Carbohydrate Tolerance: Frontline Fat Loss – Written By Nutrition Expert David Barr

If you’re looking to optimize your fat loss, then you’ve come to the right place. Unfortunately, we’ve overlooked a key factor for far too long, and it’s time that changes. I’m going to show you how to lose weight as efficiently as possible by exploring the concept of carbohydrate tolerance.

We’ll cover the theory, practice, and the specific “How To’s”, along with plenty of Quick Tips along the way.

What Is Carbohydrate Tolerance?

Before we get to this critically important concept, let’s back up a minute and consider another point called insulin sensitivity. This simply refers to how responsive a particular tissue is to the hormone insulin.

A tissue with high insulin sensitivity will respond quite well to this hormone, while another with low sensitivity won’t be as responsive. This is important because insulin is known as the storage hormone, and it’s our goal to keep it as low as possible in order to lose bodyfat. In addition to the overall quantity, it’s our goal to maintain high insulin sensitivity in muscle, but keep low insulin sensitivity in fat cells. That way, insulin can do its job better in muscle, but not so well in fat cells (and as you probably guessed, the job of the latter is to store fat).

Now, insulin sensitivity sounds important, and it is, but it’s been the sole focus for far too long. The parameter that comes into play, even before insulin is affected, is known as carbohydrate tolerance. What’s perhaps even more important is that carb tolerance can even indirectly affect insulin sensitivity and hormonal control.

Quick Tip:

Ideal insulin sensitivity is critical for not only the maintenance of muscle mass when on a diet, but also optimal fat loss. By optimizing carbohydrate tolerance we maximize insulin sensitivity, thereby preserving muscle and burning more fat!

So What Is It?

Although carbohydrate tolerance is similar to insulin sensitivity in many ways, it specifically pertains to the way in which our body deals with carbohydrates alone. The concept is best explained by treating our muscle as a sponge that’s responsive to carbs. For the optimal fat loss we want it relatively “dry,” so that when the time comes, it can suck up as many carbs as possible. As long as the sponge has a little dryness to it, it’ll be able to absorb the water (a.k.a. carbs) without affecting the rest of the body. (Remember that insulin isn’t involved quite yet. This is how we maintain an optimal fat burning state for as long as possible.)

After the muscle has absorbed a relatively large amount of carbohydrates, it’s considered full, and reaches what is known as the saturation point. Only after the saturation point has been reached do the carbs begin to “spill over,” at which time insulin, and our sensitivity to it, becomes important.

Quick Tip:

For an easy to conceive analogy, consider the following: if fat loss is a battle, then insulin sensitivity can be considered the reserves, while carbohydrate tolerance is the front line! Only by engaging all of the troops can we win the battle.

The Key Benefit

Having a high carb tolerance relates to fat loss because it performs a vital role: it keeps insulin levels low. Because insulin is our storage hormone it has the double impact of not only stopping any fat loss that is occurring, but also directly induces fat storage itself.

Obviously if we’re trying to cut, then having as little of this hormone as possible is a very good thing. And by having optimal carb tolerance, this is exactly what we’re doing!

Added Bonus: The Buffer Zone

Another benefit of maintaining a high carbohydrate tolerance is that it acts as a buffer zone for those times when we overindulge in carbohydrates. This ensures that these carbohydrates are not stored as fat, but rather sucked up by the muscle such that insulin levels are minimized. One might, if in the middle of a carb binge, think of it as a get out of jail free card. The diet won’t be ruined, which can have great physiological and psychological implications.

Quick Tip:

Stimulant use also greatly assists with fat loss, and can help mitigate any damage done by slipping on our diet.

Getting There

So how do we enter a state of optimal carb tolerance, and subsequent fat loss? Well, there are 2 main ways:

  1. Diet
  2. Exercise (no surprises here).

Key 1: Diet

The most efficient way to induce a longer-term state of carb tolerance is to maintain a low carbohydrate diet. This serves to deplete muscle glycogen stores such that they’ll be far more responsive to absorbing carbohydrates. Going back to our sponge analogy, carb depleting is our practical version of drying out the sponge.

Key #2: Exercise

Our short-term path to carb tolerance is exercise, particularly that which is able to significantly deplete muscle carbohydrate stores (a.k.a. glycogen). Resistance exercise is particularly efficient at inducing an elevated carbohydrate tolerant state — something that most people take advantage of with a post-workout drink like Surge.

