Wednesday, May 21, 2008

Churning out harmful lipoproteins

Okay, after your liver has made cholesterol and fatty acids, it packages them with protein as very low-density lipoproteins (VLDLs), which have more protein and are denser than their precursors, the chylomicrons. As VLDLs travel through your bloodstream, they lose triglycerides, pick up cholesterol, and turn into low-density lipoproteins (LDLs). LDLs supply cholesterol to your body cells, which use it to make new cell membranes and manufacture sterol compounds such as hormones. That’s the good news. The bad news is that both VLDLs and LDLs are soft and squishy enough to pass through blood vessel walls. The larger and squishier they are, the more likely they are to slide into your arteries, which means that VLDLs are more hazardous to your health than plain old LDLs. These fluffy, fatty lipoproteins carry cholesterol into blood vessels, where it can cling to the inside wall, forming deposits, or plaques. These plaques may eventually block an artery, prevent blood from flowing through, and trigger a heart attack or stroke. Whew! Got all that?
VLDLs and LDLs are sometimes called “bad cholesterol,” but this characterization is a misnomer. They aren’t cholesterol; they’re just the rafts on which cholesterol sails into your arteries. Traveling through the body, LDLs continue to lose cholesterol. In the end, they lose so much fat that they become mostly protein — turning them into high-density lipoproteins, the particles sometimes called “good cholesterol.” Once again, this label is inaccurate. HDLs aren’t cholesterol: They’re simply protein and fat particles too dense and compact to pass through blood vessel walls, so they carry cholesterol out of the body rather than into arteries.
That’s why a high level of HDLs may reduce your risk of heart attack regardless of your total cholesterol levels. Conversely, a high level of LDLs may raise your risk of heart attack, even if your overall cholesterol level is low. Hey, on second thought, maybe that does qualify them as “good” and “bad” cholesterol.

Living with lipoproteins

A lipoprotein is a fat (lipo = fat, remember?) and protein particle that carries cholesterol through your blood. Your body makes four types of lipoproteins: chylomicrons, very low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs). As a general rule, LDLs take cholesterol into blood vessels; HDLs carry it out of the body. A lipoprotein is born as a chylomicron, made in your intestinal cells from protein and triglycerides (fats). After 12 hours of traveling through your blood and around your body, a chylomicron has lost virtually all of its fats. By the time the chylomicron makes its way to your liver, the only thing left is protein. The liver, a veritable fat and cholesterol factory, collects fatty acid fragments from your blood and uses them to make cholesterol and new fatty acids. Time out! How much cholesterol you get from food may affect your liver’s daily output: Eat more cholesterol, and your liver may make less. If you eat less cholesterol, your liver may make more. And so it goes.

Cholesterol season

Even if you allow yourself to indulge in (a few) high-cholesterol ice cream cones and burgers every day of the year, your cholesterol level may still be naturally lower in the summer than in winter.
The basis for this intriguing culinary conclusion is the 2004 University of Massachusetts SEASONS (Seasonal Variation in Blood Lipids) Study of 517 healthy men and women ages 20 to 70. The volunteers started out with an average cholesterol level of 213 mg/dl (women) to 222 mg/dl (men). A series of five blood tests during the one-year study showed an average drop of 4 points in the summer for men and 5.4 points for women. People with high cholesterol (above 240 mg/dl) did better, dropping as much as 18 points in the summer.
U. Mass cardiologists say one explanation for the summer downswing may be the normal increase in human blood volume in hot weather. Cholesterol levels reflect the total amount of cholesterol in your bloodstream. With more blood in the stream, the amount of cholesterol per deciliter declines, producing a lower total cholesterol reading. A second possibility is that people tend to eat less and be more active in summer. They lose weight, and weight loss equals lower cholesterol.
The first bit of wisdom from this study is obvious:
Being physically active reduces your cholesterol level. The second is that environment matters. In other words, if you’re planning to start a new cholesterol-buster diet, you may just do better to start during the cool weather, when your efforts may lower your total cholesterol as much as 12 points over a reasonable period of time, say, six months. Then when your doctor runs a follow-up test the following summer, you’ll get the added benefit of the seasonal slip to make you feel really, really good about how well you’re doing.

