> Although researchers have rarely thought to control for energy intake in their experiments, when they did, testing whether their animals get fatter than lean controls even when eating as little or less food, they almost invariably report that they do. “These mice will make fat out of their food under the most unlikely circumstances, even when half-starved,” as Jean Mayer wrote about obese mice he studied in the 1950s.
It is possible for everything in this quote to be true without contradicing the grandparent, because the quote doesn't explicitly address whether any of these animals were eating a caloric deficit.
It is physically impossible to gain weight while eating a caloric deficit. The same kind of impossible as perpetual motion.
A living body can be quite clever,
it can change your BMR (what you assumed was a deficit is now a surplus) perform muscle catabolism, or burn glycogen stores (more than one kind of fuel) during starvation. All the while taking pains to store away the calories you do intake as new fat cells. It's precisely this kind of direct and overly simple appeal to thermodynamics that the article tries to address.
Burning fuel in a calorimeter is not the same thing as a human body.
/Fat/ loss and creation aren't the body's /only/ response to calorie deficits and excesses.
You can create new /fat/ cells while still losing energy and mass overall without violating thermodynamics. As I said above, all you need to do is have your metabolism prefer your other stores first.
> It is physically impossible to gain weight while eating a caloric deficit.
Is it? As much as I want to agree, what if my body decides that 50% of calories input must be stored? It might mean that I will have to eat 200% of my daily required input just to be functional.
Not saying that this is the case, but I think it’s what the article is arguing.
If your body were doing this, you'd be burning more calories than if it didn't.
Your body requires some number of calories to keep the lights on for a given day--to move, to breath, to run your brain. Google says the average is 1800/day.
If you only eat 1700 calories per day (a 100-calorie deficit) for a month, and you don't stop moving, breathing, or thinking, then your body managed to get those missing 100 calories from somewhere (i.e. from fat).
In your example, say you burn ~1800 calories per day, but you only eat 800 calories (a 1000-calorie deficit)--and your body, because it hates you, stores all 800 calories as fat! Well, your body still used up 1800 calories (assuming you're still breathing, etc). So you would've burned 1800 calories of old fat, and stored 800 calories of new fat. But wait! Turning fat into energy isn't free, that requires energy, too! So you'd actually be burning more than your base rate of 1800, meaning your deficit would be even higher than the expected 1000.
It's all much more complicated than this. Your body has multiple ways of generating energy, storing, and releasing energy. Eating less signals your body that you need to preserve calories, which may lower your metabolism and make it harder to eat a caloric deficit. But at the end of the day, physics dictates that you can't get more energy out of a system than you've put into it.
Your body might make you move less throughout the day, "underclock" your brain, and do other things to push your BMR lower and lower. I've heard of people who end up having to eat so little to lose weight that they get severe nutrient deficiency.
If you don't eat enough, you'll feel lethargic and unable to perform normally, so I doubt it will still use 1800 calories. According to the article, if you eat 800 calories and your body stores them all, you'll feel as hungry as if you never ate at all.
Of course this likely isn't so drastic ("50%") but it would explain why many people keep gaining weight over their lifetime (or until the body reaches a balance).
As I understand it, the fat mice in the study were fed half the amount of food that other mice were fed and still gained weight. It makes me wonder if a calorie surplus is necessary but not sufficient for weight gain which could also mean that a calorie deficit is not necessary for weight loss.
