It has been claimed that a Ketogenic diet is not compatible with CrossFit. The reasons most commonly given include:
- Some athletes who tried “low carb” have complained about performance losses
- CrossFit used to do Paleo and now does Zone
- CrossFit requires topped off Glycogen stores
- There are no high level athletes who consume a Ketogenic diet
- Ketogenic diet results in hormonal imbalances
I’d like to look at these claims one at a time.
Performance Losses on Low-Carb
Performance is a thing which is really hard to define. For CrossFit one definition of performance may be defined as the time to complete a particular combination workout such as Fran:
Three rounds, 21-15- and 9 reps, for time of:
This is a very specific workout consisting of two movements. A Thruster is an Olympic weight lifting move down with a barbell loaded to 95 lbs total. Pull-ups are a body weight exercise with a form that is [more or less] particular to CrossFit.
The event is for time – faster is better.
The workout consists of 21-reps of the Thrusters followed by 21-reps of pullups are followed by 15 reps then 9 reps of each movement. The total time is considered the athlete’s “Fran time”.
Fran is picked as a representative set of movements and there are numerous other “benchmark” workouts (WODs) named after women (like hurricanes) and fallen warriers (the hero WODs).
These workouts allows a person to test and retest their performance over time. As a person gains strength and endurance their times will decrease (barring injury of course).
Judging Claims of Performance Losses
The claim, then, could be made that a low carb diet made someone’s Fran time longer. However, since Fran isn’t performed often it is hard to judge a diet based on Fran times and there are no studies offered of that particular metric. None of the athletes I’ve spoken with provided specific metrics for before and after the diet. Unlike other things in CrossFit which can be measured this claim is often more anecdotal than evidence based. This is important given CrossFit’s commitment to measurement as a gauge of improvement. From the man himself Greg Glassman: Understanding CrossFit:
the three most important and interdependent facets of any fitness program, can be supported only by measurable, observable, repeatable facts; i.e., data
Turns out that there actually is a specific study of this very subject. A randomized control trial (gold standard of science) was done at the James Madison University and took a mix of trained and untrained individuals and compared a group put on a Low Carb diet to another group who were not on a Low Carb diet (James Madison University. A low-carbohydrate ketogenic diet combined with six weeks of crossfit training improves body composition and performance. Rachel M. Gregory). (Link to the complete study).
[2018-07-05 – Link to interview with Rachel on Keto for Normies podcast sheds additional light on the selection criteria.]
This study was done for the Masters Degree thesis of Rachel M Gregory in the Spring of 2016. Credit goes to BoxRox for uncovering this paper. The subjects of the study were:
Twenty-seven non-elite CrossFit subjects (mean ± SD age = 34.58 ± 9.26 years) were randomly assigned to a LCKD (males, n = 3; females, n = 9) or control (CON) (males, n = 2; females, n = 13) group.
LCKD (Low Carbohydrate Ketogenic Diet) was instructed to consume an ad libitum diet and restrict carbohydrate intake to less than 50 grams per day (<10% of total energy) and CON (Normal Diet) maintained usual dietary intake.
All subjects participated in four CrossFit training sessions per week during the 6 weeks.
The participants were measured through DEXA scans to determine body composition before and after. The results were:
Compared to the CON (Control) group, the LCKD (Low Carbohydrate Ketogenic Diet) group significantly decreased weight (0.18 ± 1.30, -3.45 ± 2.18 kg), BMI (0.07 ± 0.43, -1.13 ± 0.70 kg/m2), percent body fat (%BF) (0.01 ± 1.21, -2.60 ± 2.14%), and fat mass (FM) (0.06 ± 1.12, -2.83 ± 1.77kg), respectively. There was no significant difference in lean body mass (LBM) change between or within groups. We found no significant difference in total performance time change between the CON group and the LCKD group; however, both groups significantly decreased total performance time (CON: -41.20 ± 43.17 sec.; LCKD: -55.08 ± 44.29 sec.).
So the Low Carb group:
- Lost more weight (about a lb a week)
- Lost more body fat (as a percent)
- Lost more fat mass (as lbs)
That’s not a surprise since the effectiveness of the ketogenic diet is well established. In fact, the control group actually gained a small amount of weight and body fat (the fat both as mass and a percentage). If you want to go CrossFit to lose weight, this study says it’s not going to happen. That matches the observations of some of the people I have gotten to know at CrossFit and fits other studies showing exercise doesn’t contribute much to weight loss (Diet Plus Exercise Equals Diet).
Since many and perhaps even most people get into Crossfit with the purpose of lowing weight this is a significant eye-opening finding. Six weeks of hard CrossFit with your old diet isn’t going to make you skinny.
But, Surely the Keto Dieters Performance Was Worse, Right
What is significant is the performance differences. The Low Carb group decreased their performance times (faster times) than the control group although the times were not statistically significant (because there were wide variations in both groups). The time difference (average) was 14 seconds better in the Low Carb group than the control group.
Since the scientific evidence doesn’t support performance differences how can I account for the claims of local athletes that they lost performance while on Low-Carb? The answer may be in what sort of diet these athletes were actually on.
The “Official” CrossFit Diet Used to be Paleo
Most of the athletes were on Paleo diets (Flexible Dieting: Why CrossFit Athletes are Ditching Paleo, June 23, 2016). The Paleo diet is usually a lower carb diet than the standard American Diet but it is not necessarily low carb.
For most people, the Paleo diet may not be low enough carb to transition to fat adapted. I’ve taken a look at fat adaptation here. For example, if an athlete consumes too much fruit they may never become fat adapted. The fat adaptation process can take anywhere from weeks to months and in the transition it is widely known that performance can be lower. Additionally, cheating may result in a reset out of the ketogenic state which can take some time to re-enter. Basically, it’s a complete lifestyle change choice.
