- The science behind ketosis
- What is a ketogenic diet and how is it different from a low carb diet?
- A look at the research: how ketosis affects performance
- What results can you expect on a ketogenic diet?
- Mistakes to avoid when following a ketogenic diet
- Why ketogenic diets won't help you lose fat and build muscle
The nutrition scene is all over the place.
How many diet “trends” are there going to be? It's exhausting trying to put out the flames when a new one arises.
Now one of the more widely used diets is the ketogenic diet (I get sick of typing ketogenic diets so from here on it will be referred to as KD). Despite a lot of people using it to lose fat and get a shredded physique, there is so much nonsense and misinformation going around out there. Even “experts” miss the boat a lot when we talk about ketogenic diets.
Perhaps the most misunderstood aspect is how a KD impacts performance and your ability to add muscle and strength.
Ketosis: What is It?
Alright folks, it's time to put the nerd glasses on because in order to get to the bottom of this, we have to have a quick science lesson.
Ketosis is a metabolic state that occurs when dietary carbohydrates are in such low quantities that your body must rely almost exclusively on fatty acid oxidation and ketone metabolism. That sounds simple on the surface, but let's unpack it a bit because it will help partially explain why the body goes into ketosis.
To function, your body requires a substantial amount of energy in the form of ATP. For the purpose of this article, let’s just assume that the average person uses about 1,800 kcal per day to create enough ATP to keep us alive (and by that I mean simple lay on the couch, eat cool ranch Doritos, and binge watch Netflix).
Now this is where it gets interesting. You have this thing in your skull, we call it a brain. . . well, at least most of you have one. That squishy organ uses about 400 or so kcal per day and it runs almost exclusively on glucose (there is some evidence it can use small amounts of fat and lactate, but in the larger context that is not all that important).
This means you need on a minimum 100g of glucose per day just to fuel your brain.
What the #$%& does this have to do with ketosis… well frankly, everything.
Let's say we cut out all carbohydrates from our diet. That means we effectively remove any dietary source of glucose for the brain. Contrary to some of your daily experiences with people, you need a brain to function so we are going to need to get it from somewhere.
Thankfully the liver stores glucose and can pump some into the blood to fuel the brain. Your liver, on average, can store around 100-120 grams of glucose. Ok, awesome, your liver lets you function for about a day. Then what? You eventually run out because we can’t replace it fast enough.
Houston, we have a problem. We need more brain fuel.
Your muscles are also a huge store of glucose (around 400-500g) in the form of glycogen. Sadly your muscles can’t break that glycogen down to ship it out to the blood and eventually the brain because your muscles lack the enzyme that breaks glycogen down (glucose-6-phosphatase). Now we are really in a bind.
Without carbohydrates around, our liver begins to do something really interesting. It starts producing ketone bodies that are released into the blood for our brain and other tissues that don’t utilize fat for energy.
Let's talk about the biochemistry of this process really quickly. When you “burn fat” you are really taking a fatty acid molecule and converting it to acetyl CoA that is then combined with oxaloacetate, which then begins the Kreb cycle.
The wonders of science never cease!
During ketosis your liver is utilizing so much fat for energy that it begins to have excess acetyl CoA hanging around and starts turning it into ketone bodies (Beta-hydroxybutyrate, acetoacetic acid, and acetone).
Since your body is in need of a new energy source, your liver begins to dump these ketones into the blood stream. Once your body reaches a state where it begins to do this continually and there are noticeable increases in blood levels of ketones, you are officially in ketosis.
Now I understand that was a lot to digest. But understanding ketosis is incredibly important for understanding the context of ketogenic diets in application.
What is a Ketogenic Diet?
Now we need to define what a ketogenic diet is and how it differs from low-carb and “fat adapted.”
Low carb utilizes fat and carbs for your daily energy needs. Your body does not accumulate blood ketones and your tissues are not using ketones primarily for energy.
A ketogenic diet means your body has reached the point where it is actually producing ketones in sufficient amounts, that there are elevated levels of ketones in your blood, and it is being utilized for fuel.
During “nutritional ketosis” your blood levels of beta-hydroxybutrate typically fall between 0.5 and 3.0 mM. You can be super cool and buy some keto sticks and pee on them to see if you are in ketosis.
Ketogenic diets tend to utilize more ketones and substances like lactate preferentially over glucose and fat.
Low-carb diets often restrict carbohydrates to a low level (often under 100g/day), but do not consistently obtain levels of B-OHB between 0.5 and 3.0mM.
Let’s make this crystal clear. Low-carb and KD are not the same thing.
Ketogenic dieting induces a substantial metabolic change that results in different physiology beyond just low carb dieting.
