Does saturated fat boost liver fat?

Replace saturated fats (in foods like red meat, cheese, butter, coconut oil, and most fatty sweets) with polyunsaturated fats (in foods like nuts, fish, mayo, and most oils and salad dressings).

An estimated one out of three U.S. adults—and one out of 10 children—have non-alcoholic fatty liver disease, or NAFLD.

“It’s one of the most common liver diseases worldwide,” notes Fredrik Rosqvist of Uppsala University in Sweden.

The chief cause: excess weight around the waist.

“NAFLD is a spectrum of diseases,” explains Rosqvist. In the beginning, the liver simply accumulates extra fat. “That can progress to a fatty liver with inflammation. And that may progress to cirrhosis or liver cancer.”

Only about 20 percent of people with NAFLD have that severe, inflammatory version. But even a fatty liver without inflammation can cause trouble.

“NAFLD is strongly associated with both type 2 diabetes and cardiovascular disease,” says Rosqvist.

How diet plays a role

Although excess weight is the key driver for fatty liver, replacing saturated fats with polyunsaturated fats may help limit liver fat.

In the HEPFAT trial, researchers randomly assigned 61 people with abdominal obesity to eat a diet high in either saturated fats (from butter and scones made with butter) or polyunsaturated fats (from sunflower seeds, sunflower oil and spreads, and scones made with sunflower oil) for 10 weeks.

“Saturated fat increased liver fat content, whereas polyunsaturated fat actually decreased it,” says Rosqvist.

In two other trials, researchers had people with normal or excess weight consume an extra 750 calories a day by eating muffins made with either palm oil (a satu­rated fat) or sunflower oil (a polyunsaturated fat). In a third trial, the saturated fat came from coconut oil, butter, and blue cheese, while the unsaturated fat came largely from olive oil, pesto, and pecans.

After three to eight weeks, all the groups had gained three to five pounds. “But for the same weight gain, saturated fat increased liver fat, whereas polyunsaturated fat led to little or no liver fat accumulation,” says Rosqvist.

“And it improved the blood lipid profile.” That is, the polyunsaturated fat lowered LDL (“bad”) cholesterol, while the saturated fat raised it.

“In our most recent study, the people eating more saturated fats only gained about an ounce of liver fat, so few crossed the threshold for having a fatty liver,” notes Rosqvist.

How many would have crossed the threshold if the study had lasted several years rather than weeks? Researchers haven’t looked.

Nevertheless, says Rosqvist, “it’s important to exchange some of your saturated fat intake with unsaturated fats.”

That should lower your LDL cholesterol. And if it also helps prevent fatty liver, think of it as a bonus.

The bottom line

Replace butter, cheese, red meats, and palm or coconut oil with other oils, nuts, seeds, and fish. 

Photo: stock.adobe.com: nblxer (pie), stocksolutions (burger), ritablue (tofu), New Africa (cheese & salmon), baibaz (peanut butter), dream79 (nuts), jfunk (cupcake), fotofabrika (butter), Greg (oils).

The information in this post first appeared in the March 2021 issue of Nutrition Action Healthletter.


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