Too much of a good thing is bad. In health and fitness, trying to do too much to achieve your goals faster often has the opposite effect. Not only may it slow you down it may just bring your progress to a screeching halt and bring you down in a blaze of burnout, starving failure.
It's something I encounter often in people training for a deadline: be it a fitness competition, a wedding or a summer vacation. Over-training and under-eating for an extended period is the best way to do it all wrong.
Training, especially if it's intense, stresses the body. Resistance training breaks muscles, cardio demands the heart and lungs to work overtime. These things when balanced with adequate rest are a good thing. When not, you're going the wrong way on a one-way street. Remember, the body develops when at rest -- not when you're working out.
Working out too much will elevate your stress hormone levels. Too much cortisol has the disastrous effect of making you catabolic (where your body eats away at your hard-earned muscles), causes you to store fat and messes with your sleep.
If you love doing HIIT or other intense workouts that leave you used and abused, don't be afraid to mix them up and alternate them with lower-intensity workouts. Not every workout should leave you absolutely depleted.
And damn it, take a day off. You'll find you'll come back stronger and better.
Obviously, how you fuel your body has a great affect on your body composition. If you are trying to loose weight, you may believe the longer you can stick to an uninterrupted low-calorie, and low-carb diet, the better. Your scale readings can only go down, right? Wrong.
Long-term, low-calorie diets slow down metabolisms. Your body will realize that it only has access to so many calories and recalibrate it's energy consumption to meet it. Two of the many ways it does this is by cannibalizing muscle and slowing down cell renewal. Both things will have you looking old and anything but vibrant.
Also, dieting can mess with your leptin levels. Leptin, the saity hormone, sends the signal to your body that it is full and controls your metabolic rate. The longer your body is in a calorie defiecit the lower you leptin levels and metabolic rate become. Both factors will make it extremely difficult to lose more fat.
To ensure your leptin levels are at a healthy level, At least once a week enjoy in a "cheat meal" that contains roughly twice or more the amount of carbs and calories than your regular meals. Bodybuilders and fitness models call this a re-feed day. I do this - even when I'm preparing for a competition or shoot.
If you fear a cheat meal will derail you, remember, one "bad" meal will do little to reverse all the "good" meals you take. Just like the one good meal will not undo all the bad ones.