Cholesterol and heart disease

Doctors measure your cholesterol level by taking a sample of blood and counting the milligrams of cholesterol in 1 deciliter (1⁄10 liter) of blood. When you get your annual report from the doctor, your total cholesterol level looks something like this: 225 mg/dl. Translation: You have 225 milligrams of cholesterol in every tenth of a liter of blood. Why does this matter? Because cholesterol makes its way into blood vessels, sticks to the walls, and forms deposits that eventually block the flow of blood. The more cholesterol you have floating in your blood, the more cholesterol is likely to cross into your arteries, where it may increase your risk of heart attack or stroke. As a general rule, the National Cholesterol Education Program (NCEP) says that for adults, a cholesterol level higher than 250 mg/dl is a high risk factor for heart disease; between 200 mg/dl and 250 mg/dl is considered a moderate risk factor; below 200 mg/dl is considered a low risk factor. Cholesterol levels alone are not the entire story. Many people with high cholesterol levels live to a ripe old age, but others with low total cholesterol levels develop heart disease. Worse yet, recent research indicates that low cholesterol levels may increase the risk of stroke. In other words, cholesterol is only one of several risk factors for heart disease. Here are some more:
  • An unfavorable ratio of lipoproteins
  • Smoking
  • Obesity
  • Age (being older is riskier)
  • Sex (being male is riskier)
  • A family history of heart disease
To estimate your own risk of heart disease/heart attack, check out the NCEP heart attack risk calculator at

Considering Cholesterol and You

Your body actually needs fat, and here’s another sentence that may blow your (nutritional) mind: Every healthy body needs cholesterol. Look carefully and you find cholesterol in and around your cells, in your fatty tissue, in your organs, and in your glands. What’s it doing there? Plenty of useful things. For example, cholesterol
  • Protects the integrity of cell membranes
  • Helps enable nerve cells to send messages back and forth
  • Is a building block for vitamin D (a sterol), made when sunlight hits the fat just under your skin (for more about vitamin D)
  • Enables your gallbladder to make bile acids, digestive chemicals that, in turn, enable you to absorb fats and fat-soluble nutrients such as vitamin A, vitamin D, vitamin E, and vitamin K
  • Is a base on which you build steroid hormones such as estrogen and testosterone

Tuesday, May 6, 2008

A nutritional fish story

When Sir William Gilbert, lyricist to songsmith Sir Arthur Sullivan, wrote, “Here’s a pretty kettle of fish!” he may well have been talking about the latest skinny on seafood.
The good news from a 2002 Harvard survey of more than 43,000 male health professionals shows that the ones who eat 3 to 5 ounces of fish just once a month have a 40 percent lower risk of ischemic stroke, a stroke caused by a blood clot in a cranial artery. The Harvard study did not include women, but a report on women and stroke published in the Journal of the American Medical Association in 2000 says that women who eat about 4 ounces of fish — think one small can of tuna — two to four times a week appear to cut their risk of stroke by a similar 40 percent.
These benefits are, in large part, because of the presence of omega-3 fatty acids, which are unsaturated fatty acids found most commonly in fatty fish such as salmon and sardines. The primary omega-3 is alpha-linolenic acid, which your body converts to hormonelike substances called eicosanoids. The eicosanoids—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — reduce inflammation, perhaps by inhibiting an enzyme called COX-2, which is linked to inflammatory diseases such as rheumatoid arthritis (RA). The Arthritis Foundation says omega-3s relieve RA joint inflammation, swelling, and pain.
Omega-3s also are heart-friendly. The fats make the tiny blood particles called platelets less sticky, reducing the possibility that they’ll clump together to form blood clots that might obstruct a blood vessel and trigger a heart attack. Omega-3s also knock down levels of bad cholesterol so effectively that the American Heart Association recommends eating fish at least twice a week. Besides, fish also is a good source of taurine, an amino acid the journal Circulation notes helps maintain the elasticity of blood vessels, which means that the vessels may dilate to permit blood or — horrors! — a blot clot to flow through.
Did I mention that omega-3s are bone builders? Fish oils enable your body to create calciferol, a naturally occurring form of vitamin D, the nutrient that enables your body to absorb bonebuilding calcium — which may be why omega-3s appear to help hold minerals in bone — and increase the formation of new bone.

Consumer Alert No. 1
Before you shout, “Waiter! Bring me the salmon, mackerel, herring, or whatever,” here’s the other side of the coin. Earlier research suggests that frequent servings of fish may increase the risk of a stroke caused by bleeding in the brain. This situation is common among Native Alaskans who eat plenty of fish and have a higher than normal incidence of hemorrhagic, or bleeding, strokes. True, the Harvard study found no significant link between fish consumption and bleeding strokes, but researchers say more studies are needed to nail down the relationship — or lack thereof.

