Should You Cycle Your Carbs?

Have you ever tried to cycle your carbs?  Maybe cut back on off days and go higher on training days?  Maybe you tried going low-carb all week and then going carb-crazy on the weekends to restore glycogen.  Perhaps you've heard of other diets touting that if you do their "carb system" you can eat anything you want while losing fat.

But lets get one thing straight right off the bat: carb cycling is calorie cycling.  Unless you adjust fat UP while carbs go down (which most people do not do) having low-carb days also means having lower-calorie days.  And if your calories are low enough to put you in a deficit, you'll lose body fat.

Essentially there is nothing magical about cycling your carbohydrates if you take it at face value.  But there are a LOT of ways to implement carb cycling and in this case, I want to discuss cycling them in a fat loss scenario.

Is Carb Cycling Even Necessary?

Before we jump into how we implement this, lets briefly chat about if you even need to do it.  And we need to understand the role of carbohydrates, glucose and glycogen in maintaining blood sugar and power exercise.  Thanks to SCIENCE, we know how carbohydrates impact the system.  Lets look...

Glucose Disposal and Storage

In healthy subjects, the majority of ingested carbohydrate is oxidized or stored as muscle glycogen.  Some is also stored in the liver, which actually has higher concentrations of glucose by weight(10% versus 2% by weight), but is much smaller than total body skeletal muscle.  The average liver can hold 100g while you could store around 500g average in skeletal muscle, with that number going up or down based on size and muscle mass.

Muscle glycogen serves to fuel activity 70% Vo2 max or higher and you cannot release muscle glycogen into the bloodstream to maintain blood glucose - the liver serves as a blood glucose regulator and will see much more depletion by percent than skeletal muscle will. Essentially, once glucose is in the muscle and stored as glycogen, there it stays until it is used to power muscular contractions.

Exercise (especially strength training) is fantastic for diabetics and those with impaired insulin sensitivity because depleting muscle glycogen allows for ingested glucose in the future to be stored in the muscle rather than the fat cell.  Chronically exercising means you are chronically using up glycogen which signals cells to deposit glucose FIRST in muscle, rather than fat. Not to mention intense muscle contractions allow for non-insulin mediated glucose uptake which means you can pull glucose into the muscles without insulin being present.

The system clearly wants to store muscle glycogen to fuel flight or fight activity, and the liver wants to store glycogen to maintain blood sugar. Like Dr. Ben House says, PULLING energy through the system (through exercise) is so vitally important for maintaining cell health.  And this means engaging in activity that depletes glycogen, pulls energy through the system and allows for better regulation of future energy (calories) coming in.

Here's Where It Gets Interesting

Although clearly, I am already interested....I want to get you sucked into this too.  Learning even the basics of science helps cut through the bogus nutrition dogma we hear all the time.  And I want you to be interested in this so you can understand the implications for your own nutrition plan! 

Calories Burned At Rest

At rest, an average person consumes about 3.5 ml O2/kg body weight/min or expends about 1 kcal/kg body weight/hr.  So if I weigh 200lbs and divide that by 2.2 to get my kilogram weight, I'd be 91kg.  And 1 calorie per kilogram of bodyweight per HOUR means I am expending 91 calories per hour, at rest. Over a 24 hour period that is 2,184 calories.

Go ahead, figure this out for yourself: 

(weight in lbs) / (2.2) = bodyweight in kilograms.

KG x 24hrs per day = Basal Metabolic Rate in Calories

What Kind of Energy You're Using

To measure whether your're burning fat for fuel or carbohydrate, scientist use the Respiratory Quotient (RQ).  RQ is the ratio  of CO2 production/O2 consumption. Think of how much carbon dioxide you are breathing OUT and how much oxygen you are pulling IN.

 An RQ of 1 indicates 100% CHO oxidation, while a general value of 0.7 indicates 100% fatty acid oxidation.  I know, you're thinking "why isn't the range 0.1 to 1"? We're talking about utilization of fuel and the exhange of gases so the ratio doesn't flux super low or over 1 because those would be states you could not survive.

