Surprisingly, they found an unlikely culprit between the two factors – late breakfast times. "Breakfast time mediates the association between morningness-eveningness preference and BMI," the researchers wrote.
In particular, obesity – the state of having a BMI of 30 and higher – is common in people with Type 2 diabetes, and having an evening preference has been identified as a risk factor for obesity. However, there isn't a lot of information on how these two factors contribute to Type 2 diabetes. The team discovered the link by using mediation analysis to understand the relationship between morningness-eveningness preference and BMI in people with Type 2 diabetes – and how meal timing fits the bill.
To understand how these two factors are related, the researchers, led by Dr. Sirimon Reutrakul of the University of Illinois at Chicago College of Medicine, held a clinical trial that involved 210 non-shift workers in Thailand that already had Type 2 diabetes. To get the respondents' preference between the morning or evening, researchers used a scale called the Composite Scale of Morningness (CSM), a questionnaire that contained questions asking a person's preferred time for waking up and going to bed, his time of day to exercise, and his time of day for mental activities such as reading and working. Participants also answered a one-day food recall – providing data regarding meal timing and daily calorie intake – had their weight taken, and BMI calculated. For information on sleep quality and duration, the researchers measured these based on self-reported data from the participants.
Based on the results, their average self-reported sleep duration was 5.5 hours per night. In terms of preference, 97 reported preferring evenings, while 113 had morning preference. Their average BMI was 28.4 kg per square meters and had an average calorie intake of 1,103 kilocalories a day. Participants who reported to have morning preference had breakfast between 7-8:30 a.m., while those with evening preference ate between 7:30-9 a.m. Those who had a morning preference also followed an earlier mealtime, which included lunch, dinner, and the last meal. (Related: Eating breakfast (meal timing) lowers heart disease risk by more than twenty-five percent.)
The researchers found that those who had a greater preference for evenings had a higher BMI. Having a late breakfast time, on the other hand, was non-significantly associated with a higher BMI. Other meal times or calorie intakes were not associated with BMI increase. Moreover, eveningness was linked to late breakfast times. Consequently, those who had a preference for mornings were associated with taking their breakfast early, having a lower BMI by 0.37 kg per square meter. The direct relationship between BMI and morningness-eveningness, however, did not yield significant results.
People with Type 2 diabetes who had an evening preference and a later breakfast time might have a higher BMI, researchers deduced, following the mediation of breakfast times between morningness-eveningness preference and BMI. "Later breakfast time is a novel risk factor associated with a higher BMI among people with Type 2 diabetes," added Reutrakul. "It remains to be investigated if eating breakfast earlier will help with body weight in this population."
She also explained that eating meals at a later time may negatively affect the body's internal biological clock, which regulates the body's sleep-wake cycles. In previous studies, circadian misalignments can result in problems with metabolism, which also plays a role in the onset of diabetes.
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