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Among individuals at high cardiovascular risk, eating a Mediterranean diet supplemented with extra-virgin olive oil (EVOO) reduced the risk of developing type 2 diabetes, an analysis of the PREDIMED study showed.

Compared with a control group that was advised to consume a low-fat diet, the Mediterranean diet with EVOO was associated with a significantly lower risk of being diagnosed with diabetes during follow-up (HR 0.60, 95% CI 0.43-0.85), according to , of the Universitat Rovira i Virgili in Reus, Spain, and colleagues.

However, a similar risk reduction was not seen for individuals eating a Mediterranean diet that was supplemented with nuts (HR 0.82, 95% CI 0.61-1.10), the researchers reported online in .

The diet -- rich in grains, fruit, fish, and vegetables, and light on red meat and poultry -- has been tied to a number of beneficial health outcomes, such as protecting against kidney disease, slowing cognitive decline, defending against damage to small blood vessels in the brain, preventing and/or slowing progression of metabolic syndrome, reducing liver fat and increasing insulin sensitivity, and improving heart function.

The authors noted that weight-loss interventions have protective effects against diabetes, but prior research had not evaluated changes in diet without calorie restriction on diabetes outcomes. They evaluated this association through the Prevención con Dieta Mediaterránea (PREDIMED) trial over a median follow-up of 4.1 years with a population of 3,541 adults ages 55 to 80 who were at high cardiovascular risk.

Participants were stratified by region, sex, and age and were randomly assigned to receive coaching on a Mediterranean diet supplemented with EVOO or nuts, or a control, low-fat diet. They were not required to increase physical activity or otherwise lose weight, and they were not stratified by diabetes status when randomized.

Those in the study had no cardiovascular disease at baseline, but did have three or more cardiovascular risk factors, which included current smoking status, hypertension, hypercholesterolemia, low high-density lipoprotein, overweight or obesity, and family history of premature cardiovascular disease. Participants with diabetes were included in the study, but were not included in the analysis.

Participants received a baseline and quarterly dietary training session, where they learned about meal plans and seasonal shopping lists, and received advice on diet adherence. Additionally, those in the Mediterranean diet groups received supplementary amounts of EVOO or nuts, while those in the control group received nonfood items such as kitchenware or shopping bags.

Baseline and annual questionnaires were also administered to record food frequency, physical activity, and education, lifestyle, medical history, and medication use.

Diet adherence was significantly higher in the Mediterranean diet groups (P<0.01) compared with the control group over the study.

Over the follow-up period, 273 participants developed new-onset diabetes, including 80 in the olive-oil group, 92 in the mixed nut group, and 101 in the control group.

, of Chaim Sheba Medical Center in Tel Hashomer, Israel, noted that an earlier analysis of the data found "apparent substantial and improbable ultra-short, early excess risk of cardiovascular morbidity outcomes in the control group, already apparent after 2 to 3 months" -- a result he said may be attributable to "a significant imbalance between the control and intervention groups in several key-baseline characteristics such as obesity."

In addition, the low-fat intervention group had actually consumed fat consistently during the follow-up period, "between 37% to 39% total fat in their diet, much higher than the level recommended in the American Heart Association guidelines for a low-fat diet (<30% fat)," Kopel told 乌鸦传媒.

"The current secondary analysis on diabetes outcome would need to model the data much differently than was done" by the authors, he added, noting that "I would be very careful before concluding anything from this secondary ad-hoc analysis, particularly that a fat-rich diet without calorie restriction and with an extra supplement of fat would benefit in terms of health outcomes."

From the American Heart Association:

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