First of all, this post was sparked by all the bodybuilding comments that you can't gain muscle without a calorie surplus and you can't lose fat without a calorie deficit. Their definition of a calorie surplus or deficit is the amount of calories consumed in a day versus the number of calories spent which is completely useless in determining whether or not muscle was built or fat was lost. Your body's internal systems aren't on that kind of cycle.
So today, I decided to forget everything I knew about how the body used energy from food and how it drew it from fat and I did some research. Here's my conclusion. Your body has several layers of stored energy. The first is blood sugar. This is readily consumable by muscles/the brain/organs/whatever. The next layer is glycogen stores in the liver. When blood sugar is too high, the liver will store the excess sugar in glycogen. And when blood sugar is too low, the liver will use it's glycogen stores to boost blood sugar. Your liver should have enough glycogen to last for a few hours after digestion is complete. Remember that digestion can take up to 3 hours. The next layer is muscle glycogen stores. I call this the next layer, because this is the next layer that gets used in the case of fasting. When there is no longer enough glycogen in the liver, it will turn to glycogen in muscles. Here's the bad part: this is the same energy store used to fuel the rebuilding of muscles. So here's where fat loss and muscle grow become contradictory goals. We haven't gotten to fat loss yet and we're already stealing energy from our muscle regrow. Strength trainers have know of this negative effect for decades, but unfortunately, most of these published trainers don't back up this knowledge with the science behind it. Once the muscle's glycogen stores are depleted which can take several more hours, the body begins to seriously break down fat for energy. This is explains the success of intermittent fasting diets that dictate eating for 8 hours after a workout then fasting for the next 16 hours. Muscle glycogen is easily replenished once a person starts eating normally again so for 8 hours plus the time it takes for the liver's glycogen store to run out, their muscles don't have to compete for glycogen. Then there is short period of time when the muscles' glycogen stores run out and the body pulls directly from fat. This will last for a few hours before the 16 hour fast is up and muscles have another good period for growth. That is how intermittent fasting accomplishes fat loss and muscle gain "at the same time". I put "at the same time" in quotes, because you can see that intermittent fasting doesn't actually accomplish both at the same time. It focuses on one at a time, but switches focus repeatedly so that over the course of a week or month, it would look like both happened in the same time period. If you were to have a consistent calorie deficit this whole period, your muscles would spent most of their time competing for their own glycogen stores.
In conclusion, your muscles won't grow to their fullest potential when you are restricting your calories everyday. A calorie surplus everyday is great for muscle growth though. If you want both effects of fat lose and muscle growth at the same time, you need to create a large calories deficit very quickly (fasting) and then eat a surplus for 8 hours after working out.