Find out how nutrition science has evolved in the past decade. Here's what we know now—and didn’t then.
"Such a well sourced article Karen! It's very interesting to see how the common-knowledge assumptions change over time, thanks for the read! "
2. Not all fat is bad fat
At the end of the 20th century, “low fat” seemed to be the ubiquitous mantra of health professionals, government organizations and countless food products, but today, research suggests that trimming fat to less than 25 percent of our calories isn’t a great idea. “Cutting too much fat out of your diet can raise triglycerides and decrease healthy HDL cholesterol, which are both risk factors for heart disease,” says Penny Kris-Etherton, Ph.D., R.D., F.A.H.A., a distinguished professor of nutrition at Pennsylvania State University. “When we replace fat with carbohydrates—refined carbohydrates in particular—our liver steps up its production of triglycerides.”
Low-fat diets get a failing grade for weight loss too. “For many people, low fat really translates to high carb, which prompts a big glucose (and insulin) spike, causing blood sugar to then drop quickly, ultimately resulting in hunger,” says Kris-Etherton. “Instead, aim for about 30 percent of calories from fat.”
The type of fat matters too. For optimal health, experts now recommend choosing mostly unsaturated fats (think: liquid vegetable oils, nuts, avocados) and limiting saturated fat because of its negative impact on cholesterol and heart health.
We’re also learning that the villainization of saturated fats might not be so black and white. What we call saturated fat is actually a mosaic of building blocks called saturated fatty acids, such as lauric, myristic, stearic and palmitic acids. Emerging research suggests that some of these may not be harmful. That’s good news if you like dark chocolate, a food plentiful in stearic acid, which has little impact on cholesterol. Then there’s lauric acid, the main fatty acid in coconut oil, which research suggests boosts beneficial HDL cholesterol (although it also raises unhealthful LDL). “Coconut oil is slightly less evil than other saturated-fat-rich foods like palm oil and shortening because of its impact on HDL,” says Kris-Etherton. “But it still isn’t good for you.” Until more is known, stick with foods rich in heart-smart unsaturated fats, olive and canola oils, rather than scrutinizing the individual fatty acids in food.