The theory on this subject is that carbohydrates and fats should not be deliberately mixed in the same meal. The reasoning is as follows: carbohydrates raise insulin and increase the risk of storing calories from fat as stored fat.
In reality, it’s a pretty narrow view if you consider the meal itself, even ifit is in no way advisable to combine large amounts of carbohydrates and fats at the same time.
The dose makes the poison
There is absolutely no harm in consuming a moderate amount of each macronutrient at the same meal. There is very little scientific evidence to support the opposite and humans have always eaten meals that combine carbohydrates, fats and proteins.
Bodybuilders contradict this theory
Most motivated bodybuilders eat every 2-3 hours, which means the nutrients present from the first meal are still being assimilated when you attack the 2nd snack. Whether we like it or not, the meals combine, even if it is not in our intentions.
A recent study conducted by Golay.et al. Compared different types of food. People on a diet with meals containing both carbohydrates, fats and proteins lost more fat than others. We tend to focus on carb-induced insulin whereas the insulin response to carbs depends on saturated fat intake! Unsaturated fat tends to lower the carbohydrate insulin response or not affect it at all.
Think especially about caloric intake. If you have a reduced calorie intake, the insulin elevation from a meal that combines carbohydrates and fats can be a definite plus. On the other hand, if you eat a lot, you must be very careful.