by Siim Land
The Arctic variant was selected by the environment about 6000-23 000 years ago to be an advantage because of some unknown reason, which simply swiped the entire population through positive adaptation to become normal[581]. Maybe, during some time in the past, it was simply not advantageous to be in ketosis and avoid fasting. Because of the cold Nordic regions of the Inuit, it probably had to do with the continuous need for calories and heat in such a harsh climate. Instead of producing ketones, the fats they ate got converted into glucose for the brain and the triglycerides were used up by muscles and heart. Ketones became simply secondary. Furthermore, persistent ketosis in such extreme living conditions was not favourable because of potential ketoacidosis in conjunction with other environmental stressors. Whatever the case might have been, it’s simply fascinating to see that even on the evolutionary scale, it’s not always the best to be in ketosis. It also says that humans evolved under intermittent ketosis, not a continuous ketogenic diet.
As I said, you don’t need to maintain nutritional ketosis 24/7 to be keto-adapted. You’re not going to get into ketosis by eating keto for one day, and you’re not going to lose your fat-burning metabolism by getting out of ketosis from time to time either. The body is trying to maintain homeostasis and not go through random changes all the time.
Why Bother With Keto?
You’re always burning a mixture of different energy molecules whether from glucose, ketones, fatty acids, lactate, and many more. What proportion of each you’re currently using depends on the intensity of physical exertion, your overall metabolic condition, and your degree of keto-adaptation.
The simplistic view of fuel utilization is that your body will burn primarily fat at lower intensities of exercise and at higher levels of exertion it starts using more glycogen and glucose[582][583][584]. This is known as the Crossover Effect, with a progressively increased contribution of carbs as a fuel source (See Figure 81). It promotes the idea that you can’t perform high-intensity sports while eating a low carb ketogenic diet.
Figure 81 The Crossover Effect
In reality, your body needs glucose from carbohydrates under certain metabolic conditions. At other times, or during periods of starvation, the body will come up with many alternatives that are actually much more suitable in certain situations.
Ketogenic Diets and Endurance Performance
In 2016, Jeff Volek and Steven Phinney did a study called FASTER (FASTER=Fat-Adapted Substrate oxidation in Trained Elite Runners), which showed that ultra-endurance athletes who had keto-adapted for 9-36 months showed extraordinarily higher rates of fat oxidation[585]. Here are the main findings:
They were using fat for fuel even at intensities of 70-80% of their VO2 max, compared to the 55% of the high carb control group.
Peak fat oxidation was 2.3-fold higher in the low carb group and it occurred at a higher percentage of VO2 max.
During submaximal exercise, fat oxidation was 59% higher in the ketogenic group.
There were no significant differences in resting muscle glycogen and the level of glycogen depletion even after 3 hours of exercise.
Over the course of a 3 hour run at 65% of VO2 max, the low carb group was burning 30% more fat and 30% fewer carbohydrates than those who ate high carb. Some of the subjects on the keto diet actually burned 98% fat and only 2% glucose at 65% intensity. (See Figure 82).
Figure 82 Fat oxidation rates between low carb and high carb athletes
Keep in mind that, fat oxidation doesn’t refer to losing body fat directly – it refers to what proportion of fatty acids get burned in the Krebs cycle for energy. In the case of these low carb athletes, they were able to fuel their exercise with primarily fat. Therefore, they could’ve continued to exercise for several more hours without running into an energy crisis as long as they still had enough body fat with them. The fat from food and the fat on your belly are metabolically very similar.
These results contradict the consensus view of the Crossover Effect that states you can’t burn fatty acids above 60% of your VO2 max. They show that after keto-adaptation, the body becomes increasingly more efficient at using fatty acids during higher intensities of exercise, which, in turn, spares muscle glycogen for only near maximum efforts and decreases the need for carbohydrate refeeding for maintaining performance.
Despite glucose being the body’s default main fuel source, most of the day you’re still using fat for fuel because doing daily chores, walking, or even low-intensity cardio maintains aerobic respiration. You only tap into your glycogen stores whenever you’re sprinting, lifting heavy stuff or training hard. Even then the degree of how much glycogen you’ll end up burning depends on your level of keto-adaptation because as we’ve seen ketones can be used at even higher intensities of exercise.
You don’t want to burn glycogen for nothing because it can only be stored for a limited amount. With keto-adaptation, you’re able to sustain most of your submaximal exertions by tapping into your unlimited adipose tissue stores. Even people with 7% body fat have over 40 000 calories with them at all times. That’s why the ketogenic diet is amazing for low-intensity exercise.
In the 1980s already, it was shown that a 4-week ketogenic diet with less than 10g of carbs a day didn’t compromise endurance performance in elite cyclists[586]. These athletes were using more than 90% of fat oxidized fuel during exercise at 64% of their VO2 max. They also showed a 3-fold drop in glucose oxidation, a reduction of resting muscle glycogen by half, and they used 4 times less glycogen during exercise.
