[0] https://cardiab.biomedcentral.com/articles/10.1186/s12933-02...
[1] https://diabetesjournals.org/care/article/38/12/2354/29088/L...
[2] https://www.sciencedirect.com/science/article/pii/S026156142...
In the absence of data my guess is that glycemic spikes simply share common root causes with health risks: overeating, junk food etc.
I say this because there's plenty of meals like white rice that cause glycemic spikes but not the health issues. And at the same time e.g fructose has low GI but seems to be linked to obesity and type 2 diabetes.
In the same way sunglasses correlate with sweating but removing the sunglasses won't make you sweat any less.
1. The excess glucose is turned into fat. This is a causal link with obesity.
2. To turn the excess glucose into fat, insuline spikes (there is also an insulin index, which can be different than the glycemic index). This is a causal link with developing diabetes (the insulin insensitivity variant).
3. The associated glycemic crash (which is very significant) causes a desire to eat more, especially more quickly digestible food. Again, a causal link with obesity.
In a relatively nutrient-poor environment the effects make complete sense: Get as much of the cheap energy providing stuff as possible and store the energy for later. In the Western world it leads to issues.
If there are issues in the "Western world" I would look elsewhere. The theory about "nutrient-poor environments" doesn't really fit the case of France which is consuming 3x more bread per capita than US while having 4x less obese people.
[1] https://pubmed.ncbi.nlm.nih.gov/34352885/
[2] https://jn.nutrition.org/article/S0022-3166(22)01097-5/fullt...
French people eat lots of bread, but it's not like American white 'bread' and it is often eaten together with plenty of cheese, olives, butter, etc. From your linked study: "Dietary carbohydrate content may not fully represent glycemic response, because other aspects of the diet, such as fat content and cooking methods, can also influence glycemic response."
Said otherwise: glycemic index != glycemic response.
> The theory about "nutrient-poor environments" doesn't really fit the case of France which is consuming 3x more bread per capita than US while having 4x less obese people.
I think you're misinterpreting. The nutrient-rich French (or American) environment doesn't cause glycemic spikes, but those spikes are problematic when they occur due to that environment. If there were only a very limited source of food in the US, the spikes wouldn't be as problematic (with regard to obesity, not insulin insensitivity).
You're just dolling up a trivial claim that excess energy causes obesity, or you're suggesting that excess energy consumption without a glucose spike (like gulping down butter) somehow wouldn't lead to obesity.
But you are right that a lot of the health problems are caused through obesity; I will not deny that.
The thing with gulping down butter is that almost nobody does that, because it quickly leads to satiety and does not trigger the desire to eat (or drink) more.