A guy I work with is really into this. I have to tell you, I've selectively modified my diet based on monitoring my body's reaction to the food I eat over the past two years, independent of this diet, and my results have been very similar to what's listed for the type A diet. When I go far from it (eat too much meat, refined sugars, or dairy), I suffer from lethargy, [more severe] a.d.d., "cloudy" thinking, and general discomfort. Before I started modifying my diet I was suffering from chronic sinusitis, abdominal-discomfort/poor-digestion, high blood pressure, and high cholesterol. All of my numbers are back to normal, and I'm convinced that if I ever made a final push to give up all dairy (what can I say, I love the cheese), I think my sinuses would clear up 100%.

Fad or not, I dunno...I will say that it's important to listen to your own body and make conscientious choices for your own health. It's a one-time-use body, best to take care of it as well as you can while you have it.