Download 2/19/08 Hello Biol 221 Students… I am sorry to have to cancel class

2/19/08
Hello Biol 221 Students…
I am sorry to have to cancel class today—both of my kids are sick (as in barfing), and as
much as I like all of you, I care about them much more!
We will still have the test this Thursday. It will cover all the material that we have
covered since the last exam, including my lecture notes (please see below) that I had
planned to talk about today. (I know, I know, I know. I had said that if it wasn’t covered
in class I wouldn’t test you on it. The information below IS our class notes for today, so
be prepared to be tested on it as well.)
Please feel free to e-mail me ([email protected]) if you have any questions.
Last week we had begun discussing Lipids: Triglycerides (TG), Phospholipids, and
Sterols.
We had left off talking about cholesterol, and I had stated that our livers manufacture
much more than is typically in our diets. Which leads to some very important points:
#1: Cholesterol is a non-essential nutrient
Because our livers make more than enough to meet our needs (for making all that
important stuff like sex hormones and bile)
#2: Because an organism needs a liver to make cholesterol,
Cholesterol is only found in animal foods
Some foods high in dietary chol are also high in fat, some are not (ex: shrimp)
Most is in organ meats, eggs (170-200 mg each, all in yolks), meat/poultry/fish, dairy
There is no cholesterol in plant foods—they may be cholesterol-free,
BUT, they may contain fats that affect what type of cholesterol your liver makes!
Remember: sat fat (like coconut oil) & trans fat (like Crisco) in foods can increase “bad”
blood cholesterol (LDL) production -- PUFAs and MUFAs foods don’t
Which leads us to:
#3: Dietary cholesterol ≠ “blood cholesterol”
So if a patient/client asks what type of cholesterol in food is the “good” type, the answer
is that there really isn’t a “good” or “bad” dietary cholesterol.
But there are “good” (MUFA, PUFA) and “bad” (saturated, trans) fats in foods, which
can lead your body to produce “good” (HDL) or “bad” (LDL) blood “cholesterol”.
(I’ve kind of been throwing around those terms HDL and LDL…I’ll explain it better in a
second.)
But eating a lot of dietary cholesterol probably isn’t good for you in general. (But the
jury isn’t 100% yet…remember, we can’t decide whether eggs are okay or not!)
So, how does “dietary cholesterol” become “blood cholesterol”?
As you may recall, during digestion, triglycerides are emulsified by bile so that
pancreatic and intestinal enzymes can break them up into absorbable particles.
Right? And then I told you that…
The smaller fat particles (glycerol, short- & medium-chain fatty acids) are absorbed
easily by the intestinal cells and go straight into the blood.
What I didn’t totally explain was that…
The larger fat particles (monoglycerides, long-chain fatty acids, also dietary
cholesterol), take a little more processing before they can get absorbed and transported:
First, they form micelles—droplets of fatty stuff (hydrophobic), surrounded by that nice
emulsifying bile. In this form, the intestinal cells can now absorb them.
Then, once they get absorbed into the intestinal cells, the monoglycerides & long chain
F.A. get rearranged into new triglycerides.
Now how is all this fatty stuff going to get anywhere in our very watery bodies?
Well, I’ll tell you. (And pages 149-153, especially the figures!)
The new triglycerides and cholesterol get packaged up for transport—they are surrounded
by phospholipids (which, as you should know, are both water & fat soluble) and some
protein into a type of lipoprotein (lipid + protein!) called chylomicrons.
So now these chylomicrons can go into the lymph (which is watery—basically just blood
minus RBC and platelets) and get squished around until they reach the thoracic duct, near
the heart, and go into the blood.
Once in the blood circulation, the cells of the body can remove and utilize triglycerides
from the chylomicrons. After lots of its TG are removed, the remains of the
chylomicrons eventually travel to the liver where they get “re-packaged” (along with
some other lipids that the liver has produced) into another type of lipoprotein—the
Very-Low-Density-Lipoproteins (VLDL)
Like the chylomicrons, the VLDLs circulate through the blood, and the body’s tissues
remove triglycerides from them. As they lose TGs, their proportions change, becoming
mostly cholesterol (see figure 5-18) and are called Low-Density-Lipoproteins (LDL).
The job for LDL is to deliver TG, chol, phospholipids to the body’s cells.
