Maybe this will help:https://www.marksdailyapple.com/guide-to-blood-sugar
People often refer to junk food as "carbs," when they can be high in fat, too. The trifecta for junk food is fat, sugar, and salt. Food scientists engineer these processed items (which shouldn't be called "food") for maximum palatability -- called the "Bliss Point."
Anyway, the body has two fuels it can use: glucose and fatty acids/ketones.
If present in the bloodstream, the body will utilize glucose preferentially. After a period of time, assuming no additional food intake, the glucose should get cleared from our bloodstream and the liver will then begin turning stored fat into ketone bodies to utilize for energy. Metabolically healthy people should be able to switch back-and-forth between these two fuel sources, without much issue.
If we stop eating 3-4 hours before bed, sleep 7-9 hours, and not eat immediately upon waking, we automatically "fast" 12 or more hours per night and should naturally slip in-and-out of a mild state of ketosis. Being ravenously hungry and ready to commit a homicide after only two hours would make me think a person isn't metabolically flexible. That's how I was, up until 2009 -- lightheaded, headache, deep hunger, impatient, and angry. What fun.
However, if we're constantly eating foods high in fat AND sugar, we'll continue to preferentially metabolize the sugar and store the fat for later. (see the "Randle Cycle") But, "later" never comes, if we keep eating the wrong foods and eating them too often. We keep "topping off" the glucose tank and never get to deplete it. Meanwhile, we continue to store more and more fat. This can lead to problems such as Insulin Resistance, Type 2 Diabetes, and Non-Alcoholic Fatty Liver Disease (NAFLD), and other complications.
Some diet camps say that fat is the problem and that eating low fat (10-15% of calories) and high carb is the way to go. Other diet camps say we need to keep the fat high (75-85% of calories) and the (non-starchy) carbs low.
So, who's correct?
With consideration to the Randle Cycle, it seems both sides can be correct. Indeed, there are seemingly healthy people eating low-fat and high-carb, as well as those eating high-fat and low-carb. Staying in the middle of the spectrum -- high-fat AND high-carb -- is the problem. This is what Denise Minger referred to as the "Macronutrient Swampland," in a blog post and subsequent YouTube video titled "In Defense of Low Fat."
Finally, I'll mention that, in many cases, Type 2 Diabetes is reversible with diet. Some do it with a low fat-diet, some do it with a low-carb diet, and others do it with a low-calorie diet (see the "Newcastle Diet"), so, like most things, there's often different paths to the same destination.
I realize this went off into the weeds a bit. But, hopefully, you'll be able to extract something useful.