Back to a practical example:  Imagine if you exhaled 250ml of carbon dioxide but breathed in 300ml of oxygen.  250/300 = RQ of .83.  Showing you are still using more fat for fuel than carbs.  That might be light jogging.  Now imagine you're breathing out 290ml of carbon dioxide and breathed in 300ml; your RQ would be .96 and almost entirely glucose powered, such as high intensity intervals, weight training to failure and activities that cannot be sustained for more than a few seconds.  This is because when you engage in exercise that demands a LOT of oxygen, at some point you'll tip the scales so that you cannot breathe fast enough or hard enough to meet the demand.  Since you need oxygen to burn fat you have to use carbohydrates.  And even carbohydrates don't give you much energy without oxygen (which is why you end up creating lactate to be converted in the liver into ATP and hence why short, intense exercise is associated with lactic acid) So in a short time, like a bank account where you spend faster than you save, you fall behind the energy demand.  And you simply cannot make the muscle contract.

This safeguard of protecting us from using up way more glycogen is probably why we cannot deplete it lower than 40%.  We have much greater calorie stores as fat in our body compared to glycogen.  And since glycogen is THE powerhouse behind "fight or flight", we need it stocked and ready to go in times of peril. A 65kg person with 12% bodyfat has over 72,000 calories stored as fat and only slightly over 2,000 calories stored as glycogen.  So it makes a lot of sense that those glycogen calories have a higher protection rate.

How Many Calories You're Burning

I've gone over this time and again so just check out this table from Harvard HERE.  It lists calories burned for 3 different bodyweights through dozens of activities.  For average exercise, we're looking at 300-500kcal per hour and the upper end is for larger people.  When you take into account that the longer you do the SAME exercise, the fewer calories you burn doing it, we can see that it ain't much.

Hypoethetically, lets say a 155lb person expended 450 calories during an hour of hard weight training.  They'll probably expend more carbohydrates than fat for fuel, maybe with an RQ of .9 on average while exercising. you'd be using about 2/3 glycogen and 1/3 fat.  2/3 of 450 calories is 297 calories. And since carbs have 4 calories per gram, 297 calories divided by 4  = 75g glycogen.  So one hour of hard training only expended 75g stored glycogen.  Thats 1.5 cups rice.  

So if that's ALL you're expending, why can you eat 300g carbohydrates per day and not gain tons of fat?  Well....consider that most of the calories you eat simply go to running the system.  Four organs: the heart, liver, brain and kidneys: these account for 60% of resting metabolic rate.  Then we've got daily non-exercise activity on top of that.  And before you go thinking excess carbohydrates turn right to fat, even in 3 day overfeeding studies, VERY little carbohydrate is converted to fat.  Normally it is used almost exclusively for fuel while dietary fat is converted to body fat.  So this is a pretty strong case for not nickle and diming your carb intake.

Figuring Out if You Need To Carb Cycle

Now that we know we:

A. Don't use THAT many carbohydrates during exercise and

B. We can eat more carbohydrates and not necessarily store them a fat

We can conclude that a fat loss diet doesn't need to be chronically low-carb and a moderate approach will still let us train hard. In fact, as long as the calorie deficit is set and held constant, there is no reason more carbohydrate as a percentage of your daily calories should not be warranted.  And in a calorie deficit, your cells are much more sensitive to nutrients and insulin so having slightly higher insulin levels from more carbohydrates does not result in insulin resistance.  Obviously in an over-fed state the cells are so inundated with nutrients that they become insulin resistant as a protective mechanism.  But when calories are scarce?  Those bad boys stay sensitive!

My Two Cents

In most clients I work with, I don't carb cycle for a long time.  Some of them I don't ever carb cycle. The reason is I don't tank their carbohydrates from the beginning meaning there is no reason they specifically need a "high carb" day.

What most people miss is that if you diet long enough, eventually calories from EVERYTHING have to be lower and since going TOO low in fat can cause hormonal issues, taking carbs down is just a fact of life.  So in time, carbs only come down because the calorie reduction demands it, not because there's something specifically magic about going low-carb.

In these cases, carb refeeds DO become necessary to restore enough glycogen so that this individual can still have productive training sessions.  And the leaner they are the more insulin sensitive they become which means they can not only handle bigger refeeds but more of them.

But for a 300lb man who needs to lose 75lbs, he'll never need a carb refeed unless it's purely from a social perspective.  He will be consuming enough calories, even on a fat loss diet, to keep his carbs perfectly reasonable throughout his time leaning out.  Throwing him a carb refeed is just throwing a dog a bone, you do it because it might work better in his social life, not because he HAD to have it.

