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Chemistry 1002 Chapter 17Nutrition |
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Introduction
Nutrition is probably most widely debated and least
understood field of our time with the exception of religion (which
is even more widely debated and less understood). Attempts to
improve health via nutrition are largely attempts to practice
biochemistry without adequate biochemical knowledge.
Case in point involves fat/cholesterol debate raging
for decades. Initially all fat was bad (milk). Next saturated
fat (butter) was bad and unsaturated (margarine) good. Then it
was decided that making unsaturated fats out of saturated was
bad because this produced some trans fatty acids (margarine; really
bad).
Debate about cholesterol took similar path. First
all cholesterol was bad (eggs). Next there was good (fish) and
bad (red meat) cholesterol. Now some people are saying cholesterol
is irrelevant and real issue is homocysteine levels (fast food
and insufficient green vegetables).
The cereals debate was entertaining too. About thirty
years ago nutritional value was tested by how much weight baby
rats gained eating certain foods (milk was a "perfect"
food back then). A big media hype was started when it was found
that American breakfast cereals were "less nutritious"
than the box they came in.
People stopped eating cereal and then it was decided
that indigestible fiber (cereal) was crucial to keep us all from
dying of cancer and heart disease. People started binging on
oat bran and then it was decided that too much fiber was bad for
intestines.
If all this sounds a little obsessive what is "common
sense" approach to "nutrition and lifestyle"?
Eat as wide a variety of foods as possible;
try to get a balance of fruits, vegetables, meat, starch,
grains, etc.; take the time to do something fun that requires
mild (not obsessive) exercise frequently; get plenty of sleep;
adjust your lifestyle to minimize stress.
Currently there are no miracle diets, and probably
no real "killer" foods. Body suffers more from deficiencies
of nutrients that too much of one particular type (exception:
fat-soluble vitamins). Biochemical issues involving nutrition
will eventually be worked out but this will take time; biochemistry
is very complex and new field.
Some Relevant Nutritional Topics
DIGESTION
Digestion mostly breaking down large molecules into
smaller molecules by breaking bonds and adding water ("hydrolysis").
Biopolymers experience reverse of condensation reactions (depolymerization).
Fats (mostly triesters of glycerol) broken down to glycerol and
fatty acids with water.
PROBLEM 1.
What's digestion?
@ Chemical decomposition (text) or breakdown of larger
molecules into smaller molecules by hydrolysis.
PROBLEM 4.
What are digestion products?
@: Carbohydrates: monosaccharides
Proteins: amino acids
Fats: glycerol + fatty acids
METABOLISM
Anabolism: reactions which consume energy (anabolic
steroids consume energy and build muscle mass).
Catabolism: reactions which produce energy (ATP).
BMR: Basal Metabolic Rate. Rate of production/consumption
of energy (ATP) when body at rest and no digestion occurring.
Digestion requires energy; use energy to get more energy out
like combustion. Rate ATP produced = rate ATP consumed; ATP unstable,
doesn't hang around for more than a few seconds.
PROBLEM 5.
What's BMR?
@ Energy usage rate when body is fasting and
resting.
NUTRIENTS
Proteins. Important thing is to get
enough variety so that we eat proteins containing all of
essential amino acids (we cannot make these biochemically).
If we lack one or more essential amino acids we develop "kwashiorkor"
in mild form. In US only vegetarians need to even concern themselves
with this problem. Nearly impossible for rest of us not
to get all essential amino acids.
Carbohydrates. There are three different
categories of carbohydrates we consume. Simple sugars and
disaccharides (ie. table sugar) sweeten many dessert or breakfast
foods. Complex digestible carbohydrates (starches, fruit
pectin, etc.) are digested to simple sugars by body, but slowly.
Fiber (ie. cellulose, bran, fruit pulp, etc.) contains
indigestible beta links between sugar units in polysaccharides,
and supposedly good for intestines.
Vitamins and minerals. Vitamins and
minerals are needed by body to make coenzymes and cofactors (ie.
iron in heme in hemoglobin carries oxygen in blood) which help
proteins do their work. Generally minerals are inorganic ions
and vitamins are organic molecules which not made of amino acids.
