I left medical school with an understanding of metabolism that can be explained by two analogies, each of which I now think are false. In the first one our body is like a steam engine and when we eat it is like shoveling coal into the furnace. Whatever we eat, tacos, burgers, just throw it in and it will get burned up.
The second analogy is that our energy stores are like a bank. You deposit $50 in the bank and it just sits there until we make a withdrawal. That is like eating 50 extra calories and then it sits there till you take a walk and you burn it back off.
Neither analogy describes what is happening in the body. It turns out we have two separate but complementary energy systems.
Carbohydrate Based System.
The carbohydrate system is where the quick acting and easy to burn energy is. This is also where all food energy temporarily exists after we eat and before the excess is stored away. You can think of this as the short term energy system.
Fat Based System.
Think of body fat as long-term energy storage. Hard to get to but very high capacity. Your body had to spend some energy to make the fat tissue out of excess food and it will have to spend a bit to get the energy back.
The key is to understand that the body will always do the most efficient thing it can. It will never waste energy unnecessarily. This is why it is so hard to lose weight. You have to clear out the short term system first. Insulin is the hormone the body uses to make sure this happens.
Insulin sits in the middle of these two systems. You can think of it like a gatekeeper of sorts. Food is coming in on the short term side of the system. This is also where energy is going out through exercise and our basal metabolic activity.
In a typical situation we are eating 2,000 calories per day and expending about 2,000 calories per day. We keep about 2,000 calories of stored sugar energy in the form of glycogen on hand which we can think of as basically a one day energy slush fund.
Insulin has two primary roles. When we take in more energy that we need insulin’s job is to take that extra energy and store it away. This is how insulin lowers blood sugar. Primarily by jamming it into liver, muscle and adipose cells.
Insulin’s other function is to block fat cells from being accessed. Think of insulin as a protector of the fat. To the body the fat is a precious resource. That is what is going to keep you alive when the food runs out. As long as food is coming in the insulin is there to make sure the fat is not touched.
This is the primary reason low carbohydrate diets can be effective. Do you get less calories, yes. But you are also reducing insulin which lowers the barrier to the body fat.
Now It Gets A Little Tricky
Typical dietary practices involve reducing calories. The idea is that we have 50,000 extra body fat calories that we want to burn off. So this should be simple. We just start eating 1,500 calories per day and we should be -500 calories as we will continue to burn 2,000 calories per day. Since a pound of body fat is 3,600 calories we should basically be losing a pound a week and we should be able to set the date on the calendar when we reach our goal.
Unfortunately it just doesn’t work that way as many know to be true from repeated trial and error. The large majority of people experience a similar phenomenon. You go on a new diet. Initially things are going well. You lose the first 5 or 10 pounds. Then things level off. You seem to plateau. In the long term you don’t really want to eat 1,500 calories per day. You start eating 1650 calories per day and before you know it the weight is coming back on, sometimes even more than before. But you are eating less than when you started. It’s a total mind job! What is going on?
The difficulty is there is a radical difference between eating less all the time (The standard 3 meals per day or 6 small meals throughout the day) and eating nothing some of the time.
When you are eating constantly in small amounts throughout the day you are always stimulating insulin. And since insulin blocks fat from being burned you are undermining your body’s ability to access the body-fat for energy. The body wants to either be burning food for energy or body-fat. It can’t really do both at the same time, at least not in the long term.
This is Where the Trouble Really Starts
When you go on a diet and calorie restrict, but spread those calories out through the day, you do not give any space to the body to activate the natural fat burning pathways. You stay in food burning mode. But because you are calorie restricted you are also not getting enough food energy to run your metabolic processes.
We think things are good because we are running a deficit and will burn fat. But what the body sees is an energy crisis.
We are not getting enough food in to meet our needs but insulin is blocking access to the fat. What is the body supposed to do? It does the only thing it can do. It slows down our metabolism to match the amount of food energy coming in. We have not appreciated the dynamic nature of our metabolism. It can adapt to a variety of situations in ordered to give us the best chance of survival.
The idea of dialing down the metabolism is like this. We have a bit of food but not enough. The body slows down and tries to string things along as long as possible on this food source. It plans to run this state as long as it can until the food completely runs out. Then it will flip over to body fat. This is how it would preserve the fat as long as possible and therefore keep you alive as long as possible.
It really is a beautiful system. It is just not a system that is designed to operate in the modern world of infinite food. We really can be thankful we are so fortunate. We just need to learn how to operate these systems.
Here is the Good News
The way out of this cycle of dieting and negative metabolic adaptation is a lifestyle that incorporates routine periods of fasting. When you create a food free interval in each day that is larger than 12 hours you allow the body to head into Pathway B. In Pathway B there is no insulin and you have direct access to the fat stores. This is how the body wants to burn fat. And in Pathway B there is no need for negative adaptation. In fact the opposite happens. The body up regulates the metabolism.
Here is why this happens. Imagine you are a primordial human and it is day one that the food has run out. What is the top priority. Get more food! Your body knows this is a critical time.
In ordered for you to get more food you are going to have to work. In ordered to work you need energy. Your body doesn’t hold back. Where as it was throttling things back to string things along on the limited food supply, in the fasted state the breaks are taken off. Full power. Hunt something down.
By understanding these hardwired pathways in our metabolism we can organize our intake to work in line with this natural rhythm. A period of eating balanced out with a period of fasting. I look at it almost like a dance. A natural flow that can lead to wellness. The body has goals. We have goals. We work together with the body to accomplish something great.