When you begin a fat loss transformation you are likely to be feeling highly motivated so it can definitely be tempting to under eat and do excessive amounts of cardio to get a "head start". I understand all of those things and the reasons for doing it, however it will potentially slow down your fat loss and it will eventually have a negative impact on your overall body composition.
This is why...
Your metabolism is effected by the number of calories you consume each day, it adapts to this and will respond accordingly to this. Therefore, if you dramatically drop your calories for too long whilst you will lose weight, you will also be causing your metabolism to slow down quickly. As a result, it is likely that you will hit a plateau prematurely and then begin to struggle with further progression. The issue then is, there are less calories left in your diet to remove from here and there's also only so much cardio you can do per day.
The best way to lose fat is being progressive, gradually feeding allowing your body to utilise fat stores whilst feeding it correctly to protect your metabolic rate.
Loss of muscle mass
The other very common outcome of under eating on a diet is loss of muscle tissue. Muscle will be catabolised very quickly if you're not consuming enough calories and along with that, enough amino acids from high quality sources throughout the day.
This doesn't only impact on the image of your physique, it also slows your metabolism down further. Why? Simply because muscle tissue is metabolically active - it dictates how many calories your body requires, to an extent.
Another obvious negative will be an instant drop in performance as your body runs low on readily available fuel. The irony is because your performance drops you will struggle to stimulate muscle properly and burn off as much energy, as if you had fed yourself properly in the first place!! Every workout and cardio session will become harder to do, which in itself doesn't make sense.
All of these negatives can be avoided or at least managed very well, just by being very specific with your diet, ensuring you're NOT under eating and allowing gradual positive changes to take place.
Written by Neil Hill