Australasian Science: Australia's authority on science since 1938

Biggest Losers, Biggest Gainers

By Tim Olds

How much weight can we lose or gain, and how quickly?

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How much weight can a person lose in a day, do you think? Would 137 kg surprise you? It’s true, but it’s a bit of a trick – it was the result of the removal of a massive abdominal cyst.

Aside from surgery, the limit appears to be about 10 kg per day, and that’s due almost entirely to fluid loss: 9.7 kg from voluntary dehydration in an American, Ron Allen; 8 kg in a superobese patient, a loss accompanied by urine outputs of up to 6 litres per day; and 7 kg by Australian cricketer Dean Jones during a single day’s play (8 hours) while batting under hot, humid conditions in India.

But even that’s cheating a bit. The average gym-goer is interested in muscle and fat, which are deposited and broken down much more slowly. Weight loss and gain depends on how much we eat, how much energy we use up in physical activity, and the “P-ratio”: the proportions of energy mobilised from, or deposited as, protein or fat.

The P-ratio varies from person to person and from time to time, and is affected by hormones. Testosterone and human growth hormone will encourage muscle synthesis, while cortisol will encourage increases in fat.

Sustainable energy expenditures may range between 1.1 and 5.5 times the basal metabolic rate, the upper limit being achieved by Tour de France cyclists and Arctic explorers and the lower limit by people with stroke and British housewives...

The full text of this article can be purchased from Informit.