Why Do Mountain Climbers Waste Away?

What happens at high altitude may help patients in the ICU.

Joel Shurkin, Contributor

(Inside Science) -- The old folklore admonition to "feed a cold and starve a fever" is not only good medical advice; it may explain something weird that happens to mountain climbers.

Climbers who spend extended periods at high altitude lose weight and eat less while they are there. Two British researchers think this phenomenon is the consequence of an evolutionary adaptation that protects vital organs in cases of severe illness and injury, and may give important insights into the treatment of patients in intensive care units.

The effects are shown with mountain climbers who are at high altitude -- 15,000 feet or higher -- for several months, the kind of acclimation climbers develop on Mount Everest expeditions, explained Andrew Murray, a professor of physiology and neuroscience at the University of Cambridge.

Murray and his collaborator Hugh Montgomery, a professor of intensive care medicine at University College, London, admit that the conclusion of their research is speculation, but still a hypothesis worth studying. They reported their findings in the journal Bioessays.

"It's not just fat that [climbers] are losing; the greatest proportion is muscle loss," Murray said. People climbing to higher altitude also make more red blood cells, the cells that distribute oxygen to the body.

Climbers at altitude are exercising strenuously while fighting frigid temperatures and low oxygen (otherwise known as hypoxia). Climbers exerting themselves in these conditions should work up big appetites, but amazingly, they actually eat less than they need. "So something extraordinary is going on here," he said.

Murray said that humans evolved at sea level and anything that happens at high altitudes is incidental. People who live in the Andes and Himalayas have bodies that do not produce more red cells at elevation, as would non-natives, perhaps a matter of genetics. For most people, the response resembles the reaction to blood loss through injury or infection, Murray said.

Patients in intensive care and those seriously injured -- particularly with head injuries -- show the same kind of weight loss and lower blood oxygen levels that are seen in climbers acclimated to high altitude.

Many severely injured patients also have problems producing enough red blood cells to keep the blood oxygen level up, said Montgomery.

Substances involved in the process of conserving oxygen are called ketone bodies. Ketones use body fat to keep producing fuel for the brain and to protect it. Because of their particular function, large amounts of ketones usually only appear in patients with Type 1 diabetes, or when a person is starving.

As climbers ascend a mountain and eat less and less, their bodies produce ketones for protection and fuel.

Ketones, posit Murray and Montgomery, could also be useful to protect the brains of patients with severe head injuries.

The body's tendency to take such extreme measures appears to be a last-ditch survival attempt that also governs the body in other low-oxygen conditions, such as those encountered by mountain climbers. Murray and Montgomery are testing their concept on laboratory animals in low-pressure chambers.

If ketones do protect against low oxygen, an edible or injectable form might be used to increase blood oxygen in ICU patients, Murray said, which would be an enormous help in stabilizing people who are seriously ill or injured by using oxygen more effectively.

Starvation might work too, stimulating the production of ketones, which can then protect the patient's brain after a trauma. Several laboratories are working on edible forms of ketone bodies. Feed a cold, starve a fever.

"We believe very strongly this might have clinical utilization in such sick, infective patients." Starved mice do better after a head injury than fed mice in laboratory studies, he said.

No one has suggested starving patients for long periods of time. If left too long, starving patients would become profoundly debilitated, he said. If he and Murray are right, giving ketones initially may increase a patients' oxygen utilization, giving them significant advantages as they recover.

It may also help mountain climbers because it would slow their inevitable muscle loss.But not everyone is convinced, noting that the two scientists are speculating and there is no experimental evidence to support their hypothesis.

Robert Mazzeo, a physiologist at the University of Colorado Boulder, said studies he has done at Pike’s Peak indicated the weight loss and appetite suppression were "likely related to alterations in the autonomic nervous system [the part that controls involuntary actions] as well as other hormones sensitive to acute hypoxia. Also contributing to the weight loss is the increase in resting metabolic rate observed with high altitude exposure."

The metabolism changes just because they are up at altitude. "They present a compelling theoretical case," said Jim Stray-Gundersen, sports science advisor to the United States Ski Association. "Their hypothesis remains to be experimentally tested."

"However, other than interesting metabolic science, I don't see the 'so what' of their ideas. For weight loss programs, it would not be desirable to lose what skeletal muscle one has while preserving fat stores." He added that any potential protection against strokes or other events caused by reduced or impeded blood flow is not worth the trouble.

"The evidence suggests that [the change in body function] has very little to do with improving performance at altitude," said Benjamin Levine, director of the Institute for Exercise and Environment Medicine in Dallas.

"There is little adaptive pressure to increase red blood cells in a population living at high altitude," he said.

Both Murray and Montgomery urge further research to test their hypothesis.