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DENVER -- Late sleepers who got at least 6.5 hours of shut-eye a night were more likely than early risers to have poor eating habits and they also tended to get less exercise, researchers reported here, although body mass index didn't seem to be affected.

Late sleep timing in healthy subjects and late biological timing, measured by , were associated with higher fast food and lower vegetable and dairy consumption.

However, calorie intake was not higher in study participants who slept late and showed late biological timing, and late sleepers actually tended to weigh less than those who woke earlier, researchers , of Feinberg School of Medicine at Northwestern University in Chicago, and colleagues noted.

Baron presented study findings June 12 at .

"This finding suggests that there may be some sort of compensation going on," she said. "Late sleeping was associated with worse diets, but it was not associated with consuming more calories."

The goal of the study was to explore the associations between measures of circadian and sleep timing with body mass index, body fat, and diet and exercise.

The trial included 96 healthy people between the ages of 18 and 50 (mean age 26.8, 61% female) recruited by telephone or internet outreached. All participants reported sleeping at least 6.5 hours a night and none were shift workers.

The participants wore wrist actigraphy devices for 7 days to measure their sleep and wake patterns and they also completed food diaries during this period to measure their caloric intake and dietary patterns. Exercise levels were measured with physical activity armbands.

DLMO was evaluated in the clinical setting, and body fat was evaluated using dual axis absorptiometry (DXA).

The average nightly sleep duration among the participants was 443.7 (SD 50.4) minutes, and the average DLMO was 22.36±1.27. Most participants had BMIs in the normal range.

Sleep onset time and DLMO were significantly related to fast food intake (P<0.05), and sleeping later was associated with eating fewer vegetable servings (P<0.04). These relationships were stronger in males than females. Later wake time, but not late biological timing, was associated with lower physical activity.

Baron said more research will be needed to confirm the findings and, if confirmed, explore how late sleeping leads to poorer quality diets, but not higher BMIs in healthy adults.

"There is some interesting work to be done to unpack the biological versus social factors involved in the health effects of being a late sleeper," she said.