I wouldn't call it a “Fat burn smoothie” per se, rather one that'll keep you fuller with a bit of an energy boost.
Blend a cup of skim milk, 1 banana, 2 teaspoons of coffee, 1 Splenda sachet, and 6 ice cube blocks.
Have a cup of green tea in between them smoothies and meals and that should get you started.
Of course, keep your diet clean and be consistent with your cardio and resistance training.
I don’t have to remind you that there are heaps of fantastic articles and forum topics at getbig.com and bodybuilding.com regarding nutrition and diets.
