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Metabolic Flexibility

Updated: May 22

Mitochondria Image

Inside almost every cell in your body you have thousands of little organelles called mitochondria.  Each heart muscle cell for example can have 5000 to 8000 mitochondria. These tiny machines make all your energy by manufacturing ATP, the energy molecule.

To do this they use oxygen plus glucose or fat. But they “mostly” only use one at a time.  Ref: The Randal Cycle, which shows that when they are using glucose they can lock out fat and when they are using fat they can lock out glucose.

Over the last about 100 years we have developed a glucose centric food supply by developing  low cost ways to grow and process carbohydrate based foods. Sugars and grains now dominate our food supply even supplying most of our fats by way of vegetable/seed oils.

The human body has evolved to store excess energy from glucose as glycogen or to store excess fat.  We can store thousands of calories as fat, sufficient for many weeks, but our glucose storage is very small and limited to about 3 hours of energy.  This is why people who are mostly using glucose for energy get hungry regularly and snack frequently.

Your body prioritizes glucose over fat, possibly an evolutionary development due to the ancestral sporadic availability, so when glucose becomes available your mitochondria stops using fat and switches to using glucose for energy.  Another reason for this switching is that any more than about 6 grams or 1 teaspoonful of glucose, in the blood, is toxic.  Therefore, once glucose starts flooding into your blood after eating, the body immediately has to start using it up or removing it.  To do this it releases the hormone insulin, and one of its functions is to signal muscles and the liver to take up the excess glucose. If you are using up this glucose then it will be removed immediately but if you are not removing it or have too much to remove then your body has to store it somewhere.  The process it uses converts the excess glucose to fat to store it.   This is a normal process (De novo lipogenesis) and the fat is stored to be available at a later time.   

Glucose comes from dietary sugars, carbohydrates and a little from excess protein.   If you eat these regularly throughout the day then your body very seldom gets to switch back to burning fat and your level of glucose can remain elevated.  Insulin therefore remains elevated with high levels also toxic for the body.

Continuously high glucose and high insulin, over a number of years, eventually becomes so normal that you can develop what is known as insulin resistance.  To combat this and try and restore the insulin signaling, your body compensates by releasing yet more insulin.  Unfortunately, this creates a vicious cycle and even more insulin is needed to try and control the excess glucose.  This is one of the symptoms of metabolic syndrome and is a precursor to Type-2 diabetes.

It can get so bad that some people require external insulin to manage their continuous high glucose levels.  They are then classified as having Type-2 diabetes. While all this is going on, the toxicity of the glucose and insulin is slowly damaging parts of their body such as eyes, brain, heart, nerve endings in extremities and, they may be storing further excess fat in their abdominal body cavity around their heart and organs.  Common end game conditions for this toxicity, after years of damage, include amputations of extremities due to nerve damage, blindness, Alzheimer’s disease and cardio vascular disease.

Many people do not understand that carbohydrates are a form of sugar and they are converted into glucose, starting as soon as they enter your mouth.  Some who believe they don’t eat much sugar, actually get lots of sugar from these sources.  Bread, pasta, pizza crust, biscuits, cookies, sugar sweetened beverages, beer, muffins, bagels, breakfast cereals, noodles, porridge, all grains, cakes, pastry, sugar, almost all factory made foods transform to sugar (glucose) immediately they are eaten.  They have high levels of calories (energy) but relatively poor nutrition which is why many countries require their flour to be enriched or fortified.  Vegetables also contain carbohydrates, are usually lower in energy levels but offer better nutrition.

A simple but seemingly uncommon way to control this and restore the body to full health and glucose management, is to reduce the incoming flood of dietary glucose.  Because our food supply is carbohydrate heavy and people are conditioned to always eating carbohydrates including sugar plus snacks between meals, they find this adjustment very difficult.  Unfortunately, the standard of medical care for dealing with this is to prescribe glucose lowering medication or to prescribe additional insulin.  On the surface, this will enable relative simple management of the high glucose levels but, it will not address the cause or the tissue damage that the excess glucose and insulin does to the body.

The hormone insulin not only signals the muscles and liver to take up glucose, it also prevents fat stores from releasing their fat, perhaps to safeguard against putting too much total energy into your blood.  This means that the fat which has been stored from excess glucose, does not get used.  If your body gets accustomed to using glucose for energy, then it gradually becomes inefficient at utilizing fat.  When this happens, and your body senses that it is low in energy, it triggers hunger for additional glucose rather than switching to using stored fat.  You can change this fat resistance by forcing your body to use fat. This is achieved by eating a very low carbohydrate diet for a period of time.  After approximately three weeks your body can become fat adapted and once you reach this stage you will be metabolically flexible.  This means that your mitochondria can easily switch between using glucose for energy or using fat for energy, whichever is available.