Consumer Alert No. 2
Not all omegas are equally beneficial. Omega-6 fatty acids — polyunsaturated fats found in beef, pork, and several vegetable oils, including corn, sunflower, cottonseed, soybean, peanut, and sesame oils — are chemical cousins of omega-3s, but the omega-6s lack the benefits of the omega-3s.

Consumer Alert No. 3
Wait! Don’t go just yet. Despite all the benefits fish bring to a healthful diet, I want to remind you that some fish, particularly those caught in the wild (rather than raised on a fish farm), may be contaminated with metals such as mercury, which has made its way into the water as industrial pollution and may be hazardous for women who are or may be pregnant. Check the food bulletins in your local newspaper or check the FDA’s hotline for the most up-todate data.
Now it’s really a pretty kettle of fish!

Defining fatty acids and their relationship to dietary fat

Fatty acids are the building blocks of fats. Chemically speaking, a fatty acid is a chain of carbon atoms with hydrogen atoms attached and a carbon-oxygenoxygen-hydrogen group (the unit that makes it an acid) at one end. All the fats in food are combinations of fatty acids. Nutritionists characterize fatty acids as saturated, monounsaturated, or polyunsaturated, depending on how many hydrogen atoms are attached to the carbon atoms in the chain. The more hydrogen atoms, the more saturated the fatty acid. Depending on which fatty acids predominate, a food fat is likewise characterized as saturated, monounsaturated, or polyunsaturated.
  • A saturated fat, such as butter, has mostly saturated fatty acids. Saturated fats are solid at room temperature and get harder when chilled.
  • A monounsaturated fat, such as olive oil, has mostly monounsaturated fatty acids. Monounsaturated fats are liquid at room temperature; they get thicker when chilled.
  • A polyunsaturated fat, such as corn oil, has mostly polyunsaturated fatty acids. Polyunsaturated fats are liquid at room temperature; they stay liquid when chilled.
So why is margarine, which is made from unsaturated fats such as corn and soybean oil, a solid? Because it’s been artificially saturated by food chemists who add hydrogen atoms to some of its unsaturated fatty acids. This process, known as hydrogenation, turns an oil, such as corn oil, into a solid fat that can be used in products such as margarines without leaking out all over the table. A fatty acid with extra hydrogen atoms is called a hydrogenated fatty acid. Another name for hydrogenated fatty acid is trans fatty acid. Trans fatty acids are not healthy for your heart. Because of those darned extra hydrogen atoms, they are, well, more saturated, and they act like —what else? — saturated fats, clogging arteries and raising the levels of cholesterol in your blood. To make it easier for you to control your trans fat intake, the Food and Drug Administration now requires a new line on the Nutritional Facts label that tells you exactly how many grams of trans fats are in any product you buy.

The same smart food chemists who invented hydrogenation have now come up with trans fat–free margarines and spreads, including some that are made with plant sterols and stanols.
Plant sterols are natural compounds found in oils in grains, fruits, and vegetables, including soybeans, while stanols are compounds created by adding hydrogen atoms to sterols from wood pulp and other plant sources. Sterols and stanols work like little sponges, sopping up cholesterol in your intestines before it can make its way into your bloodstream. As a result, your total cholesterol levels and your levels of low-density lipoproteins (otherwise known as LDLs or “bad cholesterol”) go down. In some studies, one to two 1-tablespoon servings a day of sterols and stanols can lower levels of bad cholesterol by 10 to 17 percent, with results showing up in as little as two weeks. Wow!

Fats are characterized according to their predominant fatty acids. For example, as you can plainly see in the table, nearly 25 percent of the fatty acids in corn oil are monounsaturated fatty acids. Nevertheless, because corn oil has more polyunsaturated fatty acid, corn oil is considered a polyunsaturated fatty acid. Note for math majors:

