Fasting and Lipolysis – Part 4

By Jason Fung, MD

Insulin is the main driver of both obesity and type 2 diabetes.  The key to reversing both conditions is therefore not “How do we reduce calories?”, but instead “How do we reduce Insulin?”  There are almost no drugs that will do this.  There are actually two classes of medications that consistently reduces insulin – one by a lot, one by a little. Not by co-incidence, they are the only drugs that consistently reduces weight.

But the problem is that they are both expensive and have side effects.  Short of drugs, we need an efficient, effective way to lower insulin if we are to be successful in losing weight.  A diet low in refined carbs and sugar will certainly do the trick for some, but for others it is not enough. The answer, if you haven’t guessed yet, is fasting.

The classic descriptions of fasting physiology were written by Dr. George Cahill. We reviewed this in a previous post, but here’s a pictorial version. Essentially, fasting is the gradual shift of burning glucose to burning fat.

In stage 1, most of the body is using exogenous glucose.  By stage 2 and 3, glycogen (stored sugar) provides much of the glucose needed. Most tissues are still using sugar, but the liver, muscle and fat cells have started to burn fat.

By stage 4 and 5, glycogen stores have run out. Hepatic and renal (liver and kidney) gluconeogenesis is now providing all the glucose, but only the brain, red blood cells and the renal medulla (the inner part of the kidney) uses glucose.  Everything else has shifted over to burning fat.  By stage 5, the brain has mostly shifted to burning fat in the form of ketone bodies.  Only a small amount of glucose is needed for red blood cells.

You can see that the origin of the blood glucose gradually switches from exogenous (dietary) to gluconeogenesis made from glycerol.  Fat is mostly triglyceride, which contains one glycerol backbone and three fatty acids of varying lengths.

Most tissues in the body are able to use fatty acids directly as fuel. By stage 5, only the brain and red blood cells require glucose. So most of the body is now fuelled by fat, not sugar.

You can see the effect of this in the free fatty acid (FFA) concentrations in the blood in response to fasting (also called starvation). The FFA levels in the plasma just skyrocket from almost undetectable.  Ketones (to feed the brain) are betahydroxybutyrate and Acetoacetate which also show an increase.

The triglyceride is broken down into the glycerol backbone and the 3 fatty acids. The fatty acids are used directly by the body. The glycerol goes to the liver and is turned into glucose by the process of gluconeogenesis. Therefore, fat is able to provide the necessary small amount of glucose for the brain, red blood cells and renal medulla. You do not need to break down muscle for this.

So, fasting does not really ‘starve’ the muscles of fuel.  Instead, scarcely available glucose is replaced with widely available fats as the fuel of choice.  That’s good, because the body is able to store virtually unlimited amounts of fat, but only a small amount of glucose. Mother Nature, again, has proven herself far, far smarter than us.

It’s analogous to deciding to switch from hydroelectric power to solar power in the middle of the Sahara desert. Just smart. If there is no glucose, we will burn fat. That’s really good news because if there is anything we really, really want to do is BURN FAT. For all the miracle cures pushed by Dr. Oz that don’t really burn fat, there is one that does – fasting.

One of the reasons why bodybuilders have a vested interest is that their sport demands extremely low body fat levels combined with high athletic performance.

The brain is now powered mostly on ketones.  This is a normal situation.  This is the way our body is designed.  This should not be confused with diabetic ketoacidosis where excessive ketones are produced in addition to very high glucose levels.
In that situation, there is lots of glucose for the brain to use. However, due to the pathologic lack of insulin, the body also produces lots of ketones.  The ketones are not burned for fuel, but instead pile up outside, like unused logs.
As ketone requirements go up, glucose requirements goes down.  In type 1 diabetes, both are very high and this causes a life-threatening problem.
Here’s a question I get sometimes. Can my overweight child fast? Seven hells, no. Here’s a graphical description of why. Children simply may not be able to produce adequate amounts of ketones. Even if they could, I sure as hell would not want to take that risk.

In fact, every major religion in the world requires fasting – but ONLY for adults.

In a more recent study of 4 days of fasting, virtually identical results were found. Let’s take a closer look
There are many interesting details here.  First, you will notice that fatty acids increase 373%.  Blood glucose drops from 4.9 to 3.5 – lower but still in the normal range, maintained by hepatic gluconeogenesis. Beta hydroxybutyrate increases 2527% percent! The brain is powered on ketones and the body is powered on fat. That’s the mythical fat burning – Burn, Baby, Burn!

Second, you can see that over 4 days of fasting, there is a continuous increase in norepinephrine, while epinephrine remains relatively stable.  The increase in adrenalin increases energy and prevents the decrease in resting energy expenditure (REE) or metabolism. REE increases more than 10%.  There is no metabolic shut-down.  Fasting instead revs the body’s metabolism. VO2 also increases slightly indicating a greater capacity of the body for physical exertion.

So here’s a summary so far of what fasting does for the elite athlete, or even the regular person.

1. Train harder – Increased adrenalin, increased VO2
2. Recover faster and build muscle faster – Increased growth hormone.
3. Burn fat – increased fatty acid oxidation.
4. Insulin goes down. This we will consider in more detail later.

This is all available to every person in the entire world, free of charge.  Not only do you NOT have to buy expensive supplements. You will save money because you don’t need to buy food. You will save time because you don’t need to cook or clean up.

Will you lose weight? Well, DUH. If you don’t eat, you will definitely lose weight. So there is no question that this is an effective treatment of weight loss. There are virtually no circumstances where it will not work. Is it unhealthy?

The surprising answer is that fasting is extremely healthy.  There are a huge number of incredible benefits to fasting. Train harder, build muscle, burn fat. Love it! All legal and totally free! Sounds like a cheesy late night infomercial. Call in the next 10 minutes or I’ll double the price! Read this post today, or I’ll triple the price! (Okay, well this blog is free, too)

This is only the beginning – we haven’t even touched on the benefits to obesity, diabetes, cancer, and even the anti-aging effects.

Start with Fasting Part I
Continue to Fasting part 5
Start with Calories Part I
Watch the lecture “The Fast Solution” – The Aetiology of Obesity 4/6

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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