I would like to build my stomach muscles, but can't afford to have a specified diet (I am not working yet). I eat home-prepared meals and no fastfoods etc.. often salads with chicken meat. I have been regularly exercising before with some good effects. They say, that 70% of building muscles is diet, but does that mean, that we need diet prepared by dieticians for making even small progress?
They say, that 70% of building muscles is diet, but does that mean?
It means you cannot out-exercise a poor diet.
Read through this question and answer to help you design a balanced diet.
Your diet sounds great. If your body fat is good then you're probably eating fine. Chicken and salad is great.
You're probably talking about protein requirements. Top end stength training usually asks for 1gram of protein for every pound of bodyweight, every day.
It's not like coming in a little short sometimes will be horrible. Chances are it won't make a difference at all.
But yeah, if your body is repairing damage and growing tissue in a big way you need to eat more protein. Whey protein is pretty cheap and effective, check prices.