How We Get Fat - Lyle McDonald Let’s work through this backwards. When you eat dietary fat, it’s primary fate is storage as its intake has very little impact on fat oxidation (and don’t ask me a bunch of questions about “But people say you have to eat fat to burn fat?” in the comments. That idea is fundamentally wrong but would take an entire article to address). It also doesn’t impact greatly on the oxidation of the protein or carbohydrates. Carbohydrates are rarely converted to fat (a process called de novo lipogenesis) under normal dietary conditions. There are exceptions when this occurs. One is with massive chronic overfeeding of carbs. I’m talking 700-900 grams of carbs per day for multiple days. Under those conditions, carbs max out glycogen stores, are in excess of total daily energy requirements and you see the conversion of carbohydrate to fat for storage. But this is not a normal dietary situation for most people. A few very stupid studies have shown that glucose INFUSION at levels of 1.5 total daily energy expenditure can cause DNL to occur but this is equally non-physiological. There is also some evidence that DNL may be increased in individuals with hyperinsulinemia (often secondary to obesity). There’s one final exception that I’ll use to finish this piece. But when you eat more carbs, you burn more carbs and burn less fat. And that’s why even if carbs aren’t directly converted to fat and stored as such, excess carbs can STILL MAKE YOU FAT. Basically, by inhibiting fat oxidation, excess carbs cause you to store all the fat you’re eating without burning any of it off. Did you get that? Let me repeat it again. Carbs don’t make you fat via direct conversion and storage to fat; but excess carbs can still make you fat by blunting out the normal daily fat oxidation so that all of the fat you’re eating is stored. Which is why a 500 cal surplus of fat and a 500 cal surplus of carbs can both make you fat; they just do it for different reasons through different mechanisms. The 500 calories of excess fat is simply stored; the excess 500 calories of carbs ensure that all the fat you’re eating is stored because carb oxidation goes up and fat oxidation goes down. Got it? If not, re-read this paragraph until it sinks in. Oh yeah, the same holds for protein. Protein isn’t going to be converted to and stored as fat. But eat excess protein and the body will burn more protein for energy (and less carbs and fat). Which means that the other nutrients have to get stored. Which means that excess protein can still make you fat, just not by direct conversion. Rather, it does it by ensuring that the fat you’re eating gets stored. Of course protein also has the highest thermic effect, more of the incoming calories are burned off. So excess protein tends to have the least odds of making you fat under any conditions; but excess protein can make you fat. Just not by direct conversion to fat; rather it’s indirectly by decreasing the oxidation of other nutrients. Ok, is the above clear enough? Because I can’t really explain it any simpler but will try one last time using bullet points and an example. Let’s assume someone is eating at exactly maintenance calories. Neither gaining nor losing fat. Here’s what happens with excess calories. Assume that all three conditions represent identical increases in caloric intake, just from each of the different macros. Here’s what happens mechanistically and why all three still make you fat: Excess dietary fat is directly stored as fat Excess dietary carbs increases carb oxidation, impairing fat oxidation; more of your daily fat intake is stored as fat Excess dietary protein increases protein oxidation, impairing fat oxidation; more of your daily fat intake is stored as fat Got it? All three situations make you fat, just through different mechanisms. Fat is directly stored and carbs and protein cause you to store the fat you’re eating by decreasing fat oxidation. And I’d note again, since someone will invariably misread this that that doesn’t mean that a low-carb and/or low-protein diet is therefore superior for fat loss. I’m not saying that and don’t think that I am. Because in such a situation, while you may be burning more fat, you’re also eating more dietary fat. So net fat balance can be unchanged despite the dicking around with macronutrient content. It still comes down to the deficit.
Posted on: Fri, 26 Sep 2014 23:32:36 +0000
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