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Protein, carbs and fats are the three macronutrients that compose your calorie intake – unless you drink enough alcohol to count that as a major contributor, in which case, maybe training isn’t very high on your priority list! For those of us that train hard and care about results in a big way, we know that nutrition is very important to optimize results. Most of us know that getting enough calories to grow muscle, eating fewer calories to burn fat, and consuming enough protein are all super important steps. And that’s totally spot on. But what about carbs? Some people extoll them, some disparage them. Are carbs a super fuel for hard training or a surefire fat gain indulgence? We’ll spare you the BS and cut straight to the truth: carbs are a huge and indispensable advantage to hard-training athletes, including those that want to better their endurance add size, or get leaner. But you don’t have to take our word for it. We’ve come armed with a comprehensive description of what carbs are and how they help you with your fitness goals.

Carb Basics

Carbs are one of the three main macronutrients. Produced almost exclusively by plants and found mostly in plant foods, carbs provide about 4 calories of energy per gram of nutrient. When any kind of carbs are ingested by humans, they undergo an extensive process of digestion, absorption, and finally, conversion into glucose (if not ingested as glucose already). All eaten carbs pass through the liver and are mostly either converted to glucose and sent out into the blood or stored as glycogen (a bunch of glucose molecules linked together and stored for when they are needed) right there in the liver. Sometimes, carbs are converted into fat or other molecules, but in hard-training this is relatively rare, especially if calories are not massively (and too far) over maintenance levels.

The Roles of Blood Glucose and Glycogen

Glucose that doesn’t stay in the liver is secreted into the bloodstream, and for good reason. This blood glucose supplies nearly every single body cell with the energy it needs to function. Especially needy of blood glucose are nervous system cells such as brain cells and the nerves that activate and control the skeletal muscles. They prefer glucose very highly over either protein or fat for energy, and work much more smoothly and productively when their blood glucose supply is high.

When muscle cells take up blood glucose, they can use it to power their main processes of activity and repair. However, muscles usually store, right there in the muscle fiber itself, much of the glucose that arrives via the blood as glycogen. Glycogen is incredibly efficient as a rapid energy source. Your muscles can pull glucose from the blood only very slowly, so if you rely on blood glucose for anything more intense (rapid in its energy demands) than a walk, you’re not going to be able to get enough to meet energy demands, and your performance will be far off your best. Glycogen, however, can provide glucose to the muscle’s energy systems at much, much higher speeds, and is thus the dominant fuel for most high-intensity activities.

Carb-Dependent Activities

How high an intensity are we talking about glycogen supplying? Well, anything under about 3 reps (singles or doubles, one jump or one throw at a time, for example) relies on basically pure ATP and doesn’t even rely on the energy system (glycolysis) that utilizes the glucose from glycogen. Anything slower than a fast walk can rely mostly on fat oxidation for fuel, and thus also doesn’t require too many carbs, nor is performance in it limited much by low carb intake. Now, just about every activity less explosive than a two rep max and more explosive than a walk through the park is predominantly fueled by glycogen. If you’re wondering what an example of such an activity is, we can give you a hint; pretty much almost every single sport or training kind and type. Explosive activities rely hugely on glycogen when they are repetitive since it’s the fuel that recovers your muscles between jumps or snatches or cleans even when it’s not the fuel actually being used to directly produce those motions. So unless your training consists of hitting one snatch, one clean, and a couple of jumps and then going home, glycogen is critical to your best performance in that training.

Research on glycogen and sport performance is quite overwhelming. In study after study, the reduction of muscle glycogen stores show a very tight correlations to performance outcomes and ratings of perceived exertion. In short terms, if you don’t get in enough carbs to replenish your glycogen stores, you’re gonna train like shit, compete like shit, and feel like shit doing it. To add to these matters, blood glucose is such an important fuel for the nervous system that when it drops too low, fatigue increases radically and performance drops off precipitously. Your muscles need glycogen to perform and your nervous system needs blood glucose to tell your muscles to give you all they have. These functions reflect themselves in multiple advantages to the training process.

Advantages to Eating Carbs

When you get in enough carbs in your diet, your blood glucose and glycogen are not deficient, which gives you several distinct advantages in performance and adaptations. Here are some of the more well-studied ones:

  • Higher Training Intensity

Fully stocked glycogen stores and high blood glucose levels allow both your muscular and nervous systems to perform at their peaks. If you want to lift heavier weights for your sets of 5, run faster 400s, and do quicker pullups, getting in enough carbs helps.

  • Quicker Recovery Between Sets

You might be able to put up a couple of good explosive performances while low on carbs, but a couple of reps or sets later, your ability to recover will simply not measure up, and your performance will fall off fast. High glycogen and blood glucose levels will allow you to recover more completely between sets if you don’t change your rest intervals, or they can allow you to shorten your rest periods without lowering performance compared to the effects of a low carb diet.

