The last year or so, I've been more active on twitter. What a brutal space. I find it a place where people have no filters and can be downright rude. One thing the hardcore bro-science followers are very sure about is that intermittent fasting is the same as cutting calories. It is not the same. There is something fundamental that happens with a calorie restriction that does not occur with IF (I will refer to intermittent fasting as IF)
I have seen in myself and many friends over the years, we go on a diet, restricting calories, exercising hard, losing weight but in a year we've just picked up the weight again and a little bit more. Slowly our weight creeps up, gradually increasing our body set weight. When you restrict calories on a diet, your basal metabolic rate slows down but with IF that doesn't happen.
Why does calorie restriction decrease metabolic rate but IF not?
When you restrict your calories, the body doesn't understand what you are doing. The body doesn't measure calories; it responds to hormones and will do what it wants according to the hormonal signals. Intermittent fasting is not about the calories you eat; it is all about the time you are NOT eating. It is not the same to eat 1200 Cal once a day or to spread those 1200Cal over the day.
When you eat equal portions of food throughout the day, there is a different hormonal response to eating it all in one sitting. Every time you eat, you stimulate insulin and tell the body to store food. Because that is what insulin does, that is insulin's job. You are also using this incoming food as fuel for your body during the day. You keep insulin constantly stimulated, and when insulin is present, the body can't switch fuel sources. It can only use the fuel that is coming in via your mouth.
When you IF, you can drop insulin low enough to be able to switch fuel sources and you can start to burn your body fat as fuel. There is no reason for your body to slow down your metabolic rate when you switch fuel sources.
If you eat all the time, insulin is high; it blocks lipolysis (breaking up of fat). There is no access to your fat stores because, in the presence of insulin, you can't switch fuel sources. Metabolic rate slows down because there is only 1200Cal coming in. The body needs energy for many processes; your heart has to beat; the food needs to be digested. Metabolic rate slows down to have enough fuel to keep you alive. When you fast, insulin drops low, the body switches fuel sources and see there is all this body fat to burn as fuel. There is no need to slow down the metabolic rate to do what it needs to do; there is enough fuel available.
We all have been there, dropped our calorie intake, lost some weight, but then we get hungry. We revert to eating more, but because our bodies slowed down our metabolic rate while we were cutting the calories, we quickly pick the weight up again and a little bit extra. The vicious cycle of our weight yo-yoing. Instead, work your way up to only eat during 8 hours of the day. Make a 16 hour fast part of your typical day. You get an insulin drop every day of your life, you burn some body fat every day of your life, and you get to keep a fast metabolic rate.
Fast and feast.