"The Metabolic Harms of Night Shifts and Irregular Meals"
Shift workers may have higher rates of death from heart disease,
stroke, diabetes, dementia, cardiovascular disease, and cancer.
Graveyard shift, indeed! But is it just because they're
eating out of vending machines or not getting enough sleep?
Highly controlled studies have recently attempted to tease out
these other factors by putting people on the same diets, with the same sleep,
but just at the wrong time of the day. Redistributing eating to the nighttime
resulted in elevated cholesterol, blood pressure, and inflammation.
No wonder shift workers are at higher risk.
Shifting meals to the night in a simulated night shift protocol
turned about a third of the subjects effectively prediabetic in just 10 days.
Our bodies just weren't designed to handle food at night.
Just as avoiding bright light at night can prevent circadian misalignment,
so can avoiding night eating.
We may have no control over the lighting at our workplace,
but we can try to minimize overnight food intake, which has been shown
to help limit the negative metabolic consequences of shift work.
When we finally do get home in the morning, though,
we may disproportionately crave unhealthy foods.
In this experiment, 81% of participants in a nightshift scenario chose
high-fat foods such as croissants out of a breakfast buffet, compared
to just 43% of the same subjects during a control period on a normal schedule.
Shiftwork may also have people too fatigued to exercise,
but even at the same physical activity levels
chronodisruption can affect energy expenditure.
Researchers found that you burn 12-16% fewer calories while sleeping
during the daytime compared to night.
Just a single improperly timed snack can affect how much fat you burn every day.
Study subjects eating a specified snack at 10 am burned about 6 grams more fat
from their body than on the days they ate the same snack at 11 pm.
That's only about a pat and a half of butter's worth of fat,
but it was the identical snack, just given at a different time.
The late snack group also suffered about a 9% bump
in their LDL cholesterol within just two weeks.
Even just sleeping in on the weekends may screw up our metabolism.
Social jetlag is the discrepancy in sleep timing between our work days
and our free days. From a circadian rhythm standpoint,
when we go to bed late and sleep in on the weekends, it's as we flew
a few time zones west on Friday evening and fly back on Monday morning.
Travel-induced jetlag goes away in a few days,
but what might the consequences be of constantly shifting your sleep schedule
every week over your entire working career?
Interventional studies have yet put it to the test, but population studies suggest
that those who have at least an hour of social jetlag a week,
which may describe more than two-thirds of people,
have twice the odds of being overweight.
If sleep regularity is important, what about meal regularity?
The importance of regular meals at roughly the same time every day
was evidently emphasized by such luminaries such as Hippocrates
and Florence Nightingale, but wasn't put to the test until the 21st century.
A few population studies had suggested that those eating meals irregularly
were at a metabolic disadvantage,
but the first interventional studies weren't published until 2004.
Subjects were randomized to eat their regular diets split up
into 6 regular eating occasions a day, or 3 to 9 a day in an irregular manner.
Researchers found that eating an irregular pattern of meals every day
can cause a drop in insulin sensitivity and cause cholesterol levels to rise,
and reduce the calorie-burn immediately after meals
in both lean and obese individuals.
They ended up eating more, though, on the irregular meals,
and so it's difficult to disentangle the circadian effects.
The fact that overweight individuals may overeat on an irregular pattern
may be telling in and of itself,
but it would be nice to see such a study repeated using
identical diets to see if irregularity itself has metabolic effects.
And just such a study was published in 2016. During two periods,
people were randomized to eat identical foods in regular or irregular meal pattern.
During the irregular period, people had impaired glucose tolerance,
meaning higher blood sugar responses to the same food, and lower diet-induced
thermogenesis, meaning burned fewer calories to process each meal.
The difference in thermogenesis only came out to be about 10 calories per meal,
and indeed there was no difference in weight changes over the two-week
periods, but diet-induced thermogenesis can act as a satiety signal.
The extra work put into processing a meal can help slake one's appetite.
And indeed, lower hunger and higher fullness ratings
during the regular meal period could potentially translate
into better weight control over the long-term.