  • Quicker Recovery Between Workouts

Not only do carbs let you recover between sets in a more complete and rapid fashion, but they also provide much the same effect between workouts. Why have 2 hard sessions a week when you can recover from 3?

  • Less Intensity Drop-off with Long Duration

The longer you work out, the lower your muscle glycogen drops, which lowers your training intensity. In addition, your blood glucose drops too, which lowers your intensity further still as the nervous system becomes less effective at stimulating your muscles to move you. By consuming adequate carbs to have high muscle glycogen levels and getting in enough carbs to power the nervous system (even during the workout for long workouts over an hour in duration), the intensity you can put out late in your workout or your competition will go up. That’s a BIG deal for most hard training athletes and especially in sport competition when the last several minutes can be so critical in determining the final outcome.

  • Resulting Higher Training Volumes Above Overload Threshold

Combining the first four advantages yields us a very important independent advantage: a higher training volume at overload. You don’t get better by just doing work… you can’t walk your way to elite marathon performance and you can’t do pulldowns with 50lbs to get better at pullups weighing 200lbs. You get better by doing as much HARD work as you can recover from. Not only do enough carbs in your diet give you enough energy to do the most hard work you can to stimulate adaptations and improvements, they also help you recover so that you can keep sustainably cranking out those high workloads – and keep improving.

  • Anti-Catabolic Role, Possible Anabolic Role

As a bonus feature, carbs are very anti-catabolic. They prevent muscle from being broken down and used as energy to a very high extent, especially during and right after hard workouts. There are also some tentative reasons to believe that carbs might be anabolic in the post-workout window. So not only are carbs sure to be able to let you train hard and let you recover better, they can also save your hard earned muscle from being burned too much during that very training and might even help you grow a bit of extra muscle directly as well.

Ok, fine, carbs are great. How many should we eat, when should we eat them, and what foods should we get them from?

How Many Carbs?

Protein needs are fairly easy to determine. Around a gram of protein per pound of bodyweight per day is a rough figure for most athletes, and values a bit lower or higher seem optimal for muscle mass building and retention. Fat needs simply seem to have a lower-bound, where anything above 0.3g per lb of fat per day keep the athlete performing and recovering well. In contrast to the constant needs of proteins and fats, carb needs are closely tied to physical activity levels. There are two sources of physical activity that need to be considered for determining rough carb intake: training volume and baseline physical activity. The training volume consideration is easy; the more you train, the more carbs you take in. But it’s important to consider baseline physical activity. The more active you are in your work and leisure, the more carbohydrate you’ll need to make sure that those carbs aren’t just burned in activity and not available to support training. The end result of combining physical activity and training volume considerations is a general beginning guide to determining carb intake according to needs:

0-1g carbs per lb bodyweight per day: Sedentary work (office job), vehicular commute (taking mostly car, bus, or train to work, gym), low training volume (sets of 3-5 reps or lower)

1-2g carbs per lb bodyweight per day: Moderately active job (personal trainer, waitress…), walking or cycling commute, moderate-high training volume (multiple sets of 8-12 reps, workouts that last 1-2 hours)

2-3g carbs per lb bodyweight per day: High activity job (fitness instructor/class leader, construction worker…), high use of walking or cycling to get around, high volume training (workouts that last 2 hours or more, multiple workouts a day, combinations of weight training and endurance work)

3g+ carbs per lb bodyweight per day: High level endurance or fitness sport training with multiple (2-3 sessions) per day of high-output activity

Carb Timing

Carb timing is not nearly as important to results as are carb amounts, but it does have some influence on outcomes. A couple of easy rules apply:

  • Consuming carbs in the last meal before training can improve performance of the training session
  • Consuming fast-digesting carbs, usually as sports drinks, during an activity that lasts longer than an hour can improve tail-end performance of that activity and spare muscle loss, especially when combined with a fast-digesting protein like whey
  • Consuming carbs in the 4-6 hour window post-workout replenishes glycogen faster and more completely than eating the equivalent amount of carbs during other parts of the day

The simple take-home message of carb timing is this: you have a certain amount of allotted daily carbs, so when you make the choice as to when to eat them, having most of them before, after, and possibly during training is a good idea. If you train more than once per day, having carbs during and after training becomes even more important, and no longer just a small detail.

Carb Sources

There are two major concerns for carb sourcing: how quickly the carbs digest and how many other nutrients the carbs are paired with. Some carbs like sugary cereal and Gatorade digest very rapidly, and are ideal sources for during and right after hard workouts, especially if other workouts are planned later that day. Meanwhile, slow digesting sources like oatmeal and whole grain bread are best for sustaining energy when eaten in most of the meals of the day.

