Why Fats (And Not Carbs) Are The Body's Preferred Fuel Source


Insulin.  Not only does it look cool...it's also the key to understanding how your body stores fat.

If you keep up with the Synchro Life Design System, you'll know by now that I'm a huge advocate of eating a diet that is low-glycemic load and fuels the body primarily with high-quality, easily digested fats.

Switching to this diet was hugely transformative for me, and if you look around a bit online, you'll find it's a rapidly growing movement that has produced similar results for hundreds of thousands of people.  If your goals are stable vibrant energy, high cognitive performance and low body-fat - this diet produces results better than any other I have come across.

Initially, it looks a little counterintuitive.  Why does eating lots of fat produce high energy and low body fat?

First, it's important to make a distinction between types of fat.  There are a lot of undesirable types of fat out there - but even many types of fats commonly regarded as "healthy" turn out to be closer to "OK" than "beneficial".

Secondly, understanding how our body processes fats and carbohydrates differently is key to understanding why certain types of foods make you feel or look a certain way.  We'll cover both in detail below.

Carbs = Sugar

Sugar in your food generally requires little to no digesting or processing and will be in your bloodstream inside 60 minutes after eating.  In response, blood sugar shoots up for a bit before coming back down rapidly a short while later.

Other carbohydrates, referred to as complex carbohydrates, will be sugar in your bloodstream as well eventually.  It takes your digestive system a little longer to convert complex carbs into simple sugars, so blood sugar will rise and fall a bit slower depending on a few factors.  These include the type of carbohydrate (how "complex" it is) and how fibrous and/or fatty the food is. 

Once in the blood, your metabolism begins to use sugar in a variety of ways.  Particularly if you are active or exercising, some of the sugar in your blood will be used quickly for energy.

Glucose and/or fructose are the end-products of all carbohydrate breakdown.  These simple sugars enter into either glycolysis (for glucose) or fructolysis (for fructose).  In these processes, the metabolism uses the simple sugars to generate the compounds that, in turn, power all of the body's other metabolic processes.  Put more simply, glycolysis and fructolysis convert simple sugars into energy.  

(A quick note on fiber: fiber is classified as a type of carbohydrate and is listed on nutrition labels under the carbohydrate section.  Most fiber will pass through the body undigested.  The remainder will be digested quite slowly over the course of many hours.  Fiber does not have a meaningful effect on blood sugar.)

Insulin: The Storage Hormone

Most of the time, however, sugar is not used immediately but is stored in cells for use later.  This is where insulin comes into the equation.  Insulin is a protein that acts as a hormone in the digestive process.

When a protein is classified as a hormone, it means that its presence in the bloodstream triggers a cascade of other related and interdependent processes in the metabolism.  Insulin is perhaps the single most important element of nutrient metabolism, and understanding its function is critical for understanding what your body is doing with the food you eat.

When there is more sugar in the bloodstream than the body is immediately using, insulin is released and initiates the storage process.  Insulin causes glucose to be absorbed into cells, upon which, it is stored in one of two ways.

The primary storage method for glucose is as triglycerides in adipose (fatty) tissue.  The secondary method is as glycogen, essentially a matrix of glucose that is stored in muscle and liver cells for later use as quick energy, primarily in times of exertion.  

To summarize, when you eat carbs they are broken down into sugars by the digestion process.

Sugar causes the release of insulin and insulin causes the sugar to be stored, primarily as fat in adipose cells.  Particularly when forming a large portion of your caloric intake, carbohydrates are the primary source of any fat your body is storing.

Fueling With Fats

Fat digestion and metabolism happen via completely different pathways than the ones used for carbohydrate metabolism.

The first major difference in the digestion of fats relative to carbohydrates is that the breakdown and absorption is a much slower process.  Most fats are broken down slowly in the gut via a series of enzymes called lipases and eventually make their way into the bloodstream as free fatty acids.  Like sugars, once in the bloodstream free fatty acids can be used for energy (via the process known as ketogenesis) or stored in adipose (fatty) tissue for later use.  

One notable exception to this digestion pathway is medium-chain triglycerides (MCT's).  Because they are smaller than other fats, MCT's can pass directly into the bloodstream without needing digestion in the gut by lipases.  These smaller fats are broken down into free fatty acids by lipases in the blood rather than in the gut.

While other types of fat take too long to digest and process to be a legitimate alternative to carbohydrate as a primary fuel source, the quicker availability of MCT's makes them not only a legitimate alternative, but a preferable one.  MCT's are also unique among fats in that they can be used by the brain for energy.

Other types of fat must go through the long process of being converted into sugars before they can be used by the brain.  Eating primarily other types of fats would leave the brain under-fueled.

Once again, MCT's and SCT's not only solve this issue, but offer a superior alternative to carbohydrate.  Unsurprisingly, MCT's and SCT's are critical to any diet using fats as the primary calorie and fuel source.

