How can an athlete perform at the highest level with a near total absence of carbohydrate in their diet? Well, the simple answer is, they can’t. But hold on, that’s not to say a low-carb approach should be avoided altogether. Most athletes likely will experience some sort of benefit from implementing some variation of carbohydrate restriction when done at the right time in a competitive season – be it a ketogenic diet all the time, a ketogenic diet in the off-season, or carbohydrate periodization. You may think you know what a ketogenic diet is, but let’s take another pause, and think about that…
What is a Ketogenic Diet?
Here’s the problem, people have misinterpreted the definition of a ketogenic diet as the dietary parameters of the diet – they are not looking at the word “ketogenic” as an adjective, but they should be. A ketogenic diet is NOT 75% fat, 20% protein, 5% carbohydrate, although it very well can be and often is ketogenic, but that does not automatically mean that those macronutrient percentages (the dietary parameters) of calories will induce a state of ketosis. I would bet that 99% of the time, the aforementioned macros will induce a state of ketosis in humans, but for the remaining 1%, that so-called “definition” is invalid. If you take those exact same macronutrients and feed them to a dog, I would bet that 99% of the time, that dog would NOT be producing measurable increases in ketones. To determine if a diet is indeed ketogenic, we must observe a measurable increase in blood or urine ketone bodies.
Ketone bodies are essentially short-chain fatty acids of 3-4 carbons in length, and 2 carbon length chains are short-chain fats, but lack the keto group to make them a ketone. Traditional nutritional biochemists don’t like this classification because it would mean that the body converts glucose into fat (pyruvate and acetyl-CoA) to obtain energy under all circumstances. That really has to make you wonder what the heck was going on when the energy systems were investigated. Glucose is converted to an alpha-ketoacid, but glucose is the primary energy substrate preferred by the body? No, not if it needs to be converted to a fat first! Just because culture and availability and dietary conditioning emphasized carbohydrate does not mean that’s mankind’s “main” metabolism. And now you, the glorious reader, is fundamentally smarter than most nutrition docs. Anyhow…
The most common ketone body is beta-hydroxybutryrate, a.k.a. BHB, followed by acetoacetate, acetone, and pyruvic acid. When measuring ketones in the blood using BHB as a marker, you’re looking for a level above ~0.3 in a semi-fasted state (~2-3 hour fast). If you are fasting even just overnight, you may read at or over 0.3 even if consuming a carbohydrate-based diet. This can get confusing because early on in a ketogenic diet, fasting numbers will be high, but months and months into the diet, the body becomes adept at using the ketones, and the peripheral tissues (muscle, organs, etc.) will pull the ketones out of the blood to use for fuel, and you may read as a false low, so the measure is certainly imperfect. In the urine, you’re looking for a level above “trace.” Thus, an increase in ketone bodies – that’s a ketogenic diet! Even intermittent fasting or alternate day fasting may be ketogenic during and after the fast, but that would be “starvation” ketosis (you’re not really starving) versus nutritional ketosis.
The truth about measuring ketones is that you don’t actually want a ton if performance is the goal. Increases in accumulated ketone bodies signifies that you’re in ketosis, yes, but biochemically, it means that fat is not being completely metabolized. As short-chain fats, they leak out of the cell when fat metabolism lacks the enzymes to continue the process. Ketones do have therapeutic properties, and they are used as fuel substrate, but only slightly more so than larger fats. When considering that ketones are being released from the tissue into the blood anyway, they would have to re-enter the space they just exited in order to make ATP. This may be relevant for exogenous ketone supplementation, but endogenous ketone production is signifying that there is enough.
What Do We Want as An Athlete?
Too often – far, far, far, too often – athletes get all caught up in their diet archetype of choice and they forget why they are dieting in the first place. There’s one or two reasons that nearly every athlete “diets” and that may be to improve performance or to improve body composition. This may be to run faster, jump higher, have less body fat, or move up a weight class. Whatever the goal may be, it’s very important not to lose sight of that goal.
