Originally Posted by
wolfchild
Eating carbs does not prevent fat burning...You can eat carbs and still burn fat.
https://pubmed.ncbi.nlm.nih.gov/21864752/
The major effects of insulin on muscle and adipose tissue are: (1) Carbohydrate metabolism: (a) it increases the rate of glucose transport across the cell membrane, (b) it increases the rate of glycolysis by increasing hexokinase and 6-phosphofructokinase activity, (c) it stimulates the rate of glycogen synthesis and decreases the rate of glycogen breakdown. (2) Lipid metabolism: (a) it decreases the rate of lipolysis in adipose tissue and hence lowers the plasma fatty acid level, (b) it stimulates fatty acid and triacylglycerol synthesis in tissues, (c) it increases the uptake of triglycerides from the blood into adipose tissue and muscle, (d) it decreases the rate of fatty acid oxidation in muscle and liver. (3) Protein metabolism: (a) it increases the rate of transport of some amino acids into tissues, (b) it increases the rate of protein synthesis in muscle, adipose tissue, liver, and other tissues, (c) it decreases the rate of protein degradation in muscle (and perhaps other tissues). These insulin effects serve to encourage the synthesis of carbohydrate, fat and protein, therefore, insulin can be considered to be an anabolic hormone.
You are correct, but the question is if your body is predominantly burning fat vs predominantly burning carbs. Everyone knows that if you eat carbohydrates, your pancreas concomitantly releases insulin for your body to absorb that carb load. Since you're physically fit, you likely are metabolically flexible and can quickly switch from predominantly burning carbs to predominantly burning fat. The presence of insulin slows fat metabolism and promotes carbohydrate metabolism. And once you've released insulin, depending how carb/fat adapted one is, it may take 1 to several hours for the insulin to drop back down to baseline. From the above summary of insulin effects after eating glucose, why would the body want to both burn fat while it's actively trying to synthesize it? And why would it want to make glycogen at the same time that your body wants to break it down? Yes, the physical activity you're doing will eventually overcome these opposing metabolisms and eventually will lead to both carb and fat burning. But the insulin effect by eating carbs is still a transient physiologic obstacle to ultimately burning primarily both fat and ketones.
But if performance is crucial to you, especially if you're used to carbs, then carbs is a must. Carbs gives you instant energy. When you "bonk", for a carb burner, that's when you've run out of carbs. When people get their "second wind" it's because their carb metabolism has switched to a fat/ketone metabolism.