Why can the exact same breakfast give me completely different readings?

NorthBridge82 said:

I’ve been eating almost exactly the same breakfast several days a week because I wanted something predictable. Oddly, my readings afterwards are anything but predictable. Some mornings everything looks great, while on another day the same food gives me a much bigger rise even though I haven’t knowingly changed anything. Sleep and stress are the only variables I can think of. Do other people see this much variation from identical meals, or am I missing something obvious?

Click to expand...

So do, some don't.
I do. I'm type 1 on insulin and I eat the same breakfast every day at the same time and never know what is going to happen.

Some days I go high.
Some days I go low.
Some days I am fine.

I have no idea how I could cope without my Libre letting me know what type of day it is.

I was very frustrating at the start, but I have now mostly got used to it.

But eating new meals is a whole other ballgame and I still find that frustrating, especially as I have now idea how much insulin to take. (I guess I should be grateful that I am not a 'foodie' and quite content to eat the same meals every day and never eat out!)

You mention stress and some people find that does make a big difference. I have even seen some people mention that they stopped using a CGM like a libre because it stressed them out and actually caused their blood sugar to rises more.

There are also a lot of other factors that can affect blood sugar - see https://diabetesresearchconnection.org/42-factors-affect-blood-glucose.

I've also seem some people mention others that are on this list, such as the order in which you eat the food.

NorthBridge82 said:

I’ve been eating almost exactly the same breakfast several days a week because I wanted something predictable. Oddly, my readings afterwards are anything but predictable. Some mornings everything looks great, while on another day the same food gives me a much bigger rise even though I haven’t knowingly changed anything. Sleep and stress are the only variables I can think of. Do other people see this much variation from identical meals, or am I missing something obvious?

Click to expand...

Food is the biggest single influence on BG but there are many others. Basically, whatever causes your liver to increase making glucose will probably result in your BG rising, and vice versa for things that slow down glucose manufacture.

Even without breakfast my blood sugars can range from 4.5 - 6.5. First thing in the morning. I have given up trying to figure out why my body ‘s blood sugars vary. I’m a person who sticks to the same foods, the same time to bed, the same everything, and still my blood sugars fluctuate. So when it comes to breakfast as long as my blood sugars stay within the 4.5 to 10.5 I’m happy.
There are so many variables above and beyond food. How much quality sleep you had, restlessness, what you dreamt that night, temp, stress , the weather, what internal stresses your body is dealing , and even stressful thoughts, you name it and you bet it will impact your blood sugars.

I think sleep and stress can make a much bigger difference than people expect, especially first thing in the morning. Even with the same breakfast, things like poor sleep, cortisol, activity the previous day and just your starting glucose level can change the response quite a bit.
I’d probably look for the overall pattern rather than expecting identical numbers every time. I’ve also found it useful to read up on general health information from sources such as click pharmacy, but if the swings are unusually large or becoming more frequent, it’s worth discussing them with your diabetes team rather than trying to explain every individual reading.

This is the "42 factors" list - at least, it's the one I found some years back. There may well be otjhers. I'd be a bit happier if it was titled "42 factors That Are Reported To Affect Blood Glucose" but that's a minor quibble.

As far as I'm concerned, some of the things on this list don't seem to affect my BG at all. We've all probably got slightly different "applies to me" versions.

My blood glucose will rise as soon as I have my first cup of decaf tea, regardless if with taken with full fat milk or unsweetened almond milk which is what I would normally have. It will hit 8.5 and hover there for about 40 mins then drop down to the mid 5s or 6s. It will also rise if I have nothing for breakfast and that's hard for me as I have to force myself to eat something, never was a breakfast person before diagnosis. For me it is what it is and I have given up on trying to find out the whys. I have just found out I can eat raw carrot sticks though which is a plus for me!

There is one major factor we all need to consider that affects our BG in the morning, the most. What and when did you eat your dinner. If it was carb loaded dinner, it will spike your BG in the morning. If you had your dinner late, it will spike your BG in the morning. Can any of you track you last meal last night, the calories, the carbs and the time you are for a week and get back to us please.

Littleknowledge said:

There is one major factor we all need to consider that affects our BG in the morning, the most. What and when did you eat your dinner. If it was carb loaded dinner, it will spike your BG in the morning. If you had your dinner late, it will spike your BG in the morning. Can any of you track you last meal last night, the calories, the carbs and the time you are for a week and get back to us please.

Click to expand...

It is very unlikely that something I ate at 7pm would be affecting my BG 12 hours later. I would expect my BG to be at or close to the pre-meal reading two hours post-meal. So even if I had a meal late I would definitely not expect it to be affecting my BG in the morning. For example - we ate around 8pm yesterday, some carb included, and my BG this morning was 4.5.

The only exceptions for me would be either an unfeasibly huge amount of carbs so that my insulin response is completely overwhelmed for hours; or a large amount of alcohol so that my liver's ability to fabricate new glucose is restricted.