Dangers of the high volume cardio
I don’t like cardio for several reasons, but reason #1 - cortisol level. Every physical load leads to an increase in cortisol and testosterone. The question is what will you receive besides such an increase + high physical load.
Stop being delusional: strength training also increases the cortisol level, but they lead to maintaining the needed muscle mass. Moreover, episodic raise of cortisol is beneficial as it speeds up the acidation of fats (one of the main cortisol functions). But the chronic increase of cortisol causes the accumulation of fat, especially abdominal one, which means that during the weight loss process, the belly will remain the same.
If to look through the workout schedule with strength training, almost no one can do 5-6 workouts per week. Usually, there are 3 strength workouts, which is good - rare raises of cortisol level are healthy.
But in case of adding 3-4 cardio workouts to the existing strength load (a common situation), we’ll receive the chronic increase of cortisol.
One of the crucial factors of adequate renewal after a workout is testosterone-to-cortisol level. According to the survey «The effects of four weeks aerobic training on saliva cortisol and testosterone in young healthy persons», 4 weeks of mild-intense cardio, the testosterone-to-cortisol level significantly lowered. It means that physical load was too high for the survey volunteers.
Conclusion #1: adding cardio does not boost positive changes related to the strength training (muscle mass gaining and maintaining), but leads to the increase of cortisol level and, thus, causes A) water retaining; B) slows down the renewal time. It’s for sure that calorie deficit caused by cardio helps to lose the weight faster, but this juice doesn’t worth the squeeze.
Conclusion #2: Cardio increases cortisol, which in turn increases the ghrelin level. And hunger as a result. You can study it in details here: «Lifestyle factors and ghrelin: critical review and implications for weight loss maintenance».