Finding fat in all kinds of foods

As a general rule:
  • Fruits and vegetables have only traces of fat, primarily unsaturated fatty acids.
  • Grains have small amounts of fat, up to 3 percent of their total weight.
  • Dairy products vary. Cream is a high-fat food. Regular milks and cheeses are moderately high in fat. Skim milk and skim milk products are low-fat foods. Most of the fat in any dairy product is saturated fatty acids.
  • Meat is moderately high in fat, and most of its fats are saturated fatty acids.
  • Poultry (chicken and turkey), without the skin, is relatively low in fat.
  • Fish may be high or low in fat, primarily unsaturated fatty acids that —lucky for the fish — remain liquid even when the fish is swimming in cold water. (Saturated fats harden when cooled.)
  • Vegetable oils, butter, and lard are high-fat foods. Most of the fatty acids in vegetable oils are unsaturated; most of the fatty acids in lard and butter are saturated.
  • Processed foods, such as cakes, breads, canned or frozen meat, and vegetable dishes, are generally higher in fat than plain grains, meats, fruits, and vegetables.
Here’s a simple guide to finding which foods are high (or low) in fat. Oils are virtually 100 percent fat. Butter and lard are close behind. After that, the fat level drops, from 70 percent for some nuts down to 2 percent for most bread. The rule to take away from these numbers? A diet high in grains and plants always is lower in fat than a diet high in meat and oils.

Friday, May 2, 2008

Essential fatty acids

An essential fatty acid is one that your body needs but cannot assemble from other fats. You have to get it whole, from food. Linoleic acid, found in vegetable oils, is an essential fatty acid. Two others — linolenic acid and arachidonic acid — occupy a somewhat ambiguous position. You can’t make them from scratch, but you can make them if you have enough linoleic acid on hand, so food scientists can work up a good fight about whether linolenic and arachidonic acids are actually “essential.” In practical terms, who cares? Linoleic acid is so widely available in food, you’re unlikely to experience a deficiency of any of the three — linoleic, linolenic, or arachidonic acids — as long as 2 percent of the calories you get each day come from fat.
In 2002, the Institute of Medicine (IOM) published the first daily recommendations for two essential fatty acids, alpha-linolenic acid and linolenic acid. The former is an omega-3 fatty acid (more about that later on in this chapter) that’s found in fish oils, milk, and some veggie oils. The latter is an omega-6 fatty acid (ditto), found in safflower and corn oil. IOM recommends that
  • Women get 12 grams linolenic acid and 1.1 grams alpha-linolenic acid per day
  • Men get 17 grams linolenic acid and 1.6 grams alpha-linolenic acid per day

How to get the right amount of fat and calories for your diet

Getting the right amount of fat in your diet is a delicate balancing act. Too much, and you increase your risk of obesity, diabetes, heart disease, and some forms of cancer. (The risk of colon cancer seems to be tied more clearly to a diet high in fat from meat rather than fat from dairy products.) Too little fat, and infants don’t thrive, children don’t grow, and everyone, regardless of age, is unable to absorb and use fat-soluble vitamins that smooth the skin, protect vision, bolster the immune system, and keep reproductive organs functioning. In the fall of 2002, the National Academies’ Institute of Medicine (IOM) recommended that no more than 20 to 45 percent of daily calories should come from fat. On a 2,000-calorie daily diet, that’s 400 to 900 calories from fats a day. The Dietary Guidelines for Americans 2005 (see Chapter 16) lowers that to 20 to 30 percent of total calories. Translation: 400 to 600 of the calories on a 2,000-calorie/day regimen.
Because your body doesn’t need to get saturated fats, cholesterol, or trans fats from food, neither IOM nor the Dietary Guidelines for Americans 2005 have set levels for these nutrients, except to say, “Keep them as low as possible, please.” This advice about fat intake is primarily for adults. Although many organizations, such as the American Academy of Pediatrics, the American Heart Association, and the National Heart, Lung, and Blood Institute, recommend restricting fat intake for older children, they stress that infants and toddlers require fatty acids for proper physical growth and mental development, and that’s why Mother Nature made human breast milk so high in fatty acids. Never limit the fat in your baby’s diet without checking first with your pediatrician.

Three kinds of fat

Food contains three kinds of fats: triglycerides, phospholipids, and sterols.
Here’s how they differ:
  • Triglycerides: You use these fats to make adipose tissue and burn for energy.
  • Phospholipids: Phospholipids are hybrids — part lipid, part phosphate (a molecule made with the mineral phosphorus) — that act as tiny rowboats, ferrying hormones and fat-soluble vitamins A, D, E, and K through your blood and back and forth in the watery fluid that flows across cell membranes. (By the way, the official name for fluid around cells is extracellular fluid. See why I just called it watery fluid?)
  • Sterols (steroid alcohols): These are fat and alcohol compounds with no calories. Vitamin D is a sterol. So is the sex hormone testosterone. And so is cholesterol, the base on which your body builds hormones and vitamins.