In a Weight Watchers discussion group, someone recently posted this advice:
The key to successful weight loss is simple mathematics . . . ingest fewer calories than calories expended in a day.
That second part of that sentence is, of course, correct. Your body won’t tap the energy reserves in your fat cells unless the energy is needed. You have to expend more than you ingest. But that doesn’t mean successful weight loss is all about “simple mathematics.” Biological systems aren’t simple.
Unfortunately, too many people grasp (again, correctly) that gaining or losing weight requires an imbalance between the energy consumed and the energy expended, but then take a leap in logic and conclude that:
- Consuming additional calories is the root cause of becoming fatter (as opposed to a response to storing more calories as fat).
- Everyone who becomes fatter is either eating more or moving less than before.
- Consuming fewer calories will automatically lead to a lower weight and less body fat.
In a study published earlier this year, researchers conducted two experiments, each lasting three or four weeks, in which obese mice were divided into two groups: a control group that ate freely (ad libitum) and a calorie-restricted group. In the first experiment, researchers first recorded the average caloric intake of the mice when they were allowed to eat freely, then limited the calorie-restricted group to 95% of that intake. In the second experiment, researchers observed the on-going caloric intake of the mice allowed to eat freely, then limited the calorie-restricted group to 95% of that intake. In other words, if the mice eating freely ate more, the calorie-restricted mice were given more food … but they were still eating 5% fewer calories than their freewheelin’ cousins.
A legitimate criticism of many diet studies is that the researchers relied on food-recall surveys or diet journals to determine how much people ate. Those methods can be notoriously inaccurate. Realizing this, the researchers on this study elected not to allow the mice to keep their own diet journals. Instead, the researchers precisely measured and recorded how much each mouse ate — even going so far as to examine the little critters’ cages and subtracting any bits of food they found from the food-intake totals.
In both experiments, researchers took precise before-and-after measurements of weight, lean body mass, and adipose-tissue mass. In the second experiment, they also used infrared sensors to track locomotor activity levels (”moving around” to us laypeople), and measured oxygen consumption and carbon-dioxide output to calculate how much energy the mice expended. I’d say that’s about as precise as a diet study gets.
Now, according to Jillian Michaels and the other leading experts in thermodynamics, there are only a couple of possible outcomes for these experiments:
- The calorie-restricted mice, who were prevented from making little pig-mice of themselves, ended up weighing less and were leaner.
- If the calorie-restricted mice somehow ended up fatter, it could only be because they were far less active than the mice who ate freely.
At the end of first experiment (four weeks), the calorie-restricted mice weighed a teeny bit less than their free-eating counterparts — the difference was not statistically significant, but it was there. However, the calorie-restricted mice also had 68.5% more fat mass, and 12.3% less lean mass.
Being put on a diet made them fatter.
At the end of the second experiment (three weeks), the average weight for both groups was virtually identical — it was also virtually identical to their baseline weights. But the calorie-restricted mice had 43.6% more fat mass and 6.4% less lean mass than the free-eating control mice. Once again, being put on a diet made them fatter.
Well, clearly, those fat little calorie-restricted mice must’ve spent too much time sitting around watching reruns of The Biggest Loser while their free-eating cousins were whipping themselves into shape by running on the big wheel, right?
Nope. According to the study data, there was no difference in locomotor activity levels between the two groups.
The calorie-restricted mice ate less, they moved around just as much, but they ended up weighing the same as the mice allowed to eat freely, and also ended up with more fat and less muscle. Oh, dear me … did these mice find a way to violate the laws of thermodynamics?
No, heck no, for the thousandth time, NO.
The researchers didn’t take body-heat measurements (too bad), but reported that the calorie-restricted mice expended significantly less energy: 5% less overall, and 20% less while at rest. Simply put, their metabolisms slowed down, even though they were just as physically active. No laws of thermodynamics were violated in the process.
I once sent a link to this study to someone who insisted that according to the laws of thermodynamics, weight gain is caused by eating more or moving less, period. His reply was something like, “That doesn’t prove anything! I’m not a mouse. I’m talking about people.”
Well, I agree that mice aren’t little furry people, which is why I’m not concerned when this-or-that food is shown to trigger cancer in mice. (Mouse chow probably wouldn’t agree with me either.) But remember, we’re talking about The Laws of Thermodynamics here. They don’t apply to one species, but not another. If mice can become fatter without eating more or moving less, yet somehow avoid violating the laws of thermodynamics in the process, then so can people.
The researchers were at a bit of a loss to explain why the calorie-restricted mice grew fatter, but I’m pretty sure we can rule out gluttony and sloth. They suggested perhaps the mice were reacting to the stress of a limited food intake.
“Reacting,” of course, means something hormonal was going on. (It wasn’t thyroid hormone. The researchers checked.) Perhaps the calorie-restricted mice produced more cortisol. Perhaps evolution geared the mice to respond to the threat of starvation by accumulating more fat, even if it means sacrificing lean tissue.
The point is, they didn’t get fatter by eating too much, and they didn’t get fatter because they decided to expend less energy. They began to expend less energy (in spite of being just as active) because they were being hormonally driven to accumulate more fat, even on less food.
Doesn’t that sound something like the process described by a best-selling science journalist who supposedly doesn’t understand that his hypothesis would violate the laws of thermodynamics?
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