Just make sure after you strength training session have a high GI food so you can flush back the nutrients your body has used up in the gym. This needs to be done in a 1 hour window for best results. The reason why you should be doing this is because your body needs to repair itself after gym an can't do this without food. Make sure you have protein, carbs and fat in your diet as these are all needed to grow muscle.
Having a protein shake straight after gym is a good source to flush back all the nutrients quick that your muscles need to build and recover.
Depending on what you do during the day and how hard you train depends how much food you need. Make sure you always have eaten something 2 hours before you do something such as work or gym. This is so your body has the energy it needs without breaking down other sources of energy such as muscle.
You don't need huge amounts of food to build muscle, you just need an average diet like the average person eats. Its how you eat the food and when. So try to eat 5 - 6 small meals a day and always flush back the nutrients your muscles need after exercise. If you work is hard work then you would probably eat a bit more because your work will be burning up all that food you ate and you will need more.
Also it might not be your diet it could be from over-training! This usually occurs when your muscles are still sore and you train them, feel fatigue, loss of motivation, loss of muscle mass, sore joints and bones. Make sure your not training everyday unless you have a split program to avoid training the same muscle all the time. You need to let your muscles rest to grow, muscle growth occurs outside the gym not in the gym. Over-training will send you backwards so be careful.
