Obesity is common among people with Type 2 diabetes (T2D). Having an evening preference -- waking up later and going to bed later – and late meal times have been linked to an increased risk for obesity, but research is lacking regarding this phenomenon among individuals with T2D.

Researchers led by Dr. Sirimon Reutrakul, associate professor of endocrinology, diabetes and metabolism at University of Illinois College of Medicine at Chicago, USA, went on to determine if morning or evening preference among T2D individuals was associated with an increased risk for higher BMI and if so, what specific factors about evening preference contributed to the increased risk.

Researchers recruited 210 non-shift workers with T2D living in Thailand and their 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 mental activity (working, reading, etc.). Scores on the questionnaire could range from 13 (indicating extreme evening preference) to 55 (indicating extreme morning preference). Participants were interviewed regarding their meal timing, and the 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 of the participants was 5.5 hours/night. On average, participants consumed 1,103 kcal/day. The average BMI was 28.4 kg/m² -- considered overweight. Of the participants, 97 had evening preference and 113 had morning preference. Participants with morning preference had earlier meal timing, including breakfast, lunch, dinner and the last meal. Evening preference was associated with higher BMI, whereas 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 T2D," said Reutrakul. "It remains to be investigated if eating breakfast earlier will help with body weight in this population." Reutrakul speculates that later meal times may misalign the internal biological clock, which plays a role in circadian regulation. Circadian misalignment can lead to dysregulation of energy metabolism according to previous studies.

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