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CR diets typically lead to reduced body weight, and in some studies, low body weight has been associated with increased mortality, particularly in late middle-aged or elderly subjects. One of the more famous of such studies linked a body mass index (BMI) lower than 18 in women with increased mortality from noncancer, non−cardiovascular disease causes.[30] The authors attempted to adjust for confounding factors (cigarette smoking, failure to exclude pre-existing disease); others argued that the adjustments were inadequate.[31] "epidemiologists from the ACS (American Cancer Society), American Heart Association, Harvard School of Public Health, and other organizations raised specific methodologic questions about the recent Centers for Disease Control and Prevention (CDC) study and presented analyses of other data sets. The main concern ... is that it did not adequately account for weight loss from serious illnesses such as cancer and heart disease ... [and] failed to account adequately for the effect of smoking on weight ... As a result, the Flegal study underestimated the risks from obesity and overestimated the risks of leanness."[32] While low body weight in the elderly can be caused by conditions associated with aging (such as cancer, chronic obstructive pulmonary disorder, or depression) or of the cachexia (wasting syndrome) and sarcopenia (loss of muscle mass, structure, and function),[33] the results of a large epidemiological study published in the fall of 2011 show that among the Japanese, an association between a BMI under 21 (under 65 kg for a 1.75 m tall individual (or in imperial units, under 140 lb for a 5'-9" tall individual)) and increased mortality persists even when confounders like age, smoking, and disease are carefully controlled for.[34] Such epidemiological studies of body weight are not about CR as used in anti-aging studies; they are not about caloric intake to begin with, as body weight is influenced by many factors other than energy intake. Moreover, "the quality of the diets consumed by the low-BMI individuals are difficult to assess, and may lack nutrients important to longevity."[18] Typical low-calorie diets rarely provide the high nutrient intakes that are a necessary feature of an anti-aging calorie restriction diet.[35][36][37] As well, "The lower-weight individuals in the studies are not CR because their caloric intake reflects their individual ad libitum set-points, and not a reduction from that set-point."[18] |
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