Saturated Fat: The Good, the Bad and the In-Between
Dear Readers,
If there’s anything more frustrating than eating right, it’s trying to figure out what it means to eat right.
In the last couple of decades alone, we’ve seen: Low fat, high protein, low carbohydrate, high fiber … the list is endless, and there’s no lack of “authorities” to support almost any claim for healthful eating.
My January newsletter, “Simple Steps to More Healthful Living in 2014,” encouraged readers to try the Mediterranean diet. It’s based on less meat, more fish and nuts, fewer carbohydrates and more plant-based foods. It has fat, but more of the unsaturated type found in olive oil than saturated fats in foods from animals.
The chemical differences among fats affect how people metabolize them, and for a long time, saturated fat has been considered particularly threatening to heart health.
But a large, international study got big media play recently when it found no evidence that eating saturated fat increased heart attacks and other cardiac events. So can we go back to the burgers and fries? Forget about the fish and nuts?
This month, I’ll examine whether saturated fat is the evildoer we’ve long suspected, if it’s just the subject of bad publicity, or if we can even be sure.
Three Kinds of Dietary Fat
We need to start with energy: fast, medium and slow.
Our bodies get fast energy from burning simple carbohydrates: glucose and its cousins sucrose (table sugar), fructose (in fruits) and lactose (in milk). A bit more of a timed-release energy boost comes from burning complex carbohydrates such as found in vegetables.
Fat is the slow source of energy. Fat is where our bodies store long-term energy. Ounce for ounce, fat has about twice as many calories as simple sugars do.
Everyone has to eat fat (or fatty acids — we’re using fat and fatty acids interchangeably) because fatty acids are essential for cells to grow, and these acids are not produced by the body.
So: You have to eat fat or you die. And we all want to eat fat because it tastes good — fat is flavor, as any cook will tell you.
A quick trip back to high school chemistry:
There are three main types of fatty acids: saturated, monounsaturated and polyunsaturated, as explained by the Science of Cooking. They’re all composed of chains of carbon atoms with hydrogen atoms attached.
Saturated fatty acids have the maximum possible number of hydrogen atoms attached to every carbon atom, so they’re said to be “saturated” with hydrogen atoms. Their carbons are attached to each other with single bonds.
If a pair of hydrogen atoms in the middle of a fatty acid chain is missing, the gap leaves two carbon atoms connected by a double bond rather than a single bond. Because that chain has fewer hydrogen atoms, it is said to be “unsaturated.” A fatty acid with one double bond is “monounsaturated” (one gap) and a fatty acid with more than one gap is “polyunsaturated.”
The fat in foods has a mixture of the three kinds of fatty acids. In foods from animals — meat, milk, eggs — a large proportion of fatty acids is saturated. Foods from plants and some seafood have a large proportion of mono- and polyunsaturated fatty acids.
Trans fat is an artificial creation — food manufacturers use a process called hydrogenation to make polyunsaturated oils more stable. They add hydrogen to prevent food from becoming rancid (for longer shelf life), and to make oil solid at room temperature. Foods such as stick margarine, commercial baked goods, processed foods and fast food use trans fats.
The New Study About Saturated Fat
Health officials have long encouraged people to avoid saturated fat and replace it with the unsaturated fats found in nuts, fish, seeds and vegetable oils. Essentially, that’s the Mediterranean diet, which has been shown to keep blood sugar more stable, lower blood cholesterol and fats and generally promote better heart health and reduce the risk of diabetes.
But as a recent story in the New York Times explained, the new study published in the Annals of Internal Medicine challenges the idea that saturated fat is uniformly bad for you.
The study did not find that people who ate higher levels of saturated fat had more heart disease than those who ate less. It did not find less disease in people who ate higher amounts of unsaturated fat, including olive oil (monounsaturated fat) or corn oil (polyunsaturated fat). But the research did show a link between trans fats and heart disease.
The study didn’t involve any original research. Instead the authors sat down with nearly 80 studies, involving more than a half million subjects, and raked over their findings closely. They focused on what people reportedly ate, and levels of the fatty acids in their blood and fat tissue. They also looked at controlled trials — the gold standard in scientific research, but very difficult to do with human diet — that assessed whether taking polyunsaturated fat supplements such as fish oil promoted heart health.
