He's right to point out the difference. Human metabolic pathways for processing carbs and fats are capable of functioning independently and lab animals used as

He's right to point out the difference. Human metabolic pathways for processing carbs and fats are capable of functioning independently and lab animals used as human analogs can live happy healthy lives exercising either. But they seem to interfere with each other when both are operating simultaneously, even in the lab animals, and that results in obesity and decreased quality of life outcomes.