A new 20-year study originally launched in 1993 has found a low-fat diet rich in fruit, vegetables and grains is associated with less risk of death following breast cancer, less risk of coronary heart disease, and a slower progression of diabetes. It’s confirmation of the lifetime benefits of a long-term healthy diet.

But benefits are different from cures. Diets, even healthy ones, cannot cure anything. It’s an important distinction that often gets lost amid the touting of the benefits of a healthy lifestyle and charlatans promoting miracle cures for serious diseases like cancer. Diets, depending on what they comprise, can lower or increase one’s odds of living a longer or shorter life; of developing an illness or recovering from one — but they aren’t cures. This is because diets are complex, often inconsistent, things that interact with nearly all of the body’s other processes. “… foods are not consumed in isolation, but rather in various combinations over time — an ‘eating pattern.’ … dietary components of an eating pattern can have interactive, synergistic, and potentially cumulative relationships,” according to the U.S. Office of Disease Prevention and Health Promotion.

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This latest study, from the Fred Hutchinson Cancer Research Center in the U.S. and published in the Journal of Nutrition, followed 49,000 post-menopausal American women for 20 years. To start, participants received integrated lessons on nutrition and behavior from trained nutritionists and committed to dietary changes toward low-fat diets. Participants revisited these lessons every quarter for nearly a decade.

Designed as a long-term, randomized controlled clinical trial to limit bias and establish causes, the study checked in on the women’s health after nine years of the low-fat diet and again after 20. They found no credible effect after nine years, but by 20 years of a low-fat diet, the cohort saw a 15% to 25% reduction of death from any cause among women who had had breast cancer; a 13% to 35% reduction of death from insulin-dependent diabetes, and a 15% to 30% reduction in heart disease among women without prior hypertension or cardiovascular disease, compared to similar cohorts within the control group.

However, it’s important to note what these low-fat diets comprise: primarily fruits, vegetables, and grains — not ‘lite’ or ‘diet’ or ‘low-fat’ processed foods, which are known to be low in fat, but often high in sugar and thus, are not particularly healthy.

“The sheer number of new diets and nutrition trends can be overwhelming to people who simply want to know, ‘What should I be eating?'” said Dr. Garnet Anderson, a co-author of the study and senior vice president and director of Fred Hutch’s Public Health Sciences Division, said in a statement. “While there are many diets that provide short-term benefits like weight loss, this study scientifically validates the long-term health effects of a low-fat diet.”