When an athlete considers, or acts on, following a ketogenic diet, it’s likely they want to achieve one of these two goals or both, but I can guarantee you that what most individuals will end up doing is sticking to the archaic definition of a ketogenic diet rather than their goals, and this is exactly why you don’t see more support for the use of a ketogenic or low-carb diet in athletics – people are simply doing it wrong because they misinterpret what a ketogenic diet is in the first place.
The crux of any application of the ketogenic diet for athletic purposes rests on metabolic flexibility.
What is Metabolic Flexibility?
Metabolic flexibility is conditioning the body to use BOTH carbohydrates and fat as fuel. However, current nutritional recommendations for athletes and the general population do NOT create an appropriate environment for metabolic flexibility.
The prevalent recommendations actually do just the opposite – they very much force the body into using carbohydrate. This is so true that when carbohydrate is removed from the diet, we have adverse reactions that may be headache, lethargy, fatigue, irritability, and intense cravings. These are literally withdrawal symptoms. They are present because the human body has not evolved to completely rely on carbohydrates for fuel, yet that is what is constantly provided.
Carbohydrate dense foods were not common throughout our evolutionary history. This is why there are no essential carbohydrates. Fiber is not essential, but it is debatable based on risk of becoming impacted and known health benefits of fiber. However, eating fibrous foods does NOT mean we ate foods with high carbohydrate availability (non-fiber carbs).
You may not believe this, but our ancestors literally ate tree bark. What would drive someone to eat tree bark? Low availability of foods that don’t taste horrendous. If foods with high carbohydrate availability were present (keep in mind they are all plants), they would be eaten. Plants would just be hanging around waiting to be chomped on. However, early humans survived on meat, which contains fat and protein, and meat only came once in a while, and between kills, tree bark and grasses were there to stave off the hunger pangs. Archeological data exists that says human diets were indistinguishable from carnivores based on remains found on teeth; humans have the same digestive machinery (intestines/stomach/etc.) as carnivores completely dissimilar from large herbivores; and even obligate carnivores like big cats eat grass to obtain fiber and "clear out the tubes"
So where do carbs come in? Just like early humans may happen upon some meat, they may find some dense carbohydrate source(s) - just less frequently. This may be once in a while or seasonal. Carbs were around, but they were not around so much that we could evolutionarily develop an essential need for them in the diet like we have with essential fats and amino acids (proteins). However, when they were consumed, they were fairly easily metabolized and with some degree of priority. If sugar was thoroughly abundant, its deliciousness would have been our imminent downfall thousands and thousands of years before modern medicine could keep us propped up.
An athlete is interested in metabolic flexibility for a number of reasons. Carbohydrates are preferred and are the only nutrient that can be used at very high exercise intensities that last more than just a few seconds. However, they’re poorly stored (compared to fat) and are, therefore, needing to be replaced during exercise in durations longer than about 60-90 minutes. Fat is a more efficient fuel, providing much more ATP (energy) per gram than carbs, and we would generally like to be able to use up all this “extra fuel” sitting on our bodies. However, fats can’t fuel high-intensity exercise, and that encompasses nearly all sports. A metabolically flexible person can use carbohydrates effectively during high-intensity efforts, and use fat during less intense efforts, thereby sparing carbohydrate that would otherwise be used during “obligate glycolysis” (a.k.a. traditional dieting).
This is a tricky balancing act, however. In the modern world, we can pretty much do whatever we want with our diet. It’s no longer up to chance. Unfortunately, consuming large amounts of carbohydrate, reduces the ability to use fat, and consuming very little carbohydrate eventually leads to reduced capacity to fully utilize carbs. What’s an athlete to do?
Low-Carb and Ketogenic Diets for Athletes
The answer, broadly, is to manipulate carbohydrate consumption quantities and/or patterns. If you’re an athlete totally unwilling to go “totally” low-carb, I strongly encourage you again to check out our article on carbohydrate periodization. Carbohydrate periodization essentially means you eat carbs when you need them and you don’t when you don’t. What follows is an extrapolation of this concept further down the spectrum.
