The Pharmaceutical Journal
Vol 272 No 7284 p120
31 January 2004

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  Decision support
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  Alcohol metabolism
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Letters to the Editor

Alcohol metabolism

Body fat is the key to differences between the sexes

From Mr T. Harris, FRPharmS

In my opinion I. ab I. Davies (PJ, 3/10 January, p15) has succeeded only in creating problems which do not exist. He has not mentioned the cardinal fact that alcohol is completely miscible with water and negligibly so in fat. Thus when alcohol is consumed, after absorption from the gut it is distributed exclusively throughout the body water (extracellular and intracellular) including, of course, the blood.

The blood alcohol concentration (BAC) at any given time after absorption may be determined by analysis but also may be predicted by calculation.

It has been established that, irrespective of sex, the water content of the fat-free body is remarkably close to 72 per cent. It follows, therefore, that if the proportion of body fat is known, an estimate of the maximum blood alcohol level concentration is possible, viz:

Maximum BAC =

Weight of alcohol consumed
------------------------------------
Effective volume of distribution (Vd)

and Vd = (0.72 / 0.85) (1 - F/100) W

where F = percentage fat content of body weight (W) and blood contains 85 per cent water

An algorithm established by experiment gives a reasonable estimate of F:

For males F = (BMI x 1.34) – 12.47
For females F = (BMI x 1.37) – 3.47

where BMI = body mass index

In practice the maximum BAC is never achieved because of metabolic loss of alcohol during and following absorption. I cannot agree with Dr Davies’s theory that a difference in liver size between the sexes is the reason for women having a higher BAC than men after taking the same oral dose of alcohol.

Alcohol is metabolised in the liver through the action of alcohol dehydrogenase in the hepatocytes. This enzymic activity depends only upon the concentration of alcohol presented to it and is capable of dealing with all concentrations up to and beyond 300mg of alcohol per 100ml of blood. In higher BAC concentrations a microsomal ethanol oxidising system kicks in.

The quantitative estimation of metabolic loss is of importance in forensic work (eg, in cases of drink-driving and assault following consumption of alcohol). In such cases it has long been established that the rate of decline in BAC is related to substrate concentration and not to liver size.

In short, the reason why women show a higher BAC than men following the same consumption of alcohol is that in women the relative proportion of body fat is greater than that in men and thus the distribution volume is smaller.

Tennyson Harris
Southport, Merseyside

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