How to Eat For Ketosis
As we discussed above, consuming a high amount of dietary fat and a low amount of dietary carbohydrate are the key features of a ketogenic diet.
Exactly how high fat and low carb?
Traditional, strict, ketogenic diets are structured with about 70-75% of your daily caloric intake coming from fat and about 5% from carbohydrates. The range of carbohydrates you can consume and stay in ketosis varies from person to person, but you can usually eat up to about 12% of your daily caloric intake and stay in nutritional ketosis.
Now the really important part for most people to consider is their protein intake. For most of us in the training world, we have it pounded into our head that high protein intakes are the way to go, and I think this is a large part of why people’s foray into ketogenic diets fail.
As we discussed above, protein above certain quantities is glucogenic and will prevent you from staying in ketosis.
Practically, consuming about .8 grams of protein per pound is enough to kick you out of ketosis. Bro . . . put down the protein shake and walk away.
So ideally, to optimize a ketogenic state and maintain lean mass your diet should be about 75% fat, 5% carbohydrates, and 20% protein.
The "Adaptation Phase"
If you look in the ketosis literature and ask for anecdotes, you will see a common theme emerge. There is most definitely an adaptation phase where in the initial stages people will experience “brain fog”, feel sluggish, and have noticeable changes in energy levels.
Basically, a lot of people feel like garbage the first week or two they try a ketogenic diet. This is likely due to the body’s lack of enzymes needed to convert substrates and oxidize them efficiently.
Essentially your body is learning to change fuel sources and to rely primarily on fat and ketones for fuel. Typically after about 4-6 weeks of “keto adaptation” these symptoms disappear at normal activity levels.
Ketosis and Performance
All of what we have discussed so far is incredibly straightforward. Now we get to ruffle some feathers.
There have been epic debates about whether ketogenic diets affect “sport” performance.
Related: Best Workouts for Sport Performance
While I don’t claim to be a guru or have the final answer, let’s look to a few studies to see how ketogenic diets affect performance and draw conclusions that might elucidate an answer.
The first study involved twelve people (7 males, 5 females, age 24-60 years) who went on a self-prescribed KD for a median of 38 days. They followed moderate to intensive exercise routines and underwent blood, body composition, and VO2 testing.
Let me just let the authors of the study drop some knowledge bombs on you, “The drastic reduction of carbohydrates had no statistically significant influence on running performance judged by the time to exhaustion and VO2 max.. . [body composition] measurements showed improvements of body composition with an estimated decrease of 3.4 kg of fat mass (p=0.002) and gain of 1.3 kg of fat free mass.”
Ok, so these people basically lost weight (with about 28% of that coming from lean mass), but didn’t see much change in a running test.
Also the people on the KD diet had impaired ability to recover.
Onto study two. Eight males in their late twenties/early thirties, with at least five years of training experience, went on 4 weeks of a mixed and ketogenic diet (KD) in a crossover design and then performed a continuous exercise protocol on a bike with varied intensity.
This is what a “crossover” design looks like:
Here is what happened.
The KD caused favorable changes in body mass and body composition, as we saw in the first study.
Interestingly, there was a significant increase in the relative values of maximal oxygen uptake (VO2max) and oxygen uptake at lactate threshold (VO2 LT) after the KD.
The increase in VO2 can be explained by the reduction in body mass (when you lose fat mass your VO2 goes up because that is how the equation works! VO2=ml/kg/min, if you reduce body mass you reduce the number in the denominator thus you increase the relative value).
However, the max work load and the work load at lactate threshold were lower after the KD.
Basically, this means that the KD led to weight loss, but that it also greatly reduced power output and the ability to train at high intensity.
Want to be more powerful and train harder? Don’t think a KD is the way to go.
For our 3rd study let’s get off the treadmill and the bike, because honestly, I could not care less about that.
Study 3 examined how 30 days ketogenic diet (4.5% carbs) would affect performance during: hanging straight leg raise, ground push up, parallel bar dips, pull up, squat jump, countermovement jump, and 30 sec continuous jumps. They also measured their jackedness (aka body comp).
So. What happened?
- The KD caused a “spontaneous reduction in caloric intake” compared to the normal diet.
- There was no loss of performance in these “measures of strength” on the KD. But there was also no improvement in performance.
Similar to the other studies, differences were found in body weight and body composition: after the KD there was a decrease in body weight (from 69.6 ± 7.3 Kg to 68.0 ± 7.5 Kg) and fat mass (from 5.3 ± 1.3 Kg to 3.4 ± 0.8 Kg p< 0.001).
Note that these individuals were already incredibly lean (~7% body fat).
