Cranky Fitness: Will Restricting Carbs Make You a "Fat-Burning Beast?"

So for years I've been intrigued by notion of "Fat Adaptation," a concept advanced by Mark's Daily Apple and others. The idea is that by strategically restricting carbohydrates, you can reprogram your body to use fat as fuel instead of glycogen.

According to Mark:

If you’re fat adapted, the genes associated with lipid metabolism will be upregulated in your skeletal muscles. You will essentially reprogram your body. 

With that comes great benefits!  Like more energy available during exercise and throughout the day, and an easier time burning fat and losing weight than if you are a "sugar burner."

However, most mainstream nutritional advice says almost the opposite: Watch the fat, eat more carbs. These experts claim you need a crapload of carbs for optimal nutrition, especially if you are doing something athletic.  

And yeah, everyone agrees you need protein and that you should avoid refined and processed foods as much as possible and you should be eating plenty of produce.  But as to what else you should be fueling with, the "Are Carbs Good or Are They Bad" debate rages on.

I got so tired of hearing the contradictions that I asked Tiffany Reiss what she thought.  As regulars may recall, Tiffany is a smarty-pants professor type who knows a lot about exercise physiology. (Her bio is below).

So, is her answer simple and straightforward?

Hell no! Because it turns out it's a complicated question!

So those of you who like to geek out, here's Tiffany take on the whole "Should I restrict Carbs" question.

--Crabby

To Carb or Not to Carb

It’s such a simple question: Are carbs good or are they bad? Should we eat them or shouldn’t we?

The answer is: Yes….and No. It depends. So what does it depend on? Genetics, muscle fiber type, activity level, activity type, gut microbes and age to name a few. For now I will just focus on the genetics of it all.

Genetics/Epigenetics

You are your genes, and your environment impacts your genes. We all have a genetic construct and everyone’s is slightly different.

But we now know that our environment influences our genes by turning some genes on and some genes off. It turns out both nature and nurture play roles in who we are and what we ultimately become.

What’s important is which genes are turned on and active, and that can be influenced by our environment. What constitutes our environment? Diet, activity, stress, smoking, exposure to chemicals, toxins, etc… Pretty much how and where you live your life. These are actually new fields of study called: Epigenetics and Nutragenomics. How our environment influences our genes (Epigenetics) and how what we consume influences our genes (Nutragenomics).

Now why is this important? Our bodies adapt. They are amazing machines that adapt pretty well to the myriad of environmental stimuli to which we expose them, if we have the genes that can adapt or turn on/off based on the environmental stimuli. Below is a good example of an adaptation:

Muscle Fiber Type/Activity Level/Activity Type

Your muscle fiber type is genetic. There are 2 basic types of muscle fiber tissue:

• Type I: endurance oriented and aerobic (long distance running, swimming, biking, yoga, etc….)
• Type II: strength/power oriented and anaerobic (resistance training, football, sprints, baseball, etc….)

You get the picture. Type 1 tissue dominates during long duration, lower intensity activity; Type II during short duration, high intensity activities.

Most people are a good combination of Type I and Type II and there are varying levels of isoforms that actually give us a broad spectrum or range of that muscle tissue based on the way we train or exercise. They may vary a bit one way or the other, say 55% Type I and 45% Type II, but the average individual is a good mixture.

Then there are individuals who are less balanced. One individual may be 75% Type I and 25% Type II or vice versa. They are predisposed to excel in a particular type of activity, whereas the more evenly balanced individuals will be good at both kinds of activities (and some sports like say soccer). More Type I than Type II will naturally excel at endurance oriented events. Switch it and you have a great linebacker, 100 m sprinter or running back in football. Of course, the percentages vary, but they influence our ability to gain muscle mass, efficiency in oxygen utilization at the cellular level, excel in different types of sports or activities.

But, coming back to the original question: muscle tissue composition will also dictate which substrate (carbs or fat) we like to use both at rest and during exercise.