LDL is correlated with heart disease, hence it’s nickname, “Bad” or “Lousy”
cholesterol.
When fatty particles get released by the body’s cells, they travel via HDL (high-densitylipoproteins) which are mostly protein (which is what makes them more dense!)
In other words, the job for HDL is to carry cholesterol from the cells back to liver,
where it is broken down & excreted (which is a good thing!)
It seems to protect us from heart disease, so its nick names are:
“Good” or “Healthy” or “Happy”
So, going back to the point that:
Dietary cholesterol ≠ “blood cholesterol”
• you can see that what people call their good or bad “cholesterol” in their blood is
really the lipoproteins that contain cholesterol
• And that the proportion of cholesterol to protein in a lipoprotein is what makes it
“good” or “bad”—the cholesterol isn’t a different—but its lipoprotein “packaging”
is!
• Also, dietary cholesterol (as listed on labels, or nutrient composition tables) reflects
the amount of plain old cholesterol—not what type of lipoprotein “packaging” it is in the
food.
• But it’s sort of a non-issue, because a lot of things determine how much and what type
of cholesterol your body will make (and for that matter, your heart disease risk), and
dietary cholesterol intake is not one of the bigger factors!
Dietary Lipid Intakes: Recommendations and Reasons
How much fat should we eat? It depends on whom you ask, but if we go with the Dietary
Guidelines for Americans 2005 (HINT: know the guidelines for the test), it includes:
Keep trans fat intake as low as possible
Why? Raises LDL and lowers HDL, may also have other negative health effects
Less than 10% of kcal from SATURATED fatty acids
Most of them appear to raise LDL—although some chain lengths may be worse
than others
Less than 300 mg/day of cholesterol
To a lesser extent, high dietary cholesterol intake raises LDL.
How the body handles dietary cholesterol may be largely genetic
20-35% of kcal from fat--mostly MUFA & PUFAs from fish, nuts, and vegetable oils
(Actually, a high fat diet is not necessarily a risk factor for heart disease…but it
would probably be high in kcalories (9 kcal/g!), contributing to obesity, and too much
may crowd out other important nutrients)
Not specifically in the 2005 guidelines, but probably should be:
Eat fish 2-3x/wk
To get in adequate omega-3 f.a.—the eicosaniods your body makes from them prevent
blood clots, lower blood pressure, reduces inflammation, regulates heart beat)
Eat 5-10 grams/day soluble fiber
Reduces cholesterol through several possible mechanisms
Please note that the American Heart Association has tighter guidelines, which may be
important to follow if you or your family is predisposed to heart disease:
FYI see www.americanheart.org
(AHA also has a funny website at: http://www.badfatsbrothers.com/BFB.html)
Translation into the food guide pyramid and food labels:
(see p. 161-167 and Highlight 5 too)
In general:
Look for labels that have 0 g of trans fat AND don’t list partially hydrogenated oils
(you have to look at the ingredients because they can round numbers down!)
Look for low numbers for saturated fat content
Grains:
Eat lots of whole-grains
Watch those processed goods (crackers, etc.) for sat fat & trans fat
Limit “rich” baked goods (cakes, cookies, etc.)
Vegetables & Fruits:
Enjoy lots, but don’t fry them or drown them in fats
Fats:
Cook foods in ways that don’t add extra fat (grill, bake, non-stick pans)
Enjoy small servings of nuts & seeds several times per week
Use mostly olive and canola oils, less butter
Stay away from shortenings (Crisco) and stick margarine
When picking a margarine:
Use soft; ≤ 2 g sat fat/serving; liquid veg oil as first ingredient;
Avoid trans fat/partially hydrogenated fats
Milk:
Use low-fat dairy products (skim or 1% milk, limit cheese)
Meats:
Pick lean meats & trim the excess fat; increase fish, poultry, and legume intake
One egg per day is about 200 mg—some are okay, but don’t overindulge!
Enjoy a variety of fish (will help avoid potential contaminants) 2x/wk
What about that fat substitute Olestra (O’Lean): p. 164-5 example: Lays-brand
“Light” (formerly WOW!) Chips—side effects—could cause loss of fat-sol vits AND
anal leakage. We kind of got away from fat-substitutes during the anti-CHO Atkins
phase for the past decade or so. Simplesse is another one. Inulin is an up & comer.