It’s been a tempestuous relationship, these past 40 years or so, between Americans and dietary fat. We love it—in our premium ice creams, crispy deep-fried chicken and butter-drenched buckets of popcorn. We hate it—for what we’ve been told it does to our waistlines and our hearts. We’ve flirted with fake potato chips and ersatz cream cheese. Then we’ve turned around and embraced diets that let us gorge on steak and bacon.
The USDA’s most recent set of Dietary Guidelines, released in 2005, recommend that adults get between 20 and 35 percent of their daily calories from fat. Photo: Jean-Blaise Hall/Getty Images
Is it possible to have a healthy relationship with fat?
Yes, say researchers. In fact, for almost a decade the nutrition establishment has been recommending moderate fat intake—there’s no need to be swept away by either a low-fat or high-fat passion. And, they stress, it’s important to distinguish among the various types of dietary fat.
“If you look at the accumulated body of data, what it’s really suggesting is that consuming unsaturated fat has health benefits, especially when used to displace saturated and trans-fatty acids from the diet,” says Alice H. Lichtenstein, the Stanley N. Gershoff Professor of Nutrition Science and Policy at the Friedman School. Lichtenstein, who is also director of the Cardiovascular Nutrition Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, has devoted much of her research to the effects of dietary fats on lipoproteins (they carry cholesterol through the blood) and cardiovascular health.
The USDA’s most recent set of Dietary Guidelines, released in 2005, recommend that adults get between 20 and 35 percent of their daily calories from fat. That allows a little more latitude than previous guidelines, which called for no more than 30 percent of total calories from fat. And it certainly shows a more flexible attitude than some of the advice that was being dispensed during the height of the low-fat-crazed ’90s, when some well-publicized diet plans were calling for as little as 10 percent of total calories from fat.
But regardless of recommendations, most Americans are still eating too much of the wrong kinds of fat. The American Heart Association recommends that saturated and trans fats should be limited to 7 percent of total calories. According to data from the National Health and Nutrition Examination Survey, in 2005–06 adult men and women consumed about 11.3 percent of their daily calories from saturated fat.
On a molecular level, fats are made up of chains of carbon and hydrogen, with some oxygen atoms at one end. Depending on the level of interconnectedness between the carbon and hydrogen atoms within the fat chain, fats can be either saturated, polyunsaturated or monounsaturated.
Learn about the right and wrong kinds of fat in the slideshow above. Photos: Vito Aluia and Betsy Hayes
There is also the phenomenon of trans-fatty acids, commonly referred to as trans fats—unsaturated fats that behave in the body like saturated fats. While some trans fats occur naturally, most trans fats in our diet are man-made, the result of a process known as hydrogenation.
All fats—sat, trans, poly, mono—contain nine calories per gram, more than twice the calorie content of proteins or carbohydrates. So a diet high in fat may be higher in calories—thus, the concern over the connections between dietary fat, obesity and disease.
After that, things become murkier. A high intake of saturated and trans fats has been tied to higher levels of plasma low-density lipoproteins (LDL), a type of cholesterol that is associated with increased risk of coronary heart disease. But the degree to which these particular fats directly influence cardiovascular disease risk and death rates from heart disease is still being explored. At the same time, scientists are investigating how the ratio of all the fats in the diet affects heart health.
While initial recommendations surrounding fat intake were geared toward people with established risk factors for cardiovascular disease, they were extended to the American population as a whole in the 1960s. As awareness of the connection between saturated fat and cardiovascular risk grew, intake of saturated fat dropped—for instance, U.S. beef consumption declined from a high of 89 pounds per person annually in the mid-1970s to about 64 pounds per person in the early part of this decade.
In addition, the proportion of fat calories Americans consumed from beef, pork, dairy products and eggs, the primary sources of fat in the American diet, fell from 50 percent in 1965 to 33 percent in 1994. (However, the proportion of fat that Americans consumed from fast-food and takeout—pizza, hamburgers, cheeseburgers, French fries, Mexican food and Chinese food—increased from 1.9 percent to 10.8 percent during that same period.)