In general, Type I muscle fiber tissue likes to burn fat as a fuel source when it is activated, and Type II likes to burn carbohydrate as a fuel source when it is activated.

So how can we tell the difference between Type I and Type II muscle fiber tissue, and what happens when we exercise?

Enzyme concentration and number of mitochondria are a piece of that puzzle. Type I has a lot more mitochondria…and you know what mitochondria do? Mitochondria help the cell utilize oxygen efficiently and the energy system that primarily can burn fat as a substrate is located within the mitochondria.

Type II muscle fiber on the other hand has way fewer mitochondria, doesn’t require oxygen to provide energy (hence their anaerobic nature) and have lots of enzymes to breakdown, you guessed it: glucose (or carbohydrate).

But what happens when say someone who happens to have more Type II muscle fiber tissue trains to run a marathon? This is where epigenetics comes into play. By training more aerobically, some of the Type II muscle tissue will start to become more like Type I muscle fiber tissue. Not all of it will convert and it won’t convert all the way but it will start adding mitochondria and fat burning enzymes while decreasing some of the factors associated with it being anaerobic. It will become more like Type I but to date there is no evidence it will become 100% Type I.

Now of course, muscle cells don’t just start adding more and larger mitochondria and fat burning enzymes, this has to initially happen at the genetic level. Once this individual stops training for the marathon, or completes it ideally and stops training for endurance, those genes will turn back off and back to the Type II muscle fiber tissue that is more, let’s say natural for that individual. This person, although well trained, will never be as efficient at endurance activities as the more Type I individual and there is some evidence, some people (up to 20% of the population) just don’t have the genes to convert at all. So regardless of all of the endurance training, they never increase the number or size of the mitochondria and can’t produce more enzymes for burning fat. 

Why is this important? Well, when engaging in lower intensity, longer duration activities (even sitting at your desk) our bodies prefer to burn fat, how much fat will depend on genetics and muscle fiber type. Burn more fat at rest and during exercise = ability to consume more fat throughout the day.

It makes sense that someone with more Type I muscle fiber tissue will likely burn fat more readily than someone with more Type II, even if they train for endurance oriented activities both at rest and during activity. Ironically, our brains (which actually suck up a lot of daily energy needs) prefer carbohydrates (glucose) as does Type II muscle fiber tissue. So individuals with more Type II, even at rest are likely not very efficient at burning fat and prefer glucose. Which means those individuals likely would do better consuming less fat and more carbohydrates (the good kind of course). 

Consumption of Carbohydrates, Fat, and Protein

We adapt to our environment.  Some better than others.  We can up-regulate and down-regulate hormones and enzymes, change cellular structure (which changes efficiency of substrate utilization), all by changing our activity patterns (Epigenetics) and something else: what we consume (Nutragenomics).

So a logical question is “If I consume less carbohydrate and more fat (and protein) will my body adapt by becoming more efficient at utilizing that fat; will I then burn more fat?  Again, if the genetics allow for it, yes!  If not, not so much.

It’s important to remember here that both your brain and your muscle tissue use about 20% of your total daily energy needs respectively and for the muscle tissue that only increases when you are active. So ultimately what kind of muscle tissue you have, or can shift via training will play a role in your ability to burn fats and/or carbohydrates efficiently both at rest and during activity.

The real problem with carbohydrates seems to be the kinds of carbs we are consuming in the standard American diet.  Way too much sugar and processed carbohydrates and way too few vegetables, fruits and whole grains.   That however, is an entirely different post.

Dr. Tiffany Reiss is an an exercise physiologist and adjunct faculty member at Seattle University, Lake Washington Institute of Technology, American Public University and Walden University. She is also a contributor for the Sports and Fitness Network and the co-founder of TheHubEdu: A Learning Library.

What do you guys think about carbs?

By Tiffany Reiss; With a Long-Winded Intro by Crabby McSlacker

http://www.crankyfitness.com/2014/07/will-restricting-carbs-make-you-fat.html