Conventional wisdom is that weight control is all about calorie restriction, and a calorie is a calorie — it doesn’t matter when you eat it, as long as you don’t eat more calories than your body can use. But calories you eat late in the day may do much more harm than those eaten earlier, a new study suggests. Eating dinner late can mess with your metabolism, cause your body to burn less fat and increase your risk for obesity and type 2 diabetes.

In order to see what the effects of eating dinner late might be, Johns Hopkins University researchers followed 20 young adults who were not obese, did not have diabetes or sleep problems. Half of the participants were male and half were female.

The effects in someone who is already obese or has diabetes could be made worse by chronically eating late dinners.

Each person in the study was admitted to the research unit twice, three to four weeks apart. During one visit they ate dinner at the regular time (6 pm), and during the other visit they ate a late dinner (10 pm). They slept from 11 pm to 7 am. Everyone ate standardized meals, had a sleep study and also had a dual-energy X-ray absorptiometry (DEXA) scan to estimate fat mass.

On day one, they were admitted in the evening and slept there overnight. On day two, they ate four standardized meals and engaged in sedentary activities. Beginning at 5 pm, blood was drawn every hour until noon the next day. The dinner meal included palmitate, a lipid tracer, that was used to measure fat oxidation overnight. On the morning of the third day, the participants ate a standardized breakfast and left after their blood was drawn at noon.

The Johns Hopkins Medicine team found that when people ate later, they had higher spikes in blood sugar, slower fat breakdown and even increased cortisol, a stress hormone that is believed to be a factor in promoting weight gain. Those who normally went to bed early — closer to 11, rather than 1 — experienced an even bigger impact from eating late.

An occasional late dinner is not a problem, but if late dinners are your norm, this study suggests that the metabolic effects could eventually lead to weight gain or diabetes. The effects in someone who is already obese or has diabetes could be made worse by chronically eating late dinners.

Do yourself a favor and aim to eat dinner at a reasonable hour, say by 8 pm or at least two to three hours before you go to bed. It’s an easy way to possibly avoid weight gain and metabolic problems like diabetes.

The study was published in the Journal of Clinical Endocrinology & Metabolism.