The CENTRAL trial looked at that question. The researchers randomly assigned 278 sedentary Israeli adults (mostly men) with oversized waists or high triglycerides and low HDL cholesterol to one of two diets with equal calories: low-fat or Mediterranean low-carb.

(The study was partly funded by the Atkins Foundation.)

What each group was told to eat

  • The Mediterranean low-carb group was told to eat more vegetables, beans, poultry, and fish instead of beef and lamb. And they were given an ounce of walnuts to eat each day. On average, they got about 37 percent of their calories from carbs.
  • The low-fat group was told to eat whole grains, vegetables, fruits, and beans, and to cut back on sweets and high-fat snacks. On average, 53 percent of their calories were carbs.

Each group was served either a low-fat or Mediterranean low-carb lunch—the main meal of the day in Israel—at their workplace.

The impact on weight, liver fat, and more

After 1½ years, both groups had lost about six pounds. But waist size, triglycerides, and liver fat fell more in the Mediterranean low-carb group.

And liver fat matters.

“It’s strongly linked to type 2 diabetes and the metabolic syndrome, and it can cause liver damage over the long term,” says Meir Stampfer, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health. “So it’s a serious problem.”

More troubling: the incidence of fatty liver disease is rising, even in children.

“That’s concerning because the liver can sustain some damage and still function for some time, but at some point, it can’t,” notes Stampfer.

Replacing some carbs with unsaturated fat can help. “It’s an easy fix,” he says.

Does making that change matter for everyone?

“The people in the CENTRAL study were overweight, and they were at risk for metabolic syndrome and fatty liver disease,” says Stampfer. “So they needed that shift more than lean people.”

Was it fewer carbs or the extra unsaturated fat they ate that mattered?

“It’s hard to know because you can’t reduce one source of calories without increasing something else,” says Stampfer. “But if you replace carbs with healthy fats, you get a double win,” because it’s a plus for the heart and maybe also for the liver.

Photo: pasta mizina/stock.adobe.com.