Total energy requirement is the
absolute amount of energy that is required to maintain energy
balance. You neither lose nor gain weight, as total energy intake
= total energy expenditure.
At altitudes greater than 2500m one of the most common observations
is weight loss reported to be due to a reduced appetite and
in turn a reduced energy intake, and an increase in basal metabolic
rate. Several studies have showed that the energy intake to
maintain body weight at high altitude in moderately active individuals
is significantly higher than that required at sea level.
In a study of a military expedition to the Bolivian Andes (5600m)
it was shown that after 18 days, when the subjects had acclimatised,
all had lost weight (mean weight loss 4.35kg, SD 1.60). Weight
loss over a short period of time may be acceptable but losses
sustained over a longer period would give cause for concern
due to a loss of muscle. Some of the subjects reported deliberately
gaining weight prior to departure. However, if food is readily
available during your stay at altitude increasing body weight
before ascent will not protect against muscle wasting and weight
loss. The subjects also reported feeling fuller and considered
there to be too much to eat at altitude yet subjects were issued
with the same military arctic ration packs which they had been
given at sea level leading up to the expedition in the Andes.
The arctic packs consisted of porridge, chocolate drinks, instant
soups, potato powder, sugared tea and coffee, mint cakes, biscuits
including fruit biscuits, nuts and raisins, sugar tablets, and
some milk chocolate. These are all energy dense foods.
In view of the above study and many others, it is now the general
consensus that your total energy intake at high altitude
should be higher than sea level, despite a possible lack of
appetite.
To overcome this lack of appetite it is recommended that you
plan your daily food intake if you are going to be at altitude
for a prolonged period. For example, agree to consume a set
amount of food that would meet your sea level requirements and
some extra food to cover the increased energy needs of altitude
as well as the possible increases in energy requirements due
to harder terrain, loads carried and the level and type of activity.
It has been estimated that for men an additional energy intake
of 1050-1260Kj (252-303kcal) per day and women 756-840kJ (182-202kcal)
per day is required to maintain an energy balance whilst at
rest.
Now that it is established that energy needs are increased
at altitude the next question is what type of energy should
you predominantly be consuming - Fat, carbohydrate or protein?
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