I tried the South Beach diet and lasted only a couple of weeks. I could tell a big difference in my energy levels, especially on bike rides over 30 minutes. It may work for inactive folks but you need carbs for energy to workout. I agree with others about having a balanced diet. The best advocate of balance with a diet and excercise is Oprah's trainer Bob Greene. He has the Best Life diet. Another diet plan that was originally developed for body building is Lean Bodies. I have used both Best Life and Lean Bodies and they give you enough energy to workout and lose weight.

Another easy way to loose weight is cut out the soda. Dr Oz has a 28 day soda challenge that can have a big impact if you are a soda drinker.