You Are When You Eat: Study Explores Body Clock Effects On Blood Sugar

You know the old saying (or maybe you should): "Eat breakfast like a king, lunch like a prince and dinner like a pauper."

A new study in the journal PNAS looks into some of the underlying biology: that our bodies tend to regulate blood sugar better after breakfast than after dinner.

Led by researchers at Brigham and Women's Hospital, it also helps explain why night shift workers tend to be at heightened risk for Type 2 diabetes.

Says the study's senior author, Frank A. J. L. Scheer of the Brigham, on Radio Boston today: "What we wanted to explore was whether the biological clock — the internal clock — is playing an important part in this day/night variation, or that it might just be due to the sleep/wake and feeding/fasting cycle."

The study pinpoints two separate mechanisms at work:

• Our basic body clocks, also known as circadian rhythm, have major influence on our blood sugar regulation: our glucose tolerance is naturally higher in the morning than the evening.

• And, independently, when our clocks are misaligned — when we're forced to flip our days and nights — that, too, lowers our glucose tolerance.

Bottom line, for those of us who are not shift workers: The same exact meal can lead to more of an increase in blood sugar when eaten at night than when eaten in the morning (and higher blood sugar is considered a risk factor for developing diabetes.) Chalk one up for the writers of old sayings.

On the study:

Confined to a lab for eight days, the 14 healthy subjects were monitored during "normal days" — breakfast at 8 a.m., dinner at 8 p.m. — and flipped days, with breakfast at 8 p.m., dinner at 8 a.m. and wakefulness through the night. From the press release:

The team found that glucose levels after identical meals were 17 percent higher (i.e., lower glucose tolerance) in the evening than in the morning, independent of when a participant had slept or had their meals. They also found that simulated night work (sleeping during the day, having breakfast at 8 p.m., etc.), lowered glucose tolerance throughout multiple days.

In other words — and this jibes with longer-term studies on shift workers — the body never fully adjusts to a night-for-day schedule. What is to be done? Dr. Scheer says work is under way on whether meal timing might help, and researchers elsewhere are seeing whether drugs hold the potential to offset the health effects of overnight work.

Hat-tip to Haley Bridger of Brigham and Women's for phrasemaking "You are when you eat."

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Carey Goldberg Editor, CommonHealth
Carey Goldberg is the editor of WBUR's CommonHealth section.



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