The limits of human starvation

Summary of published paper^*

"The combined effect of drought and cattle eradication in Ngami East resulted in a two to threefold increase in total malnutrition rate"

The metabolic and physiological adaptations of individuals under going starvation have fascinated scientists for over a century. However, knowledge of the biology of starvation in humans is still imperfect owing to the great difficulty of obtaining reliable data from subjects undergoing severe food deprivation. Famines do not generally lend themselves to scientific investigation. A recent study has examined the literature on starvation, using Body Mass Index (BMI) to define the limits of human survival to starvation. Data included is based on normal weight subjects who died from starvation, famine or anorexia nervosa.

Despite the diversity of sources, the data shows a remarkable consistency. In particular, the review illustrates a sex difference in the limits of survival when based on BMI classification. In males, a BMI of around 13 appears to be fatal. The coefficient of variation (CV) of the BMI is 8.7%. In contrast, females survive to a lower BMI of around 11, although with greater index variability (CV 14%). Several females had BMI's as low as 9 and 10. Based on these figures a mean BMI of 12 as the lower limit for human survival emerges - a value first proposed by James et al (1988). The ability of females to withstand a greater degree of food deprivation may be due to the following reasons:

• females have greater body stores of fat than males, and this can be used as a source of energy for a much longer period (fat is more energy dense than protein)
• the contribution of fat energy to total energy expenditure is greater in the female, resulting in a greater conservation of protein
• females appear better able to mobilise adipose tissue from most sites in the body

The author concludes that these three factors appear to give females a biological advantage but that much remains to be learned concerning the critical levels of BMI and body weight for survival, and their implications for health and function.

^*The Biology of Human Starvation: Henry. CJK (2001) British Nutrition Foundation Nutrition Bulletin Vol 26, pp 205-211