While previous research has demonstrated that avocados could help lower low-density lipoprotein (LDL) cholesterol, researchers from Pennsylvania State University wanted to discover whether avocados could also help lower oxidised LDL particles.
In their randomised, controlled feeding study, the researchers found that eating one avocado a day was associated with lower levels of LDL (specifically small, dense LDL particles) and oxidized LDL in adults who were overweight or obese and they suggest this may be due to the lutein found in avocados.
Lead author Penny Kris-Etherton, professor of nutrition, says that small, dense LDL particles are particularly harmful for promoting plaque buildup in the arteries and oxidation is also bad for the human body.
She said: "A lot of research points to oxidation being the basis for conditions like cancer and heart disease.
"We know that when LDL particles become oxidised, that starts a chain reaction that can promote atherosclerosis, which is the build-up of plaque in the artery wall.
"...If you can help protect the body through the foods that you eat, that could be very beneficial."
The researchers recruited 45 adult overweight or obese participants for the study. All participants followed a two-week 'run-in' diet at the beginning of the study. This diet mimicked an average American diet and allowed all participants to begin the study on similar nutritional 'footing'.
Next, each participant completed five weeks of three different treatment diets in a randomised order. Diets included a low-fat diet, a moderate-fat diet, and a moderate-fat diet that included one avocado a day.
The moderate-fat diet without avocados were supplemented with extra healthy fats to match the amount of monounsaturated fatty acids that would be obtained from the avocados.
After five weeks on the avocado diet, participants had significantly lower levels of oxidised LDL cholesterol than before the study began or after completing the low- and moderate-fat diets. Participants also had higher levels of the antioxidant lutein after the avocado diet.
Kris-Etherton said there was specifically a reduction in small, dense LDL cholesterol particles that had become oxidised.
"When you think about bad cholesterol, it comes packaged in LDL particles, which vary in size," she explained.
"All LDL is bad, but small, dense LDL is particularly bad. A key finding was that people on the avocado diet had fewer oxidised LDL particles. They also had more lutein, which may be the bioactive that's protecting the LDL from being oxidised."
The researchers added that because the moderate-fat diet without avocados included the same monounsaturated fatty acids found in avocados, it is likely that the fruit has additional bioactives that contributed to the benefits of the avocado diet.
Kris-Etherton said that while the results of the study are promising, there is still more research to be done.
"Nutrition research on avocados is a relatively new area of study, so I think we're at the tip of the iceberg for learning about their health benefits," Kris-Etherton said.
"Avocados are really high in healthy fats, carotenoids—which are important for eye health—and other nutrients. They are such a nutrient-dense package, and I think we're just beginning to learn about how they can improve health.
"CPeople should consider adding avocados to their diet in a healthy way, like on whole-wheat toast or as a veggie dip."
Source: Journal of Nutrition
Wang. L., et al
"A Moderate-Fat Diet with One Avocado per Day Increases Plasma Antioxidants and Decreases the Oxidation of Small, Dense LDL in Adults with Overweight and Obesity: A Randomized Controlled Trial."