Flip back to someone getting into single digit body fat or training for specific athletic competitions while trying to lean out. Now, training is so important for an athlete that we need to use carb cycling to keep their training productive.  And same goes for the super-lean dieter.

In essence, the person's level of leanness and athletic goals determine their carb cycling needs. 

The Kicker

When you consider that with chronic dieting, you need about 48 hours of maintenance calories to start to reverse the negative effects on the metabolism, a one day carb refeed per week is almost purely psychological, with a slight boost to training.

You stuck with me this long, lets wade into the good stuff together..

How To Carb Cycle

Step 1:

Find your fat loss calories. This is usually your maintenance calories minus 10-20%.

Find your protein.  Minimum 1g per lb for fat loss

Find your fat and carbs.  If you are insulin resistant and have lots of weight to lose, err towards more high quality fats.  If you are already sort of lean and athletic, err towards more carbs.

Run that program for weeks.  Yep, even on training days, run the same darn thing.  The reason is everything above we discussed.  The training calorie and carb deficits aren't that huge and at the beginning of the diet you feel fresh anyway, no sense in complicating things.  Plus, introducing a constant deficit makes it easier to switch into your mental fat loss mode and nail every day consistently. Send a consistent signal to your body that you are leaning out.

Run this program until fat loss pretty much stalls,however long that takes.  If you get wildly bored and stir-crazy, a higher carb meal once a week is fine and is not considered a real carb refeed.

As a bonus, pay more attention to peri-workout nutrition.  When your're in a deficit, nutrient timing matters more and how good you feel during a workout is much more sensitive to the day.  So time your post-workout shake of whey and you might need or benefit from some small carbohydrate serving immediately pre or during your workout. Could be fruit 30mins before or even a G2 during.

Step 2:

Introduce 1 carb refeed per week. Yeah, I know I said this doesn't do too much but it is the start of more frequent carb refeeds and thus just a piece in the puzzle.

Bring yourself back up to maintenance for this one day, with all of the additional calories coming from carbohydrates.

Implement this on a day you'll benefit socially from it, like a Friday or Saturday.

Run it untl you stall

Step 3:

Repeat Step 2, with TWO refeeds per week with the second one before your hardest training session.  Try to make sure these are non-consecutive days.

Step 4:

Repeat the same, adding a third refeed. At the end you'll only have four deficit days and three maintenance days.

This brings you DOWN in calories from the start and then back up as you get leaner and more insulin sensitive AND more diet fatigued. Not only does this accomplish smart and sysematic carb cycling but it also acts as a body recomp protocol because you hit the fat loss hardest at first and then allow for some muscle accruement as you add the refeeds

Bonus Step!

If you follow it this far and get nice and lean, you can try one of two things.  One is add a fourth maintenance day and the keep adding them back in until you're at mantenance all the time.  Or you can tinker with adding muscle while staying really lean and turn those three maintenance days into calorie surplus days.  Add 10-20% surplus on top of the maintenance days (while keeping four deficit days) and see how much muscle you can gain while still staying lean or getting even leaner.  Yeah, it's kind of complicated and that's why we save it for last!


For athletes with high volumes of training or already lean individuals, they probably will start with 2 refeeds per week right off the bat. Having a much higher priority on recover and more to "lose" so to speak from a performance perspective means we can't go too low and we probably don't need to.  I would expect training expends a huge portion of calories in this case and we don't need too much nudging from nutrition to get things moving. In addition they'd have much stricter nutrient timing as well.  But athletes are not the norm and this would be overkill for most.

Carb It Up

I love carbohydrates and any excuse to eat more certainly seems like a good one to me!  But choosing an advanced method means having more plates to keep spinning and more room for error. A straight forward high-protein, veggie and fruit loaded diet with an appropriate deficit is going to kick ass every time.  So don't look for an ace in the deck when you've got one in your hand. 

But as my nutrition mentor, Dan Garner says, "with nutrition, don't show all your cards at once, you want to be able to play that Ace when it matters". In essence save the fancy stuff for when you really need it and play out the basics first.

When you're leaner and ready to go, follow the protocol above and rest assured you're SMART carb cycling.