Intended for healthcare professionals

Rapid response to:

Education And Debate

Tobacco and obesity epidemics: not so different after all?

BMJ 2004; 328 doi: (Published 24 June 2004) Cite this as: BMJ 2004;328:1558

Rapid Response:

Calorie Excretion

Almost to a man, the world's top nutrition and obesity authorities
believe that weight control necessitates a balance between caloric intake
and energy expenditure. We're told that because fat contains more than
twice as many calories per gram as protein or carbohydrate, eating too
much fat is a major factor in the obesity epidemic. Another half truth.

Sifting through weight control literature, one encounters occasional
evidence that the body does not absorb every calorie that finds its way
into the stomach. The digestive system is basically a chambered tube with
an entrance and an exit. Just as a wood stove does not transfer all energy
released through combustion to the environment being heated, the transfer
of digested energy molecules is considerably less than 100 percent
efficient. Researchers report overall calorie excretion rates ranging from
20 to 60 percent and fat excretion rates ranging from 2 to 42 percent. The
soluble fiber fraction in the food is largely responsible for the
percentage of calories that exit with the fecal material.

Another important consideration is the fact that, physiologically,
the body constantly remodels itself internally to accomodate the quality,
quanity, and timing of food intake. For example, the size of the stomach
and the surface area of the small intestine tend to increase with food
restriction and decrease with increased fat consumption, thus changing the
absorption efficiency of the digestive system.

Clearly, there is much to be learned about how the digestive system
responds to different mixes of fiber, macronutrients, and micronutrients.
Calorie excretion deserves some attention.


A. Antonis et. al., "The Influence of Diet on Fecal Lipids in South
African White and Bantu Prisoners," American Journal of Clinical
Nutrition, Vol. 11, August 1962, pp 142-155.

J.O.Hill,H. Douglas, and J.C.Peters, "Obesity Treatment:Can Diet
Composition Play a Role?" Annuls of Internal Medicine 119(2):7 (1993):694

Competing interests:
None declared

Competing interests: No competing interests

27 June 2004
David E. Brown
Layman nutrition scholar
Self employed carpenter residing at 1925 Belmar Dr., Kalispell, MT 59901, USA