Changes in these eating habits were strongly associated with lower obesity and weight (BMI), and smaller waist circumference, the researchers found.
They base their findings on health insurance data for nearly 60,000 people with diabetes In Japan who submitted claims and had regular health check-ups between 2008 and 2013.
The claims data included information on the dates of consultations and treatments, while the check-ups included measurements of weight (BMI) and waist circumference, and the results of tests for blood chemistry, urine, and liver function.
During the check-ups, participants were quizzed about their lifestyle, including their eating and sleep habits, as well as alcohol and tobacco use.
They were specifically asked about their eating speed, which was categorised as fast, normal, or slow. And they were asked whether they did any of the following three or more times a week: eat dinner within two hours of going to sleep; snack after dinner; and skip breakfast.
More than a third (36.5%) of participants had one check-up over the six years, while just under a third (29.5%) had two. One in five (20%) had three.
At the start of the study, some 22,070 people routinely wolfed down their food; 33,455 ate at a normal speed; and 4192 lingered over every mouthful. The slow eaters tended to be healthier and to have a healthier lifestyle than either the fast or normal speed eaters.
Around half of the total sample (just under 52%) changed their eating speed over the course of the six years.
All the aspects of eating and sleeping habits studied, as well as alcohol consumption and previous obesity – defined as a BMI of 25 kg/m2 – were significantly associated with obesity.
After taking account of potentially influential factors, the results showed that compared with those who tended to gobble up their food, those who ate at a normal speed were 29 percent less likely to be obese, rising to 42 percent for those who ate slowly.
And although absolute reductions in waist circumference – an indicator of a potentially harmful midriff bulge – were small, they were greater among the slow and normal speed eaters.
Snacking after dinner and eating within two hours of going to sleep three or more times a week were also strongly linked to changes in BMI. But skipping breakfast wasn't.
This is an observational study, so no firm conclusions can be drawn about cause and effect, added to which eating speed was based on subjective assessment, nor did the researchers assess energy intake or physical activity levels, both of which may have been influential.
Nevertheless, eating quickly has been linked to impaired glucose tolerance and insulin resistance. This is possibly because it may take longer for fast eaters to feel full, whereas this might happen more quickly for slow eaters, helping to curb their calorie intake, the researchers suggest.
And they conclude: "Changes in eating habits can affect obesity, BMI, and waist circumference. Interventions aimed at reducing eating speed may be effective in preventing obesity and lowering the associated health risks."
Effects of changes in eating speed on obesity in patients with diabetes: a secondary analysis of longitudinal health check-up data. BMJ Open; http://bmjopen.bmj.com/lookup/doi/10.1136/bmjopen-2017-019589