ridecamp@endurance.net: availability of energy sources

availability of energy sources

Beth Glace (lb@nismat.org)
Fri, 11 Jul 1997 12:30:48 +0000

In general simple carbohydrates [sugars] are absorbed very quickly,
within 30 minutes or so. Fiber, fat and protein can all slow
digestion if consummed at the same time as the sugar since they slow
emptying of the stomach into the intestine.
The topic of high fat diets and exercise is a relatively new one and
is "hot" right now. We know that the delivery of fats and
carbohydrates to the cells can limit exercise capacity. Since
carbohydrate is stored only in small quantities in mammals, and since
its depletion correlates with fatigue, it has been the focus of many
nutrition research studies.
One way to "spare" your muscle carbohydrate stores may be to adapt
the animal to using fats during training. In a study on rats
[Lapachet et al] it was found that a very high fat diet during
training increased the rat's ability to run for long periods. Rats
receiving an 80% fat diet [YIKES!] ran longer than those who had been
training with a 70% carb diet. The rats that performed the best were
those who had been fed a high fat diet during training, but who then
carbo loaded for 3 days prior to exhaustive exercise. So, they had
good carbohydrate stores, and they were adapted to using fats during
exercise. A negative consequence of this diet was that the rats on
the high fat diet were 17% fatter after 2 months, despite eating
fewer calories. Another study found that sprint performance in horses
was improved after a high fat diet [14%] [Taylor et al]. Work done
in humans using diets ranging from 32-42% fat demonstrated
improvements in maximal oxygen consumption or aerobic capacity
[Pendergast]. These authors speculated that the improvements occur
because the high fat diet during training caused more fat to be
stored in the muscle itself where it can be easily utilized during
aerobic exercise. So, I guess you could say that there is some
evidence that increased fat during training [not during a race!] may
improve exercise endurance. However, the long term health
consequences are not known.
Beth Glace, M.S.
Sports Nutritionist
lb@nismat.org

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