Many aspiring bodybuilders and strength enthusiasts want to know what’s the most important factor for making progress in the gym: training, nutrition, genetics, or drugs. The question can’t be adequately answered in one sentence, so allow me a few paragraphs…
If your primary goal is to get healthy and/or lose bodyfat, then nutrition is the most important factor – no question. Losing weight is a matter of eating fewer calories than you burn, and the most effective way to do that is by restricting calories and eating healthy foods. Exercise certainly has health benefits and can assist your quest to lose fat, but it’s secondary to diet. As they say, abs are made in the kitchen. So are clogged arteries.
If your primary goal is to build strength and/or muscle, then the question is a bit more complicated. For a beginner or intermediate lifter, training is the most important factor. Training is the stimulus that causes muscle growth. Without it, you will never “look like you work out”. Most people are capable of doubling their untrained level of strength and adding 20-30 pounds of muscle to their frame (half of that is more realistic for a female) after several years of hard and consistent training, which amounts to a fairly dramatic transformation. A specialized nutrition plan can assist the muscle building process, but it’s secondary to the training stimulus.
Advanced lifters will eventually plateau in their training, where additional gains become very difficult. At that stage, drugs can become a bigger factor than training. While I would never advise anyone to take anabolic steroids due to the health risks, the truth is they can increase strength by upwards of 20% and add a corresponding amount of muscle in a short period of time. For example, a natural lifter might build their bench press from 150 pounds to 300 pounds over several years, while drugs would get them up to 360. Based on those numbers, it’s clear that training is the bigger factor, but drugs can take an advanced lifter to an otherwise unattainable level.
Genetics make a big difference in how your physique will ultimately look, particularly with regards to muscle shape and bone structure. However, most of us have roughly similar abilities to gain muscle and lose fat, meaning that genetics rank low as a factor for making progress in the gym. There are certainly outliers among us who grow muscles just by looking at weights or who have abs despite eating like a horse, but those are few and far between. 90% of us are in the same boat and will find that training is the biggest factor for gaining muscle and strength, and nutrition is the biggest factor for getting lean.
Hope that answers the question!