mihou
Rang: Administrateur
Nombre de messages : 8092
Localisation : Washington D.C.
Date d'inscription : 28/05/2005
 | | A Carbohydrate Is Not A Carbohydrate! | |
A Carbohydrate Is Not A Carbohydrate!
by Dr. John
Berardi
Not all carbohydrates were created equal. Below, I'll briefly
discuss:
1. The insulin index vs. the glycemic index
2. The superiority of low-GI and II diets
3. The difference between liquid carbohydrates
While older carbohydrate classification schemes were centered on
the notion of simple vs. complex carbohydrates (a structural
classification), newer schemes focus more appropriately on the
absorption profiles (glycemic index) and physiological effects
(insulin index) of these carbohydrates (a functional
classification).
The Glycemic Index (GI) is a classification scheme based on the
blood glucose rise after consuming a carbohydrate food. This
measure is based on the absorption profile of the food and was
originally considered an indirect, but adequate measure of the
insulin response to food. The assumption was that the insulin rise
would be proportional to the glucose rise. However, recent research
has demonstrated a dissociation of the glycemic response and the
insulin response to the food. Therefore the insulin index was created.
The Insulin Index (II) is an index of the magnitude of insulin
secretion as a result of food ingestion. Of course, this is the
direct measure that the glycemic index could only approximate.
Since insulin is a tricky hormone to manage, it's best to know
exactly what's happening with this guy, especially if you have poor
insulin sensitivity or poor carbohydrate tolerance.
Studies by Holt et al (1996) and Ostman et al (2001) highlighted
some of these differences between glycemia and insulinemia.
Interestingly, while the glycemic and insulin indices of many foods
were similar, some foods caused unpredicted responses. As shown in
the following graph, foods like yogurt and milk had relatively
low-glycemic indices, but very high insulin indices. White and
brown rice, on the other hand, had high-glycemic indices, but low
insulin indices. The point here is that if you want to effectively
manage body composition, you should choose your carbohydrates based
on both the glycemic and insulin indices. Unfortunately, there are
only limited insulin data out there, leading us to continue to rely
in some cases only on the glycemic index.
More complete glycemic and insulin indices can be easily located
by doing an Internet search on these two terms.
So the next appropriate question would be, "What does the
literature say about low GI and II diets vs. higher GI diets?"
Well, here's a summary:
Ludwig et al (2000) described the following list of benefits for
eating a low GI diet:
• Better nutrition (better micronutrient profile and more
fiber)
• Increased satiety
• Decreased hunger
• Lower subsequent energy intake (second meal
effect)
• Fat loss
• Better fasted insulin and glucose
In a study by Agus et al (2000), it was demonstrated that during
a short, 6 day, low-calorie diet, a low-GI carb intake preserved
metabolism and enhanced fat loss vs. a high-GI diet. The low GI
group saw a 5% decline in metabolic rate and a 7.7lb weight loss
while the high-GI group saw an 11% decline in metabolic rate and a
6.6lb weight loss. In these subjects, fasted glucose and insulin
values were lower in the low-GI group, indicating better glucose
and insulin sensitivity.
Spieth et al (2000) and Ludwig et al (2000) showed that 4 months
of low-GI eating was superior to 4 months of high-GI eating in
overweight teens. The low-GI group lost 1.5 points on the BMI scale
and 2.2 lbs while the high-GI group gained 2.88lbs and increased
their BMI. In addition, these studies showed that a low GI meal
reduced food intake during subsequent meals while the high GI meal
lead to overeating.
Finally, Pawlak et al (2001) showed that in rats, a low-GI diet
led to decreased fasting insulin and glucose values, decreased fat
mass, and decreased insulin and glucose values during a glucose
tolerance test. Therefore, body comp as well as glucose and insulin
sensitivity improved.
The bottom line here is that when all else is equal, a diet
containing mostly low-GI carbohydrates is superior to a high-GI
diet for losing fat, preserving metabolic rate, and maintaining
healthy insulin sensitivity and glucose tolerance.
Next, I'd like to illustrate the differences between popular
liquid carbohydrates including maltodextrin, dextrose, fructose,
and sucrose.
Maltodextrin is a glucose polymer (a string of glucose units put
together, similar to the protein peptide). It is therefore, by
definition, a complex carbohydrate. However it's more complex
nature does NOT slow digestion. Therefore, the GI and II remain
high. Maltodextrin is the absolute best carbohydrate to consume
during exercise for rapidly delivering blood glucose and for muscle
glycogen recovery. It's also best for fluid uptake.
Dextrose (glucose) is a simple carbohydrate unit (similar to the
amino acid). While it's good for exercise situations (malto is
better), you're probably better off adding some dextrose to your
maltodextrin formula. A little bit of dextrose may enhance the
already excellent fluid uptake that occurs with maltodextrin during
exercise.
Fructose is a simple carbohydrate unit, but it's structurally
different from glucose. Due to its structure, it can possibly cause
GI problems and/or decrease fluid uptake with exercise. Fructose,
unlike other simple carbs, has to be "treated" in the liver and it
reaches the muscle slowly.
Finally, sucrose consists of glucose and fructose units bonded
together. Therefore, upon digestion, you get glucose and fructose
in the GI (and the benefits and consequences of
each).
Based on the three studies I reviewed (Blom et al 1987, ven Den
Burgh et al 1996, Piehl et al 2000), it appears that dextrose is
72% faster than fructose for muscle glycogen resynthesis . As a
result, at the end of 8 hours, muscle glycogen was 30% higher with
dextrose ingestion. However, in another study, at the end of 4
hours, muscle glycogen was 15% higher with maltodextrin ingestion
vs. dextrose. So dextrose kicks fructose's butt although malto
beats up on dextrose.
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