When your metabolism is using primarily fats as an energy source, you are essentially "training" your metabolism to use fats more often and more efficiently.

The metabolic pathways involved in ketogenesis (fat-burning) become more robust, and the body becomes better at using fat stored in adipose tissue when available sufficient calories are not available from food intake.  Fats also don't directly trigger an insulin response, so the body doesn't go into "storage mode" as often when fats are your primary fuel source. 

So what are the best sources of MCT's?  Coconut oil (and related products) and grass-fed butter are hands-down the top choices.

Coconut oil is about 2/3 MCT's by weight.  In addition to its many other benefits, coconut oil is the go-to fuel source for many people adhering to this type of high-fat diet.

A few companies isolate the MCT's from coconut oil and sell  "MCT oil" by itself.  This is a pricey option as an every-day fuel source, but if you're looking to accelerate the fat-burning capacity of this diet, MCT oil is a powerful tool.  Coconut butter is also a great choice, as it is the "meat" of the coconut before the protein and fiber is pulled out in the process of making coconut oil.

I personally keep a jar of Cocotella in my office as my constant snack food.  Like other coconut oil products, Cocotella fuels the brain and doesn't meaningfully interrupt the fat-burning process (which a carb-based snack would).  

Additionally, grass-fed butter is an excellent source of short-chain fatty acids (as well as many vitamins and Omega-3 fatty acids).  These short-chain fatty acids behave in much the same way as MCT's and can be used for the same purposes.

It is important to source only 100% grass-fed (sometimes called "pastured") butter.  Conventional butter has a significantly different nutritional profile and is more likely to contain toxins.  I use a grass-fed ghee (clarified butter) to avoid the milk proteins and sugars that are present in butter. 

Fats vs. Carbs 

As I mentioned above, the metabolism tends to adapt to the types of fuel it is receiving most frequently.  If the metabolism is being fueled disproportionately with carbohydrates, the metabolic pathways that use and store carbohydrates will dominate while fat metabolism pathways will diminish.

The reason for this is two-fold.  The first reason is that the pathways required to store or use carbohydrates require a set of enzymes unique from those the metabolism uses to process fat.  The body is remarkably good at not being wasteful and will decrease production of fat metabolism enzymes when they are used infrequently.

The second reason is that insulin specifically stops the use of fat for energy by inhibiting the release of glucagon, a hormone that increases blood sugar and thus directly competes with insulin.  

Because of this "competition" between fat and carbohydrate metabolism pathways, fat will only be used for energy in the absence of insulin.  If you're going to train your body to use fat for energy, it becomes critical to minimize both the magnitude and duration of any spike in blood sugar and thus, the magnitude and duration of the corresponding insulin release.

Glycemic Load, Glycemic Load, Glycemic Load

If you're aiming to minimize insulin response and support your body's fat-burning metabolism - there is one concept that stands above all the rest to use when judging the effect of a given food.  That concept is, of course, glycemic load.

Glycemic load is essentially a measure of how much a given amount of a certain food will increase blood glucose levels after eating.

With the exception of a few specific situations (nutrition during an intense workout is one such exception), you should focus on keeping the glycemic load of any meal relatively low.  Keeping the glycemic load low will minimize the amount of insulin released during and after eating.  This will, in turn, minimize both the amount of carbohydrate from your meal that is stored as fat - and - minimize the time in which fat-burning metabolism is suppressed.  

Some of judging glycemic load is intuitive.  A piece of cake is naturally going to create a serious spike in blood sugar and thus, will have a high glycemic load.

Foods composed primarily of fat and protein like nuts and fish will have a minimal effect on blood sugar and have a low glycemic load.  Many foods, however, are not as obvious.

I frequently use a great website, www.nutritiondata.self.com, to find the glycemic load of foods I am less familiar with.  I recommend heading there to find the glycemic load of any food you eat on a regular basis so you know how to adjust your diet accordingly.

Beyond choosing low-glycemic foods, there are several strategies you can employ to lower the glycemic load of your meals.

The obvious first step is to reduce the amount of carbohydrate in your meal, particularly sugar or simple carbs that have a high glycemic load.  If you're going to get the results you're looking for using this diet strategy, it's inevitable you'll be increasing the relative proportions of quality fats and proteins in your meals and decreasing the portions of carbohydrate.  For desserts and sweets, choose a low-sugar, fatty food like dark chocolate or (again) Cocotella.

There are also less obvious strategies you can use to lower the glycemic load of a meal.  Fat, protein and fiber all slow the digestion of a meal and thus increase the time of digestion.

Blood sugar will raise more gradually and never peak as high as if you had consumed the same amount of carbohydrate without fat, protein or fiber.  The overall insulin response will be less and the body will store less of the meal as fat.

Stay Synchro,

     Graham Ryan




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