It is important to note that none of these tests would have heavily relied on glycolysis to provide energy, nor were the tests of “metabolic exhaustion”, they were more tests of power production, the phosphagen system, and muscle fatigue tests.
Study 4 is perhaps the most well known of the ketogenic diet studies.
In this study, 5 highly trained cyclists performed a VO max2 and Time to Exhaustion (TEE) cycling test before and after a 4 week ketogenic diet.
While this paper is rich in data, I want to focus on the “performance” aspect of it and the muscle glycogen levels.
The TEE test showed extremely high variability between the participants. 1 showed a huge increase in TEE (not sure how a highly trained cyclist increases their TEE by 84 minutes in 4 weeks), another showed a 30-minute increase, while two showed roughly 50 minute declines and 1 showed almost no change. . . check out this figure I made just for you!
As for muscle glycogen stores, muscle biopsies showed that the KD reduced muscle glycogen to almost half of normal. That alone is enough to indicate high-intensity performance might be impaired.
What The Data Says about Ketogenic Diets
Let’s take a look at what is consistent across the 4 studies. What can we learn from these 4 studies about ketogenic diets and performance?
Improved Body Composition
The first consistent theme is improved body composition. I would argue this is most likely from spontaneous caloric restriction and not some magical fairy dust from the KD.
Why do I say this?
Because in a substantial amount of other studies focusing on diets and body composition, diets that reduce caloric restriction from any source (even those that reduce fat) improve body comp.
Just look at Study 3. These individuals were already super lean (like 7% body fat) and the ones who were on a KD consumed about 10,000 less calories over a 30 day span (~333/day) than on the normal diet and I’ll be darned.. but they lost weight.
Now, it is plausible that there may be additional benefit on body comp from a ketogenic diet but I think the research hasn’t fully fleshed that out yet.
Additionally, there is no literature to support that a ketogenic diet is beneficial for promoting increases in muscle mass, just losing weight.
Impaired High-Intensity Performance
The first two studies both showed a decreased capacity to perform at high intensity. This is likely due to two mechanisms: 1) reduced intramuscular glycogen, 2) reduced capacity for hepatic glucose output during high-intensity training.
Reduced Levels of Intramuscular Glycogen
The reduction in performance at high-intensity is likely a feature of the reduced levels of intramuscular glycogen seen across the studies. This may also impact recovery for hard training athletes and impair the ability for muscles to increase in size.
I don’t know about you but if I want to hammer out a decent training session I am not about to go into it with a half full tank.
Mistakes People Make On Keto Diets
Now a KD can be a tool to use. If you want to drop some pounds pretty quickly (albeit at the likely expense of some lean tissue), then it might be worth exploring. That being said, lets go over some of the mistakes people make so you can avoid them.
Not Allowing Adequate Adaptation Time
The transition to ketosis can be tough for some people. Often people quit during their adaption phase and never fully transition.
Personally, I have tried ketogenic dieting in the past and the adaptation phase was a few weeks of feeling a little sluggish and had some brain fog, but after about 2-3 weeks my energy levels returned to normal.
If you want to try a ketogenic diet, give it adequate time for adaptation.
Eating Too Much Protein
As we learned earlier, too much protein can prevent ketosis. People often offset the reduction in carb intake with more protein at their meals.
Put down the protein shake! Make sure you are limiting your protein intake to less than 0.8 grams per pound.
Using it Indefinitely on High Intensity Training Volumes
In high-intensity, anaerobic exercise, your body relies mainly on glucose from blood glucose, muscle glycogen, hepatic glucose output, and gluconeogenesis for fuel.
Since ketogenic diets reduce muscle glycogen, it is really hard to train at a high level.
If you want to mess around and experiment with KD and train at high intensity, a “carb-cycling” or cyclic ketogenic approach might be more beneficial for your training capacity than a traditional ketogenic diet.
Ketogenic Diets Don't Optimize Muscle Gain
Ketogenic diets may be good for losing weight, but they certainly don’t optimize muscle gain nor do they optimize your training capacity.
A KD will likely hamper your ability to put on lean tissue and to train at high intensities. So if those are your goals, you can skip trying a KD.
Trust me. I’ve been there, done that. It wasn’t fun or exciting.
Look at both the research and the anecdotal information and you will find that people who have had great success at gaining muscle have not used ketogenic diets for their gains.
Why is this? Well nutrition science (not bro science) has found that consuming both carbohydrates and protein elicits a greater anabolic response than either in isolation.
On a ketogenic diet you strip out the carbohydrates. And since both protein and carbs are needed for Optimal Muscle Gain, you are missing a key ingredient.
Ketogenic diets are not optimal, and probably not even effective for building mass and optimizing training performance.