Saturated fat has a bad rap because it increases low-density lipoprotein (LDL) cholesterol, which has been shown to raise the risk for heart attacks. High-density lipoprotein (HDL) has been shown to be heart healthy. Cholesterol tests give three values. For healthy adults, the ideal total value is 200; ideal LDL is less than 130, and ideal HDL is greater than 60.
According to the new study’s lead author, Dr. Rajiv Chowdhury, the relationship between saturated fat and LDL is complex. Saturated fat raises LDL, but also HDL. The subtype of LDL that saturated fat raises generally is benign. Smaller, denser forms of LDL are more dangerous.
They’re more likely to cause inflammation and promote artery-clogging plaque. Usually, the more of this kind of LDL you have, the more blood fats you have, as well as lower HDL levels. That’s a profile of greater risk for heart attack and stroke.
Chowdhury said the smaller, more dangerous LDL was increased not by saturated fat, but by sugary foods with too much carbohydrates.
Although the study didn’t show a meaningful relationship between saturated or polyunsaturated fat intake and cardiac events, according to The Times, there are lots of fatty acids within these two groups, and they might not all be equal.
Didn’t we say this stuff is complex?
For example, the researchers found that blood levels of a kind of saturated fat in dairy products was associated with lower cardiovascular risk. Two types of omega-3 fatty acids (think: fish) also were protective. But some of the omega-6 polyunsaturated fatty acids (vegetable oils and processed foods), might be risky.
To complicate things further, the researchers analyzed the data from the randomized trials and concluded that taking fish oil supplements had no cardiovascular benefit. (See our blog, “The Costly Appeal of Alternative Medicine.“)
But … as Chowdhury pointed out, the supplement trials involved mostly people who had pre-existing heart disease or were at high risk of developing it. So can you really draw a firm conclusion? Large clinical trials designed to learn more are underway.
Figuring Out Your Fat Formula
So: Is saturated fat bad for you?
Given the Annals of Internal Medicine study, some people would say no. “But to my mind,” says Kevin Lomangino, editor of the newsletter Clinical Nutrition Insight, “this question can’t really be answered without first considering a second question: What are you comparing it with?”
If you eat less saturated fat, he says, you’ll probably replace its calories with something else. And if it’s refined carbohydrates, you’re not likely to improve your health, and you might be worse off. But if you replace saturated fat with unsaturated fat, the evidence shows you could realize some cardiovascular benefit.
Remember, Chowdhury is concerned about too much sugar and too many refined carbohydrates. If you replace steak with donuts — not so good. Better to go with the red meat, even a fatty cut.
Lomangino is probably one of the best informed lay people out there on diet, having spent a couple of decades at the interface between science and the dinner plate. (His newsletter just expired for business reasons.) He recalls one large, significant study that found a 14% reduction in heart problems when subjects reduced or replaced the saturated fat in their diet with both kinds of unsaturated fat. Another significant study that replaced saturated fat with only polyunsaturated fat also showed a meaningful reduction in coronary heart disease events.
Lomangino acknowledges “These studies have limitations, of course, and some researchers say there’s not enough proof to conclude that replacing saturated fat with polyunsaturated fat is causally related to heart benefits. Then again, diet studies are hard to do and almost always yield messy evidence. It’s unlikely that better studies will be available any time soon to guide our thinking.”
All things considered, he believes that there’s a clear benefit to replacing saturated fat with unsaturated fat.
But you shouldn’t obsess about a specific food or nutrient. That’s why the Mediterranean diet still seems like the smart choice — it’s varied, it’s got a scientific foundation, it doesn’t depend on deprivation … and it tastes good!
We agree with Lomangino: “Where reasonable and feasible, replace butter and solid fats in your diet with a variety of plant oils such as olive, canola, soybean and peanut. Eat fatty fish twice a week. Limit processed junk food that is usually rich in saturated fat and refined carbohydrate, and fill up most of your plate with fruits and vegetables instead.”
Here’s to a healthy 2014!
Patrick Malone
Patrick Malone & Associates
