I get from the book Optimal Nutrition that when he says that, he's talking overall. Not like food combining. He says for health it's best to decide what is going to be your energy source - fat or carb - and then stick with that. It's in the part where he talks about high-carb diets like the Okinawan or Kitavan that seem healthy - but he still thinks that the OD, with fat as the major energy source, is best.

Has to do with your body ramping up the machinery to deal with each. Worst of all is carbs over 35% and fats over 35% combined....