In case you haven't heard, researchers just discovered that losing weight is harder than they once thought. Why? Well, because, as I have explained many times, simple straight-up calorie restriction causes a person's metabolism to slow down so that eating, say 500 calories per day less doesn't translate into 500 calories less body fat. It usually means about half that much and the reason is that the "missing" fat, the 250 calories worth of body fat that have not been lost have been saved because of a reduction in metabolism of about 250 calories. Big surprise! We have all know this for years and it is the primary reason why long-term weight loss requires eating habits that account not just for the calories in food, but for the drug-like and metabolic effects of food. So the "new weight loss math" is nothing more than a reflection of a very old adage: that when we reduce calorie intake the body "fights back".
To be fair, the recently publicized findings that gave rise to the term "new weight loss math" go a lot farther than merely confirming an obvious truth. Researchers actually derived new mathematical formulas to predict the real rate of weight loss in most people. So they have succeeded for the first time in predicting not merely that weight loss is slow, but in predicting exactly how slow. And it's only a rough approximation to state that weight loss is about twice as slow as once believed. That actual math involves a set of differential equations ("higher math" to be sure). Basically though it works like this: the more weight you lose, the slower it gets because your body adapts to weight loss by, as noted above, slowing its metabolic rate. But it's not a zero-sum game: metabolism slow, but weight loss is still possible. To get a feel for how this all works, you can use the National Institutes of Health's new body weight simulator.
The body weight simulator uses pretty accurate math to explain the relationship between calories and weight loss over time. What it doesn't attempt to account for is how painful (or easy) a particular form of weight loss might be. To put it another way, it doesn't predict or explain hunger. The fact is that merely reducing calories might have a predictable if complex effect upon weight loss, but in the real world what matters most is whether that weight loss is sustainable and that is all about hunger and hunger, in turn, is a vastly complex phenomenon that is influenced not merely by food quantity but by food quality. And I hope it goes without saying that the same is true for human health: calories are only a part of the issue.