If you test a meal under exactly the same conditions, you would roughly see the same pattern in glucose levels. However, these conditions are almost impossible to reproduce every day. A couple of things, why a meal can trigger sometimes a higher, or less high peak:

You ate something before the meal, that had an effect on your meal. Especially when this contained fats or fibers, which promote a slow release of blood sugars
You ate something after a period of fasting. This will create a peak in your blood sugar levels, in almost all cases
The meal was slightly different in composition. It is difficult to exactly construct the same meal (e.g., a curry is a complex dish of rice, meat, sauce and vegetables, so an interplay of fats, sugars and fibers)
A banana can be higher in sugars, when it has more brown spots
The portion size was larger or smaller
The time of the day might affect the inclination in blood sugar levels. An apple might spike more in the morning, than in the afternoon
How long do you take to complete your meal? This might influence the height of your sugar peak
Did you finish your entire plate, or left something uneaten?
With your meal, did you drink something differently (e.g., a glass of water vs. a can of Coke)
Sometimes, after a bad night of sleep, your glucose patterns can be more 'wobbly'
Did you take medication (or pain killers) with or after the meal? The pain killer typically won't influence your blood sugar levels, but can reveal a different cause of elevated glucose levels (like an illness)
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