This is the first of eleven posts to go with the classroom content. (The addition of which has made no difference to the ranking?) So this is a different tack. Most people treat fat loss as a subtraction problem. Eat less, lose more. Push harder, lose faster. It's half right, and the other half can hurt people. Getting fat out of storage is the easy part. Your body is extremely good at that. Everything after it- ferrying it, gating it into the mitochondria, oxidising it- is regulated, and it runs at whatever rate the deficit demands. There is no daily ceiling on doing it. ( I was always taught that there was ) Three lean men in a chamber on about 3,350 kJ (800 kcal) a day oxidised 177 g of fat a day, two-thirds of everything they spent. (R§8) A man in Dundee fasted under supervision for 382 days and ran his whole day, about 10.5 MJ (2,500 kcal), from his store the entire time. (R§9) @Mika Bray started all this off many moons ago without knowing it 😀 So what goes wrong when you push too hard? Two things, and neither is a ceiling. The first is where the loss comes from. At 2,090 kJ (500 kcal) a day, 8.8% of what one trial's subjects lost was lean tissue. At 5,230 kJ (1,250 kcal) a day, 1.3%. (R§11) Same total loss. Different tissue leaving the body. The second is what happens to fat you mobilise and don't oxidise. It doesn't disappear. At rest, about 70% of it goes straight back into storage. (R§23) The rest can end up in the liver, which is the subject of Post 4. This is why the person on 3,350 kJ (800 kcal) and two hours of cardio often isn't leaner than the person doing something sane. Not because the fat couldn't come off. Because the wrong tissue came off with it. Over the next ten posts, I'll walk through the machinery, what regulates it, and what only pretends to. So - What's the most aggressive deficit you've ever run, and what actually happened?