Even without weight loss, adhering to a diet rich in fresh produce, chicken, fish and olive oil is 40 percent more effective in heading off the development of Type 2 diabetes than following a low-fat diet, a new study has found.

The research suggests that for the nation’s 78 million obese adults, a diet that minimizes red meat and sweets but incorporates plant-based fats may be a sustainable way to improve health — even if permanent weight reduction proves elusive.

The findings add to mounting research that suggests a traditional Mediterranean diet may be easier to adhere to and more likely to improve health than more restrictive regimens.

Compared to those on a low-fat diet, trial participants whose Mediterranean-style diets were supplemented with a daily dose of tree nuts — almonds, walnuts and hazelnuts — were 18 percent less likely to develop Type 2 diabetes. The researchers called that a positive trend but acknowledged that the difference fell short of demonstrating beyond doubt the superiority of a Mediterranean diet rich in nuts over a standard low-fat diet.

Published Monday in the Annals of Internal Medicine, the latest entry in the diet fray followed for more than four years 3,541 older Spaniards who were at high risk of developing cardiovascular disease. They were a subgroup of a larger clinical trial that demonstrated the effectiveness of the Mediterranean diet in reducing the risk of heart attacks and strokes.

That trial of 7,447 subjects — documented in February in the New England Journal of Medicine — found those placed on a Mediterranean diet supplemented with either nuts or extra-virgin olive oil were 30 percent less likely than those prescribed a low-fat diet to suffer a heart attack, stroke or death due to cardiovascular disease.

Nearly half of those recruited for the parent trial already had Type 2 diabetes.

The subjects used in the current subgroup analysis started the trial with at least three risk factors for developing premature cardiovascular disease: They were active smokers; were overweight or obese; had a family history of premature heart disease; or had hypertension or worrisome cholesterol readings. None, however, had been diagnosed with Type 2 diabetes at the start of the trial.

Some 273 participants went on to develop Type 2 diabetes. Among those in the Mediterranean diet-supplemented-with-extra-virgin-olive-oil arm, 6.9 percent of participants developed diabetes; among those in the Mediterranean-diet-plus-nuts group, 7.4 percent did so; and among the low-fat dieters, 8.8 percent developed type-2 diabetes.

Dr. Meir J. Stampfer, professor of medicine and epidemiology at Harvard University, called the research published Monday a significant step in further demonstrating the clinical benefits of the diet that until recently predominated in southern Europe. In showing the Mediterranean diet to be sustainable and beneficial, Stampfer said, the study should help put to rest many health-conscious Americans’ aversion to nuts and oils, which are as calorie-dense as they are rich in unsaturated fats.