I am a 270 pound male that would like to lose weight and body fat. I am doing cardio every day twice a day for 45 minutes each session. I am also using weight lifting machines three times a week. Am I doing too much cardio?
If you are doing your cardio in such a way to be burning fat, you're probably not giving your body enough time to recover from each session. I don't know that this will prevent fat loss, but it's certainly not good for your physical fitness.
However, it seems like you may be putting too much focus on the cardio and not enough on the more important component of health & fitness with regards to fat loss: your diet. If you cut out your second 45 minute cardio session each day and dedicate your extra 45 minutes to educating yourself on proper nutrition, you'll be much better off in the long run.
I think that what im about to say was already said before in one of the other answers, but i think there is room for clarification. When you asked if you are doing to much you were basically asking if you are over training, which can lead to hindered weight loss, so then to answer your question we simply need to know if you are over training. In order to determine if you are doing to much you simply need to listen to your body. In some cases you may feel theat your performance is slowing down as in you may not be able to keep up your usual tempo, or with the weightlifting you may find it hard to lift the same 25 pounds you lifted last time. This can happen even if the source of the over training is from the cardio and not the strength training. Another symptom can be your mood. You may find yourself being more irritable. My best suggestion for you is to Google symptoms of over training because you will find several articles that will list almost 10 symptoms that your body is telling you that it's tired.
Hope this was helpful.
How much weight are you losing? How sore are you getting? If you are losing weight, and not too sore, you're not overtraining, and "Total time" is what's important for your goal. (2 x 45 minutes is the same as 90 minutes) If you're getting fatigued, you could be overtraining for your fitness level, and cutting back to an hour total per day spanning all activities should be enough to support weight loss.