Legendary bodybuilding trainer Vince, "The Iron Guru" Gironda was famous for saying, "Bodybuilding is 80% nutrition!" But is this really true or is it just another fitness and bodybuilding myth passed down like gospel without ever being questioned? Which is really more important, nutrition or training? This IS an interesting question and I believe there is a definite answer:
The first thing I would say is that you cannot separate nutrition and training. The two work together synergistically. Regardless of your goals - gaining muscle, losing fat, athletic conditioning, whatever -you will get less than-optimal or even non-existent results without paying attention paid to both.
In fact, I like to look at gaining muscle or losing fat in three parts - weight training, cardio training and nutrition - with each part like a leg of a three legged stool. pull ANY one of the legs off the stool, and guess what happens?
In reality, it's impossible to put a specific percentage on which is more important - how could we possibly know such a number to the digit?
Nutrition and training are both important, but at certain stages of your training progress, I do believe placing more attention on one component over the other can create larger improvements. Let me explain:
If you're a beginner and you don't posses nutritional knowledge, then mastering nutrition is far more important than training and should become your number one priority. I say this because improving a poor diet can create rapid, quantum leaps in fat loss and muscle building progress.
For example, if you've been skipping meals and only eating 2 times per day, jumping your meal frequency up to 5 or 6 smaller meals a day will transform your physique very rapidly.
If you're still eating lots of processed fats and refined sugars, cutting them out and replacing them with good fats like the omega threes found in fish and unrefined foods like fruits, vegetables and whole grains will make an enormous and noticeable difference in your physique very quickly.
If your diet is low in protein, simply adding a complete protein food like chicken breast, fish or egg whites at each meal will muscle you up fast.
No matter how hard you train or what type of training routine you're on, it's all in vain if you don't provide yourself with the right nutritional support.
In beginners (or in advanced trainees who are still eating poorly), these changes in diet are more likely to result in great improvements than a change in training.
The muscular and nervous systems of a beginner are unaccustomed to exercise. Therefore, just about any training program can cause muscle growth and strength development to occur because it's all a "shock" to the untrained body.
You can almost always find ways to tweak your nutrition to higher and higher levels, but once you've mastered all the nutritional basics, then further improvements in your diet don't have as great of an impact as those initial important changes...
Eating more than six meals will have minimal effect. Eating more protein ad infinitum won't help. Once you're eating low fat, going to zero fat won't help more - it will probably hurt. If you're eating a wide variety of foods and taking a good multi vitamin/mineral, then more supplements probably wont help much either. If you're already eating natural complex carbs and lean proteins every three hours, there's not too much more you can do other than continue to be consistent day after day...
At this point, as an intermediate or advanced trainee who has the nutrition in place, changes in your training become much more important, relatively speaking. Your training must become downright scientific.
Except for the changes that need to be made between an "off season" muscle growth diet and a "precontest" cutting diet, the diet won't and can't change much - it will remain fairly constant.
But you can continue to pump up the intensity of your training and improve the efficiency of your workouts almost without limit. In fact, the more advanced you become, the more crucial training progression and variation becomes because the well-trained body adapts so quickly.
According to powerlifter Dave Tate, an advanced lifter may adapt to a routine within 1-2 weeks. That's why elite lifters rotate exercises constantly and use as many as 300 different variations on exercises.
Strength coach Ian King says that unless you're a beginner, you'll adapt to any training routine within 3-4 weeks. Coach Charles Poliquin says that you'll adapt within 5-6 workouts.
So, to answer the question, while nutrition is ALWAYS critically important, it's more important to emphasize for the beginner (or the person whose diet is still a "mess"), while training is more important for the advanced person... (in my opinion).
It's not that nutrition ever ceases to be important, the point is, further improvements in nutrition won't have as much impact once you already have all the fundamentals in place.
Once you've mastered nutrition, then it's all about keeping that nutrition consistent and progressively increasing the efficiency and intensity of your workouts, and mastering the art of planned workout variation, which is also known as "periodization."
The bottom line: There's a saying among strength coaches and personal trainers...
"You can't out-train a lousy diet!"