First things first. If you are a coming from the more traditional perspective of dieting, it’s important to understand that sometimes being “in ketosis” is perfectly fine. It’s not a threat to your health, and if done correctly, it’s not a threat to your performance.
If you are coming from the ketogenic perspective of dieting, it’s important to understand that sometimes being “out of ketosis” is perfectly fine. It’s not a threat to your health, and if done correctly, it’s not a threat to your performance or body composition.
Okay, now that we’re all on the same page, the next step to an athlete’s ketogenic diet is to understand that although this is being referred to as a “ketogenic” diet, and we thoroughly explored the definitions, the athlete will NOT constantly be in ketosis. It would be more appropriate to say that this is the “Athletes Low-Carb Diet that is Sometimes Ketogenic,” but that is too wordy.
Step 3. Consume a traditional ketogenic diet for 4 weeks. This phase should include a eucaloric diet (maintenance calories) with not more than 5% of those calories coming from carbohydrate, and not more than 25% of those calories coming from protein (15-20% would be a safer bet for this phase). The goal of this phase is to jump start fat adaptation. It is very important not to “slip” and eat carbs because, for at least the first 1-2 weeks, you may be in a tough transition phase and you want to get through ASAP by moving forward, not backward. Different people have different experiences. I notice that younger people (< 35 years) and endurance/ultraendurance usually experience few to no withdrawal symptoms. After the 4 weeks, you will be pretty well adapted to this style of eating. You may notice that your high-intensity efforts (>70% VO2Max or 6-20 repetitions per set) may be compromised due to low carbohydrate availability. Your performance will return.
Step 4. This is a re-introduction phase that will last 2 weeks. If you are a runner, cyclist, or other endurance athlete, have 20 grams of “extra” carbs before all exercise sessions. If your session will last longer than 1 hour, have an extra 20 grams per hour of exercise during the session, and try to cease carbohydrate consumption 15-30 minutes before the session ends. Stretching and warming up does not contribute to exercise duration. Resume the “ketogenic” diet afterwards until the next exercise session.
If you are a bodybuilder, powerlifter, or other resistance training-based athlete, have an “extra” 20 grams of carbohydrate before your exercise sessions. That’s it. If you’re doing a high volume leg workout, an extra 20 grams during the workout won’t break you. If you’re doing cardiovascular exercise that could appropriately be described as HIIT, have the 20 grams before. If you’re doing cardiovascular exercise that is not HIIT, skip ‘em! If you’re over 200 lbs and under 15% body fat, do 30 grams for each instead of 20. Resume the “ketogenic” diet afterwards until the next exercise session.
“Extra” carbs means on top of your existing dietary amounts and that the 20 or 30 grams are actually contributing calories. That means that they are NOT fiber or sugar alcohols. You want available carbohydrate to use as fuel during the exercise bout.
Step 5. This is the maintenance phase. Maintenance is not to imply that your performance will be stagnant, but that you’ve reached a degree of metabolic flexibility that you can more liberally manipulate your dietary carbs. There will be some discussion on the topic here, but the ultimate goals of this phase and really the culminating reason for the previous steps is to ensure that the body will be using carbohydrates at maximal rates during high-intensity exercise but otherwise using nearly all fat to yield athletically advantageous results. What this ends up looking like for you as an individual may vary. During this phase, you may also have slightly more freedom in developing your meal plan. Keep in mind, calories are the #1 factor in weight change.
For endurance activities, first identify the intensity of the session. If this will be a high-intensity effort (> 75% VO2Max or heart rate reserve; yes this is different from the 70% before – the metabolism is a little different now after adaptation!), replace 85-100% of the energy that will be used during the session as carbohydrates before and/or during (if longer than 1 hour) the session. If the intensity will be below that threshold, but would accurately be described as moderate (e.g., ~60 - 74.9% VO2Max or HRR), replace 25-50% of the energy that will be used during the session as carbs before and/or during the session. You can find estimates of caloric expenditure during running/cycling via Google search or rough estimate of 110 Cal per mile running or 50 Cal per mile cycling. Below 60%, there is no need to replace. If you are performing a cardiovascular activity for fat loss, only replace if it is a high-intensity session, as it is the performance during the activity that will drive fat loss versus the mere act of performing the exercise, as is the case with moderate to low intensity activity.