These kind of muscle glycogen responses in low carb athletes have been shown to share similarities to that of highly trained Alaskan sled dogs[587]. Sled dogs often perform at submaximal intensities for several hours in a row with incredible endurance capacity by eating a high fat low carb diet. In a study, dogs who run 160 km/day for 5 days showed no cumulative depletion in muscle glycogen, despite eating a diet with 15% carbohydrates. A subsequent study on dogs who ran 140 km/day for 4 days reduced muscle glycogen by 66% (similar to the 64% glycogen reduction in the FASTER low carb athletes) and a progressive increase in muscle glycogen over the following days of running[588]. A low carb diet has also been shown to increase the time to exhaustion during prolonged exercise[589].
Keto and Anaerobic Training
It’s clear that keto-adaptation is excellent and even optimal for endurance activities that prefer fat for fuel. However, compared to glycolytic pathways, the ketogenic path is less ideal for tapping into the anaerobic threshold at higher intensities.
High-intensity training, such as HIIT cycles, CrossFit, sprints, bodybuilding, and gymnastics are anaerobic by nature and span the creatine-phosphate system which requires you to be using glycogen in the presence of no oxygen. Because of that anaerobic environment, you can’t maintain it for any longer than a few seconds. You’re only burning glycogen for that specific time length and will revert back to using other fuel sources during rest.
Some reports suggest that muscle can use circulating glycerol for intramuscular triglyceride synthesis[590]. Previous studies have shown that after a short-term low carb high-fat diet, the ability to transport circulating fatty acids into muscle greatly improves[591]. This means that keto-adapted individuals experience higher rates of adipose tissue oxidation, which results in an increased release of both glycerol and fatty acids into circulation, which increases the overall uptake of fatty acids into skeletal muscle.
A study done on recreational CrossFit people showed that 3 weeks of ketogenic dieting didn’t lead to a decrease in performance compared to the control group[592]. However, they showed an improvement in body composition and decreased whole-body adiposity. They lost fat mass and thus improved their relative fitness.
Comparative studies between resistance trained individuals who eat a ketogenic diet and a standard diet have also shown that although both of them lead to similar improvements in workout performance and muscle gain, the keto subjects tend to have more lean body mass and less fat mass[593].
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Another study was done in 2014 by Jeff Volek, Dominic D’Agostino, and Jacob Wilson compared the effect of a very low carb diet with a traditional diet in resistance trained individuals[594]. The results showed that lean body mass increased to a greater extent in the VLCKD (4.3 +/- 1.7 kgs) as compared to the traditional group (2.2 kg +/- 1.7). Muscle mass increased in the keto group as well (0.4 +/- 25 cm), as opposed to the other one (0.19 +/- 0.26 cm). On top of that, fat reduction followed the same pattern, benefitting the ketogenic individuals (-2.2 kg +/- 1.2 kg) versus the (-1.5 +/- 1.6 kg).
Another study done on elite level artistic gymnasts showed that after going on a low carb diet, the athletes didn’t lose strength or muscle but actually lost body fat while increasing lean muscle mass[595]. They only followed the keto protocol for 30 days and already showed great improvements in body composition. These aren’t your recreational fitness enthusiasts either - they train at high intensities for several hours a day. If they can do their crazy explosive routines and superhuman feats of strength without carbohydrates, then it’s safe to say that the average person will do perfectly fine on a less strenuous workout routine.
Based on these findings so far, we can say that a ketogenic diet hinders exercise performance in neither endurance or anaerobic sports. In fact, with the knowledge we currently have, it’s safe to say that it’s actually more superior to decreasing fat mass and improving body recomposition, especially if eating at a caloric deficit.
In summary, for the vast majority of people, a ketogenic diet can provide all the necessary fuel sources needed for maintaining daily aerobic activities as well as giving enough energy for short anaerobic exertions.
However, when it comes to high-intensity training, then there are still some implications and constraints that have to be kept in mind.
If you’re performing high-intensity exercise for longer and with fewer rest intervals, then your body will have troubles resynthesizing its glycogen with just fatty acids. Examples would include Ironman triathlon, a competitive sports game, a 2-hour high volume bodybuilding workout, a CrossFit game event, or having more than 2 workouts a day.
Workouts that aren’t as taxing or frequent don’t require the addition of carbohydrates although they may still help. Examples include Olympic weightlifting, powerlifting, gymnastics, endurance, cycling, or short HIIT cardio.
The 2 main ways of adding carbs around workouts are the targeted ketogenic diet where you consume a small number of carbs during high-intensity exercise and the cyclical ketogenic diet where you eat low carb for a week and then have a refeed day.
Do You Need Carbs
This also raises the question, why bother trying to become keto-adapted if you have the possibility to refuel with carbs during exercise?
The answer is quite self-explanatory and obvious – you want to maintain lower levels of blood glucose and insulin the majority of the time as to promote your body’s ability to burn its own fat stores and reduce oxidative stress.
Carbohydrate restriction has been shown to have many health benefits, starting from fat loss, neuroprotection of the brain, better biomarkers, stable energy, and ending with mitochondrial density and longevity. Burning fat causes less damage to the mitochondria and it produces more energy per calorie, which has benefits on cellular survival.