If you are not metabolically flexible, then the fat your body stores remains locked up in fat cells and excess energy from excess carbohydrates adds to your fat stores.  A very low carbohydrate diet (20 grams/day or less) with low/medium fat diet can force your body to burn up those fat reserves gradually restoring your body to the health that many aspire to.  This is not easy to do but there is one way to help make it easier that is driven by your body’s satiety response.

Because the level of stored energy from carbohydrates is very small, and if you are not fat adapted, your body will scream hunger signals as the glucose gets depleted. The reduction in food then encourages the body to adapt to a lower level of incoming energy which impacts normal body functions such as growth, repair and maintenance.  This uncomfortable situation drives people to abandon their restrictive low calorie diets because it is too hard.

However, if you first become metabolically flexible, (fat adapted), any period of dietary restriction will result in your body switching to use stored body fat and (usually) this is done without drama i.e. without hunger signals and without the body feeling that it has to turn down the thermostat to compensate for a lower energy input.  The benefit being that a fat adapted person can restrict their diet, can fast, and will then reduce their excess body fat with relative ease to restore their health.  Many suggest it is easy to do, once you have navigated away from the excess carbohydrates and sugars available in the food supply.

Taking a birds-eye view of what is going on here, you may realize that this whole scenario is the result of too much energy going into the body.  If the energy is coming from carbohydrates then any accompanying fat is stored and any excess glucose is converted to fat and stored.  Eating too much carbohydrate is easy because it does not trigger the satiety signal as effectively as fat.   Many manufactured foods are sweetened to encourage you to eat more, plus our default celebrations are often carbohydrate and sugar feasts.

If your energy is coming mostly from fat then any excess is also stored, however eating too much fat is harder to do because you tend to feel full sooner.  If your meals are a mix of carbohydrate and fats, such as ice cream or donuts, then you can be sure that the fat is adding to your fat stores as are any excess carbohydrates.  Breast milk is one of the only natural foods with this combination of fat and carbs.

There is another factor also at play here.  Your hunger is driven by your body’s nutritional needs.  You have a protein thermostat, which signals when you have eaten enough protein which then reduces your hunger.  Farmers can encourage their animals to eat more by reducing the protein in their feed.  There are other signals that make you hungry for particular foods when your body needs them.  If you are used to eating lots of grains, your microbiome (gut bacteria) becomes populated with the types of tiny organisms that dine out on this food.  When you don’t deliver what they want, they can influence you to feed them by making you crave something sweet.

If you usually eat more veggies, fatty food or protein, then a different set of microbiome organisms will flourish in your gut and will signal for their preferred food to be delivered.   In other words, you need to eat the right food and you need to ensure what you’re eating is delivering the required nutrition without adding excessive energy.  Sugar is pure energy, it adds no nutrients but drives up your dietary energy intake.  Where does excess energy end up?  It becomes stored fat.

Another aspect of excess glucose is much more dangerous.  In the 1930’s, Otto Warburg, a German scientist discovered that most cancers have a voracious appetite for glucose and insulin.    Rather than using the normal ATP energy creating process within the mitochondria, as described earlier, they use a process called glycolysis, which uses large amounts of glucose but cannot use fat for energy. He was awarded a Nobel prize in 1931 for his work.  Breast cancer cells have huge numbers of insulin receptors on their surface which pull glucose into the cells to feed them.  Doctors can use a PET scan to search for glucose concentrations in the body to see if cancer cells are spreading.  Therefore, keeping glucose low can starve cancer cells and make them more susceptible to being eradicated by chemotherapy and may also help to prevent them becoming established.

I hope this helps you understand more about the impact of glucose from dietary carbohydrates, particularly from grains.  Because grain growing is subsidized in the USA, world wide grain prices are low, and food produced from them is very profitable for the manufacturers.  It is unfortunate that grains which are low cost, store well, can be transported easily and can be made into many foods which are not healthy for your body.  This high profitability encourages manufacturers to make health claims, designed to increase sales.

To manage through all this and remain healthy, you must learn to ignore the messaging from food manufacturers.  Make informed decisions and maintain metabolic flexibility through wise food choices based on this knowledge about your diet. Your longevity depends on it.

Buy my book HERE.

Good health, George Elder, Diploma in Nutrition.

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