Robb Wolf states that Paleo diet:
…is comprised of lean meats, seafood, fruits, vegetables, roots, shoots, tubers, nuts, and seeds.
In contrast, the Ketogenic diet excludes all fruit, many vegetables, roots, tubers and limits nuts and seeds. Each of the Paleo elements that are excluded in the Ketogenic diet are higher in carbohydrates. A Paleo person could eat potatoes and a Ketogenic person does not.
Since both diets exclude processed carbohydrates and grains they both lead to weight loss due to a net reduction in carbohydrates. Some of the people who eat Paleo also eat low enough amounts of carbohydrates to be in ketosis. Most probably don’t reach ketosis. To be in ketosis is to be fat fueled.
Failure to reach ketogenic levels is failure to access fat as the alternative fuel system.
Glycogen as fuel
It is widely known that Ketogenic diets result in less glycogen stores in the liver and muscles. Glycogen is an energy source which can be used in intense workouts. So it would seem like having less glycogen would be a detriment in these intense sorts of workouts.
What this doesn’t take into account is that ketogenic athletes have an available fuel source that glycotic athletes lack quick access to – fat. The 6 ozs or so we have of glycogen have something like 600 calories worth of energy in them. The 30+ lbs of fat we typically have has over 100,000 calories of energy available. At least over a longer haul being fat adapted seems like a smart strategy.
For endurance athletes, being keto adapted has been well established as a benefit – see the FASTER study (Metabolism, March 2016. Metabolic characteristics of keto-adapted ultra-endurance runners. Volek, et. al.).
Peak fat oxidation was 2.3-fold higher in the LC group (1.54 ± 0.18 vs 0.67 ± 0.14 g/min; P = 0.000) and it occurred at a higher percentage of VO2max (70.3 ± 6.3 vs 54.9 ± 7.8%; P = 0.000). Mean fat oxidation during submaximal exercise was 59% higher in the LC group (1.21 ± 0.02 vs 0.76 ± 0.11 g/min; P = 0.000) corresponding to a greater relative contribution of fat (88 ± 2 vs 56 ± 8%; P = 0.000).
As to the glycogen stores:
Despite these marked differences in fuel use between LC and HC athletes, there were no significant differences in resting muscle glycogen and the level of depletion after 180 min of running (−64% from pre-exercise) and 120 min of recovery (−36% from pre-exercise).
Given that the glycogen stores in the Low Carb group were half of those in the high carb group just how relevant is the glycogen sparing effect? If two people go out to eat and one has $5 and the other had $15 and they both leave with $2.50 in their pocket could you say that the person who got less food was cash sparing? The energy comes from somewhere.
Also, the FASTER study was done at a lower %VO2max, ie, it was on a three hour endurance test, not a Crossfit 20 minute workout.
But is fat as quickly accessible as Glycogen?
Turns out fat is also very quickly accessible in these high-level fat adapted athletes. The FASTER study (Volek, et. al) compared the rte of fat and carbohydrate oxidation for the same 150 minute treadmill run. HC is High Carb and LC is Low Carb.
It is worth taking note that this study was done at a relatively low %VO2max level of effort. This contrasts with Crossfit workouts which are often done at higher intensity levels.
No Ketogenic Athletes
Given the public excommunication of Robb Wolf within CrossFit it’s not much of a surprise that there are not many top athletes who say they follow a Paleo or Ketogenic diet. That would hardly earn them the endorsement of top CrossFit personalities.
Also, these are people who would risk their health for the sake of winning (CrossFit and Steroids. Just How Juiced Is CrossFit? by John Romano | 10/16/15). If they think they can beat out the next guy by a second or two on Fran they will.
But this raises the question. Suppose it is determined that a ketogenic diet does affect performance by some small amount. A top athlete is dealing with very small percentages between herself and the next gal and is willing to risk their health. Is that the case for the average box-goer?
Also, given the very high level of training that goes into making a top CrossFit athlete they probably have a lot of wiggle-room in diet. They are burning it all off. But how many of us who do a 20 minute WOD a few days a week are doing anything like what these athletes are doing? And why should we follow their diets if we are not doing the same intense workout program?
Diet of the World’s Most Fit Woman
Digging around on the Interwebs for the diet of Katrin Davidsdottir, the winner of the 2015 CrossFit Games turns up this (This Is What the ‘Fittest Woman on Earth’ Eats Every Day How does your diet stack up? by EMILY ABBATE August 10, 2015):
I’ve got to have my eggs, otherwise my day starts off wrong,” she says. “In an effort to get more fat in my diet for fuel, I eat half of the avocado and then the cream in my coffee.
On a good day, when she gets to eat lunch, it’ll be chicken salad and the other half of the avocado. On the days she doesn’t? “I’ll eat as soon as I finish training, and leave practice drinking coconut water with a scoop of chocolate protein powder and a serving of fruit. For dinner, I try to eat lots of dark green stuff-spinach, kale, broccoli. For protein I’ll have chicken. For dinner, which would come soon after that late lunch, I try to eat a portion of salmon for its healthy fats and vitamin D.”
Other than the single serving of fruit her diet is ketogenic. And given her workout schedule that’s not a whole lot of carbohydrates. Note that was back in 2015 (Robb Wolf’s split from CrossFit was about 2009) so this is long after that split.
So at least the world’s most fit woman eats a diet very much like a ketogenic diet, even if she doesn’t call it that.
Keto and Hormones
I am going to do a followup article on this subject.