1) Having a BMI of 26.1 kg/m2, you don't lose 7.4 kg over one month just by eating less (unless you just stop eating), 2) I'm sure what the article explains goes a bit beyond "eat less"

Since I have the advantage of having read the article, I can say that your speculation is correct: the author describes a systematic way to control how much less to eat. But "eat less" is still the bottom line. He lost weight because he ate less over the month of the experiment that he had been eating previously. How else did he lose the weight? Note that he doesn't report increasing his caloric expenditure through exercise, for example.

I have occasionally remarked, you can't gain more weight than the weight of the food you eat, because conservation of mass. This is sometimes my response to people who don't eat a single donut on a special occasion. Naturally the pound or less of food you might eat in a day is not permanently conserved. I also think that a pound of food sounds like an enormous amount, but it really isn't. If you like hamburgers (and let's say you make your own so they are wholesome) you might cook a third of a pound of ground meat to make one.

> you can't gain more weight than the weight of the food you eat, because conservation of mass

Not, strictly speaking, true: not only must we consider mass-energy equivalence (the chemicals bonds in food vs metabolic byproducts could contribute unequally to mass), but more importantly, we inhale mass well as ingest. From the article, one mass-unit of inhaled oxygen produces less than one unit of exhaled carbon dioxide (although I suspect that more than enough water is lost though net exhalation alone to make up for it). So we have to be a little careful with this conservation of mass argument. It's still basically correct, though, and more-or-less blows the "weight gain is exactly proportional to excess calories" argument out of the water.

In fact, the implicit basis behind the method described in the article is exactly conservation of mass.