Longest-living people swear by 'Hara Hachi Bu' dieting trick - what you need to know

Italy, Japan, and Costa Rica might appear very different on the surface, but they are actually connected by a surprising common trait. These countries boast three of the globe's six exclusive 'Blue Zones' where inhabitants are reportedly 10 times more likely to live to 100 than anywhere in the United States.

However, not living in these longevity hubs isn't a reason to despair. A potentially game-changing key to the residents' long lives has recently been revealed—it's all about a strict practice called the '80% trick' or 'Hara Hachi Bu.'

This dietary rule is particularly unfavourable for those who want to eat three large meals daily. People in Blue Zones usually have a small meal later in the day, deliberately stopping at about 80% fullness, hence the name of the rule.

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It's said this practice helps prevent the common 'food coma' feelings that can occur after overeating, while also enabling residents to stay active throughout the day. It is mainly practised by Okinawans on one of Japan's smallest islands, as noted by Blue Zones explorer Dan Buettner.

According to a previous Mirror report, he wrote online: "The secret to eating in moderation in the long run is emulating the environment and habits of the Okinawan people. There is a significant calorie gap between when an American says, 'I’m full' and an Okinawan says, 'I’m no longer hungry'."

Previous research suggests that they exist in a 'calorie deficit', consuming only 1,900 calories instead of the usual 2,000 to 2,500, which is associated with a reduced risk of diseases related to ageing.

These views are echoed by Dr Deborah Lee, a GP at Dr Fox Pharmacy, too. She told the Mirror that eating less may even help to reduce ageing.

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"Imagine what 80% of your meal would look like, and aim to leave 20% behind," she said previously. "Calorie restriction is believed to slow the ageing process. Eating less lowers the metabolic rate.

"With less metabolic processes underway, less oxidation is taking place. Oxidative stress probably underpins the development of many of the chronic diseases we see today – heart disease, cancer, type-2 diabetes and dementia."

Dr Lee suggested that eating slowly can help one adhere to the 80% rule. Research supports this theory, with a 2012 study indicating that slower eating is associated with increased satisfaction and less hunger between meals.

She continued: "Nutritionists believe that when you look at your plate, if you eat mindfully, eating slowly and chewing every mouthful thoroughly, you can feel satisfied by eating only 80% of that is on your plate.

"The diet has many benefits. You don’t have to count calories, and no foods are absolutely forbidden. It can fit in with your work and social schedule. You are still eating large amounts of healthy foods and getting good nutrition."