Body fat is not broken down by any kind of calorie equation. The breakdown, lipolysis, as it's known, is the result of six hormones elevated in the absence of elevated blood sugar. This is an incontestable biological fact. It is not my opinion. There exists no debate. This is not an article to examine one type of diet or program versus another. This is just the description of lipolysis. If you want to understand it, read on.
Lipolysis is set in motion by any one of or the variant combinations of six hormones: cortisol, adrenaline, noradrenaline, growth hormone, testosterone and even ghrelin. Consider each.
Cortisol, adrenaline and noradrenaline usually come along the same stress cascade. If you workout, take caffeine, or diet in such a way that drops blood sugar, your body will respond to those stressors with these hormones. You will unlock stored fat and use it up. This is why different nutritional and dietary regimens can work. As long as they elevate some stress response in the absence of insulin, they will help the person following that program to retrieve and lose stored fat. As such, different people will swear by slim fast shakes, others by weight watchers, some by vegan lifestyle, some by Paleo, some by sprints, some by endurance training, some by Crossfit and others by long walks. Guess what. They're all gimmicks. The principles don't, can't and won't change. So it's no surprise that different people with different lifestyles will find different programs more or less effective. Simply stimulate cortisol, adrenaline and noradrenaline in the absence of insulin and you burn fat.
Growth hormone can be a little trickier. It burns fat. It fights aging. But it comes out in bursts and works on a tipping balance with insulin. Whereas stress hormones can be high while insulin is high (though this is bad), growth hormone cannot be high while insulin is high. The two largest bursts of growth hormone should be in the middle of your sleep and about an hour after you wake up. If insulin remains elevated, however, you cannot produce any meaningful amount of growth hormone. This is why people who eat a lot of carbohydrates, people who don't sleep well, night eaters and breakfast eaters all have a much harder time getting a six pack than their counterparts. This is also why most type II diabetics who start using insulin gain fat initially. Insulin can grow fat and does stop growth hormone. However, if you strike the balance right, a big blast of insulin clears the blood of glucose AND insulin. With the blood cleared of both glucose and insulin, ideal things can happen: you'll raise stress hormones, and growth hormone will be boosted. As such, in rare cases, administered just right, using insulin can make someone much leaner and more muscular. This may sound confusing, since at different times different hormones are good or bad. Thus different foods are good or bad depending on timing as well. Many elite bodybuilders use exogenous insulin and growth hormone because they are such powerful substances. But the dosing and timing is absolutely everything. Get either one wrong, and the result can be fatal. Also, if blood sugar drops too substantially (and you don't fall asleep permanently), the stress hormone release can be so high as to force your liver to dump more sugar in the bloodstream and now you're back at square one. It's a delicate balance.
Testosterone is the king of fat burners. Many elite athletes use testosterone or a derivative steroid because it's so adept at increasing lean mass and decreasing fat mass. It is fairly gender and age dependent. This is why, on average, a 17 year old male is usually far more muscular, lean and powerful than a 65 year old female. The young male's and the older female's measurements of stress hormones are only a bit different. Their growth hormone levels are some different. But their testosterone levels are so incomparable that the concentrations are measured on separate scales. Results are obvious. There are a lot of ways to dramatically improve testosterone levels: sleep more, and sleep better; ensure that you get sufficient mineral intake (supplementing magnesium and zinc before bed and upon waking if need be); lift heavy weights and/or do sprints of some sort; avoid long bouts of stress (including endurance training and long cardio routines); eat saturated fats. The cells which make testosterone in your body CANNOT make any sex hormones without LDL, just an FYI. Look it up. This means that if you're taking a statin or avoiding dietary fat you could be making fat loss a lot harder than it needs to be.
Ghrelin is the easiest to raise. It is the hunger hormone. So... get hungry. When your stomach is growling and hunger pangs are stabbing you in the belly right before you cave to the pressure and eat the storehouse of food, ghrelin is hitting its peak concentrations in your body. Unfortunately, this is a real willpower battle, so not one I recommend. But whenever you feel the hunger, you are just annihilating stored bodyfat. Controlled fasting and ghrelin have a lot of benefits actually, like curing all digestive disorders, resting your organs, accelerating detoxification and increasing your life expectancy by, oh, 50 YEARS! During elevated levels of ghrelin your body is hitting a freak out point where it is going to bend your mind and force you to eat, thus regrowing the bodyfat you've been starting to use up. Don't give up or give in. When you overcome that intense hunger, know that you've gotten a little leaner. Over time, as you practice this on a regular basis, you'll soon find that you haven't got any fat on your stomach. Be careful. Like all hormones, this should not be high or low all the time. But you should be able to get hungry and forego eating at least once every day - preferably in the morning.
Even though we don't want to raise insulin at night, you also don't want to raise ghrelin prior to bed or you won't sleep well. Larger meals of greens and fats or small servings of high glycemic index carbs ( which will be cleared from the blood quickly) are better for the end of the day, so as to keep ghrelin and insulin low, growth hormone and testosterone high and enable stress hormones to spike right around when you are supposed to wake up.
Oddly, completely different diets and exercise programs get some of the same things right and some of the same things wrong. The fundamentals don't change. No matter what, raise these six hormones as best you can; and minimize the duration you're exposed to insulin. But be careful. These are hormones. So timing is everything. If you eat and raise insulin before raising stress hormones (I.e. - food before workout) the result is proteolysis (lean mass breakdown) not lipolysis. Many people make this mistake, lose "weight" but don't get leaner. They keep getting fatter and weaker (skinny fats) despite a dedicated workout regimen and clean nutrition. They're working the timing equation the wrong way. Similarly, people who feel stressed and anxious all the time AND snack just keep growing a bigger and bigger gut. If they simply fasted through the bouts of stress, then ate like a pig after sprints or heavy lifting, they'd look more like a fitness model.