Cordain addressed this topic in an article. He hinted that there may be something to it. Some people, like the Gracies', follow a food combining diet. They only combine certain food groups. The wrong combination can turn otherwise good foods into a toxic mess. At least according to their folklore. I am looking forward to getting their diet book when it is released. I am hoping they will address some of the chemistry of food combinations beyond macronutrients percentages.

My understanding had to do with stomach ph reaction to do with meat and with digesting carbs compete and therefore are a bad mix

enter the Standard American Diet, SAD Hamburger.

While eating a more dense carbohydrate with protein, or fat will blunt the insulin response, by delaying gastric emptying. This can also be accomplished with lime juice, or vinegar I believe. The acid also serve to delay the gastric emptying. In practical terms for fat loss I would worry less about what I combined with fruit or more dense carbs, and focus instead on both the frequency of their intake and if possible pair these foods with glycogen depleting activities (ie post workout). For most effective weight-loss and dealing with those who are severely insulin resistance the complete elimination of fruits from the diet is a common recommendation.

For me, I find that as long as I keep my carb calories under a certain percent of my total calories, I do fine. But if I were to eat fruit alone the resulting spike and drop would send me craving more carbs!!

I never eat fruit alone. With a meal or snack, always with protein and fat....mainly fat.