Why Do Low-Carb Dieters Lose More Bodyweight than High-Carb Dieters?

Dr. U. Rabast confirmed that the low- carbohydrate diet increases bodyweight loss. He studied 21 obese adults using 3 different diets: all three diets were low in calories and two were low-carbohydrate diets and the third diet was a high-carbohydrate (67%- carbohydrate and 12%-fat). Weight loss was 21 pounds on the high-carbohydrate diet, 25.1 pounds on one low-carbohydrate diet, and 27.5 pounds on the other low-carbohydrate diet.

All low-carbohydrate studies have the same result: the low-carbohydrate group loses more bodyweight than those eating a high- carbohydrate diet. Researchers, however, often credit this increased loss in bodyweight to a specific loss in fat tissue. One cannot infer, however, solely from changes in bodyweight that the body lost more fat. The major problem, then, in these early studies is that researchers did exactly that; they inferred that bodyweight losses solely reflected changes in fat and lean.

But, there’s another explanation for more bodyweight loss in low-carbohydrate dieting: water loss. The same mistake is made by modern-day researchers who have not bothered to review the historical record.

Changes in bodyweight are unreliable for analyzing the changes in body composition: muscle, fat, and water, during a weight reduction program. And, with the use of two- compartment body composition testing, instead of three-compartment that measures water along with Lean Body Mass and Fat Mass, errors occur. Variations in water content during weight loss are a difficult barrier to understanding changes in muscle and fat, particularly in the first seven to twenty days of a diet. The failure to understand this concept was the major limitation to those early scientific studies. This also tripped up Atkins.

One of the inevitable after-effects of ending a low calorie, low-carbohydrate diet is rapid weight regain. Rapid weight regain is not a common characteristic of ending a low calorie, high-carbohydrate diet. Researchers finally figured out that the rapid weight regain after ending the low-carbohydrate diet reset the body water levels that had been reduced solely from carbohydrate restriction. Many researchers have argued that this observation is proof that carbohydrate restriction leads to more water loss than that occurring by following a low calorie, high-carbohydrate diet.

Following a low-carbohydrate diet leads to significant losses of water, some increased loss of fat, and preservation of muscle. Initially, water losses represent the largest part of the bodyweight loss. The high-carbohydrate diet does not cause the same level of water loss or fat loss as does the low-carbohydrate diet. It’s difficult to distinguish the percent of the body mass that is lost as water or as fat because the body composition methods aren’t sophisticated enough to do so. That’s one of the reasons why it was so difficult to settle the controversy.

It’s important, however, to realize that most of the rapid, early bodyweight losses are water. One must not be fooled that this bodyweight loss is fat. And even with the increased fat losses, these changes won’t reflect a loss of 100 pounds of fat on a low-carbohydrate diet and none on a low-fat diet. After several months and a loss of considerable bodyweight the low- carbohydrate diet may help the dieter lose about 5-10 more pounds of fat than if he followed a low-fat diet. Good? Yes. This is my technique of “putting-the-numbers-to-it” to get a real handle in what is actually happening. The way most people talk, they act like the fat is just going to melt off the body and completely disappear. No, sorry, that’s not the way it works. And if the low-carbohydrate dieter doesn’t pay attention to the calories he consumes, he’ll lose nothing and often, even, gain weight. You gotta’ pay attention, first, to the Energy Balance Equation.