There are four main classes of nutrients that can be included in large amounts in some carbs sources and be almost completely absent in others. Vitamins, minerals, fiber, and phytochemicals are important for human survival, health, and athletic performance, so most of the carb sources you choose should be abundant in these nutrients. When trying to allocate carbs as quickly and easily as possible during and right after hard training, fiber limits digestion and absorptions speed and is not recommended. Thus, the focus on highly nutritious carb sources can be suspended for the intra-training and post training meal carbs. Other than that special exemption, the carb sources highest in vitamins, minerals, fiber and phytochemicals are fruits, vegetables, and whole grains, which should form the majority of carb intake in athletes.

Carb Supplements

Are carb supplements a good idea or a waste of money? If you’re training hard for longer than an hour and/or multiple times per day, consuming a liquid meal of fast digesting carbs and whey protein is recommended to prevent muscle loss, support high performance at the tail end of sessions, and allow for faster glycogen repletion and recovery between sessions. It’s not a magical effect that will absolutely revolutionize you training, but it will work to improve your results. This can be a big deal in competitive sports where even a small advantage can help you just enough to bump you ahead of your closest competition.

Cutting Carbs to Lose Fat

That’s just about it for this primer on carbs, but there’s on important issue that is worth mentioning. You just read a couple pages worth of some very good reasons to consume adequate carb amounts if your interest is high performance. So if carbs are so important to performance and muscle mass, should they be cut when fat loss is the goal? A lot of folks do this, so there has to be some merit to it, right?

Well, yes… cutting carbs does in fact lower calories and allow for fat loss. But with that cut in carbs comes a predictable loss in recovery and performance ability. Our best recommendation is to cut fats first. Once you’ve cut your fats to come close to the 0.3g per day minimum, then you’ll have to cut carbs. But until then, keep cutting fats and don’t cut carbs until you have to… they’re so important for results that the less of them you cut, the better.

Dr. Mike Israetel

Mike is a professor of Exercise Science at Temple University in Philadelphia, PA and was previously a professor at the University of Central Missouri, where he taught Exercise Physiology, Personal Training, and Advanced Programming for sports and fitness. Mike’s PhD is in Sport Physiology, and he has been a consultant on sports nutrition to the U.S. Olympic Training Site in Johnson City, TN. Mike has coached numerous powerlifters, weightlifters, bodybuilders, and other individuals in both diet and weight training. Originally from Moscow, Russia, Mike is a competitive powerlifter, bodybuilder, and Brazilian Jiu-Jitsu grappler. He used to hold a bunch of state, national, and world records in raw powerlifting back when everyone was in equipment, so that’s cool!

READ MORE BY Dr. Mike Israetel

8 Responses to “Carbs: The Training Fuel”

January 05, 2016 at 8:28 am, Josh Cook said:

Seems like the carbs are low for the 3-5 rep range, because when I see that, I think 85%+ for multiple sets. Even if we were to apply this to Olympic weightlifters I feel the carb is low for their demand. Am I wrong here?


January 05, 2016 at 9:12 am, Marc Ciminelli said:

What is your thought on nutritonal ketosis and performance? Well adapted, performance can actually increase even at high intensities as your body becomes somewhat of a “fat-burning machine”. Furthermore, the brain can be very efficient at using ketones for energy and does not have to rely solely on glucose for good functioning. Again, in a well adapted state (usually 2-6 weeks of adaptation with a diet low in CHO usually set at 50g or less but this can vary from person to person as some people metabolize glucose better than others).


January 28, 2016 at 7:46 pm, Mike Aders said:

So my current weight is 318 lb. I’m a new powerlifter. My initial goal weight is 265. I, following my first meet next week am hoping to get me aggressive with my fat loss training 3 days a week and contemplating li cardio 2 days per week. Thoughts on the cardio? What should my macros look like? I was planning 2000 cals per day until I get down, prior to bulking again to cut again as you mentioned in a video. I was hoping to get your thoughts on that. Thanks so much.
Evansville, IN


June 16, 2017 at 8:38 am, Mike Orme said:

I suspect he’s not a fan.


January 05, 2016 at 12:04 pm, Kyle Wheeldon said:

I would also like to hear the answer to Josh Cook’s question please.


January 05, 2016 at 2:53 pm, Charles Hwang said:

What would be the best carb intake protocol for someone who has a sedentary job, but trains 5 days a week, at sets ranging from 8-20 reps?


January 06, 2016 at 5:47 am, Tom Sandra Stepp said:

What about those of us that screwed their metabolism with excess processed carbs for 35 years and are over 25% BF. And “Carbs” ….simple carbs or complex carbs. High glycemic or low glycemic? Frustrating when you don’t have a degree in nutrition. Thanks


April 01, 2016 at 9:36 am, AJ said:

Any thoughts about cycling? I have read so much about it don’t know where to start. Also–what does the lower bound for fat mean? Thanks friends!


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