Simple:
Not a lot is simple when it comes to keto and exercise but I will summarize as best as possible and break into more of the science with a couple of studies below.
You should really know 2 things:
- Until you get fat adapted, which could take 3-6 months, exercise will be more difficult. The first couple of weeks can be especially hard. Get lots and lots of water and electrolytes, this can help immensely in the beginning.
- Know that there are 2 basic types of exercise, Aerobic and Anaerobic. Aerobic is generally a lighter pace, something you can keep up for a long time, it is when your body has plenty of oxygen to your muscles. Anaerobic is high intensity exercise that uses a different pathway as there is insufficient oxygen. Sprinting is an example of this.
The ketogenic diet is really very good at part 1, aerobic exercise, and really not very good at anaerobic for reasons I will go into more detail below.
Also remember that the easiest way to lose weight is controlling diet, not working out, so don't think you have to do super high intensity workouts to lose weight, your keto diet should handle that part and exercise should be focused around your physical goals.
This next part will provide a couple of studies and discussion of why exercise doesn't provide the weight loss many expect, later is the science of keto and exercise.
Less Simple:
This is only less simple as there is more science involved. This part of the discussion is for why exercise for weight loss isn't a good idea, more on keto and exercise science will be below.
It turns out there are a few problems when it comes to exercise, keto or not. Here is a quote from the study which I think sums it up nicely. [Source]
Weight loss resulting from an exercise intervention tends to be lower than predicted.
We conclude that the small magnitude of weight loss observed from the majority of evaluated exercise interventions is primarily due to low doses of prescribed exercise energy expenditures compounded by a concomitant increase in caloric intake.
I will get more into the Calories In, Calories Out (CICO) soon, but as this study points out it isn't that straightforward. They measured peoples weight, accurately calculated their activity and food consumption and found that weight loss was less than predicted. Why? Exercise made them hungrier, and they ate more throughout the day after exercise. They were also more tired and did less physical activity outside of exercise as well.
Less may be more. [This] study showed that people working out 72 and 136 minutes per week (25-45 minutes, 3 times a week) lost weight as predicted, but those who worked out more, 194 minutes (30 minutes 6 days a week for example) lost half of the predicted amount. This shows that some exercise is beneficial for weight loss, but too much has a very negative effect.
Harder:
One of the first misconceptions to get out of the way is that Keto depletes your glycogen. This is only partially true, it depletes liver glycogen, your muscles still contain and use glycogen. What is glycogen, in simple terms it is just a compact way to store glucose (sugar) so it can be used by the body.
Once you become fat adapted, the process in which your body adapts to primarily using ketones for its energy rather than glucose, a lot of changes occur. One of the first things you usually hear from people who don't know about Keto is that you have to have carbs to live, that your brain runs off of sugar and you will die without it, and that without carbs your blood sugar will drop and you will die. This is obviously not true and by the time you read this there should be a post on fat adaptation.
ATP (Adenosine Triphosphate) is often called the molecular currency of energy transfer, it is what stores and transports energy within cells. You can think of it a bit like electricity, if you don't have it, you can't function. Every contraction and relaxation of any muscle in the body requires ATP, so without it you can see that you would quickly die.
ATP explains why people in ketosis are great at aerobic exercise, but not anaerobic. I will not go too deep here, if you need to go further look into the Krebs cycle and the Electron Transport Chain.
For a person not in ketosis, glucose is converted to Pyruvate and releases 2 ATP in the process. Next there are 2 routes:
- Anaerobic- if there is insufficient oxygen then Pyruvate is converted to Lactic Acid, releasing 2 more ATP for a total of 4 ATP in this pathway.
- Aerobic- with abundant oxygen Pyruvate is moved to the mitochondria and converted into Acetyl-CoA (this is important to remember for a deep understanding of ketosis) which releases a whopping 34 ATP along with carbon dioxide and water.
So as you can see, in an anaerobic environment we produce 4 ATP while an aerobic environment lets us produce a total of 36 with the same consumption of glucose. The math here suggests roughly 9 times more ATP while aerobic which shows why we can go for so long at an easy pace, but fall off quickly at higher intensities.
If we think of a person on a standard high carb diet we can see that they have lots of glycogen to be used in the muscle, plus quite a bit in the blood, and then a stockpile of it in the liver so as the muscle uses it the liver can send more into the blood to the muscles. This means that you can recover muscle glycogen and are ready to go for another sprint fairly quickly. When in ketosis we do not have the liver glycogen available so while we can do a hard effort, it takes a very long time to recover.
Sounds all bad so far, why is Keto advantageous? Recall from the 2 routes I mentioned above that we get the most energy by producing Acetyl-CoA (glucose->Pyruvate->Acetyl-CoA). It turns out that Ketosis can short circuit this a bit and produce Acetyl-CoA from fatty acids (technically the liver produces a ketone (why we call this ketosis) called Beta Hydroxybutyrate (BHB) that can then be broken down into Acetoacetate and then further to Acetyl-CoA). This means that to provide energy for our bodies the liver will break down fat into fatty acid chains and release them into the bloodstream, and with sufficient oxygen will directly break down into Acetyl-CoA. This is why people in a Ketogenic state are so good at aerobic exercise and why many endurance athletes are switching, or are already on, a Keto diet. A very lean man with 10% body fat and say 150 pounds has 15 pounds of fat. Assuming 3,500 calories per pound of fat, even our very lean person has 52,500 calories available. This huge energy reservoir is a great benefit, the lack of which causes athletes on a standard diet to binge on carbs the day before to try to force glycogen into the muscles and liver and carry glucose gel packs that they must eat regularly to keep calories and energy up.
I will go into it a bit later, but there are variations on the standard Keto diet that people use to overcome some of the anaerobic issues but should probably be avoided until you are fat adapted and at the weight you want to be. These are the Cyclical Ketogenic Diet (CKD) and the Targeted Ketogenic Diet (TKD).
The net to this whole discussion is that you should exercise, and when you are in ketosis you want to stay in the aerobic range as much as possible. For running this means jogging not sprinting, cycling on flats not hills, lifting 12-15 reps for more sets rather than 3 sets of 3-5 with max weights. While you can supplement in various ways, if your goal is to sprint and build muscle as quickly as possible, ketosis is probably not for you.