A longevity specialist has shared a handy tip for ensuring you're choosing healthy options during your supermarket shop. Dan Buettner has built his reputation investigating regions across the globe where residents live unusually long lives free from major illness - areas he later dubbed Blue Zones.

Since then, he has established himself as a go-to voice for health and longevity guidance on platforms including YouTube and Instagram. Recently, he outlined the 'grandmother' principle for grocery shopping.

In an Instagram post, he explained: "Here's a rule I love: If your grandmother wouldn't recognise it as food, leave it on the shelf. The longest-lived people eat foods that existed 100 years ago - plants, grains, beans. Simple works."

He went on: "One of the simplest patterns we saw in the blue zones is that people eat real food. Not products designed in a lab, not foods with long ingredient lists. Just food that would look familiar to someone 100 years ago.

"In places like Ikaria and Sardinia, meals are built around ingredients that have been part of the local culture for generations. Nothing complicated. Nothing trendy. Over time, those simple choices create a way of eating that supports long, healthy lives."

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Healthy foods Central to Buettner's philosophy is the idea that whole foods are generally healthier than ultra-processed alternatives. Ultra-processed food refers to items that have been heavily processed and usually contain multiple ingredients you wouldn't typically find in your kitchen.

These range from ham or sausages through to crisps and biscuits. Whole foods broadly refers to foods kept close to their natural form. This can include fruit and vegetables, nuts and seeds, beans and lentils, milk, wholegrains, and unprocessed meats and fish.

Ultra-processed foods frequently contain elevated levels of saturated fat, salt, and sugar, and often leave us feeling less satisfied than whole foods, which provide more essential nutrients.

The British Heart Foundation states: "The actual processing of the food could also make a difference to how our bodies respond to it. Studies have shown, for example, that when foods such as nuts are eaten whole the body absorbs less of the fat than when the nut is ground down and the oils are released.

"Another new theory is that diets higher in ultra-processed foods could also affect our gut health."