There are two important issues involving vitamins and
minerals. The first deals with fat-soluble vs. water-soluble
vitamins.
Fat-soluble vitamins can poison you if you consume
them in too high quantity. They accumulate in body fat like THC
in cannabis (your druggie neighbors need to abstain for weeks
to pass a drug test). In a sense they like heavy metals in that
they can be cumulative toxins.
Water-soluble vitamins cook out of food easily &
wash out of body quickly; virtually nontoxic. Eat all you want.
Second issue involving vitamins and minerals concerns
macronutrients vs. micronutrients. Micronutrient
minerals (ie. selenium and chromium) needed by body but only in
trace amounts. Often heavy metal poisons if consumed in larger
amounts. Suggestion: eat your veggies and stay away from these
except maybe iron, which is fairly harmless).
Macronutrient minerals (ie. sodium, calcium) won't
generally poison you too easily, but don't go overboard with them.
Some people think too much salt (sodium) is bad for you. I personally
don't have a very strong opinion about this. Probably more important
to eat a balance of macrominerals (sodium and potassium
in particular) than to worry about too much or too little. If
you're a salt junkie eat a few bananas every day just in case.
Show Table 17.9.
PROBLEM 12.
What are (macro/micro)nutrients?
@ Macronutrients: essential nutrients needed in large
quantities.
Micronutrients: essential nutrients needed in small
quantities.
PROBLEM 16.
Discuss vitamins.
Vitamins are organic chemicals which help proteins
do their job.
PROBLEM 17.
Don't OD on which of following vitamins and why?
@ Vitamin A and Vitamin D; they're fat-soluble.
Fats. Mostly triesters of glycerol,
called "triglycerides."
PROBLEM 7.
What are triglycerides?
@ Fats.
Two related issues surround consumption of fats. First
involves "saturated" (no C=C double bonds) vs. "unsaturated"
fats.
Unsaturated fats supposedly better nutritionally because
in some way not yet understood saturated fat consumption thought
to increase quantity of low-density lipoproteins ("bad"
molecules) in bloodstream.
Some unsaturated fats thought to increase quantity
of high-density lipoproteins ("good" molecules)
in bloodstream and other unsaturated fats merely don't increase
LDL (low-density lipoprotein) as much as saturated fats.
Not all unsaturated fats "good" fats. Fats
whose double bonds are trans supposedly Screaming Banshee Ghengis
Khan Killer Molecules.
Second issue involves LDL (low-density
"bad" lipoprotein) and HDL (high-density
"good" lipoprotein) which are made from fats
and cholesterol.
Current theory holds that LDL make plaques (blockages)
in small arteries which feed blood (energy as glucose) to heart
muscle cells causing heart attacks. HDL supposedly breaks up
these plaques. Cholesterol present in both LDL and HDL.
Current theory holds cholesterol harmless. High blood
cholesterol level is a symptom and not a cause of heart
disease. For some reason when blood LDL level is high body circulates
more cholesterol in bloodstream. Body produces and excretes cholesterol
even if we do not eat it.
For most people there is no relationship between cholesterol
consumption in food and blood cholesterol level. Media has no
yet caught up with this new wrinkle.
Newer controversial hypothesis holds that even LDL
not really a culprit. Claim made that LDL is useful. Function
is to repair damage to arteries (plaques are result of damage
repair). Real culprit according to this hypothesis is whatever
is causing arterial damage. Molecule called "homocysteine"
is the new bad guy in this hypothesis.
Cholesterol debate is really entertaining if you don't
take it too seriously yet. Another new wrinkle: recent evidence
that ultralow fat diet may be as harmful as high fat diet. Apparently
atheletes who have very low body fat and low fat diets sometimes
have low HDL ("good" cholesterol) levels. Heart attacks
not uncommon in young basketball players and runners.
High body fat content and high blood cholesterol levels
are clearly linked with high heart disease risk, but the reasons
for this are not yet completely understood.
Comments?
Last Revised : Sunday, October 5, 1997
Copyright © 1997
Louisiana State University, Department of Chemistry.
All rights reserved.
http://www.chem.lsu.edu/lucid/courseinfo/chem1002/ch17.html
