confusion about calories in and carbs/fats/proteins

[Vegankit]

On page 23 of The McDougall Quick and Easy Cookbook by Dr. and Mary McDougall there is section about the fat you eat is the fat you wear.

I'm paraphrasing - carbohydrates, when injested are used for the main fuel. Approximately 2 pounds of excess carbs are stored in the liver and muscles as glycogen and the rest is dissipated as heat. The body does not store extra carbs as fat because the process is too wasteful.

Proteins in excess are eliminated from kidneys and not stored or routinely converted to carbs or fat.

Fats in excess of our daily needs are stored as fat.

How does this fit calories and weight. If you eat x calories and your body needs y calories then the difference between x and y is what allows you to gain or lose weight. If you are excreting excess protein, then what happens to their calories? What about excess carb calories?

[pinkrose]

I also would like to see a response to this from the authors!

[JeffN]

Body weight is the result of energy balance.

Eat more calories than you burn and you will gain weight. Eat less calories than you burn and you will lose weight regardless of the mixture/ratio of the macronutrients.

The body does have a limit on how many calories that it can store as "carb" in the liver and muscle tissue as glycogen.

The body also does not store excess protein as "protein."

However, "excess" calories from either fat, protein or carb (starch or sugar, fructose or glucose) can all be stored as fat.

Our body converts excess dietary glucose into fat through the process of fatty acid synthesis. Here is a schematic showing how even glucose is converted to fat.

http://library.med.utah.edu/NetBiochem/ ... /5_1b.html

What happens is excess glucose is converted to pyruvate through a process called glycolysis, then to acetyl CoA which is oxidised by the citric acid cycle for energy. If the glucose intake exceeds the body's energy needs & glycogen stores, the acetyl CoA can be used for fatty acid synthesis, which takes place in the liver and then stored as triglyceride in adipose tissue.

In Health
Jeff