Chapter 6: Basic Human Energetics and Fuel Partitioning
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This is part 7of my review in Layman's terms of the book 'The Art and Science of Low carbohydrate Living' By Jeff S. Volek, PhD, RD & Stephen D. Phinney, MD, PhD
Physiology ; This chapter is to introduce you to basic physiology and human energy metabolism. Different organs and cells use up different fuel types this is either through food or stored energy. This is looking at basic information on the concept of keto-adaption during low carb living.
There are about 4 calories per gram of carbohydrates (this is in pure form). when digested most carbs turn into glucose, also called blood sugar, the only exception is Fructose (this in turned into fat in our liver). a healthy non-diabetic individual would have on average about 2 teaspoons of glucose circulation the body at any one time. So when we eat and absorb foods such as potatoes, rice we get extra glucose entering the blood stream, our body clears it quickly or it would be an instant case of diabetes.
* Diabetes is the body's inability to dispose of glucose entering the bloodstream.
*Type-1 your body can't make insulin
*Type- 2 your body can make insulin but your cells ignore it (aka insulin resistance)
Glucose normally leaves the bloodstream into muscle and used immediately or stored as glycogen in cells for use later. The liver also stores the glycogen for release to keep the blood sugar at the normal rate. So... if there is already enough glycogen store the rest of the glucose or fructose(from carb) gets turned into fat and stored in your fat cells, this is called lipogenesis, this is irreversible.
Protein consists of 20 amino acids and is used to build and maintain structures of the body, tendons, bone, skin, hair, muscles, kidneys liver, intestine, lungs etc.amino acids are also used to make enzymes, transporters, molecules, hormones etc. As you can see proteins are extremely important for the constant development and functioning of the human body. If the body is receiving a reduced amount of protein it will break down tissue some were in your body to get the required amino acids. when first on a low carb diet more protein may be needed to replenish the body but as the body is adapted protein can be reduced to normal recommended levels.
Energy in Foods - Fat
the two types of fats we get from foods are triglycerides and phospholipids, both can be burned as energy. Because fats cant dissolve in water our fats are moved around in our bloodstream as triglycerides surrounded by phospohlipids, cholesterol and proteins. Lipoproteins are the trucks loaded with energy to transport to cells as fuel. Yes there is cholesterol on board and with out it non of this transport system will work. There is also omega-3 and omega-6 fatty acid which are used in signalling and structural functions throughout the body. (more will be discussed in chapter 9)
Body Composition and Energy Content
the estimation of fat that should be carried by humans are around 20% male body fat and 28% female body fat. this is not always in proportion and it is looked at that higher fat in the vasinety of the stomach would put you at higher risk of developing heart disease and diabetes.
What Your Organs Burn
Our body's are mad up of hundreds of trillions of cells , some cells prefer fats for fuel, some glucose and some a specific amino acid from the breakdown of proteins.
* muscles prefer fat for fuel at rest and only using glucose if levels of insulin are high in the blood.
* Heart prefers fat when not exercising and during exercise it prefers lactate
* Livers energy mostly comes from fat , it is an organ that stores, makes releases, constantly at work
* Brain cannot use fat as it is as a fuel source that where ketones come in to play, the brain can use ketones or glucose for fuel or both. The brain is a carbohydrate dependent organ until you reduce to under 50g of carbs per day at which time it will move over to a ketone dependent organ, during this transition is when fatigue and light headedness may come into play.
There is a whole lot more content on this subject in the book.
Bonking (aka "hitting the wall")
Elite athletes feel this when their body hits rock bottom and just needs food, the brain has come to the end of its supply of energy.On restrictive diets and so called balanced diets this tends to happen quite often and not only to athletes.
we can have completely different body composition, ranging from 50%-5% body fat. It is crucial to remember that carbohydrate restriction will reduce insulin levels , it may take a few weeks but it will happen. When the body is keto-adapted its lean tissue composition with a moderate protein consumption will sustain prolonged physical exertion using predominantly fat as its preferred energy
this was the longest chapter in this book and I have reduced it considerably. But I think you get the jest, further on in other chapters ketosis is touched on a little more, so it all depends how low carb you are willing to go, my advice is if you are going to go low carb, first and foremost check with your health professional and then start slow . Reduce carbs a bit more as you go along with your life and it will be easier to maintain and you will be less likely to jump off the rails.