Your cells use the nutrients from the foods you eat to fuel vital functions. If you eat too much (feast), excessive nutrients get pushed into storage. If you eat too little or not at all (fast), stored nutrients can be pulled out of storage and used to meet your body’s needs.
Feeding Your Cells
Did you know that when you eat, you’re actually feeding your cells? I say this because it’s the cells in your body that take the nutrients from the foods you eat and use them to carry out the vital functions that keep you running. In a way, you could say that food does the same thing for your body as gasoline does for your car. Of course, your body’s a bit more complex than your car.You see, your body has the ability to store nutrients in places, like fat, the liver and muscles, when you overfeed it, and then draw on these nutrients at a later date if you’re running low on fuel.
Your car can’t do this – try to give your car more gas than the tank will hold, and you will have a mess on your hands. In this lesson, we will take a look at how your cells handle the extra food that comes in during a period of feasting, as well as what happens when you fast.
When I think of feasting, I get an image of a big Thanksgiving meal. When you look at the table on Thanksgiving Day your eyes see turkey, stuffing, buttered rolls and pumpkin pie, but when you get the food inside of you, your digestive tract sees macronutrients, namely carbohydrates, proteins and fats. Your digestive tract breaks these nutrients down into their basic forms so they’re small enough to absorb into your bloodstream, which is the highway that nutrients use to reach your blood cells.One of the first priorities for your body is energy production, and we see that glucose, which is a simple carbohydrate, is a quick and easy energy source.
Glucose that is not needed for immediate energy is sent to your muscle and liver cells for storage as glycogen, which is an easily accessible form of stored glucose. This is nice to have, but there’s not a lot of room in your muscles and liver to store glycogen, so the excessive carbohydrates that you eat will get converted into fat and stored in adipose tissue, the soft substance that you think of as body fat.Body fat is not as easy to convert back into energy as glucose or glycogen, but it is an efficient way to store energy for the long-term. So, when it comes to the way your body handles carbohydrates you might want to think of glucose as gas that’s in your tank ready to be used; glycogen as a few small, easily-accessible gas cans that you have stored in your garage; and fat as the gas stored at the gas station that you can access when you really need it.Now, as you might suspect, excessive fats from your Thanksgiving feast are also stored in adipose tissue. This adds to your stored energy reserve, which is a nice way to say you gain body fat.
As for the proteins from your meal, well, they get broken down into their basic building blocks called amino acids by your digestive tract, and are then reassembled as new proteins within your cells. Excessive amino acids that are not needed to make proteins don’t really have a storage space in your body. Therefore, the extra amino acids tend to be broken down for energy. If this energy goes unused, it can be converted to fat.
Now, let’s say that after you stuff yourself on Thanksgiving Day, you decide to stop eating for a while. During the fast, the major players that we discussed earlier, namely your adipose tissue, muscles and liver, work somewhat in reverse to make sure your body has the energy it needs to keep functioning. For example, at the start of your fast your liver cells break down glycogen molecules into glucose, and your fat cells break down fats into fatty acids.
Your body can burn these fatty acids for additional energy.If your fast continues for the next few days, your muscle proteins will break down into amino acids. In your liver, a process called gluconeogenesis converts non-carbohydrate molecules, like amino acids, into glucose so they can be used as energy.
You can recall this term if you break it down into its parts: ‘gluco,’ ‘neo’ and ‘genesis.’ When translated these words mean ‘glucose,’ ‘new,’ ‘creation,’ so gluconeogenesis is literally the ‘creation of new glucose from non-carbs.’The only problem is that your body doesn’t like to burn up body proteins for energy because they’re needed for other things. So, if you continue your fast for more than a few days, your body shifts back to a preference for burning fatty acids along with ketone bodies, which are compounds produced as byproducts from the breakdown of fatty acids.
Ketone bodies are like an alternative fuel. If your body doesn’t have gas from carbohydrates, then your liver makes the alternative fuel, ketone bodies, for your cells to use as energy.
When you feast on a big meal, your body takes in macronutrients called carbohydrates, proteins and fats. Your digestive tract breaks these nutrients down into their basic forms. For example, glucose is a simple carbohydrate that your body is able to use as a quick and easy energy source.
Glucose that is not needed for immediate energy is sent to your muscle and liver cells for storage as glycogen. When those storage areas are full, the excessive carbohydrates get converted into fat and stored in adipose tissues. Adipose tissue is also the storage area for excessive fats from your feast. But, excessive amino acids from the proteins in your meal don’t really have a storage space in your body.
Therefore, the extra amino acids tend to be broken down for energy. If this energy goes unused, it can be converted to fat.During fasting, your body has to work to make sure it has enough energy.
At the start of a fast, your liver cells break down glycogen molecules into glucose, and your fat cells break down fats into usable fatty acids. If your fast continues for the next few days, amino acids from the breakdown of muscle proteins go through a process called gluconeogenesis, which converts non-carbohydrate molecules, like amino acids, into glucose. If you fast long-term, your body shifts back to a preference for burning fatty acids along with ketone bodies, which are compounds produced as byproducts from the breakdown of fatty acids.
After watching this lesson to its completion, attempt the following:
- Name the macronutrients that are drawn from food
- Specify the way in which the body processes and stores energy
- Remember that the body draws on stored energy during fasting periods
- State the roles of adipose tissues and ketone bodies