For four weeks each, all participants ate each diet, which had different amounts of lean beef in combination with the Mediterranean diet. There was a one-week break between each diet period. Researchers also drew blood samples at the study’s onset and following each diet period.
Levels of beef varied in each diet, but the Mediterranean diet plan contained 41% calories from fat, 42% from carbohydrates and 17% from protein. The control average American diet was used along with a diet that had 0.5 ounces of beef a day — this matches the recommended amounts in the Mediterranean diet pyramid. Another diet had 2.5 ounces a day or the amount a typical American eats in one day. A third diet had 5.5 ounces a day. This amount has been linked to specific heart health benefits in prior research.
The beef consumed in these diet periods were either lean or extra lean. All diet periods included a main fat source of olive oil, three to six servings of fruits and at least six daily servings of vegetables.
Fleming and the team were able to use nuclear magnetic resonance technology to measure the number and size of lipoprotein particles, which are part of LDL cholesterol. According to Fleming, this was one of the first randomized controlled trials of the Mediterranean diet that used that method.
“This is important because there is growing evidence to suggest that LDL particle number is more strongly associated with cardiovascular disease risk than total blood LDL concentrations alone,” Fleming said. She added that the team could also identify changes in specific human proteins, “which are also associated with increased CVD risk.”
After analyzing the data, researchers saw lower LDL cholesterol in all participants after the Mediterranean diet periods compared to the typical American diet. Still, the total number of LDL particles was only markedly reduced in the diet periods that included 0.5 or 2.5 ounces of beef a day compared to the typical American diet.
“Our study helped illustrate the benefits associated with a healthy Mediterranean dietary pattern that embodies balance, variety and the inclusion of nutrient-rich components, which can include low to moderate amounts of lean beef,” Fleming said.