Back in the 1980s, tens of thousands of American nurses filled out questionnaires about what they ate. They probably didn’t realize that decades later, their food logs would help crack a puzzle about aging. Fast-forward to 2025, and we have some important conclusions: the kinds of carbohydrates you eat in midlife can shape how well you age.

The quality of your carbs matters more than you think. High-quality carbs from whole grains, fruits, vegetables, and legumes were consistently associated with better odds of aging well — staying mentally sharp, physically active, and free of major diseases. In contrast, diets high in refined carbs — think white bread, sugary snacks, and processed foods — were linked to worse outcomes.

“We’ve all heard that different carbohydrates can affect health differently, whether for weight, energy, or blood sugar levels. But rather than just look at the immediate effects of these macronutrients, we wanted to understand what they might mean for good health 30 years later,” said Andres Ardisson Korat, a scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging and lead author of the study. “Our findings suggest that carbohydrate quality may be an important factor in healthy aging.”

But what does that mean, exactly?

Good Carbs vs. Bad Carbs

The term “carbohydrate” covers a lot of ground; it’s one of the most diverse types of nutrients out there. From oats to marshmallows and pasta to honey, a lot of foods are considered carbs. In this study, the researchers split carbs into two main categories:

• High-quality carbs came from whole grains, fruits, vegetables, and legumes.
• Refined carbs included processed grains, potatoes, and added sugars.

Every 10% increase in high-quality carbs was associated with a 31% increase in the odds of healthy aging. Refined carbs had the opposite effect: every 10% increase was linked to a 13% decrease in those odds. The team also looked at fiber (total, fruit, vegetable, and cereal), glycemic index (GI), glycemic load (GL), and the carb-to-fiber ratio. The amount of fiber consumed was an even stronger indicator of healthy aging.

But what does healthy aging mean? In this context, the researchers defined it as reaching age 70 and beyond without any of 11 major chronic diseases (like cancer, diabetes, or heart disease), having no significant physical or cognitive impairments, and maintaining good mental health.

This study didn’t dive deep into the biology of how this happens, but previous research offers some clues. Fiber feeds the gut microbiome, which plays a key role in inflammation, immunity, and brain health. At the same time, high-fiber diets improve insulin sensitivity, reducing the risk of diabetes — a major risk factor for cognitive decline.

Whole plant foods are rich in antioxidants and polyphenols, which help to reduce oxidative stress, another aging accelerant. Eating healthy carbs helps in all these departments (and more).

So, Should We All Eat More Carbs?

Well, eating more isn’t necessarily good, nor is eating less. The total amount of carbs matters a lot — and there’s a sweet spot.

Previous studies have shown a U-shaped relationship between total carb intake and mortality. Eat too few, and you might miss out on essential nutrients and fiber. Eat too many, especially from low-quality sources, and chronic disease risks climb.

The key takeaway is to eat healthier, more diverse carbs. Less refined, processed carbs, less added sugars; more whole grains, fruits, veggies, and legumes.

“Our results are consistent with other evidence linking consumption of fruits and vegetables, whole grains, and legumes with lower risks of chronic diseases, and now we see the association with physical and cognitive function outcomes,” said senior author Qi Sun, associate professor in the departments of nutrition and epidemiology at Harvard Chan School.

Swapping just 5% of your daily calories from one macronutrient to a healthier one can make a big difference and improve your health across the board.

It Matters More Than Ever

Diet advice can often be confusing, and in truth, there’s much we’re still uncovering about healthy eating. But one of the things scientists consistently have found is that healthy carbs and fiber are good for you, while processed carbs, especially refined sugars, aren’t so good for you.

The new findings fit with that idea, and they also come at a crucial time.

It’s not just the obesity crisis. Like much of the global population, the U.S. population is aging rapidly. By 2060, nearly a quarter of Americans will be over 65. Many will live longer — but not necessarily better. Chronic diseases, frailty, memory loss — these are the burdens of age. But they’re not inevitable. Diet is one of the few levers we can pull early on to tilt the odds in our favor.

Most Americans eat too few fruits and vegetables and too many refined carbs. According to the CDC, added sugars still make up over 13% of daily calorie intake in adults. The Standard American Diet is rich in calories but poor in nutrients and fiber.

This was an observational study, not a randomized trial. That means researchers can’t prove that high-quality carbs cause healthy aging — only that they’re strongly associated. Also, the study only included women, most of whom were White nurses, which limits the generalizability of the study.

Even so, the research adds to the growing mountain of evidence that fiber-rich, plant-based diets are protective well into old age. Eating more fiber and high-quality carbs in midlife is one of the best bets we have for aging well.

The study was published in JAMA Network.