GI vs GL

GI reflects the “speed” per unit carb; GL (Glycemic Load) multiplies by available carbs per serving, reflecting total impact.

Two Measures: speed and load

  • GI (Glycemic Index): the speed/amplitude of blood glucose rise per unit carb — a quality metric.
  • GL (Glycemic Load): the total impact of a serving, factoring in portion (available carbs).
  • Formula: GL = GI × available carbs (g) per serving ÷ 100.
  • Available carbs: total carbs minus dietary fiber (typically excluded from glycemic effect).

Shortcut: GI = how fast, GL = how much. Same GI, larger portion → higher GL.

GL ranges (per serving)

0 10 19 ≥20
Low (<10), medium (11–19), high (≥20) GL.
Low GL Medium GL High GL

Why GL feels more “real-world”

GI is measured using 50 g available carbs from a single food — excellent for standardization but not always aligned with everyday portions. GL multiplies GI by the actual available carbs you eat, better reflecting the impact of a serving or a meal.

Glucose Time (2h post‑meal) Smaller portion (lower GL) Larger portion (higher GL)
Same GI, larger portion → higher GL; steeper, higher curve.

Worked examples (approx.)

  • Carrot: GI≈71; available carbs ~7 g → GL≈71×7/100≈5 (low).
  • Watermelon: GI≈72; available carbs ~15 g → GL≈72×15/100≈11 (medium).
  • White rice (cooked 150 g): GI≈73; available carbs ~28 g → GL≈73×28/100≈20 (high).

Numbers vary by variety, cooking, and serving; examples are illustrative.

When to use GI vs GL

  • Choosing staples: start with GI (slower, steadier), then check GL for your usual serving.
  • Building meals: manage GL (total carbs) and pair with protein/fiber/fat.
  • Weight or glycemic goals: prefer low/medium GI and reduce GL via portions.
  • Personal variability: use glucose meter/CGM to see your own response.

Practical tips

  • Prefer low/medium‑GI staples: whole grains, legumes, tubers (steamed/boiled).
  • Control portions to lower GL: use plate methods or weigh common servings.
  • Pairing matters: carbs + protein + veggies/healthy fats to slow absorption.
  • Order of eating: veggies and protein before starch can blunt peaks.
  • Track available carbs: total carbs minus fiber aligns with GL math.

Limits and caveats

  • Inter‑individual differences: same GI/GL can yield different curves across people.
  • Mixed meals: GI/GL derive from single foods or summed estimates; real meals are complex.
  • Not full nutrition: also consider protein, fats, micronutrients, and energy.
  • Data variability: databases and lab conditions can differ.

Takeaway

GI captures “how fast”; GL captures “how much”. Choose low/medium‑GI foods and manage GL with portions and pairing to keep post‑meal glucose steadier. See also: What is GI · Low‑GI diet guide

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