For weight training, a lot depends on the body size and muscles being trained. There will be a little more guesswork than with endurance training. If you don’t really like math, just do this:
Arm workout only = 0.1g carbs pre workout per pound body weight
Chest or Back workout only = 0.2g carbs pre workout per pound body weight
Legs (and you sorta train – you know who you are) = 0.35g carbs pre workout per pound body weight
Legs (and you mean it) = 0.5g carbs split between pre and during workout per pound body weight
If you perform in excess of 150 reps for a single body part in a single session, add 0.05 g per pound for arms, 0.075g per pound for torso, and 0.1 g per pound for legs. If you train a single muscle group twice per week, get an extra 0.05 g per pound before the 2nd weekly upper body session and/or an extra 0.075g per pound before the 2nd weekly lower body session. Ok LET’S MATH!
Typical resistance training sessions will only deplete muscle glycogen by 20-40%. If you’re doing less than 20 sets per muscle group in a single session, this is you – put your ego away. ~1.5% of your muscle weight is glycogen, so if you’re 200 lbs and 10% fat, you have about 173 lbs of muscle (minus an estimated 7 lbs for bone) with 2.6 lbs of glycogen (1.5% of 173), which is 1.18 kg (divide by 2.2), yielding 1,180 grams of glycogen or 4,700 calories. If you are able to deplete 30%, that’s 354 grams.
Before you get too excited, that would be for your entire body. So unless you go in and do 15 sets for every muscle group on the same day (not recommended), you’re not getting that many carbs back in your diet! Since you probably do some type of body part split, consider that for women, ~60% of muscle is in the lower body, and for men, ~55% is in the lower body (unless you’ve been an upperbodybuilder for a few years). From there, we kind of just have to guess. Let’s estimate that of the remaining 40-45%, ~5-10% is in the arms, ~20-25% in the back (all of it – lats, spinal erectors, traps, etc.), and ~15-20% is in the front (all of it – chest, abs, and include delts). Also, because unlike endurance folks, there are multiple days between sessions with like muscle groups, it’s not a 1:1 replacement. It’s closer to about 50-60%. Let’s break it down using the same 200lbs and 10% fat example with 50% replacement for slightly easier math:
Leg day – 1,180g glycogen * 0.55 (% in legs) * 0.3 (% depleted) * 0.5 (replace half) = 97 grams “extra” carbs
Chest + Delts day – same math with a % in chest of 0.175 = 31 grams “extra” carbs
Back day – same math with a % in back of 0.225 = 40 grams “extra” carbs
Arm day – same math with a % in arms of 0.05 = 10 grams “extra” carbs
Except for the day-by-day carb adjustments, the diet remains relatively constant, but make sure your calories are adjusted according to your goal. Again, there is a lot of guesswork, generalization, and estimation for these, so you may have some individual differences. If you’re doing 300 reps of a single body part, you’re going to be above 30% depletion and can tolerate/will use more carbs – increase proportional to the activity and size of the muscle. Thus, make individual adjustments to make sure your performance is intact and able to improve long term, but also listen to your body and make sure you’re not going overboard. The idea is to eat just enough, maybe a smidge more depending on your goals.
