what is the difference between pre-diabetic and the non-diabetic interns of when they eat added sugars

The short version: prediabetics don't just have higher blood sugar after added sugars—their insulin system is already failing in specific, measurable ways, and the pattern differs by subtype.

The core difference is that a non-diabetic's pancreas releases a fast, strong burst of insulin right when sugar hits the blood. That first-phase response is already blunted in prediabetes. In one study, the insulinogenic index (a measure of early insulin release) fell from 1.4 in normal people to 0.7 in isolated impaired glucose tolerance and 0.6 in combined IFG+IGT [1]. The disposition index, which adjusts insulin output for how resistant the body is, dropped even harder: from 10.8 in normal to 2.9 in combined prediabetes [1]. That means the pancreas is working against a body that needs more insulin, while producing less of it.

The subtype matters. People with isolated impaired fasting glucose mainly have beta-cell dysfunction—their fasting insulin is higher but their beta-cell function score is lower (68 vs 88 in controls) [2]. People with isolated impaired glucose tolerance are more insulin-resistant: their 2-hour insulin spikes to 393 µIU/mL versus 40 fasting, showing the pancreas is dumping insulin but the body isn't responding [2]. Those with both have the worst of both worlds [2].

After a sugar load, prediabetics also show more inflammation and vascular stress. In one study, the endothelial marker ADMA rose from 0.47 to 0.81 µmol/L after a glucose challenge in impaired glucose tolerance, versus 0.3 to 0.45 in normal people [3]. The retrieval did not include a direct head-to-head trial of identical added-sugar meals in both groups, so the exact post-meal glucose curves by subtype are not fully covered here.

My call: prediabetes is not a milder version of normal—it is an early failure of the insulin system, with the specific defect depending on the subtype. Confidence: moderate.