For people on the road to weight loss, the latest advice – based on a Japanese study of 60,000 people – is to slow the speed at which they eat.
This new study also offers two other tips to start the process of shedding unwanted weight. They are to cut out after-dinner snacks and not to eat within two hours of going to sleep.
This apparently simple advice combines two theories about eating: one about the rate of ingestion and one about restricting times when eating is advisable. Following this advice won’t melt weight away, but might gradually reduce it.
While advice to eat slowly is old and intuitively sounds right, there has never been strong evidence for it.
Over the past decade a few studies have been done and now, this six-year, Japanese study has put some stronger data behind the advice. However, as an observational study, it can make suggestions but can’t prove cause and effect.
Published on Tuesday in the online journal, BMJ Open, the study verifies the effects of slow eating and highlights the disadvantages of wolfing down food.
The theory is that by eating very fast people outrun their body’s ability to register satiety.
It takes about 20 minutes from the start of a meal for the brain to signal satiety. Eating slowly provides enough time for the brain to recognise when sufficient food has been consumed. Contrary to conventional advice, the study found skipping breakfast made no difference to weight gain.
Water might be key to eating less
Conducted at Kyushu University Graduate School of Medical Sciences in Fukuoka, it is based on health insurance data of 60,000 people with diabetes.
Their claim forms and the notes accompanying their regular health check-ups provided a wealth of data from weight and waist circumference to blood chemistry, urine and liver function.
During the check-ups they were quizzed about aspects of their lifestyle and specifically asked about their eating habits.
At the start of the study, 22,000 routinely gobbled their food and 33,500 ate normally. The 4200 who lingered over food tended to be healthier and have healthier lifestyles than the others. During the study, half changed their eating speed.
Compared to gobblers, those eating at normal speed were 29 per cent less likely to be obese, rising to 42 per cent for those eating slowly.
Over the past decade, researchers from Rhode Island University in the United States have explored eating speeds too. They showed that young adults who ate slowly consumed 56 grams of food per minute. Those eating at medium speed consumed 71 grams, while the wolves took in 88 grams.
They also showed when women were told to eat quickly they consumed 646 calories in nine minutes. When encouraged to pause between bites and chew each mouthful 15 to 20 times before swallowing, they consumed 579 calories in 29 minutes.
Over time 67 calories less per meal can make a difference. When the women ate their meal quickly they reported more hunger an hour later than they did after a slowly eaten meal.
And one side benefit of slow eating is that they drank an average of 409 millilitres of water during the meal. When they ate fast, they only drank 289 millilitres, suggesting drinking more water might be key to eating less.
Professor Gary Wittert, endocrinologist and director of the Freemasons Foundation Centre for Men’s Health in Adelaide, often advises his patients to drink a full glass of water before a meal to distend their stomach.
He says the stomach recognises food by its chemical and mechanical properties and also recognises distention. These signals are sent to the brain, integrated and a message comes back telling the person to stop eating.
Wittert, who is also head of the discipline of medicine at the University of Adelaide, recommends patients eat “proper food, unprocessed and not out of a box”, don’t eat much after 7pm or 8pm and let at least 10 hours elapse before they eat again.
He says the stomach takes four hours to empty but many people stretch out dinner to 11pm and then go to bed.
His team has conducted research into restricted eating using mice. “If you feed mice when they should be sleeping and don’t give them any food during what should be their waking hours, it puts them at a metabolic disadvantage. Their metabolism functions abnormally and they gain weight.”
He says every cell in the body has a circadian clock fixed to the light/dark cycle and has a different job for day and night. During the day cells process fuel for energy and at night they busy themselves with growth and repair work. But if food keeps entering the system late into the night, the cells keep processing fuel and their functions become confused.
This happens in mice and whether it plays out long term in humans too is yet to be shown.
“We live in an environment of profound energy excess and periods where energy is restricted may help the body to reset. This is the basis of the 5-2 diet,” he says.
On this diet people eat normally for five days a week and restrict their intake on two days. Wittert advises his patients to try to eat at relatively fixed times each day to regulate the mechanisms that set their circadian clock.
He says there is no high-level evidence to support slow eating for weight loss. But observational data is increasing. Late last year, another such study from Japan showed gobbling food was bad for the heart.
Presented at the American Heart Association’s Scientific Sessions, it showed those who ate slowly were less likely to become obese or develop metabolic syndrome, a cluster of heart disease, diabetes and stroke risk factors.
It followed 1000 people aged about 50 for five years and found fast eaters had a 12 per cent risk of metabolic syndrome, normal eaters a 6.5 per cent risk and slow eaters only a 2 per cent risk.
The theory goes that because there’s not enough time to feel full, fast eaters are more likely to overeat. Eating fast causes bigger fluctuations in glucose which can lead to insulin resistance.
Men eat faster
The Rhode Island researchers also observed that men eat significantly faster than women, that heavier people eat faster than slimmer people, and refined grains are consumed faster than fibrous whole grains
At lunch, they noted men consumed about 80 calories per minute while the women consumed 52 and that the perception of speed was relative.
Men who reported eating slowly ate at about the same rate as the women who reported eating quickly.
They also noted that people who wolf their food take larger bites and chew less before swallowing. This means the food they put down is less processed and less digestible.
The digestive process starts when people see or smell food and the saliva content of mouth increases, moistening it for easier swallowing.
The stomach starts to secrete more acid and the small intestine prepares for peristalsis.
If eating slowly doesn’t reduce weight, at least it helps digestion!