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?

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.

Since the energy density of fat (38 kJ /g) is about five times greater than the energy density of fat-free mass (6–8 kJ/g), you will lose more weight if your P-ratio favours a loss of protein – but ironically you will get relatively fatter. Conversely, if you want to put on weight, you get more bang for your energy surplus buck if you put on muscle rather than fat.

Even if your energy intake and physical activity doesn’t change, and you’re putting on weight, the rate of weight gain should decrease over time. This is because as you get bigger, your body needs more energy to keep it going, so you have less surplus energy that can be used for weight gain. When you lose body mass because you have an energy deficit, the maintenance demands of the body decrease, effectively reducing the energy deficit.

There is also a protective reduction in basal metabolic rate per unit body mass during energy deficit. This tends to slow down the rate of loss. Therefore there is a tendency for both weight gain and weight loss to plateau.

So how much weight can a person of average size lose? Reports from African and Indian famines and from the Warsaw Ghetto suggest that normal people can lose about 20–50% of their initial weight before they die. The bottom limit appears to be a body mass index of about 10 – that’s about 32 kg for the average man and 27 kg for the average woman.

And how fast can we lose weight? Reports of rates of loss of body mass are extremely unreliable. Superobese people are often linked with American diet shamans, leading to inflated and incredible claims. Simulation models allow us to verify some of these claims.

Using these models, Jon Minnoch’s record reduction from a body mass of 635 kg to 215.4 kg in 487 days would be possible given a very low calorie diet and modest physical activity. Other massive reductions in body mass (Rosalie Bradford 544 kg to 128 kg in 7 years; William Cobb 364 kg to 105 kg in 3 years; Bortz’s patient 313 kg to 85.1 kg in 2 years; Sarr’s gastroplasty patient 346.5 kg to 211.5 kg in 13 months) are also plausible.

Others are less credible. Arthur Armitage’s claimed reduction from 254 kg to 178 kg in 6 weeks, for example, would require extremely high levels of physical activity with almost no food intake. By combining the appetite of Gargantua (32 MJ per day) with the activity level of Sleeping Beauty (1.2 times basal), Doris James’ alleged increase from 158.4 kg to 305.4 kg in a year is achievable. But don’t try this at home.

If we’re interested in muscle we can look to bodybuilders for the records. Anabolic steroids appear to be able to increase muscle mass by about 20%, with a maximum rate of change of about 1–2 kg per week. These rates can be sustained for 10 weeks or more with sufficiently high dosages of steroids.

Definitely do not try this at home. These rates of increase are about 5–10 times higher than those that occur during the adolescent growth spurt.

We can grow up as well as out or in. The giant Wadlow grew as much as 45 cm during his second year. In infancy, instantaneous height velocities obtained by curve-fitting may exceed 20 cm per year. During the adolescent growth spurt, increases averaged over a year are usually in the range 7–12 cm for boys and 6–11 cm for girls. The reported growth rates for giants (4 –12 cm per year averaged over 3–13 years) fall within this range. Hyperpituitary giants appear to grow in the same way as adolescents during their growth spurt, although the growth spurt just keeps on going.

The rest of us, neither bodybuilders nor superobese, go on getting somewhat heavier, somewhat fatter and slightly shorter in the most unspectacular way. Everything going in the wrong direction.

Professor Tim Olds leads the Health and Use of Time Group at the Sansom Institute for Health Research, University of South Australia.