Harvard Heart Letter

New thinking on saturated fat

While saturated fat isn't a health food, it isn't a complete demon, either.

In most situations, the KISS principle — which stands for Keep It Simple, Stupid — is a logical and practical guide. Sometimes, though, simplifying can have disastrous results. Take the case of dietary fat.

Back in 1957, the American Heart Association (AHA) proffered its first guidelines for a heart-healthy diet. In a nutshell, the AHA said that diet may influence heart disease, that both the fat content and total calories in a person's diet were important, and that people should consume less saturated fat and more unsaturated fat. By the late 1960s, though, experts had decided that Americans just couldn't grasp the dichotomy of good fats and bad fats. Instead, the message morphed into "fat is bad."

The meager research available on diet and heart disease in the 1960s didn't support a blanket recommendation against dietary fat. Neither does the abundance of research since then. What we know today is that dietary fats fall on a spectrum, with trans fats on the "avoid completely" end, saturated fats in the "go easy" middle, and unsaturated fats on the "emphasize" end.

Until trans fat slid onto the public health radar, saturated fat was the poster child for "bad" fats. Analyses brush a bit of the tarnish off its sinister reputation.

New thinking

The dozen or so saturated fats that show up in our food are important building blocks and energy depots for many organisms. Americans get most of their saturated fat from red meat, dairy products, and tropical oils such as palm and coconut oil.

The case against saturated fat goes like this: Eating a lot of saturated fat and cholesterol and little unsaturated fat increases the amount of cholesterol circulating in the bloodstream inside low-density lipoprotein (LDL) particles. LDL particles deposit cholesterol inside artery walls. These deposits, called plaque, can narrow coronary arteries, causing the chest pain known as angina. Even worse, a plaque can burst, causing a heart attack.

That cause-and-effect chain works, but only to a point:

  • The connection between saturated fat intake and the amount of harmful LDL cholesterol in circulation gets hazy when saturated fat accounts for less than 10% of calories in the diet.

  • Saturated fat doesn't exist in a vacuum. How it affects the body is influenced by the amounts of cholesterol and polyunsaturated fat in the diet, along with exercise, genes, and other factors.

  • Cutting back on saturated fat in the diet means adding something in. That something can have a huge effect — for better or for worse — on cardiovascular health.

Backed by research

Three analyses published in the American Journal of Clinical Nutrition in 2009 and 2010 offer a fresh look at saturated fats.

In one report, researchers from the University of California, Davis, and the Harvard School of Public Health pooled information from nearly two dozen long-term studies of diet and heart disease. The studies included 350,000 men and women who were followed for as long as 23 years. Those in the highest range of daily saturated fat intake were no more likely to have developed heart disease or had a stroke than those in the lowest range.

In the other two reports, the same team and another from Aarhus University Hospital in Denmark looked at what happens when saturated fat is replaced with unsaturated fat or with carbohydrates. Both groups found that cutting back on saturated fat while eating more unsaturated fat is good for the cardiovascular system (just what the AHA said back in 1957), while eating highly refined carbohydrates in place of saturated fat isn't. Cutting back on fat and adding more carbohydrates changes the mix of harmful LDL, protective HDL, and triglycerides, creating a more artery-damaging profile that increases the chances of having a heart attack.

These studies have two main messages: When you eat saturated fat in moderation (contributing 10% or fewer of your daily calories), it has little effect on cardiovascular disease. When you cut back on saturated fat, replacing it with unsaturated fats or whole grains is good for your heart and arteries, while replacing it with easily digested carbohydrates isn't.

What does this mean for you?

Foods full of saturated fat definitely aren't health foods. But that doesn't make saturated fat a demon, as it has often been portrayed. In moderation, it can be part of a heart-healthy diet.

It's wise to limit your intake of saturated fat, but you don't need to go crazy eliminating it from your diet. For one thing, that's almost impossible to do, since good sources of unsaturated fats, like olive or canola oil, contain some saturated fat as well. A reasonable limit is that saturated fat should contribute no more than 10% of your daily calories. For someone who generally takes in 2,000 calories, that's 200 calories, or about 23 grams of saturated fat. That's the amount in eight pats of butter, three glasses of whole milk, or a Burger King Whopper with fries.

This isn't the end of the saturated fat story; it may be just the middle. It's likely that future research will identify some of different saturated fats we eat as neutral for the heart — or even good for it — and others as decidedly bad. We will keep you posted.