I would like some input on the following question:
How many damn threads are you going to start tonite, Gabe! Just kidding, again, bro;-)
The physiological mechanisms behind such are a little detailed. If you prefer, I guess I could go into them in detail. The logic behind the separation is that insulin inhibits lipolysis and stimulates lipogenesis by inhibiting hormone sensitive lipase and stimulating lipoprotein lipase, respectively. That’s a very concise answer. The bottom line is that having significant carbs and fats in the blood at the same time will lead to a highly lipogenic (fat-storing) hormonal milieu.
The quantity depends on the type of carbohydrate. If you’re consuming fibrous veggies, then there really is not a strict limit in place. However, 10g of active carbs has been the number thrown around mostly in the past. That said, JB and others have mentioned that added legumes (i.e. mixed beans) and/or nuts to these P/F meals have negligible effects on blood glucose and insulin levels.