Low-carb diets get thermodynamic defence

[Guest guest]

[This is what John Berardi has been saying for some time now - that a

protein calorie is not the same as a carbohydrate calorie. See back to his

article from 1999 http://www.t-nation.com/findArticle.do?article=209lean

which references much earlier research than this article below.]

 

Published online: 16 August 2004; | doi:10.1038/news040816

http://www.nature.com/news/2004/040816/full/040816-2.html

 

Low-carb diets get thermodynamic defence

by Helen Pearson

Biochemists argue that food calories are not all equal.

Fueling controversy: Do high protein diets aid weight loss?

 

The fiery debate over the worth of low-carb regimes is being fuelled by two

US researchers. They are using the laws of thermodynamics to argue that

calories from protein are better for losing weight than those from

carbohydrates.

 

The idea that eating a diet rich in protein will help you shed more pounds

than one stuffed with carbs is driving a vast diet industry. But many

nutritionists dispute this view, saying that a calorie is a calorie

regardless of where it comes from. Formally, a calorie is the amount of

energy needed to heat one kilogram of water by 1ºC.

 

Now Richard Feinman of the State University of New York and Eugene Fine of

Jacobi Medical Center in New York are turning to physics to assert that

calories differ. They use the laws of thermodynamics: fundamental rules

that describe how heat, work and energy change in a system.

 

The first law of thermodynamics says that energy is always conserved. In

slimming terms, this means that protein, fat and carbohydrate calories are

equivalent because none of their energy is magically destroyed when you eat

them. Feinman and Fine are not arguing with this idea.

 

But the second law of thermodynamics says that energy spontaneously

disperses if it is not hindered. Feinman and Fine point out that protein

and carbohydrate are metabolized in different ways and their energy is

therefore dispersed in different forms. When protein is broken down by the

body, for example, more energy is released as heat than is converted into

chemical energy1.

 

The upshot of their argument is that, while a hunk of steak and a slice of

bread may carry equal calories, the amount of energy the body actually

gleans from them, to fuel movement or store as fat, is different. " To say a

calorie is a calorie all the time is false, " says Feinman.

 

Energy burn

 

The theoretical argument has some experimental support. In 2002, Arne

Astrup of Denmark's Royal Veterinary and Agricultural University,

Copenhagen, and his team put 12 men in a room and measured precisely how

much energy each burned when fed different diets. Those on a regimen rich

in pork protein burned 4% more energy than those on a higher carbohydrate

diet, the team found, because they lost more energy as heat2. So Astrup

says he agrees with Feinman " to some extent " .

 

But when it comes to dieting, Astrup and other experts say that Feinman is

missing the point. Even if protein and carbohydrate are processed

differently in the body, what really matters is whether low-carb diets

actually help people lose more weight than other eating plans.

 

In this regard, studies are scant and conflicting. Some of the best

evidence comes from two trials published in the New England Journal of

Medicine in May 2003, which showed that those on a low-carb, high-protein

diet shed around three times as much weight as those on a low-fat diet

after six months. However, the difference was minimal after a year3,4.

 

The main reason that some people shed extra weight on a low-carb diet is

because they eat fewer calories overall, experts say, probably because

protein makes them feel more full. They may also stick to the diet more

rigidly or for a longer time.

 

Compared with these factors, any differences in the way the different foods

are metabolized are negligible, argues George Bray, an authority on obesity

at Louisiana State University, Baton Rouge. " The epidemic of obesity isn't

due to a small biochemical defect, " he says, " it's due to large portions of

food eaten by inactive people. "

 

Food science and nutrition researcher Donald Layman of Illinois State

University in Urbana-Champaign argues that different diets suit different

people. Eventually, decisions about which regime is most appropriate will

be based on a range of health factors, such as risk of heart disease or

diabetes. " That to me is where nutrition is going, " Layman says.

 

References

1. Feinman R. D. & Fine E. J. Nutrition Journal 3, 9. (2004).

2. Mikkelsen P. B., Toubro S. & Astrup A. A. Am J Clin Nutr, 72. 1135 -

1141 (2000).

3. Samaha F. F, et al. N Engl J Med, 348. 2074 - 2081 (2003).

4. Foster G. D., et al. N Engl J Med l, 348. 2082 - 2090 (2003).