Healthy Fats
© Wiseman Family Practice
It's a mystery that has confounded nutrition scientists.

People who have high levels of cholesterol in their blood — especially LDL cholesterol, a.k.a. the "bad" kind — are at elevated risk for cardiovascular disease.

Meanwhile, foods high in saturated fatty acids — including eggs, full-fat dairy products, and red meat — raise blood levels of cholesterol, including LDL cholesterol.

It stands to reason that eating these foods would increase a person's risks for cardiovascular disease, which is the number-one cause of death in the U.S. and around the world. This logic has led both the World Health Organization and U.S. health authorities to recommend that people limit their intakes of saturated fat.

But there's a problem: People who eat these foods don't seem to develop cardiovascular disease at elevated rates (CVD).

A 2019 research analysis in the journal Nutrition Reviews looked at the findings of both observational studies and randomized controlled trials. It found no consistent associations between dietary intakes of saturated fat and heart disease — the most common and deadly form of CVD.

What explains this disconnect? A new hypothesis, published earlier this year in the American Journal of Clinical Nutrition, may provide the answer.

"I think we have been grossly wrong about saturated fats," says Marit Kolby, first author of the AJCN paper and a nutritional biologist at Oslo New University College in Norway. "In my opinion, saturated fat has been blamed for what refined carbohydrates do."

Kolby's theory revolves around the normal operation of the body's cells.

She explains that cholesterol can form up to 50% of a healthy cell's membrane, which is the semi-permeable barrier that selectively allows nutrients, waste, and other stuff to pass in and out of the cell's interior.

According to her hypothesis, which preliminary evidence supports, cells depend on cholesterol to maintain the right level of membrane rigidity.

When we eat certain foods — particularly those rich in polyunsaturated fatty acids, such as nuts, seeds, and vegetable oils — the cell membrane grows more fluid. As a result, cells pull cholesterol from the blood in order to stabilize the membrane. This helps explain why, when people eat foods that contain polyunsaturated fatty acids (PUFAs), blood tests show that their levels of LDL cholesterol go down.

On the other hand, when people eat foods containing saturated fatty acids (SFAs), cell membranes become less fluid and don't need to draw cholesterol from the blood. Instead, they may excrete cholesterol into the blood so that they have reserves to draw on later, as needed.
"We need to stop demonizing these nutrients that are parts of whole foods and that have been in our diets all the way through evolution."
And so, rather than being an indicator of trouble, the elevated blood cholesterol that researchers have linked to the consumption of saturated fats may simply be a sign of normal and healthy cell regulation, Kolby says.

"We need to stop demonizing these nutrients that are parts of whole foods and that have been in our diets all the way through evolution," she says.

But what explains the research-backed associations between blood cholesterol and cardiovascular disease? Kolby and her co-authors think this has little to do with saturated fats.

She says that inflammation interferes with normal cell functioning. If a person is unwell, metabolically or otherwise, persistent inflammation may disrupt cholesterol regulation and contribute to the development of cardiovascular disease.

And this is where refined carbohydrates enter the picture.

While the research linking saturated fat to cardiovascular disease is weak and inconsistent, recent studies have found strong associations between the consumption of ultra-processed foods and CVD. More work has tied ultra-processed foods to an elevated risk for inflammatory bowel disease, as well as Type 2 diabetes, obesity, cancer, frailty, death, and depression.

The ultra-processed foods called out in this research include breakfast cereals, soft drinks, snack foods, low-fat dairy products, and pretty much any other packaged food that includes preservatives, artificial flavors, or other additives.

Kolby says that steering people away from saturated fatty acids may be driving them to eat more of these unhealthy processed foods. "The innovation in low-fat and fat-reduced products has been detrimental to our health because of the substitution of fats with refined carbohydrates and problematic additives," she says. (You can read more about her views on nutrition here.)
"The collateral damage resulting from some of our nutrition policies is substantial, and deeply disturbing."
Others share her take. "The problem is that when you limit fat, you naturally eat a lot more carbs, including both sugars and starches that raise blood-sugar and insulin levels," says Jeff Volek, PhD, a nutrition researcher and professor in the Department of Human Sciences at Ohio State University.

He agrees that frightening people away from saturated fats and towards processed carbohydrates is hurting our health, not helping it. "[Ultra-processed] carbs fail to satiate like fat does, they trigger addictive responses in many people, and metabolically they block your ability to access body fat for fuel," he says.

He points out that at the same time America's consumption of butter, full-fat dairy, and other traditional sources of saturated fatty acids was going down, the incidence of obesity and Type 2 diabetes exploded. "The collateral damage resulting from some of our nutrition policies is substantial, and deeply disturbing," he says, referring to advice to avoid saturated fats.

None of this should be read as encouragement to pack your diet full of fatty dairy products, red meat, and other sources of SFAs. Vegetables, fruits, and true whole-grain foods are consistently linked with better health outcomes.

Instead, the lesson from this work is that a diet composed of whole and minimally processed foods — basically, the stuff Americans ate up until about 100 years ago — appears to be much safer and healthier than a diet filled with ultra-processed and packaged foods.

"Whole foods are the answer," Kolby says.