Not discounting people's experiences, but trying to suss out the science here. If you were, for example, to inject sugar directly into someone's blood stream would the result be fatigue every time?

It seems to me that there's more involved in this. In my experience (more anecdata!) I'm able to eat anything in the morning. Giant bolus of carbs and sugar, and I feel great. That same meal in the afternoon will give me such a fatigue that I need to lay down.

Clearly there's some other factor at play for me in the function whos result is fatigue.

FATIGUE_LEVEL = CARB_GRAMS * (HOUR_OF_DAY / 24)

For many people, it may not be, I can only speak for myself. There's another thing, called 'idiopathic postprandial syndrome' which is essentially the symptoms above, but without actual low blood sugar (<60mg/dl), which some people think is another form of insulin resistance, where your blood sugar is normal but your body "wants" more sugar in the blood.

Talking with endocrinologist, they say that the insulin sensitivity for most people is much higher in the AM and daytime than at night, so it makes sense that you might have more problems in the afternoon, but you should probably talk to a doctor rather than taking my word for it!

It's often difficult (in the US at least) to get primary care and endocrinologists to take you seriously if you are not actually dying of diabetes or passing out from low blood sugar - this is where dipping into the realm of concierge medicine can be helpful, or at least, it has been for me. They are often much more willing to investigate thoroughly.

Missed this the first time around. They do this, for research, it's called a glucose clamp test.

https://en.wikipedia.org/wiki/Glucose_clamp_technique

Unfortunately it's almost impossible to find someone willing to administer it to you. It's an outpatient hospital procedure lasting a number of hours, and almost no insurance would cover it, as far as I am aware.

Responses are by readers, so take with a pinch of salt

What? That is quite a boring and obvious observation because your insulin sensitivity is much higher in the morning.

I know 2 T1 diabetics, and both never touch potatoes because of the GI.

Can I ask how you deal with your reactive hypoglycemia? I switched to keto a long time ago, which took me from having hypos multiple times a day to never. But often in late afternoon I start feeling some mild hypo symptoms, even though my blood glucose is stable.

Not only did you boil the potato, but you pre-chewed it too. Mashed potato is about as close as you can get to refined potato (potato flour). What you've created is easily digestable amylopectin - pre-chewed, already gelatinized and suspension with water. The amylase in your saliva can mix extremely well with mashed potatoes, and within minutes that amylopectin will be available as glucose. Maybe you mix in a little fat with butter or oil, but probably not much.

Vs. more or less any other potato cooking method. Even though the starch will have gelatinized with the water present in the potatoe, the potato's structure is more intact than boiling & mashing. Even after chewing the starch is not as well mixed with water, and this will take longer to digest.

We don't eat much mash in our house.

But really we are talking about two different things: GI and satiety. Yes potatoes are high GI. It would follow that they will spike your blood sugar. No claims have been made to the contrary.

Satiety is about how full you will feel per calorie eaten of that food. Multiple factors contribute to satiety. Specifically boiled potatoes score super high on the satiety index.

Not mashed potatoes. Not french fries, potatoes gratin, etc.

The topic is only tangentially related to GI.

Don't mean to be cranky here but I was hoping people would talk about the article, the underlying concept (satiety), and the research, instead of going off on lengthy discussions about quasi-related personal anecdotes.

And that's where GI comes in - high GI foods cause blood sugar spikes, and the crash will make you feel hungry again.

Pasta is a good example - it feels very satiating at the time, but the feeling doesn't last long.

I tried keto but it was difficult to get the variety, especially (as you say) when you're intensely craving sugar. It obviously solved the problem but was really challenging to continue, so I only lasted a couple weeks.