The human body can get rid of blood sugar without insulin, but NOT gobs of it, and the difference between diabetes and healthy is a mere two paper clips of dissolved sugar in 1.3 gallons of blood.
Therefore, if we want to be able to pass the adult marshmallow test we likely need to be below our personal fat threshold, move throughout the day, and put on some muscle so that we don’t become metabolically dysregulated licking a date.
This is the Magic School Bus journey of that Glucose. In science, we call this an Oral Glucose Tolerance Test or OGTT. You pound 75 grams of glucose after not eating anything for at least 12 hours (fasted).
First, in the fasted state your body still produces sugar endogenously and it can dissipate this sugar without insulin, but it still needs to produce a little bit even in the fasted state.
“In the fasting state non-insulin mediated glucose uptake accounts for about 83% of whole-body glucose disposal…NIMGU was 1.62 mg/kg·min−1 which became a widely accepted static rate for NIMGU.”
-Jumpertz et al. 2010
“Basal (endogenous) glucose appearance averaged 10.9±0.2 ; µmol/kg per min (if my math is right 1.96 mg/kg·min−1).”
-Kelley et al. 1998
As you may notice by the numbers above we likely always need a little insulin to deal with even endogenous hepatic glucose production and the dysregulation of this system from insulin resistance is going to cause a reduced rate of glucose uptake by peripheral tissues and increased endogenous glucose production from the liver via a failure of insulin to downregulate glucagon release from pancreatic alpha cells
This probably doesn’t really matter in terms of glucose control when fasted but it matters A LOT when guzzle down a Coke or that unfortunate chalky OGTT liquid.
Now, the actual difference in your bloodstream between 85 mg/dL (“healthy”) and 126 mg/dL (diabetes) is a mere 2 grams (paperclips) of glucose dissolved in about 1.3 gallons or 5 liters of blood.
Per above, if you weigh 75 kilos (165 lb) you can put away an estimated 0.12 grams of carbohydrate per minute WITHOUT insulin.
This equals about 7.3 grams per hour.
Thus, 75 grams of pure CHO in an OGTT should be a huge huge problem…
In theory, without insulin or any other means of regulating blood glucose this human would still be at 1,280 mg/dL at two hours.
Luckily, (if you are not a Type 1 Diabetic) we have insulin AND glucose appears in the bloodstream somewhat slowly.
“The rate of appearance of the exogenous (orally administered) glucose increased within 30 min to a peak rate of 24.4±1.4 µmol/kg per min at 60 min and then progressively decreased to 2.2±0.3 µmol/kg per min at 300 min.”
-Kelley et al. 1988
This means glucose is showing up at a rate of 4.39 mg/kg per min
For the first hour, this 75-kilo human would have 20-25 grams of glucose appear in the bloodstream (depending on what paper from the late 1980s or early 1990s that you reference.)
LUCKILY, according to a recent 2018 study by Ferrannini et al. whole-body glucose uptake (with insulin) in insulin sensitive subjects = 23.1 (µmol/kg body weight/min)!!
For our 75-kilo imaginary person that equals 4.2 mg/kg/min or about 20 grams of glucose per hour that can be taken up after an overnight fast.
Pretty cool right!?! The math adds up and insulin almost triples a “normal” fasted human’s ability to deal with large boluses of carbohydrates.
Now let’s put a diabetic oral glucose tolerance test result of 200 mg/dL after two hours in context. This is about 10 grams of total glucose in the blood so theoretically, if they are diabetic and starting with a fasting glucose value of 126 mg/dL it is a 3.7 gram rise in blood glucose two hours after ingesting 75 grams.
“A total of 73 +/- 4% of the oral load was recovered in the systemic circulation within 3.5 hours.”
– Ferrannini et al. 1985 (Yes, I believe that is the same Italian author as above…34 years ago trying to answer the same question!)
Thus, if we know that somewhere around 75% of that 75-gram glucose load is going to hit the bloodstream over a 3.5 to 5 hour period (the other 25% will be used and stored by the liver and other internal organs). This equals about 56 grams of glucose over that entire time period so if we take the above rate from Kelley et al. and extrapolate it out probably 40 grams of that will hit the bloodstream in two hours.
In two hours, WITHOUT insulin this human will likely be able to get rid of 14.6 grams which leaves about 25 more grams to get rid of with insulin in two hours. This theoretically should be no problem, but a diabetic can only get rid of about ~20 grams in two hours which means that if you have a diabetic OGTT result you have about half of the ability to deal large amounts of sugar as a “normal” human.
And we jump back to the 2018 Ferrannini paper and whole-body glucose uptake (with insulin) in insulin-resistant subjects equals 11.1 µmol/kg/min or 2.0 mg/kg/min or about 9 grams of glucose per hour and you may notice that this is only about .4 mg/kg/min over what people can get rid of without insulin.
So you have too many extra paperclips of glucose in the bloodstream and someone is now diabetic on paper.
This legit took me days, weeks, months of scouring papers that go back to 1975 in an attempt to figure out where the hell all the glucose is going!
But, all of this research looks at fragility vs. “normal” controls…My brain immediately jumps to how bullet-proof can we make this system with exercise and the attainment of high levels of muscle mass (muscle accounts for most insulin-mediated glucose disposal).
To give you an example, I have had trained males with FFMIs approaching 25 eat well over 500 grams of carbohydrate in a day (from white rice and other “high glycemic index” foods) and their blood glucose didn’t go over 120 mg/dl EVER which means in the face of 500 grams their blood glucose stayed within a +/- 1 gram window the entire day!
In a world of cupcakes, that’s the show. Not worrying if you ate too much zucchini last night.