The vegetable Japan’s centenarians eat every week to live longer

When it comes to healthy ageing, few places in the world draw as much attention as Okinawa, Japan. This island is home to some of the longest-living people on Earth, and their secret isn’t just down to genetics or lifestyle. A big part of it comes from what’s on their plates — and one humble vegetable stands out: the Okinawan purple sweet potato, known locally as beni imo.

Why Okinawans rely on purple sweet potatoes

Okinawa boasts nearly three times more centenarians than most parts of the world. Researchers, including National Geographic fellow Dan Buettner who studied the so-called “Blue Zones,” point to diet as a driving factor. For decades, the beni imo made up as much as 70% of the islanders’ daily calories — not just because it’s nutritious, but because it thrives in harsh conditions.

Growing underground, this tuber is resilient to Okinawa’s frequent typhoons, making it a reliable and sustainable food source for generations. In other words, the purple sweet potato isn’t just a health food — it’s a cornerstone of the island’s food security.

Packed with antioxidants and nutrients

The rich violet hue of the beni imo isn’t just for show. It comes from anthocyanins, the same plant pigments found in blueberries, known for their strong antioxidant properties. These compounds help protect the body from oxidative stress, a process linked to ageing and chronic diseases.

Nutritionally, the purple sweet potato checks many boxes. It’s high in fibre, vitamin C, and potassium, while being low in calories and moderate on the glycaemic index. That means it supports steady energy levels without spiking blood sugar — a valuable trait for maintaining metabolic health as we age.

More than one ingredient in the recipe for longevity

Of course, no single food explains why Okinawans live so long. The purple sweet potato is part of a wider dietary pattern rich in vegetables, tofu, seaweed, and fish, with little red meat or processed food. Just as important, Okinawans maintain active lifestyles and close-knit social networks — factors shown by studies in The Lancet to improve both physical and mental health.

The lesson? The purple sweet potato isn’t a miracle cure, but rather a symbol of how simple, plant-based eating supports long-term well-being.

How to add it to your own diet

Beni imo is increasingly available outside Japan, particularly in Asian grocery stores or speciality markets. It can be roasted, steamed, or mashed much like ordinary sweet potatoes, but its naturally sweet, nutty flavour also makes it popular in smoothies and even desserts. In Japan, you’ll often find it in ice creams, cakes, and mochi.

For everyday meals, simply swapping regular sweet potatoes for the purple variety is an easy way to add antioxidants and colour to your diet.

A small choice with lasting impact

The Okinawan purple sweet potato is a reminder that longevity isn’t built on drastic diets or supplements, but on consistent habits: eating more plants, moving daily, and staying socially connected. Regularly including nutrient-rich foods like the beni imo is just one piece of the puzzle — but a delicious and colourful one at that.

And while we can’t all move to Okinawa, we can learn from its centenarians: sometimes, living longer really does begin with what’s on your plate.