Diet gurus love-carb diets–and dieters love them–because going on one usually causes a dramatic loss of weight the first week. Notice that I didn’t say loss of fat.
People get all excited about that first week’s weight loss of four, five, or six pounds or more. Well, there’s an easy explanation for what’s going on, and it has nothing to do with fat loss.
So what’s happening when you go on the Atkins, Dukan, or other low-carb diet and see a significant weight loss almost immediately?
In order to explain, I want to give you a little bit of background on carbohydrates first.
Fast and slow fuels
Carbs are your body’s preferred fuel source. No matter what you’re doing–whether you’re vegging out on the couch or running a marathon–you’re always burning a combination of carbohydrate and fat as fuel.
Depending on the activity, your body consumes more or less fat and more or less carbohydrate.
Carbohydrate is a very fast fuel–one your body can break down extremely quickly. So when you sprint, you’re using carbohydrate almost exclusively.
Breaking down fat is a slower process and involves more biological work. When you’re sitting on the couch or sleeping, you’re burning proportionately more fat.
Your brain runs on sugar–the glucose in your blood. Because your brain must have sugar and the rest of your body must have carbohydrate as a fast fuel, your body employs elaborate processes to make sure carbohydrate will always be available.
The body stores carbohydrate in your muscles and your liver in a form called glycogen. You can think of glycogen as fuel in the tank.
OK, stick with me–I’m about to explain how this relates to low-carbohydrate diets.
If you stop eating carbs, your body still absolutely has to have them. It immediately begins consuming the glycogen stored in your tank before moving on to the more challenging task of converting fats and proteins into usable carbohydrate.
Every gram of that stored glycogen in your liver or muscles is accompanied by four to five grams of water in your body. If your body uses up one gram of glycogen, it sheds those four to five grams of water.
What do you think happens if your body burns up one pound of glycogen? It sheds four to five pounds of water.
Bingo: you’ve got a five or six-pound “weight” loss: one pound of glycogen plus four or five pounds of water.
Let’s say you also lose one pound of fat in your first week on a low-carb diet because you are eating fewer calories than before.
By the way, there are only two reasons you lose fat: because you’re consuming fewer calories than your body needs or burning more calories through increased activity. The ratio of protein, carbs, and fats you’re consuming has nothing to do with it.
You could end up with a seven-pound weight loss during your first week on a low-carb diet, and you’d probably think, Hey, I’m making great progress!
Well, in this example, it turns out that only one pound of that loss was fat.
As soon as you start eating carbohydrates again–and you have to eventually–you begin storing glycogen, and the water you lost will come right back in proportion to the stored glycogen.
No minimum daily requirement?
Some rather uninformed people have argued that since there is no “minimum daily requirement” for carbs, that means you can do without them quite nicely.
First, there certainly are minimum daily requirements for vitamins and minerals, and if our diet consisted only of meat, dairy products, and fats, we couldn’t possibly get enough of them.
Vegetables and fruits–our primary source of many essential vitamins and minerals, as well as antioxidants–consist mostly of . . . carbs.
Second, and more to the point, because you would die without blood sugar, your body has failsafe mechanisms to turn fat and protein into sugar within your body. But these processes are far less efficient than turning dietary carbohydrate into sugar.
Anyone who tries to exercise vigorously while on a low-carb diet is going to feel like crap. The more active you are, the more you need carbohydrates. They are your body’s preferred fuel source, so how sensible do you think it is to restrict them unduly?
Granted, some carbs provide more nutrition than others. Fruit, whole grains, fibrous vegetables (e.g., broccoli and green beans), starchy vegetables (e.g., carrots and potatoes), and legumes are much better choices than Twinkies and Coke.
So please don’t get the idea that carbohydrates are making you fat–and thus that a low-carb diet will somehow magically make you lean. And if you go on a low-carb diet and see a dramatic early weight loss, don’t be too quick to assume the loss is primarily fat.
Bottom line: It’s the overconsumption of calories–no matter where they come from–that adds jiggle to our thighs and waistlines. Only eating less and moving more can change the equation.