The traditional classification of carbohydrates, based on the complexity of their molecular structure, is now obsolete. Modern science has shown that the rate of absorption is not the discriminating factor, but rather the metabolic impact on blood sugar levels.

1. The Old Classification: A Simplistic Biochemical Logic

For decades, the world of nutrition has divided carbohydrates into two blocks, assuming that the molecular structure dictated the time it takes to enter the bloodstream.

A. The So-Called "Simple" Sugars (Monosaccharides)

With a reduced biochemical structure (one or two molecules), they are associated with a sweet taste. They are found in:

• Fruits (Fructose)
• Honey and plant syrups (Agave, Maple)
• Table sugar (Sucrose)
• Processed products (sodas, pastries)

B. The So-Called "Complex" Sugars (Polysaccharides)

Mainly represented by starch, they are formed of long chains of glucose. They constitute the energy base of starchy foods:

• Pasta, rice, cereals
• Legumes
• Potatoes

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2. The Broken Paradigm: The Absorption Rate is Identical

The idea that complex sugars would take longer to be digested due to their size is a physiological error. Isotopic studies have proven that the peak of blood glucose occurs at about the same time (around 30 minutes) for a portion of white bread or a pure glucose solution.

Why is the notion of "speed" false?

• Enzymatic Capacity: The body has extremely efficient enzymes (amylases) capable of splitting complex starch chains in record time.
• Absorption Kinetics: Whether the molecule is simple or complex initially, it arrives in the small intestine in the form of monosaccharides at a nearly equivalent rate.

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3. The New Reference: Glycemic Index (GI)

If carbohydrates enter the bloodstream at the same rate, they don't all have the same impact on blood sugar levels (glycemia). This is where the notion of GI advantageously replaces the concept of "slow/fast sugars".

Criteria	Old Vision	Scientific Reality
Digestion speed	Slow for starches	Identical for almost all
Selection criterion	Molecular complexity	Glycemic Index (GI)
Hormonal response	Neglected	Variable insulin peak

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4. Factors Modulating Metabolic Impact

It's not the molecule alone that counts, but the overall food matrix in which it is found:

• Fibers: They slow gastric emptying and glucose absorption (e.g., brown rice vs. white rice).
• Cooking: Prolonged cooking (heavily cooked pasta) increases GI by making the starch more accessible to enzymes.
• Presence of Lipids/Proteins: They "buffer" the arrival of sugar in the blood.

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Conclusion: Reforming Nutritional Vocabulary

It's time to abandon the terms "slow sugars" and "fast sugars". For optimal energy management and body composition, the athlete must focus on the Glycemic Index and Glycemic Load. The starch in a potato puree can raise blood sugar as abruptly as table sugar, while the fructose in fruit will have a much more moderate impact.