parts of plant cell walls
DS
- LI (microbial fermentation)
DP
- volatile fatty acids (acetate, propionate, butyrate)
What is the function, digestion site, and digestion products of LIGNIN, CUTINS, and WAXES?
Fxn
- associated cell wall substances
DS
- not digested or fermented
DP
- excreted in feces
What is the function, digestion site, and digestion products of GUMS, MUCILAGES, and PECTINS?
Fxn
- naturally occurring polysaccharides in plants
DS
- LI (microbial fermentation)
DP
- carbon dioxide, methane, hydrogen, volatile fatty acids
Do glucose and VFA (acetate, propionate, butyrate) provide the same amount of energy when absorbed?
Propionate is not a usable form, it has to be converted back to glucose so there is energy loss = less amount of energy than glucose when absorbed
What structure affects digestibility of starch?
granular structure
What are the 3 categories of starch?
- Rapidly digestible starch
- most starches in cooked and extruded petfood easily digested - Slowly digestible starch
- raw or uncooked starch - Resistant starch
- some plant starches resist enzymatic digestion in the SI
What does the amount of each starch category depend on?
depends on starch source, type and extent of processing
- amylose vs. amylopectin; amylose has a helical structure (difficult to degrade) and amylopectin has a more open structure