Risks and Benefits of Severe Caloric Restriction

[Guest guest]

Hi All,

Regarding the Risks and Benefits of Severe Caloric Restriction,

please see:

JAMA, June 9, 2004; 291, (22) 2704

Risks and Benefits of Severe Caloric Restriction

Jun Mao

To the Editor: Drs Michels and Ekbom 1 concluded that severe

caloric restriction in humans may confer protection from

invasive breast cancer. I am concerned, however, that these find-

ings may inadvertently imply that anorexia nervosa can have

health benefits. Anorexia nervosa is a serious illness, with as

many as 15.6% of patients dying from disease-related causes

within 21 years of first hospitalization.2

I am also concerned that Michels and Ekbom did not provide

mortality information about their participants, which could

introduce significant lead-time bias. If more women from this

cohort died at younger ages from causes related to anorexia nervosa,

they would not have as great an opportunity to develop

breast cancer compared with the general population; therefore,

they would seem to have less risk for developing invasive

breast cancer.

1. Michels KB, Ekbom A. Caloric restriction and incidence of breast

cancer. JAMA.

2004;291:1226-1230.

2. Zipfel S, Lowe B, Reas DL, et al. Long-term prognosis in anorexia

nervosa: lessons

from a 21-year follow-up study. Lancet. 2000;355:721-722.

Karin B. Michels, Anders Ekbom

In Reply: In response to Dr Mao, we recognize that anorexia

nervosa is a serious and potentially life-threatening disease.

did not intend to imply that women should resort to anorexia

as a measure of preventing breast cancer. Understanding role

of caloric restriction in the etiology of cancer, particularly

breast cancer, is important for disentangling the puzzle of breast-

cancer

causation.

We do not share Mao's concern about competing rates. The

analytic model used prevents such bias since it is based on a

person-time denominator. A cohort member only contributes

person-time at risk until she is censored from the analysis (due

to a diagnosis of breast cancer, emigration, death, or the end

of follow-up, whichever occurs first). If the risk of dying

prematurely

was associated with an excess risk of breast cancer,

our results could have been biased; however, there is no known

biological mechanism to support this hypothesis.