Among nutritionists, the type of protein we should eat is always a cause for debate. A new global analysis has brought the conversation into sharper focus.

In a study spanning six decades and over 100 countries, researchers at the University of Sydney found that plant-based proteins are linked to longer adult life expectancy, while animal proteins appear to benefit survival in early childhood. The findings strengthen the case but also add a layer of nuance to the global push toward sustainable, plant-forward diets.

One World, Two Diets

The study mined national food supply data and demographic records from 101 countries between 1961 and 2018. It considered not only how much protein people had access to, but also where it came from—plants or animals.

Using a sophisticated statistical approach called the geometric framework for nutrition, the researchers matched national protein supplies to age-specific survival data, adjusting for economic disparities and population sizes.

They found that a high supply of animal-based proteins—such as meat, eggs, and dairy—correlated with better survival rates among children under five. These nutrients are dense in essential amino acids, iron, and vitamins like A and B12, which are critical during early development. In settings with adequate calories, adding animal protein seemed to give young children a survival edge.

But as people age, the balance tilts.

In adults, especially those beyond middle age, higher supplies of plant-based proteins—found in legumes, nuts, whole grains, and soy—were linked to longer life expectancy. When researchers simulated national diets where plant proteins replaced animal ones without reducing total calories, adult survival improved.

This wasn’t just a marginal effect. In some models, swapping animal protein for plant-based sources increased predicted life expectancy by up to several years.

What About Fat and Fiber?

Fat told a story similar to animal protein. High-fat diets improved survival in early childhood, likely due to their calorie density and role in carrying essential vitamins. But later in life, too much fat—especially in the presence of animal protein—was linked to higher mortality.

“Protein is a crucial part of the human diet,” said Dr. Alistair Senior, the lead investigator, “but as eating habits change and developed countries look to decarbonise, where we get our protein from has come under greater scrutiny.”

Animal protein often comes bundled with saturated fats and cholesterol, especially in processed meats. These are known risk factors for heart disease, type 2 diabetes, and some cancers. In contrast, plant-based protein sources tend to be rich in fiber, antioxidants, and beneficial fats.

These findings echo decades of research into the world’s “blue zones”—places like Okinawa, Japan; Ikaria, Greece; and Loma Linda, California—where diets are low in animal protein and longevity is exceptionally high.

What This Means for Modern Nutrition

As climate concerns accelerate calls to reduce animal agriculture, understanding the human health implications of dietary shifts is important.

Animal-based foods are resource-intensive and a significant source of greenhouse gas emissions. Yet simply removing them from food systems is downright impractical.

“This is not an argument to abandon meat altogether,” said Dr. Alistair Senior. “But it does show the importance of age-specific nutritional strategies as we rethink global diets.”

Indeed, the study underscores that a one-size-fits-all solution won’t work. While plant-based diets may optimize adult longevity, young children may still need access to animal-source foods, particularly in regions with limited overall nutrition.

The data also provide policymakers with a powerful lens for balancing environmental goals with public health. Shifting national food supplies toward plant-based proteins, while safeguarding adequate nutrition in early life, could offer a path forward that is both sustainable and equitable.

The findings appeared in Nature Communications.