They first recruited 12 healthy, active young men and asked them to report to the university’s exercise lab on three separate mornings. On one morning, the men ate a hearty, 430-calorie bowl of oatmeal and rested for several hours.
Another morning, they swallowed the same porridge before riding a bike moderately for an hour.
On a third visit, they skipped the porridge but rode the bike, not eating at all until lunch.
Each time, the men stayed at the lab through lunch, eating as much or little at that meal as they wished. The scientists also handed the men food baskets to take home, asking them to eat only from the basket and return uneaten portions, so the researchers could track their daily calories. They also used respiratory masks and mathematical formulas to estimate their 24-hour energy expenditure.
Then the scientists compared numbers, with some results they had not predicted.
Least surprising, the men wound up with an energy surplus when they had breakfasted and then sat, taking in about 490 more calories that day than they burned.
When they downed porridge and then worked out, though, they maintained their energy balance with fine precision, burning and consuming almost exactly the same number of calories that day.
It was when they had skipped breakfast before exercise that their eating became most interesting. Having presumably depleted most of their bodies’ stored carbohydrates during the cycling that day, the men seemed ravenous at lunch, consuming substantially more calories than during either of their other lab visits.
But afterward their eating tailed off and at the end of the day, they maintained an energy deficit of nearly 400 calories, meaning they had replenished few of the calories they had burned while riding.