
29/08/2025
Beyond Blood Sugar: Why the Glycaemic Index Has to Go
For decades the glycaemic index (GI) has been presented as a nutritional compass, ranking carbohydrates by the rate at which they raise blood glucose. Conceptually simple, it was once embraced as a public health tool. Yet on closer biochemical inspection, the GI framework collapses.
1. GI is glucose-centric, not insulin-centric.
The index captures the rate of glucose entry into the bloodstream but ignores the insulin response, which is far more relevant to metabolic disease. Two foods of identical GI can generate radically different insulin excursions. Chronic hyperinsulinaemia - not glucose alone, drives the pathogenesis of obesity, fatty liver disease, type 2 diabetes, PCOS, cardiovascular disease, and certain cancers.
2. GI disregards hepatic metabolism.
Fructose, ethanol, and branched-chain amino acids contribute little to post-prandial glucose, yet they are directly lipogenic in the liver. These substrates overwhelm hepatic mitochondria, increase de novo lipogenesis, and accelerate insulin resistance. By GI standards they appear “benign,” but in reality they are among the most metabolically disruptive components of the modern diet.
3. GI is easily confounded.
Fat or fibre co-ingestion slows gastric emptying and lowers GI values. This explains why ice cream scores lower than white bread. But such artefacts do not equate to improved metabolic safety; they merely obscure the true burden of the food on hepatic and systemic metabolism.
The underlying problem is not the speed of glucose entry, but the total metabolic load.
When substrate supply chronically exceeds mitochondrial oxidative capacity, excess energy is diverted into fat storage - most critically in the liver. This is the initiating step in the cascade of insulin resistance and metabolic disease.
The GI, by focusing on the wrong metric, misdirects dietary guidance.
A more meaningful question is: “What is the metabolic cost of this food in terms of insulin dynamics, hepatic fat generation, and mitochondrial function?”
Only when nutritional advice aligns with these biological realities can we begin to address the root causes of chronic disease. 🙏🤔