I read lots of posts in The Fort about weight loss, different diets, and what works and does not work for people, as well as lots of posts about people trying to shed a few extra pounds. I have some time this afternoon and thought I would write a longish post about the role carbohydrates, fat and protein play in exercise as a fuel source and how to maximize fat burning if you are looking to lose weight. A2maizeandblue had a good thread earlier today with a lot of good personal input from fellow members but I thought I would start a new thread from a different angle.
First, a little about me. I have a masters degree in exercise physiology that I received in 1986 from the University of Arizona. At the time, it was one of the best programs in the country in that field. The professors in the program were some of the leading authors and researchers in the field in the country. I taught, coached and worked in the fitness industry before I went to law school in 1989 and am coming up on 30 years of practicing law.
Let's learn about carbs, fat and protein and how the body uses those three sources of stored energy as fuel. If you are adding exercise (along with a change of diet) as a way to lose weight then understanding how the body utilizes its energy sources can help you achieve your weight loss goals.
Carbs get a bad rap, but they are critical to sustain life; your brain needs carbs to function correctly and so does your body. What is interesting is that your body can only store about 1,500-1,700 calories of carbs. Most carbs are stored in the liver while a small percentage remains as glucose in the blood stream. Excess carbs/glucose is expelled from the body or is stored in fat cells.
This is the simplest way to understand how the body uses its stored carbs, fat, and even protein as fuel sources: Picture a C, F and P for each source of fuel. Imagine a circle around each letter. That circle with a letter in it represents a calorie of energy that your body must metabolize to use as fuel. On the circle with the C, imagine 4 straight lines coming out from the circle, and at the end of each line is a smaller circle. The smaller circle represents a molecule of water. Do the same for the F and P, except for the F and P there are nine lines attached to each circle, and again, at the end of each line is a molecule of water.
So the calorie of the Carb is attached to 4 molecules of water; the calorie of Fat and the calorie of Protein are each attached to 9 molecules of water.
In order for the calorie to be metabolized into energy, each of the chains leading to the water molecules must be broken.
Now, let's change gears a bit and say you are standing on a track at the starting line and are going to run a mile. You start running. Your body needs fuel, and it needs it fast. Which energy source is easiest and quickest to metabolize into energy? The answer is carbs because there are fewer chains to break (4) as opposed to fat and protein (9). So if you run a mile, your body will burn primarily carbs because that is the quickest energy source.
Back at the starting line again and this time you walk a mile. Because your body does not need energy as quickly it will burn fat as the energy source. Why? Two reasons. First, because you body can only store between 1,500 and 1,700 calories of carbs, it will always seek to preserve that store for quick energy. Second, because your body does not need the energy as quickly there is time to break the 9 chains attached to the water molecules in a calorie of fat. Your body will burn fat whenever it can to preserve the carbs as a fuel source. Your body will always burn fat if there is time to convert it to energy. Always.
A person of average weight will burn about 100 calories to cover a mile. A person who runs a mile will burn about 80-90 calories of carbs and the rest in fat. About the opposite is true when you walk a mile -- 80-90 calories of fat will be burned and the remainder in carbs. If you have heard of a marathon runner "hitting the wall" or "bonking" it usually occurs around 20-22 miles and happens when the carb reserves are empty and the body cannot metabolize fat quickly enough to keep up with demand.
So how does this relate to weight loss? Long duration, low intensity exercise such as walking, will burn the most fat. If you walk 5 miles you will probably burn 450-500 calories of fat. Your body will not fill up those fat cells so long as your caloric intake is less than your output. Your body will always replace its carb stores so that quick energy is there when needed. For some perspective, you need a calorie deficit of about 3,500 to lose a pound of fat.
But my Peloton just told me I burned 1,000 calories in my spin class! That is probably true. However, because it was a high intensity aerobic workout and your body needed a quick fuel source most of the calories burned came from carb stores and they will be replaced. You cannot exercise for long duration at high intensity without carbs. You just can't do it.
There is a fat burning benefit from high intensity aerobic activity though. First, you do burn some fat during this type of exercise, just not as much as carbs. Your carb stores will be replaced but your fat stores will not unless your caloric intake is greater than output. And, as you become more fit, the body becomes somewhat more efficient at burning fat during high intensity aerobic activity. Carbs will still dominate as the fuel source, but fat will play a slightly larger role. Second, as your body becomes fitter and leaner through exercise your resting metabolism actually increases so you are burning more fat at rest than you were before.
Everyone has heard of Keto. What keto does to your body is that your carbohydrate stores are completely depleted, or nearly depleted and you go on a much more rapid fat burning cycle for energy. This diet is not healthy over a long period of time because of the complete lack of carbs, but I understand the benefits of shedding some fat quickly, but it is just not sustainable. I just turned 60 and would put my aerobic fitness against anyone my age or 20 years younger for that matter. I love to sweat, and I love a good aerobic workout. I don't need to lose weight but I would not last on a keto diet simply because I need the carbs for my workouts.
One last comment. Learn about carbs. Your body needs complex carbohydrates found in nuts, grains and vegetables. If you want to lose weight start reading labels. Simple sugars -- table sugar and syrups are added to so many foods and excess amounts are quickly stored as fat. It is shocking how much syrup and sugar is added to processed foods. If you want to lose weight you should be less than 25 grams a day of simple sugars. To put that in perspective a can of soda has more than 40. Finally, no one is getting fat eating fruit in its natural form. Fruit is considered a simple sugar but when eaten in its natural form the fiber in the fruit slow down the digestion and the sugars are not converted to fat. Fruit smoothies or juices on the other hand can lead to weight gain because the fiber is missing and the sugar enters the bloodstream much quicker and if not used as a fuel source can be stored in fat cells.
