IS GLUCOSE THE BODY'S PREFERRED GASOLINE?

IS GLUCOSE THE PREFERRED “GASOLINE” OF OUR BODY?

Today Stefania wrote me this message, “If our body prefers sugar as its first metabolic pathway and as soon as we give it an iota it switches, isn't it a stretch to force it to function differently?”

By the term “switcha,” Stefania was referring to the fact that when you are in ketogenic, if you eat too many carbohydrates the cells begin to burn glucose and no longer ketones.

First of all, I invite you to pay attention to the little word in red: too many.

When we are in ketogenic if the carbohydrates do not exceed 5% of the calories of the meal we are consuming, we quietly continue to burn ketones.

But how come???

About 5 liters of blood flow in a 70 kg human being. About 4 grams of glucose are dissolved in these 5 liters. If we eat carbohydrates, the grams of glucose in the blood increase (because when we digest carbohydrates become sugars) resulting in HYPERGLYCEMIA. But in the blood that glucose cannot fit, because the blood MUST contain 4 grams of glucose, no more, no less.

So what do you do???

ALARMEEEE! Excess blood glucose must be removed!

The body handles excess glucose in 3 ways:

It turns it into glycogen, which are the glucose reserves we have in our muscles and liver. They amount to about 400 g, and if we do not do sports it is very likely that the reserves are already full.
Uses it as gasoline to produce ATP
If it cannot be turned into glycogen or used to produce ATP, then the body turns it into fat

To remove glucose, the pancreas produces insulin, which:

Opens cell doors to let in glucose to use as fuel
Opens the doors of adipocytes to let in glucose to be turned into fat

So glucose is not the cells' preferred gasoline, it simply has to be used because it cannot stay in the blood because hyperglycemia is dangerous and can cause complications to the heart, blood vessels, kidneys, eyes, and nerves. (1) In addition, continuing to have high blood sugar levels leads the body over the years to develop insulin resistance for which we know the ominous health consequences: (2)

Diabetes
Obesity
Hypertension
Cardiovascular disease
Inflammation
Infertility
Tumors
Aging
Fatty liver
Metabolic syndrome
Kidney failure

But then what is the preferred fuel of the human body? The answer is as usual it depends!

At this point, however, we need some biochemistry ☺

ATP (adenosine triphosphate) is the energy used by our cells. The “fuel” to produce ATP can come from:

Fatty acids and ketones, which are obtained from the digestion of FATS
Amino acids, which are obtained from the digestion of PROTEINS
Glucose, which is obtained from the digestion of CARBOHYDRATES

Wanting to be more precise, there is an intermediate step: pyruvate and acetyl-coenzyme A.

ATP is produced in the mitochondria, the energy powerhouses of our cells, through the Krebs cycle.

But how much ATP is produced? (3)

100 molecules of ATP from 1 molecule fatty acids
42 molecules of ATP from 1 molecule of pyruvate (which is obtained from carbohydrates)
40 ATP molecules from 1 amino acid molecule (protein)

If you observe nature, you will realize that its choices are always based on a golden rule of “how can I save energy?” Because energy is difficult to create and wasting it is definitely not a good strategy for survival.

So, since fats generate twice as much energy as carbohydrates and proteins, what do you think is the human body's preferred “fuel”?

Contrary to what we are told, the truth is that muscles and adipose tissue (which account for 60% of our body mass) use mainly fatty acids. But like Elena, muscles have carbohydrate needs!!! True, but only when the intensity of exertion increases, such as a running sprint.

Think that away from meals, that is, when the body does not have to deal with possible hyperglycemia, our heart uses the 90% of fatty acids to produce energy. And the kidneys and liver also preferentially use fatty acids.

Think about it: the heart, kidneys and liver need a constant supply of energy to carry out their functions, and fatty acids ensure a continuous supply since our body's energy reserves are fat. In fact in a 60 kg body with 16% of fat mass we will have:

Fat = 9.6 kg = 86,400 calories
Carbohydrates = 0.6 kg = 2,400 calories
Total 88,800 calories including. only 2.7% comes from carbohydrates

If glucose was the human body's preferred energy, why does it account for only 2.7% of our body's energy reserves???

Mind you, there are cells that can only function on glucose because they do not have mitochondria: red blood cells, on the other hand, and some tissues found in the eyes.

What about the brain? Is it true that the brain functions only on glucose? Yes and no.

The brain can also safely function on ketones and lactate. Just think that in prolonged fasting the brain uses 60% of ketones for its energy production.(4) However, there are some cells within the brain that use only glucose, so how do they survive in a prolonged fast? You should know that the human body is perfectly capable of producing glucose through a process called gluconeogenesis. In this process, the liver produces glucose by using amino acids, glycerol or lactate to produce glucose.

Glycerol is the molecule that holds three fatty acids together in triglycerides. Triglycerides are the molecules with which our body creates our fat reserves (i.e., our energy reserves). So when we are fasting or in caloric deficit, the body takes triglycerides from our flab, transports them to the liver, and the liver turns fatty acids into ketones and glycerol into glucose. How much optimization of each aspect there is in nature, everything has its why.

That is why there are no essential carbohydrates: the body can produce the glucose it needs.

In fact, in the 2005 edition of “recommended daily allowances” published by the U.S. National Academy of Sciences, Engineering and Medicine are quoted these words “the minimum amount of carbohydrates compatible with life is apparently zero, if adequate amounts of protein and fat are consumed.”.(5)

So the fact that glucose is used before the other substrates has nothing to do with the fact that it is the body's preferred “gasoline,” but only because it needs to be “taken out of the way.” What determines which substrate to use is the concentration of glucose in the blood; if it is high, the cells will use glucose.

It works like this:

We eat carbohydrates
It raises blood glucose (the concentration of glucose in the blood)
Red alert!!! Pancreas produces insulin
Insulin activates GLUT4 transporters that increase glucose uptake by muscle and adipose tissue by 20 to 30 times (!!!)
Tissues need to get rid of the glucose they have absorbed (because it is toxic to them as well), so they use it as an energy substrate
When there is no excess glucose in the blood, most of the cells in our body use fatty acids to produce energy

I very much hope that this insight may have enabled you to UNDERSTAND how energy production works in our bodies. As you can see, we do not NEED carbohydrates. If we then want to consume them because they are cheap calories and a real treat to eat, that is another matter.

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