But it did improve diet quality and led to modest lowering of total cholesterol.
More than 1,000 adults with overweight or obesity and a large waist – at least 35 inches in women and 40 inches in men – took part in this U.S. study, called the Habitual Diet and Avocado Trial (HAT).
The people in the study were divided into two groups:
- Usual diet plus one large avocado every day
- Usual diet with only up to two avocados a month (control group).
Those in the avocado-a-day group were given a regular supply of fresh avocados along with written instructions for how to ripen and prepare them.
They had magnetic resonance imaging (MRI) scans to measure belly fat and fat around other organs (known as “visceral adiposity”) at the beginning of the study and after 6 months.
After 6 months, the people who ate an avocado a day did not have less fat around their middles – the main trial outcome – compared to people in the control group.
But at 6 months, those in the avocado-a-day group had:
- No weight gain. People's weight remained stable in both groups.
- Improved diet quality by eight points on a 100-point scale
- A 2.9-milligrams-per-deciliter (mg/dL) decrease in total cholesterol
- A 2.5 mg/dL decrease in LDL "bad" cholesterol
The study was done by researchers at Penn State University, Tufts University, Loma Linda University, and UCLA, with coordinating support from Wake Forest University.
It was published this month in the Journal of the American Heart Association.
"While the avocados did not affect belly fat or weight gain, the study still provides evidence that avocados can be a beneficial addition to a well-balanced diet," Penny M. Kris-Etherton, PhD, one of the researchers and a professor of nutritional sciences at Penn State University, said in a news release.
Similarly, study researcher Joan Sabaté, MD, a professor at Loma Linda University School of Public Health, said: "While one avocado a day did not lead to clinically significant improvements in abdominal fat and other cardiometabolic risk factors, consuming one avocado a day did not result in body weight gain."
"This is positive," he said, "because eating extra calories from avocados doesn’t impact body weight or abdominal fat, and it slightly decreases total and LDL cholesterol."
Kristina S. Petersen, PhD, another of the researchers and an assistant professor of nutritional sciences at Texas Tech University, pointed out that people are generally poor at adhering to the Dietary Guidelines for Americans.
This study suggests that an avocado a day can improve diet quality, she noted, which " is important because we know a higher diet quality is associated with lower risk of several diseases, including heart disease, type 2 diabetes, and some cancers."
But the researchers also stress that it is important to consider the diet as a whole.
"Consistent with prior observations, a change in dietary patterns rather than a single food or nutrient may be necessary to achieve clinically significant improvements" in belly fat and other risk factors for heart attack, stroke, and diabetes, they wrote in their paper.
HAT was funded by the Hass Avocado Board, which also supplied the avocados.