Eating "healthy" fats found in vegetable oil, nuts, and fish may keep diabetes at bay by improving the body's regulation of blood sugar, research suggests.
Substituting the nutrients for carbohydrates and "saturated" fat from meat and dairy products reduces risk factors for Type 2 diabetes, say scientists.
The evidence comes from an analysis of pooled data from 102 trials comparing the effects of different diets followed by 4,660 adult participants.
Researchers looked at how the foods people ate affected measures of metabolic health, including blood sugar levels, and the ability to produce and respond to the hormone insulin.
Diets rich in monounsaturated or polyunsaturated fats had a beneficial effect on key markers of blood sugar control.
Every 5% switch away from carbohydrates or saturated fats to "healthy" fats as a source of dietary energy resulted in a 0.1% reduction in levels of a blood molecule used to monitor long-term sugar regulation.
Such a change is estimated to reduce the incidence of Type 2 diabetes by 22% and heart and artery disease by 6.8%, said the researchers writing in the journal Public Library of Science Medicine.
Lead scientist Dr Dariush Mozaffarian, from Tufts University in Massachusetts, US, said: "The world faces an epidemic of insulin resistance and diabetes.
"Our findings support preventing and treating these diseases by eating more fat-rich foods like walnuts, sunflower seeds, soybeans, flaxseed, fish, and other vegetable oils and spreads, in place of refined grains, starches, sugars, and animal fats.
"This is a positive message for the public. Don't fear healthy fats."
The most consistent benefits resulted from increasing consumption of polyunsaturated fats in place of either carbohydrates or saturated fat, the study found.
Blood sugar is regulated by the hormone insulin, which controls how much of it is stored or used as "fuel" for cells.
If too little insulin is produced, or the body stops responding to it properly, blood sugar can rise leading to the health problems associated with diabetes.
British co-author Dr Fumiaki Imamura, from Cambridge University, said: "Until now, our understanding of how dietary fats and carbohydrate influence glucose, insulin, and related risk factors has been based on individual studies with inconsistent findings.
"By combining results from more than 100 trials, we provide the strongest evidence to date on how major nutrients alter these risks."