A little long, but I hope it helps to understand how your body accesses its fuel source.
First, a little about me. I have a masters degree in exercise physiology that I received in 1986 from the University of Arizona. At the time, it was one of the best programs in the country in that field. The professors in the program were some of the leading authors and researchers in the field in the country. I taught, coached and worked in the fitness industry before I went to law school in 1989 and am coming up on 30 years of practicing law.
Let's learn about carbs, fat and protein and how the body uses those three sources of stored energy as fuel. If you are adding exercise (along with a change of diet) as a way to lose weight then understanding how the body utilizes its energy sources can help you achieve your weight loss goals.
Carbs get a bad rap, but they are critical to sustain life; your brain needs carbs to function correctly and so does your body. What is interesting is that your body can only store about 1,500-1,700 calories of carbs. Most carbs are stored in the liver while a small percentage remains as glucose in the blood stream. Excess carbs/glucose is expelled from the body or is stored in fat cells.
This is the simplest way to understand how the body uses its stored carbs, fat, and even protein as fuel sources: Picture a C, F and P for each source of fuel. Imagine a circle around each letter. That circle with a letter in it represents a calorie of energy that your body must metabolize to use as fuel. On the circle with the C, imagine 4 straight lines coming out from the circle, and at the end of each line is a smaller circle. The smaller circle represents a molecule of water. Do the same for the F and P, except for the F and P there are nine lines attached to each circle, and again, at the end of each line is a molecule of water.
So the calorie of the Carb is attached to 4 molecules of water; the calorie of Fat and the calorie of Protein are each attached to 9 molecules of water.
In order for the calorie to be metabolized into energy, each of the chains leading to the water molecules must be broken.
Now, let's change gears a bit and say you are standing on a track at the starting line and are going to run a mile. You start running. Your body needs fuel, and it needs it fast. Which energy source is easiest and quickest to metabolize into energy? The answer is carbs because there are fewer chains to break (4) as opposed to fat and protein (9). So if you run a mile, your body will burn primarily carbs because that is the quickest energy source.
Back at the starting line again and this time you walk a mile. Because your body does not need energy as quickly it will burn fat as the energy source. Why? Two reasons. First, because you body can only store between 1,500 and 1,700 calories of carbs, it will always seek to preserve that store for quick energy. Second, because your body does not need the energy as quickly there is time to break the 9 chains attached to the water molecules in a calorie of fat. Your body will burn fat whenever it can to preserve the carbs as a fuel source. Your body will always burn fat if there is time to convert it to energy. Always.
A person of average weight will burn about 100 calories to cover a mile. A person who runs a mile will burn about 80-90 calories of carbs and the rest in fat. About the opposite is true when you walk a mile -- 80-90 calories of fat will be burned and the remainder in carbs. If you have heard of a marathon runner "hitting the wall" or "bonking" it usually occurs around 20-22 miles and happens when the carb reserves are empty and the body cannot metabolize fat quickly enough to keep up with demand.
So how does this relate to weight loss? Long duration, low intensity exercise such as walking, will burn the most fat. If you walk 5 miles you will probably burn 450-500 calories of fat. Your body will not fill up those fat cells so long as your caloric intake is less than your output. Your body will always replace its carb stores so that quick energy is there when needed. For some perspective, you need a calorie deficit of about 3,500 to lose a pound of fat.
But my Peloton just told me I burned 1,000 calories in my spin class! That is probably true. However, because it was a high intensity aerobic workout and your body needed a quick fuel source most of the calories burned came from carb stores and they will be replaced. You cannot exercise for long duration at high intensity without carbs. You just can't do it.
There is a fat burning benefit from high intensity aerobic activity though. First, you do burn some fat during this type of exercise, just not as much as carbs. Your carb stores will be replaced but your fat stores will not unless your caloric intake is greater than output. And, as you become more fit, the body becomes somewhat more efficient at burning fat during high intensity aerobic activity. Carbs will still dominate as the fuel source, but fat will play a slightly larger role. Second, as your body becomes fitter and leaner through exercise your resting metabolism actually increases so you are burning more fat at rest than you were before.
Everyone has heard of Keto. What keto does to your body is that your carbohydrate stores are completely depleted, or nearly depleted and you go on a much more rapid fat burning cycle for energy. This diet is not healthy over a long period of time because of the complete lack of carbs, but I understand the benefits of shedding some fat quickly, but it is just not sustainable. I just turned 60 and would put my aerobic fitness against anyone my age or 20 years younger for that matter. I love to sweat, and I love a good aerobic workout. I don't need to lose weight but I would not last on a keto diet simply because I need the carbs for my workouts.
One last comment. Learn about carbs. Your body needs complex carbohydrates found in nuts, grains and vegetables. If you want to lose weight start reading labels. Simple sugars -- table sugar and syrups are added to so many foods and excess amounts are quickly stored as fat. It is shocking how much syrup and sugar is added to processed foods. If you want to lose weight you should be less than 25 grams a day of simple sugars. To put that in perspective a can of soda has more than 40. Finally, no one is getting fat eating fruit in its natural form. Fruit is considered a simple sugar but when eaten in its natural form the fiber in the fruit slow down the digestion and the sugars are not converted to fat. Fruit smoothies or juices on the other hand can lead to weight gain because the fiber is missing and the sugar enters the bloodstream much quicker and if not used as a fuel source can be stored in fat cells.
A little long, but I hope it helps to understand how your body accesses its fuel source.
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