The problem with the GI index is that it is an average of how different foods release their glucose and as with everything biological, there is variation, so there are some people who will find that low GI works really well for them because the carbs release their glucose slowly as expected, but there will be a minority who find their digestive systems break even Low GI foods down very quickly. Like
@Drummer I find that the glucose from many low GI foods like porridge, wholemeal bread and legumes hit my blood stream quicker and harder than anticipated, so testing can be really helpful if you opt for low GI.
I think it may also help to understand that 3 teaspoons of sugar is 15g carbs but those carbs will hit your blood stream pretty quickly if they are in a cup of coffee.
A medium slice of wholemeal bread contains 15g carbs but will maybe take another 15-30mins to start hitting the blood stream. If you add a bowl of porridge as well, say 50g dry porridge oats made into porridge, even just with water, that's another 30g carbs going into the system which is a total of 45g carbs when previously it was just a cup of sweet coffee with 15g, so breakfast is now 200% more carbs by switching from a sweet coffee to porridge and a sandwich. Yes it may hit the blood stream slightly slower but it might not be a good strategy for the OP, especially at a time of day when many people are more insulin resistant and therefore BG levels may take longer to come down.
I therefore do think that testing might be a good strategy for the OP in this situation, to ensure that their choices are helpful to their BG levels rather than detrimental.
I know it is a pretty radical thought but sticking with just a coffee for breakfast and perhaps just having 1.5 or 2 sugars in it instead of 3 might be a significantly better option BG wise than replacing it with porridge and a sandwich......
...... Just saying
😱 😳