This is good analysis. However, the body can and routinely (in this era of diet historically high in carbs) does turn carbs into fats, through a process known as de novo lipogenesis, involving the liver. This is how folks get fat eating LOW-FAT stuff like bread, potato, sweet corn, rice, fruit, cheerios, oatmeal, pasta, pop, etc. Excess carbs break down into sugars and the liver converts the sugars into fatty acids, which then move through the bloodstream in the form of triglycerides (can result in high triglyceride reading in your bloodwork) and into the adipose tissue. Often these fatty acids remain in the liver - fatty liver disease.The body creates glucose from just about anything. Your brain ONLY runs on glucose. If you eat only protein, your body converts some of it to glucose. If you eat only fat, your body converts some if it to glucose. If you don't eat at all, your body breaks down your own muscle and fat to create glucose. Your body creates glucose out of whatever is available.
What your body can't do is turn carbs into proteins or fats. That's why carbohydrates are not an "essential nutrient" like protein and fat are. And while plants do contain some proteins, none of them contain all 9 of the essential proteins. Only animal products contain all of the necessary proteins in a single food source.
Blood glucose will vary day-to-day though. You can't tell much from a single fasting glucose reading. Sometimes it will be fine, other times it might be elevated. A single reading isn’t enough to make a diagnosis. You have to see what it's doing over time. An A1c is basically a "3 month average" glucose reading, but it isn't limited to fasting only. So it may indicate that on average you're fine, but you could have big peaks and valleys which aren't good either.
The tricky thing about blood glucose levels is they can be normal even though a person has been metabolically unwell and insulin resistant for years and years. The pancreas cranks out more and more insulin to combat the flood of carbs, keeping blood glucose in check. Finally, the pancreas can't keep up as the body becomes more and more insulin resistant, and then finally the blood glucose begins to rise and you get diagnosed as T2D - after you've been ill for years and years. People would be better off having their fasting insulin levels checked. A decade or two of elevated insulin (aka insulin resistance) can be damaging.
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