Good nutrition forms the base of our hierarchy of physical development.
There are a lot of myths around eating right and eating healthy so we’ll try to keep to some basic principles.
Eat whole foods:
Eat meat and vegetables, nuts and seeds, some fruit, a little starch and avoid refined sugar.
For the most part, if it has a long list of ingredients then it’s not a whole food.
If it has ingredients that sound like a chemical, that you can’t pronounce or don’t know what they are, maybe give it a miss.
Stick to the fresh produce aisle in the supermarket and you won’t go too far wrong.
It’s easy to cut too many calories out of your day in a quest to reach a leaner body. But if you’re not getting fitter (stronger, faster, more stamina) then you may not be eating enough. Whole foods can be lower calorie so more volume is needed. Be sure you eat enough protein and fat then top up with carbs. None of these is bad for you and you need a balance of all to be fit and healthy.
Eat enough to support exercise but not body fat.
You can go into as much data here as you’re comfortable with, the more you track the more effective your nutrition will be on your goals.
Generally, if you’re waistline is growing then you’re eating too much or not following point 1.
A macro and calorie tracker like @MyFitnessPal can help if you want to progress faster and a macro split of 30% protein/30% fat/40% carbohydrate is a good place to start.