Here’s a piece of COMPLETELY anecdotal data, so do with it what you will. A friend with metabolic syndrome was struggling with weight despite intermittent fasting. She began to wear a continuous glucose monitor. She found that black coffee had the same effect as eating a donut, but if she added a boiled egg, the effect on her glucose was neutral.
Now, I don’t know what effect all that has on other metabolic processes. I doubt the effect is universal. But it is interesting that the revived wisdom about black coffee being okay is not universally true.
There's apparently some significant variation between people. Some don't see a glucose spike at all, some see it vanish if they consume protein first, and some see it regardless.
That's pretty crazy. I wonder if placebo effects played a role?
(Ie if you had pumped the liquid directly into her stomach, without telling her whether it's black coffee or some substitute, would the outcome still have been the same?)
The easy test would be to see if it's the caffeine having this affect by using switching between caf and decaf.
Something I wonder about though is that if blood glucose is rising after black coffee, that energy must becoming from somewhere. i.e. stored fat, stored glycogen or stored protein.
Given that she's about do some fasted exercise that will burn that blood glucose as its fuel source, is this a bad thing if the energy is coming from stored fat?
> Give that she's about do some fasted exercise that will burn that blood glucose as it's fuel source, is this a bad thing if the energy is coming from stored fat?
For a healthy person, this might be good. For someone with various health issues (like the person in question), I don't know.
A continuous glucose monitor checks the level of glucose in your blood. Glucose can be stored in your body as glycogen (e.g. in the liver, or muscle tissue).
Your pancreas produces glucagon, which influences the process of converting it back into glucose, released into your blood.
That's generally accepted basic science, but from my own anecdotal friends/family experience, the pancreas also seems like a pretty buggy organ generally, prone to glitches both temporary (like perhaps in this coffee drinker) and chronic (type 1 diabetes), leading to undefined behavior, crashes, and even fatally bricking the system permanently.
So this anecdote isn't particularly surprising to me.
(Also, for those reasons, I would definitely wear a continuous glucose monitor myself if it wasn't so expensive and difficult to arrange when you don't actually have anything known to be wrong with your blood sugar levels. I predict that within a decade or two, they will be a fairly ubiquitous piece of human body instrumentation, like the sleep-tracking wristwatches and rings we have today.)
Now, I don’t know what effect all that has on other metabolic processes. I doubt the effect is universal. But it is interesting that the revived wisdom about black coffee being okay is not universally true.