Examples of an Athletes Targeted Ketogenic Diet
Let’s go over an example for each domain:
This is what a 150 pound runner maintaining body weight would consume per the outlined training week. All carbs are net carbs and protein is 102g daily (1.5g/kg):
Monday – off – 2400 Cals, 208g fat, 30g carbs
Tuesday – 5 mile Fartlek (>75% max) – 3000 Cals, 228g fat, 135g carbs (~80g pre/during)
Wednesday – 3 mile recovery run (~60% max) – 2700 Cals, 221g fat, 75g carbs (~20g pre)
Thursday – 6 miles (~80% max) – 3100 Cals, 228g fat, 160g carbs (~120g pre/during)
Friday – 5 miles (~70% max) – 2950 Cals, 238g fat, 100g carbs (~65g pre/during)
Saturday – 3 mile recovery run (~60% max) – 2700 Cals, 221g fat, 85g carbs (~20g pre)
Sunday – 6 miles race pace (>75% max) – 3100 Cals, 228g fat, 160g carbs (~120g pre/during)
This yields a weekly diet with averages of 14% protein, 13% carb, and 73% fat with high carbohydrate availability when carbohydrate is needed for exercise.
The following is what I, Jordan, a powerlifter and your beloved author, eats and how I train at the time of writing this article ~8 weeks out from a meet still increasing or at least maintaining body weight (212 lbs). All carbs are net carbs, and protein is 241g daily (2.5g/kg because why not):
Monday – Heavy Squat & Deadlift Assistance – 3800 Cals, 261g fat, 122g carbs (54g pre+during as Oreos, milk, and SustainElite – also a big salad with 21g net prior to that)
Tuesday – Cardio + Abs (my basic white girl day) – 3200 Cals, 217g fat, 70g carbs (0g pre, but 20g from carrots & hummus after post protein)
Wednesday – Off – 3050 Cals, 205g fat, 60g carbs
Thursday – Bench – 3450 Cals, 238g fat, 85g carbs (31g as Oreos and milk pre – also a big salad with 40g net prior to that. Mmmm BBQ Ranch.)
Friday – Heavy Deadlift & Squat Assistance – 3800 Cals, 261g fat, 122g carbs (same as Monday)
Saturday – Dynamic Effort & Shoulder Press – 3450 Cals, 238g fat, 85g carbs (same as Thursday)
Sunday – Off – 3050 Cals, 60g carbs, 205g fat (Actually, right now, I keep track of just calories and protein on Sundays, but when I start tightening up the reins to make weight, this will be implemented)
This yields a weekly diet with averages of 29% protein, 10% carb, and 62% fat. I can personally attest that every morning which I’ve tested my blood BHB (which is twice in 2 months, because, remember, it’s not that important), I’ve been equal to or greater than 0.4 mmol/L. My training is going as I’ve expected, which means my bodyweight has increased and my lifts have (pretty substantially) improved, and I’m on pace to PR in every lift at the meet and probably set a few state records.
What Makes This Type of Keto Eating “Okay” for an Athlete?
It’s no secret that athletes and active persons have better glucose tolerance than sedentary individuals. However, the research on ketogenic diets is mostly studied in sedentary individuals. That doesn’t really translate well to athletes’ needs. The fact of the matter is that carbohydrates provide energy and do little else in the body. It’s also not a secret that America consumes energy in excess. The athlete's keto diet pattern of eating provides carbohydrate energy when it is needed – It does not provide carbohydrate energy when it is not needed.
Above a 70% intensity in non-keto-adapted individuals, carbs are absolutely required for a good performance. At worst, 75% is the new threshold in keto-adapted individuals. This spares carbohydrates when exercising at lower intensities and increases the intensity at which an athlete can perform while relying on fat as fuel. Moreover, utilization of more fat and less carbohydrate reduces the accumulation of blood lactate. When introducing carbohydrate in anticipation of or during exercise that will near immediately utilize that carbohydrate energy, we maintain performance without compromising the flexibility to shift back to fat when not exercising or exercising at lower intensities.
This type of diet is NOT recommended for individuals consuming a ketogenic diet to treat epilepsy or any other medical application that benefits from a ketogenic state. When a ketogenic state may be optional, such as with diabetes, exercise is definitely encouraged, but performance is likely not a priority. Nonetheless, non-athletes consuming a ketogenic diet that can manage occasional carbohydrate consumption are actually recommended to eat some approximately once per week.
