Diet or exercise: which matters more?

On the internet, from clients and in the media, I keep hearing the same thing: "diet is 80% of success, training is 20%!" Or the other way: "training is 70% and diet 30%!" Maybe one day I will live to see these myths die. They usually come from simplifying how the body works. Here is what training and food do in your body.

Short answer: You need both. Training gives the body the signal to build muscle. Food gives it the energy and nutrients to do it. If you made me pick one for muscle growth alone, I would pick training, but without decent food you will not get far. This is about building muscle. For fat loss, the calorie deficit decides whether you lose fat, and training helps you keep the muscle while you do it.

What training does

Training, if it is set up and done properly, tells the body it has to adapt to new conditions. It has to get ready for the next load so it handles it better, or without trouble.

Very simply, this is a signal for the body to invest energy into muscle protein synthesis: building muscle, plus the energy that process costs. Without the stimulus from training, the body has little reason to spend energy on building extra muscle.

Strength training has one more upside on top of giving the body a reason to make muscles bigger and stronger. It burns energy: on the muscle work during the session, and on the muscle protein synthesis afterwards. That process costs energy, though less than most people think, so do not "eat back" big numbers for it. So you need enough macro and micronutrients in your food to pay for it. How to keep that muscle while you diet: build muscle in a calorie deficit.

What food does

Your food affects hormones, which influence muscle protein synthesis, hunger, how you feel and your health. Whether you lose fat is still decided by energy balance.

Food also gives the body energy, macro and micronutrients, so the muscles have something to rebuild from and grow with. It works together with the stimulus from training.

Food helps you recover from training and from a stressful week.

Training raises how much energy you burn, so you can eat a bit more without gaining fat. If you eat more than you burn in total, the extra is still stored. Energy balance always applies.

So even if you train, your muscles will grow slowly or not at all if you do not eat enough, and enough protein in particular. Protein is the first place to start: how much protein you need.

So which is "more" important?

You need both. Only together do they let you move forward physically, and one without the other does not work.

If I had to be really strict about what matters "more" for muscle growth, I would say training. Train hard enough and your muscles will grow even without perfect food, just not optimally. Eat perfectly but skip training, and you will gain very little muscle.

But the same goes the other way: train hard on far too little food and you will not get far either.

Frequently asked questions

Will my muscles grow if I train but do not eat well?

If you train hard enough, your muscles will grow even without perfect food, just not optimally. But if you do not eat enough, and enough protein in particular, they will grow slowly or not at all.

Will my muscles grow from good food alone, without training?

Very little. Without training the body has almost no reason to invest energy into building muscle.

What exactly does food do for your body?

It affects hormones that influence muscle protein synthesis, hunger, how you feel and your health. It gives you energy, macro and micronutrients so the muscles have something to rebuild from, and it helps you recover from training and stress. Whether you lose fat is still decided by energy balance.

Note:

This article explains the basics in plain terms and does not cite individual studies.

Martin Barna

Online nutrition and fitness coach. Since 2013 I have coached 600+ clients. I work with evidence and sustainable habits.

Apply for coaching

This article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.