According to a study conducted by the University of Illinois at Chicago, an 'evening person' is linked to higher body mass indices among people with Type II diabetes, and having breakfast later in the day seems to be what drives this association.

Obesity is common among people with Type II diabetes. Having an evening preference - waking up later and going to bed later - has been linked to an increased risk for obesity, but research is lacking regarding this phenomenon among people with Type II diabetes. Researchers, led by Sirimon Reutrakul, wanted to determine if morning or evening preference among people with Type II diabetes was associated with an increased risk for higher BMI and if so, what specific factors about evening preference contributed to the increased risk.

Reutrakul and her colleagues recruited 210 non-shift workers living in Thailand with Type II diabetes for their study. Morning/evening preference was assessed using a questionnaire that focused on preferred time for waking up and going to bed; time of day spent exercising; and time of day spent engaged in a mental activity (working, reading, etc.). Participants were interviewed regarding their meal timing, and daily caloric intake was determined via self-reported one-day food recalls. Weight measurements were taken and BMI was calculated for each participant. Sleep duration and quality were measured by self-report and questionnaire.

Self-reported average sleep duration was 5.5 hours/night. On average, participants consumed 1,103 kcal/day. The average BMI among all participants was 28.4 kg/m2 -- considered overweight. Of the participants, 97 had evening preference and 113 had morning preference. Participants with morning preference ate breakfast between 7 a.m. and 8:30 a.m., while participants with evening preference ate breakfast between 7:30 a.m. and 9 a.m.

Participants with morning preference had earlier meal timing, including breakfast, lunch, dinner and the last meal. The researchers found that having more evening preference was associated with higher BMI. Caloric intake and lunch and dinner times were not associated with having a higher BMI. Morning preference was associated with earlier breakfast time and lower BMI by 0.37 kg/m2.

"Later breakfast time is a novel risk factor associated with a higher BMI among people with Type 2 diabetes," said Reutrakul. "It remains to be investigated if eating breakfast earlier will help with body weight in this population." Reutrakul speculated that later meal times may misalign the internal biological clock, which plays a role in circadian regulation. The findings from the study are published in the journal Diabetic Medicine.