A moderate amount of cardio can be an invaluable tool for burning fat, and it is absolutely requisite for many of us with less than spectacularly functioning metabolisms. What ends up happening in all too many fat loss/contest prep programs, is that right out of the gate the person starts off with cardio, then steadily increasing cardio to the point where the person is doing an hour or two or even more per day. The problem with this protocol is that is effect of sending your metabolism into a form of stagnation as it fights to preserve all of its energy and nutrients, and losing fat becomes even harder than had you been doing no cardio at all.
The main variable is whether or not this cardio is nutritionally supported. Meaning, does your body have the fuel to burn on the cardio. If it does, you are all good, but if not, it creates a swift and significant downregulation of the metabolism. Which results in a sharp slowing of fat burning, using muscle tissue as fuel, and increasing cortisol production (as a stress response to effectually a starvation). Ultimately, any cardio that is not nutritionally supported WILL result in slowdown in thyroid production.
So how can you combat this and minimize the damage and keep the fat coming off?
Do your cardio in spurts – Nothing is more damaging than allowing your boy to accurately predict when it will be in a severe calorie deficit. It becomes so good at making thyroid adjustments that it’s like you are not doing cardio at all. Instead, do cardio at different times, different days of the week, some high intensity, some low intensity, and sometimes, stop altogether. This unpredictability will leave your body confused and unable to shut your metabolism down quite as well.
Start off at none – Start your fat loss program with no cardio. See how much fat you can lose without doing any. You may be surprised to find how well you do with just weights and diet.
Increase weight training volume – Weight training differs from cardio significantly in that the heart rate and energy expenditure is on a roller coaster. You do an intense set and the heart rate skyrockets, followed by a couple minutes to rest and recover. This is actually much less impactful to the thyroid down-regulation, yet still burns a significant amount of calories
Back off the fat burners and pre-workouts – The fat-loss diet is enough stress to the thyroid already, and taking in regular and high amounts of stimulants serves to exacerbate the problem. The body must now down regulate further for the constant flow of caffeine etc that is flowing into the system. Instead, use these sparingly and inconsistently. There is no real evidence that fat burners work anyway, but they and pre-workouts are great for supporting energy when you are depleted. Take them too often though, and you may as well not be taking them at all.
Overall, be smart and listen to what your body is doing. The first few days of cardio generally results in some great weight loss, but in most instances it stops after a couple weeks. At this point it’s best to change your strategy and take a break from the mass cardio.