ridecamp@endurance.net: yet more on carbs, fats and performance

yet more on carbs, fats and performance

Beth Glace (lb@nismat.org)
Mon, 1 Dec 1997 16:26:39 +0000

Well, Tom, you asked for it.... [hee, hee!] To everyone else,
sorry, I just couldn't resist jumping in and wallowing around through
quite a long response.
First of all I want to make sure I understand this discussion. It
seems to me that the debating began over the issue of feeding
carbohydrate sources JUST PRIOR to exercise, so I'll start with that
and then put in some other perspectives on high fat diets, and yes,
even the Zone diet [for Donna in Altoona]. If I am wrong about this
I apologize. What must be kept in mind is when we are feeding and
what we expect our horses to do. Prolonged exercise at moderate
intensity [<60% of max] increases the uptake of fatty acids by the
muscle, by as much as 70%. This is a level of exercise which can be
maintained for hours at a time, as in distance races. The better
conditioned the animal the more they will rely upon fats for any
given workload. Utilization of fats minimizes the depletion of
glycogen. It is true that when glycogen is depleted exercise will be
limited, so sparing glycogen and starting with a greater pool of
glycogen will help the animal keep going longer. If horses are like
humans, some are particularly sensitive to large quantities of carbs
right before exercise. Some tolerate it well, but others may
actually end up with blood glucose low enough as to qualify as
hypoglycemic. Why? When blood sugar rises insulin is released to
lower the sugar levels. If right around that time the animal is
exercised the body has to tolerate another sudden draw on blood
sugar, and it can drop too low. After a short time the balance is
restored, and all is well, but until blood sugar is normalized
sweating, confusion, hunger, loss of balance may result. Not good.
To avoid this simply don't feed a big dose of carbs the last 30-60
minutes before exercise. Simple. Once exercise begins insulin is
supressed so you won't see that dramatic fall in sugar levels.

What must be kept in mind when looking at all
of the studies Tom posted is WHEN the carbohydrate was fed. If we
look at the abstracts one by one - well, first of all we'll be here
all day - and I really do have work to do. But lets look at the
first few:
1] Kreider et al - this is a study which looks at effects
of nutritional manipulation during RESISTANCE TRAINING. We do not
weight train our endurance horses, Tom.
2] Tsintzas et al - this study looks at carbohydrate ingestion
during prolonged running. Carbs during exercise absolutely,
undeniably improve performance. DURING.
3] Hollozsy et al - "Regulation of carbohydrate metabolism
DURING/AFTER Running.." That says it all. It is not a discussion of
the merits of high carb diets in general but of their metabolism
during and just post exercise.
4] Lapachet et al - now Tom, it gets
interesting because this study finds that rats running for a very
long time [I read this last year, and I forget exactly how long they
ran, but it was hours and hours, like our horses] did best when
chronically fed a high fat diet. They did best if they were given a
high fat diet typically but were carbo loaded for a few days before
being run to exhaustion. To note though, the fat fed rats were much
fatter than the carb fed rats even though they ate less calories.
This study represents an extreme of manipulation since the rats got a
70% fat diet. A rodent can survive this; obviously a horse cannot.
But the point it makes runs somewhat counter to the constant high
carb diet, at least for omnivorous rats.

Other studies that show positive results in humans with a high fat
diet do exist. Muoio in 1994 demonstrated that cross country runners
ran for a mean of 91 minutes on at 73% fat diet compared to 69
minutes on their normal diets. A high carb diet also improved their
run to exhaustion but not as greatly as the high fat diet, 76
Now, I'll go on record here in saying that I do not advocate high fat
diets for human athletes. However, I am watching research as it comes
out to see if any other labs confirm positive performance effects
from high fat diets. We do know that in humans chronic ingestion of
high fat diets in sedentary people is associated with a variety of
diseases, including obesity, and cardiovascular disease so caution is
warranted. Furthermore, rats and humans are not herbivores and are
well adapted to tolerate large quantities of fat. I am not sure how
horses can be expected to fare in the long term, but perhaps they can
also increase their fat intake somewhat with good performance
As for the high protein diets, ie the Zone diet Barry Sears and so
forth. Although Dr Sears quotes himself repeatedly in his book he
really needs to show that anything he has done has been printed in a
peer reviewed journal. Saying "this is so because I say its science,
and I'm a Dr" just does not cut it. Anyone in the nutrition field
recognizes his diet as a rehash of former diets, like the Scarsdale
diet. These were high protein, moderate fat, low carb diets, and if
you want to lose weight they work. They work because following his
outline men will be eating around 1200 Kcal per day. Is is healthy
in the long run? I think probably not even if you increased the
portion sizes.

Sorry for taking up so much space...
Beth Glace, MS
Sports Nutritionist

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