I'm glad you mentioned diet, because lots of times people just focus on weight training to add muscle, and they skip changing their eating habits. It's really difficult to both add muscle and decrease body fat at the same time, because adding muscle requires consuming more calories than you burn, while losing body fat requires eating fewer calories than you burn. For that reason, I like to focus on just one variable at a time. Let's start with buiding muscle mass:

There are three crucial things to consider in your diet:
First, make sure that you're getting adequate calories. Your body expends energy burning muscle, so you need to eat 200-300 additional calories per day. If you're losing weight, you're not going to be able to add much muscle. We need to gain muscle slowly, at about the rate of 1/4-1/2 pound per week. If you're gaining faster than that, you're eating too much.

Second, make sure your protein intake is optimum. Research has shown that eating 1 gram of protein per pound of body weight works well. That means if you weigh 150 pounds, consume 150 grams of protein per day. Protein is in almost every food except fruit and fat, so it's really fairly easy to make sure you're getting enough. Keep track of your protein intake for a few days to see if you need to tweak anything.

Finally, the timing of your meals and snacks is crucial. Eat 30-60 minutes before a workout so that you have energy on board to put into the workout, and also so that your body has the necessary nutrients to start building protein. A combination of some carbohydrate and protein works well, for example a slice of toast with a smear of peanut butter, or 1/2-1 cup of yogurt and fruit, or even 1/2 sandwich. Then eat again within 30 minutes after your workout, because that's the optimum time for your body to put those nutrients to work building muscle. Whey protein works really well, and research has shown that drinking 8-12 ounces of chocolate milk is just as effective as using a commercial protein drink. You could also simply schedule a meal for that time, and include protein (such as chicken or fish), a glass of milk, and fruit or vegetables.

I hope this helps you get started.

Lynn Grieger, RD, CDE, cPT
Health, food and fitness coach
Manchester, VT
www.LynnGrieger.com