A number worth understanding, not obsessing over
Lesson 5 covered the difference between whole-food and refined carbohydrates. The glycemic index is the number behind that distinction, a genuinely useful tool for choosing between similar foods, as long as it is not treated as the only thing that matters.
What the glycemic index measures
Developed originally by Dr David Jenkins in the early 1980s and maintained today as an ongoing database by the University of Sydney, the glycemic index ranks carbohydrate-containing foods from 0 to 100 based on how quickly they raise blood glucose, compared against a reference (pure glucose, scored 100).
Low GI
55 or below
Oats, lentils, most fruit, wholegrain pasta
Medium GI
56-69
Wholemeal bread, brown rice, sweet potato
High GI
70 or above
White bread, white rice, most sugary cereals
Why wholemeal makes such a difference
Refining a grain strips out the bran and germ, along with most of the fibre. Without that fibre slowing things down, the remaining starch is digested and absorbed quickly, causing a faster, sharper rise in blood glucose. Wholemeal versions keep the fibre intact, so digestion, and the resulting glucose rise, is slower and steadier.
This is also why the volume and fibre lessons earlier keep coming back: fibre is doing real, measurable work here, not just adding bulk.
The catch: portion size and context matter too
GI alone can be misleading, because it does not account for how much of the food you actually eat. Glycemic load (GL) fixes this by combining a food’s GI with its typical carbohydrate content per portion. Watermelon, for example, has a high GI but a low GL, because a typical serving contains relatively little actual carbohydrate.
GI also shifts once a food is eaten as part of a mixed meal. Protein, fat and fibre eaten alongside a higher-GI carbohydrate all slow overall digestion, blunting the glucose response. This is one more reason the plate method from Lesson 7, protein plus vegetables plus carbohydrate, works better in practice than judging any single ingredient in isolation.
Further reading
- University of Sydney Glycemic Index Database (ongoing) — glycemicindex.com
- Jenkins DJ, Wolever TM, Taylor RH, et al. (1981). Glycemic index of foods: a physiological basis for carbohydrate exchange. American Journal of Clinical Nutrition, 34(3), 362-366.
Today’s task
Look at one refined carbohydrate you eat regularly, white bread, white rice, or white pasta, and check whether a wholemeal version is available and realistic to swap in.
Check in with yourself
- Which meal in your week is most likely to be all refined carbohydrate with little protein or fibre alongside it?
- Would a small wholemeal swap be realistic there, or would it need something else changed too?
- Any new takeaway from today’s lesson you want to remember?
Browse the cookbook for meals already built around wholegrain and high-fibre carbohydrate choices.