Have you been overeating without realising it? Here's why the 80% full rule is good for you

But what does 80 per cent full feel like exactly? How do you gauge if you don’t have much of an appetite after exercising or feel ravenous after intermittent fasting?

Growing up, many of us were taught this lesson: Finish up your rice because there are children starving elsewhere in the world.

As virtuous as it is not to waste food, it might have bred a whole generation or two of guilt-ridden people like myself. I prickle with anxiety every time I see unfinished rice on a plate or leftovers destined for the bin. So, I assuage my guilt by stuffing the remaining food down my throat, even though I’m already bursting.

We grew up with the value of not wasting food, partly due to cultural teachings and the historical context of food scarcity from earlier generations,” said Dr Edward Cheong, a senior gastrointestinal surgeon with PanAsia Surgery. “Hence, we feel obligated to clear our plates, regardless of hunger cues.”

And many of us end up eating too much. “Research shows that 50 per cent to 75 per cent of people report occasional overeating, especially on weekends or while dining out,” said Dr Cheong.

During festive periods such as Chinese New Year, overeating has even more far-reaching effects. “Once we become accustomed to eating certain portions of food and feeling good about it, it may become hard to reset our habits after the festivities,” said Dr Annabelle Chow, the principal clinical psychologist at Annabelle Psychology.

Furthermore, “this overeating disrupts normal hunger and fullness cues, creating a cycle where the appetite increases and the urge to eat more persists”, she warned.

“After the celebrations, stressors like returning to work or tackling New Year’s resolutions can also perpetuate this behaviour.”

WHY CAN’T WE STOP OVEREATING?

“Overeating is eating past the point of fullness,” said dietitian Jaclyn Reutens from Aptima Nutrition. “It also means that even when you are not hungry, you continue to eat.”

Interestingly, not everyone is conscious of their own overeating habits. “Some are aware that they are eating too much. Surprisingly, a good number did not realise they were,” said Reutens.

One of the reasons for overeating could be physiological. “It takes about 20 minutes for your brain to register satiety, the feeling of fullness and satisfaction after eating,” said Dr Cheong.

“This delay occurs because that’s how long it takes for the digestive system and hormones (ghrelin, which determines how hungry you are; and leptin, which makes you feel full) to send signals to your brain,” he said. “Eating quickly prevents this feedback loop, often leading to overeating before you feel satisfied.”

And if you also enjoy watching videos on your handphone while eating, you could be ignoring your body’s signals of fullness, added Dr Cheong.

Chinese New Year brings with it another hurdle. Dr Chow said that the variety of festive foods can contribute to the “buffet effect”. “People feel the urge to try everything, even if in smaller portions, resulting in us often eating more than we need,” she said.

“Additionally, declining food in some cultures can feel impolite or ungrateful. We’re also reminded to appreciate food and not waste it, creating feelings of guilt or obligation to finish everything on our plate, even when we’re already full,” said Dr Chow.

Highly processed items like nuggets, chips, chocolates and ice cream encourage eating for pleasure by stimulating dopamine release, making it hard to stop eating them.”

IS EATING UNTIL 80% FULL RIGHT?

This notion comes from hara hachi bu (eating until 80 per cent full), shared Dr Cheong. "It is a practice linked to longevity in Okinawa, a region known for its high life expectancy," he said.

And Japan is not alone in getting it right. There are also other similar mindful eating principles in other cultures, he said, which emphasise moderation and self-awareness.