[kszxgz]

Glycemic Load = GI * carbohydrates (g) ÷ 100. Accordingly, the GL in the example would only decrease if fat replaced some of the sugar. GL does not consider the totality of food intake but can be calculated for individual foods. (https://www.gisymbol.com/what-about-glycemic-load/)

What you are referring to may be the glycemic response, which, apart from GL, also depends on the intake of fat and protein among other things. Adding fat and protein does indeed reduce the glycemic response:

"It is generally accepted that adding fat and protein to carbohydrate reduces glycemic responses by delaying gastric emptying and stimulating insulin secretion (1,2). These effects have a number of possible implications for human nutrition, such as supporting the role of high protein or high fat diets in the management of diabetes (3,4) or being a source of criticism for the application of the glycemic index to mixed meals (1,5)." https://academic.oup.com/jn/article/136/10/2506/4746688

[woodandsteel]

Agreed. What glycemic load gets at is the concentration of carbohydrates. So for instance, watermellon has a high glycemic index because it has a form of carbohydrate that moves quickly into the blood stream. But it doesn't spike your blood sugar hardly because there is so little total carbohydrate.