Training fasted almost always leads to less energy in the gym. Since you are trying to lose weight, make sure that you are tracking your calorie intake daily to ensure that you stay in a calorie deficit.
With the deficit in place, you can eat some fast digesting carbs and protein to give you energy. The old school of thought is that sugar causes you to gain fat, but recent studies have shown that this is not the case as long as you are in a calorie deficit (http://www.bodybuilding.com/content/the-science-of-sugar-and-fat-loss.html).
I'd recommend a combination of fast digesting carbs and a fast digesting protein. For the protein, no question, a whey protein shake will do the trick. For the carbs, you have a choice: fruits, coffee with sugar, Gatorade, your favorite sugary cereal with non-fat milk, etc. You have a lot of choices that can digest rapidly and provide you with more energy in the gym.
Also, you can look into pre workout supplements if you aren't interested in the sugary route. They definitely improve energy levels.