Being dependent of carbohydrate refeeding is also quite a fragile position to be – you’re always limited by your glycogen stores and have to structure your entire day around eating. After becoming keto-adapted, you can tap into your stored body fat very fast and easily, which keeps you energized even while fasting for 5 days or more.
You don’t have to be in strict ketosis all the time to stay keto-adapted but you do need to maintain a semi-ketogenic state of glycogen depletion to build up these fat oxidation pathways into your metabolism.
Whatever the case might be, anyone who is following a ketogenic diet can benefit from some exogenous carbs when performing at higher intensities. If you’re training hard and heavy more frequently, then your body won’t have enough time to replenish your muscle glycogen stores solely via gluconeogenesis.
Carbohydrates and insulin are not the enemies here. Insulin is a powerful tool that can assist in growth and tissue repair. It governs nutrient partitioning and influences whether or not the calories consumed go into muscle or fat cells. The benefits to this are immense and useful, but only in a specific context – when glycogen stores are depleted and ready to absorb some carbohydrates. That happens after heavy resistance training, but not all of the time. This promotes metabolic flexibility as well.
How to Increase Metabolic Flexibility
The foundation for metabolic flexibility is the ketogenic diet because you need to be able to burn fat as a primary fuel source.
On a high carb diet without keto-adaptation, you’re only capable of burning glucose while not being able to use ketones. But in order to avoid bonking after your glycogen runs out and to not get the keto flu whenever you eat some carbs, you need to go through a period of keto-adaptation.
Both aerobic and anaerobic conditioning is also needed. The purpose of your training should be to increase mitochondrial density – your cells’ ability to produce energy whether from ketones or carbs.
Metabolic flexibility is a matter of degree like keto-adaptation – someone with greater muscle glycogen stores and improved insulin sensitivity can absorb more glucose than the one with lower energetic demands. If you do more resistance training, then you’ll have a bigger buffer zone for eating carbs but you’ll also increase your basal metabolic rate.
Here’s how you can improve metabolic flexibility and stay keto-adapted while eating carbs.
You have to establish nutritional ketosis by doing a low carb ketogenic diet for at least 2-4 weeks.
After the first period of keto-adaptation, you can start tinkering with some carbohydrates to improve your performance.
The fact of the matter is that you still want to be eating relatively low carb, especially at times when you’re not exercising.
If you’re able to go without food for over 24 hours and not experience hypoglycemia or muscle weakness, then that’s a good indicator of keto-adaptation.
At this point, your physical performance at all intensities is generally the same and you don’t need carbs to fuel your training. However, you can still use a few hacks that include strategic carbohydrate consumption. The Targeted Ketogenic Diet (TKD) involves consuming a small dose of carbohydrates during your most intense workouts.
The Cyclical Ketogenic Diet (CKD) involves eating keto for 5-6 days, then having a day of eating more carbohydrates, and then returning back to keto.
There’s also something called Carb Backloading (CBL) where you eat low carb all day, then you go to the gym to have a muscle glycogen depleting workout that makes you more insulin sensitive, and then have dinner with a few extra carbs like a sweet potato, a bit of fruit, or some rice.
The vast majority of people would still do best on a regular ketogenic diet, at least most of the time. Both the CKD and TKD are viable ways of boosting your performance, improving your metabolic flexibility and upregulating the metabolism.
You can use both the CKD and TKD for promoting any physical endeavor, whether that be ironman triathlon, bodybuilding, Olympic weightlifting, or Crossfit. Of course, this doesn’t apply to walking, jogging, yoga, disc golf or something else that doesn’t really tax your glycogen stores. Therefore, you want to be using these methods only as tools for becoming stronger, faster, more enduring or resilient, not as an excuse to simply eat some carbs. Let’s go through some scenarios where you can indeed use these strategies.
The Cyclical Ketogenic Diet
Training 4 or more times per week with mostly resistance training.
Examples: bodybuilding, powerlifting, weightlifting, Crossfit, obstacle course racing
Goals: build muscle, increase strength and power, have your cake and eat it too
Refeeds either on your har
der training days or the night before.
If you feel like you’re feeling sh#t the entire following week because of keto flu then dial down on the amount of carbs you’re consuming and have less frequent refeeds.
The Targeted Ketogenic Diet
Training 4 or more times per week with mostly resistance training or ultra long endurance.
Examples: bodybuilding, powerlifting, weightlifting, Crossfit, obstacle course racing, Ironman, rowing, marathon running, swimming
Goals: build muscle and lose fat while improving performance, power, and endurance
Have small amounts of easily digestible carbohydrates with protein during your workouts, such as a shake or ripe bananas.
Adjust your carb intake according to your performance requirements and how you feel. Start off with just 5 grams and slowly keep adding an additional 5 grams per 30 minutes of intense physical activity. Hard training athletes can consume up to 30-50 grams of carbs during training while staying in ketosis.
If you’re training twice a day then have a larger shake during the first workout and a smaller one during the second one. Still, eat keto in between training sessions.