By combining our intense exercise and low carb diet we are setting up an optimal internal environment for fat loss.

The “How To”

Now that we understand the basics and benefits of carbohydrate tolerance, let’s take a look at how to do it, and do it well.

Killing Carbs and Bodyfat

The majority of fat loss occurs in a carb-depleted state, in part due to the improved carb tolerance that accompanies this condition. The sooner we can enter this optimal fat burning phase, the better the results. By focusing our first carb depletion day on getting into the optimal carb depleted state, we are kick starting fat loss and setting ourselves up for a successful cut. This critical first day is known as the priming phase. The easiest way in which to enter the optimal carb tolerance zone is to dramatically reduce carbs on this day. This is because our first day isn’t about losing fat per se; it is about priming our body for a state where it is able to destroy fat. It seems like a subtle difference at first, but makes all the difference to our body.

By reducing our carbs to a great extent in the priming phase, we’re quickly able to get into the optimal fat loss zone, during which we are able to consume a low quantity of carbs in order to maintain the ideal fat burning state. On subsequent days of the diet, carbohydrates may be increased slightly such that the fat burning condition will be sustained until the carbohydrate refeed.

Quick Tip:

Refeeeding will fill our muscles with glycogen and induce a strongly anabolic state. This is critical for both the maintenance of both muscle mass and training intensity. In order to optimize these effects, excessive glycogen depleting exercise should be avoided during this short time. For this reason, only light cardio should be performed during a refeed, if any.

Divide and Conquer

Here’s a quick tip that clients love: separate your cardio and weights into different sessions, rather than trying to cram them all into one shot. This has the dual advantage of optimizing carb tolerance, and maximizing the amount of energy you can put into each session. Because each training session improves carb tolerance, you’re getting twice the bang for your buck. This means that you’ll have double the carb tolerance compared to if you performed only a single training session.

In fact, it’s likely that you’ll more than double your carb tolerance through this method. Due to the intensity that you can offer to each bout, carb tolerance will be exaggerated relative to that of a compromised intensity session.

Double Intensity

Have you ever tried to do a hard weight session after HIIT, or vice versa? If you’re human then probably not, because both are exhausting. But for those masochists who have, you’ll likely remember that there was a serious compromise of the latter session. This is because the intensity simply can’t be maintained for two consecutive exercise bouts, particularly when on a low carbohydrate diet. But, by splitting this intensity between two separate workouts, you are better able to focus your energies on a single task, thereby maximizing fat burning potential!

This is particularly critical when it comes to weight sessions because intensity is needed to maintain a strong anticatabolic stimulus to muscle. Without it, muscle will waste in the caloric deficit, metabolism will drop, and the diet is doomed.

Quick Tip:

By splitting cardio and weights into two separate workouts, you’re preserving muscle mass! This not only helps to maintain an elevated, fat burning, metabolism, but it also ensures that you’ll look better when you’re all done!

Double Fat Loss

The exercise and diet points are great on their own, but are even more powerful when combined! If you recall, the first day of a carb depletion is critical for getting us into the optimal fat burning zone. Well, this priming phase of carb depletion is also the perfect time for a double workout day!

This will ensure maximum glycogen depletion at a time when we will benefit most from it. By training twice we also take advantage of the training-induction of carb tolerance.

Sample Plan

Day 1: Priming Phase

  • AM: 30 minutes of HIIT followed by 15 minutes of low intensity jogging/walking
  • PM: Resistance training session
  • Carbohydrate intake: extremely low

Day 2-5: Fat Loss Phase

  • AM: 30 minutes of HIIT followed by 15 minutes of low intensity jogging/walking
  • PM: Resistance training session
  • Carbohydrate intake: low

Day 6-7: Refeed

  • Resistance training only
  • Carbohydrate intake: high


In our quest for the ideal body we’ve been neglecting carbohydrate tolerance for far too long. By entering an optimal carb tolerant state we are maximizing fat loss and assisting with the overall ease of the diet. Try applying the tips provided and you can be sure to maximize cuts and lose fat faster and easier than previously thought!

David Barr is a strength coach and scientist, with research specialty in nutrition and its impact on performance and body composition. In addition to his work for NASA at the Johnson Space Center, David’s research career has involved everything from the cellular basis of muscle breakdown to work on critically ill catabolic patients. He holds certifications with the NSCA as well as USA Track and Field, and can be contacted through his website.