When active volunteers tried being not-so-active, their blood-sugar levels spiked after they ate:
Exercise guidelines from the American Heart Association and other groups recommend that, for health purposes, people accumulate 10,000 steps or more a day, the equivalent of about five miles of walking. Few people do, however. Repeated studies of American adults have shown that a majority take fewer than 5,000 steps per day.
The Missouri volunteers were atypical in that regard. Each exercised 30 minutes or so most days and easily completed more than 10,000 daily steps during the first three days of the experiment. The average was almost 13,000 steps.
During these three days, according to data from their glucose monitors, the volunteers’ blood sugar did not spike after they ate.
But that estimable condition changed during the second portion of the experiment, when the volunteers were told to cut back on activity so that their step counts would fall below 5,000 a day for the next three days. Achieving such indolence was easy enough. The volunteers stopped exercising and, at every opportunity, took the elevator, not the stairs, or had lunch delivered, instead of strolling to a cafe. They became, essentially, typical American adults.
Their average step counts fell to barely 4,300 during the three days, and the volunteers reported that they now “exercised,” on average, about three minutes a day.
Meanwhile, they ate exactly the same meals and snacks as they had in the preceding three days, so that any changes in blood sugar levels would not be a result of eating fattier or sweeter meals than before.
And there were changes. During the three days of inactivity, volunteers’ blood sugar levels spiked significantly after meals, with the peaks increasing by about 26 percent compared with when the volunteers were exercising and moving more. What’s more, the peaks grew slightly with each successive day.
This change in blood sugar control after meals “occurred well before we could see any changes in fitness or adiposity,” or fat buildup, due to the reduced activity, Dr. Thyfault says. So the blood sugar swings would seem to be a result, directly, of the volunteers not moving much.
“so any changes in blood sugar levels would not be a result of eating fattier or sweeter meals than before.”
Eating fat doesn’t spike blood sugar.
Well, one thing is clear — the subjects were having some (and knowing current medical research, significant) carbs in these meals. (I couldn’t find the article easily, only the abstract at PubMed.)
If they had been eating pure protein and fat, there wouldn’t be a spike after, under either condition.
One other thing, however, that does cause spikes in glucose (and in triglycerides inter alia) is cortisol. Cortisol, of course, in induced by stress of any kind.
It would be interesting to see if this study controlled for cortisol, or instead, did not even mention it. My money is the latter.
The subjects, being Americans, were certainly eating carbohydrates. What the study would appear to document is the effect of irisin on carbohydrate metabolism and the activity threshold for natural production of this hormone in human biology.