And then in the late 1980s, the United States became gripped by a low-fat mania. No-fat and reduced-fat products of all sorts flooded the market, and the 20th century ended to the sound of frantic customers jostling for the last box of Snackwells Devil’s Food Cookie Cakes. The legacy of that low-fat orthodoxy is still coloring the way Americans make nutritional decisions—and not necessarily in a good way. People stopped counting calories and starting counting fat grams.
“The low-fat craze had unanticipated negative consequences,” says Lichtenstein. “The feeling was that anything that was non-fat or low-fat was free game to consume as much as you absolutely wanted. People’s body weights increased and we became disillusioned with low-fat foods.”
“Ever since 2000, the Dietary Guidelines for Americans, the National Cholesterol Education Program, the Daily Recommended Intakes, have all said ‘moderate fat consumption,’ ” Lichtenstein emphasizes. “But there is still an extraordinary lag time in translation, in the way it’s been presented to the public.”
Very low-fat diets, those with total fat below 15 or 20 percent, have actually been found to lower plasma high-density lipoprotein cholesterol (the good kind), Lichtenstein says. And polyunsaturated and monounsaturated fats have been shown to have health benefits, like lowering LDL cholesterol.
Omega-3 fatty acids—familiar to anyone who’s walked down the aisle of a supermarket in the past few years, as they have become a popular additive to many foods—are a type of “essential” polyunsaturated acid, meaning they are vital for biological functioning but cannot be produced by the body and so must be taken in through the diet.
The major types of omega-3s are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is found in plant sources, such as canola, soybean, flaxseed and nut oils. EPA and DHA come from marine sources, such as fish. In addition to contributing to cardiovascular health, omega-3s have been tied to a wide variety of benefits such as improved cognitive function and eye health.
OK—so you can skip the fat-free balsamic vinaigrette and have a couple of tablespoons of real salad dressing. Vegetable oils, after all, are chock full of those sexy unsaturated fats. You can even use butter, sparingly, for flavor. “If you really enjoy a little bit of butter on whole wheat toast in the morning, and you’re not a big meat eater, and you’re a consumer of low-fat dairy—fine,” Lichtenstein says.
But despite the recent Julia Child revival, you might want to steer away from Supremes de Volaille a Blanc. (That’s poached chicken breasts using no less than six tablespoons of butter and a cup of heavy cream.)
“There are some foods where low-fat is preferred—dairy and meat,” Lichtenstein repeats. “Those are the types of food where the fat is predominantly saturated fat, and that’s where we want people to cut down. Use leaner cuts of meat and smaller portions and non- and low-fat dairy products.”
And avoid trans fat—something that’s becoming easier to do as manufacturers have removed it from many foods. For years, trans fats were a godsend to food manufacturers, who used it to extend shelf life and add texture to processed foods. In fact, using partially hydrogenated oils was once considered a nutritional advantage over the use of saturated fats, such as lard.
The discovery in the early 1990s that trans fats actually posed a risk to cardiovascular health eventually led to consumer demand, and even government action, for their removal from the food supply. Since 2003, packaged foods have been required to list their trans fat content on their Nutrition Facts labels, and in 2006, New York City’s Board of Health approved a pioneering measure banning the use of partially hydrogenated fat, the major source of dietary trans fats, in the city’s restaurant food.
Within this “good fats-bad fats” split, can further distinctions be made? Is it better to use canola oil than safflower oil? Are trans fats worse than saturated fats?
“Those differences are not what’s important,” Lichtenstein says. “As far as polyunsaturated or monounsaturated, the pendulum of scientific evidence keeps swinging a little bit in each direction. As far as saturated fats or trans fats, the best thing we can do for ourselves is to minimize intake of both. What’s important is to get people to shift the type of fat they consume from saturated to unsaturated; to get producers to shift the type of fat they use; and for individuals to get total energy intake under control.” Which means, yes, calories still count.
“Everyone gets revved up about this oil being better than that oil,” Lichtenstein says. “But when you take more of a bird’s-eye view of everything, that’s not really where the emphasis should be. It should be on the whole diet.”
This story first appeared in the Fall 2009 Tufts Nutrition magazine.