NUTR 337- 5
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Why is the linoleic acid alpha-linolenic acid ratio important?
- Linoleic acid and alpha linolenic acid compete for the same desaturase emzymes
- a-linoleic acid ratio can inhibit conversion of alpha-linolenic acid to DHA
When is the ratio of linoleic acid to alpha-linolenic acid important?
The ratio is of greatest importance when diet is very low in AA, EPA, and DHA
How is the AI for C18:2 n-6 and C18:3 n-3 established?
Established based on highest median intakes in US populations where there is no evidence of deficiency
Why is the AI for C18:2 n-6 higher for men and lower for people >50 yrs?
Because C18:2 n-6 is readily used for energy
How can n-3 FA deficiency be combated?
EPA and DHA can contribute to reversing n-3 FA deficiency
How much EPA and DHA contribute to total n-3 FA intake?
EPA and DHA can contribute up to 10% of n-3 FA intake
How does a vegetarian diet affect the fetus in terms of development?
- Vegetarians have higher AA an lower DHA
- High linoleic acid intake causes n-6/n-3 ratio increased (15-20:1 vs recommended 4:1)
- Could pose risk for brain development
What is the average glucose production in overnight fasted adults?
What is the minimum amount of CHO determined by?
Brain's requirement because brai uses glucose almost exclusively for its energy needs
What happens to the brain in a fully adapted starvation state?
Ketoacid oxidation can accomodate ~80% of the brain's energy requirements
What is the EAR for CHO based on?
- Based on amount that would provide the brain with an adequate supply of glucose
- Without the requirement for additional glucose production from ingested protein or TG
What are some long term consequences of low CHO diets?
- Increased keto acids
- Bone mineral loss
- High blood [cholesterol]
- Increased risk of kidney stones
- Urinary tract deposits
- May affect development and function of CNS
Why does the CHO requirement increase during pregnancy?
- Increased metabolic rate (increased fuel requirement)
- Increased energy supply for growth and development of fetus
How does a pregnant woman's body adapt to low CHO levels?
- Decreased fasting maternal blood glucose concentration
- Development on insulin resistance
- Tendance to developing ketosis
How much glucose is transfered from the mother to the fetus in late gestation?
How much of a fetus' brain's fuel comes from glucose oxidation?
How much of the glucose transferred to the fetus is used as brain fuel?
All of it
How much is CHO intake increased for pregnant women?
EAR=100g/day+35g/day (required for fetus in last trimester)
What is fiber?
Nondigestible CHOs and lignin that are intrinsic and intact in plants
What is functional fiber?
Isolated, non-digestible CHOs shown to have beneficial physiological effects in humans
What are the physiological effets of fiber?
- Decreased blood glucose levels
- Normalization of serum cholesterol
How much fiber is recommended for heart health?
14g/1000kcal, particularly from cereals
What are some benefits of fiber?
- Ameliorate constipation and diverticular disease
- Provide fuel for colonic cells
- Decreased blood [glucose] and [lipids]
- Source of nutrient-rich low-energy dense foods, increased satiety and decreased risk of obesity
Which fibers show the greatest reduction in CHD risk?
Cereal fiber and proven functional fibers such as psyllium and pectin
Are fiber requirements different for pregnant women?
no evidence that beneficial effect of fiber is different from nonpregnant women
What is the largest single constituent of the human body?
What is water essential for?
Essential for cellular homeostasis and life
Where do we get water from in our diet?
Drinking water, water in beverages and water that is part of food
How is thirst generated?
- Via decreased body water sensed as a low blood volume
- More often an increase in [Na] sensed by brain cells
- Only when significant fluid losses or changes in Na status
How is hydration status assessed?
By plasma or serum osmolality, is the primary indicator used for assessment of water status
What dietary factors influence water requirements?
- Osmotic load created by protein
- Metabolizing dietary protein and organic compounds
- Varying intakes of electrolytes
- Must be accommodated by adequate total water consumption
What happens during dehydration?
- Impaired heat dissipation which:
- Increases body core temperature
- Increases strain on the cardiovascular system
Why is there an AI for water and not an EAR?
Extreme variability in water needs which are not solely based on differences in metabolism, but also on environmental conditions and activity
What is the AI for water used for?
To prevent deleterious, primarily acute, effects of dehydration, which include metabolic and functional abnormalities
What is hyponatremia?
- Excess fluid consumption
- Rare occurence
What is acute water toxicity?
When fluid consumption is greater than the kidney's max excretion rate (0.7-1.0L/h)
What is the AI for water?
- 3.7L/day for males
- 2.7L/day for females
What is the AI for water for pregnant women?
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