Eating one avocado per day as part of a moderate-fat diet can improve cholesterol levels, according to researchers from the American Heart Association who worked with overweight and obese individuals in a small-scale study.

The research team set out to see what would happen if saturated fatty acids from the typical American diet were replaced with avocados, which contain unsaturated fat.

They put the 45 overweight or obese participants -- who were between the ages of 21 and 70 -- on three different diets intended to lower cholesterol.

In the beginning, the dieters consumed 34 per cent of their daily calories from fat sources, 51 per cent from carbohydrates, and 16 per cent from protein -- an allocation which researchers say mirrors an average American diet.

After two weeks on this diet, researchers placed each participant randomly on one of three cholesterol-lowering diets until each person had followed each of the three diets for a total of five weeks, each.

They stuck to a regime that was either low-fat with no avocado, moderate fat with one avocado per day, or a moderate fat diet without avocado.

In the two moderate-fat diets, 34 per cent of calories came from fat, with 17 per cent from monounsaturated fatty acids (MUFAs) and the lower fat dieters sourced 24 per cent of their calories from fat with 11 per cent coming from MUFAs.

Following the moderate fat diet with the daily avocado resulted in a drop in 'bad cholesterol,' low-density lipoprotein (LDL), of 13.5 mg/dL on average, when compared to readings taken after having followed the average American diet.

Compared to baseline readings taken after having followed the average American diet, following the moderate fat diet without the avocado resulted in an 8.3 mg/dL drop in LDL levels and the lower fat diet resulted in a drop of 7.4 mg/dL.

"This was a controlled feeding study, but that is not the real-world," says Kris Etherton, Ph.D., R.D., senior study author and Chair of the American Heart Association's Nutrition Committee and Distinguished Professor of Nutrition at Pennsylvania State University, in University Park, Pennsylvania. "So it is a proof-of-concept investigation. We need to focus on getting people to eat a heart-healthy diet that includes avocados and other nutrient-rich food sources of better fats."

The study was published in the Journal of the American Heart Association.