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NEWS
14th May 2007

Nutrition and Weight Loss Studies At Extreme High Altitude

Measuring body fat

Life at high altitude has many different effects on the body. One interesting and important effect is the pronounced weight loss observed in people. Over the course of our 3 month trip on Everest, I have been warned to expect a 7-14kg (1-2 stone) weight loss. The Caudwell Xtreme Team are doing weekly weight, bio-impedance and skin fold thickness measurements to chart and quantify our losses.

Why is this interesting? It is interesting because 70% of the weight loss is lean tissue (i.e. muscle) rather than fat. This is counterintuitive to what you would expect - everybody knows that fat is the body's high energy reserve. Also, if you are exercising vigorously (be that climbing up the mountain or just the increased effort of breathing, walking etc.) then you would expect to preserve or increase your muscle bulk. This explains why gaining weight before the trip isn't particularly useful - since the easiest way of gaining weight is fat. Why is this weight loss important? As you can imagine, most climbers are already pretty lean and fit, so losing muscle tissue at such a high rate is both physically and psychologically deleterious.

Why does this weight loss occur? In short, we don't know, but there are some possibilities which we are investigating. This work is being led by Dr Mike Stroud, consultant gastroenterologist and polar explorer. One option is that we are simply expending more calories than we are eating, similar to the profound weight loss seen in polar explorers. However this isn't the case as there is adequate food at EBC; indeed I'm munching a big bowl of cereal and full cream (UHT) milk as I type. I've not done any exercise today apart from walking around camp. I'm currently wearing an activity monitor to record my calorific expenditure and weighing my food intake to support this. This theory also doesn't explain the predominant lean tissue loss.

Measuring body fat
Measuring body fat

Another option is that our gastrointestinal system is hypoxic (low in oxygen), so cannot function normally, causing delayed gastric (stomach) emptying and decreased intestinal absorption. This theory is being examined in a study which involves 6 climbing team members eating a boil in the bag meal, mixed with an egg. The egg has been premixed with a carbon labeled medium chain fatty acid (octanoin). Every 15 minutes for 4 hours after the meal, breath samples are taken to look for the presence of the labeled carbon, which can only appear on the breath once the fat has been both absorbed and processed by the liver. On some of the tests, blood samples are also taken every 15 minutes to look at the absorption of other nutrients. These tests have been carried out at sea level, Namche, EBC and in the Western Cwm and the results at each location will be compared for each climber to see if there is, for example, an altitude threshold when mal-absorption occurs. Simultaneously, 6 base camp staff are recording exactly what and how much they eat (intake) and collecting their faeces (output) to see if there is any change in absorption rate.

Another theory is that muscle (lean) tissue is broken down to help to meet an increased requirement by the body for the amino acid glycine. Glycine is involved in haemoglobin production (the body's oxygen carrying pigment) and it is known that one of the acclimatization responses is to increase the blood's haemoglobin concentration. We are measuring our haemoglobin concentration and haematocrit (measurement of the different proportions of red cells to non-cellular material) weekly and both have increased significantly. Muscle loss could therefore be the payback for the advantage of elevated haemoglobin concentration (presumably to increase oxygen transport to cells) and to test this theory, 6 base camp staff and 6 climbers are making 24 hr urine collections to evaluate a metabolic marker of glycine status. In some cases, the same urine collections are also being used to assess overall levels of nitrogen balance and rates of whole body protein synthesis and breakdown to see if there is a change in the normal pattern (when both rates are approximately equal) towards that seen in illness (when breakdown rates may far exceed synthesis rates). In these studies, as well as collecting their urine for 24 hours, subjects must actually consume a labeled glycine dose and eat strictly protein controlled meals (boil in the bag).

We look forward to seeing the results. In the meantime I'll have another bowl of cereal?

Jules Harvey



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