How the F*#$ do You Eat That Much Fat?!
You probably asked, or would ask, the same question if you had to eat a typical endurance athlete’s diet of 6 – 12 grams carbohydrate per kg per day (~400-800 grams at 150 lbs!). Speaking from experience, I’ve had trouble getting fat up enough, then protein up enough, then too much protein, and just enough of either with too much accompanying carbs. I don't want to say that my diet is boring - I like it - but I generally eat the same things with small adjustments in quantity. My main foods (basically all of the foods) are coffee with heavy cream and sometimes MCT oil, eggs, sausage, full-fat greek yogurt, pork loin, cauliflower mash, salads with ranch or blue cheese, ribeye steaks, chicken thighs, salmon, pesto, broccoli, nuts, nut butter, cheese, milk, burgers, avocado, and whey protein. Occasionally carrots and hummus – like once per week – salami or other cold cuts, and bacon. Right now, Oreos pre workout, but I’m looking forward to switch it up to some Chips Ahoy after eating through this box … but that won’t help with your fat intake! One of the biggest bits of advice is to use vegetables as a vehicle for fat – butter up your veggies, make use of salad dressing, and cream some spinach! Also, take note the use of fattier cuts of meat.
Targeted Ketogenic or Athlete’s Ketogenic Diet Modifications and Options
The word targeted simply means that carbs are consumed before training. While the athlete’s version does include “targeting,” the overarching theme is to consume as many carbohydrates as are necessary to perform your best while maintaining some metabolic flexibility. This may include extra carbohydrates in a meal before or after training; this may include carbohydrate loading; this may include an “off-day” of dieting – as you see in my personal example on Sundays. Sometimes, this is not ketogenic, but again, the most accurate name has no “flow.”
During the day or two leading up to competition, you will NOT undo the majority of fat-adaptation you’ve obtained by eating like this if you need to carb load. If you have a race or some other competitive event, there’s no reason to skimp on the carbs – make sure you have enough and remember that performance is the goal, not sticking to your idyllic diet. Similarly, you may not want to eat like this at all during a competitive season. Save it for the off season – some of the adaptations will persist, and you can still take a “low-carb day” on a rest day to prolong the adaptations longevity. If weight gain is a goal or not a concern, you can use a rest day or your most active day for a calorie- and protein-only tracking or a less intense variation by just having a single “cheat” meal. If you’re competing in a tournament or have 2-a-days or another scenario with a high frequency of exercise, you may benefit from post-exercise carbohydrates as well. Remember, this is meant to be individualized, so you may have to figure out what is best for your own needs by trial and error. I tend to keep carbs pretty low at 10-15% of calories, but on certain days, this can easily increase to 40% or more when warranted.
A ketogenic diet is not accurately defined by its macronutrient composition – it is defined by whether or not it induces a state of ketosis. A deep state of ketosis is not a worthwhile goal for athletic purposes – it is simply an accumulation of short-chain fatty acids that cannot enter the Krebs cycle, which then serve as a marker for a predominately fat-based metabolism. Athletes should be able to inconsequentially transition between carbohydrate-dominant and fat-dominant metabolisms to generate energy as needed to fuel exercise. This involves training the metabolism to use both pathways under the correct conditions. High-intensity exercise = carbs. Low-intensity exercise & rest = fats. The athlete unilaterally training the metabolism to use only one source of fuel does so at the detriment of their ability to use another fuel substrate, which ultimately limits performance during energy-demanding events (most sporting events are energy demanding!). Using an Athlete’s Ketogenic Diet, or a variation, can be a tool to maximize both fat and carbohydrate oxidation. Such an approach may be okay during a competitive season for some (e.g., ultraendurance athletes definitely; marathoners, maybe; powerlifters, doesn’t matter as we only use phosphagen). It may be best reserved for the off-season in athletes with frequent high-intensity bouts during competition (e.g., basketball players, sprinters, obstacle course racers). In any case, enhancing an athletes ability to use both fuel substrates enhances their overall exercise tolerance.