Thus far in my blogs, I have discussed endurance activity using carbohydrate as the primary fuel source. In the last three weeks we outlined the protocol for pre, during and post workout fueling. While our body does prioritize carbohydrate as the primary fuel source for activity and brain function, many endurance athletes agree that carb-centered fueling is both frustrating and time consuming. In recent years, the ketogenic diet has emerged as a popular choice among extreme endurance athletes for a couple key reasons. Today’s post will discuss an introduction to ketogenic dieting, what it means, the potential benefits, as well as potential concerns and obstacles. This post will not discuss the physiology of the process in detail. For those interested in a greater level of detail, I have posted links to some of my favorite resources on ketogenic dieting.
Simply stated, the ketogenic diet is built for those interested in running on fat. As mentioned repeatedly in this blog, our body will use carbohydrates for activity first when they are available. Since they are such a common part of our diet, many go through life never considering another way to eat. But what happens when our body has no carbohydrate stores left, and none are in the diet? Our body adapts to use a fuel that is always available, fat. When the body has no carbohydrate, and does not have enough protein to make carbohydrate from, the body will begin to adopt fatty acids as the primary energy source. Metabolism of fat in the body produces a group of compounds called ketones, which can be used by all systems in our body, including the brain. As I may have eluded to above, it takes quite a bit of time to enter ketosis, and is not done without resistance from the body. Once in ketosis, most people report a return in energy and mental clarity, and our body runs on ketones without any significant problems.
The application and interest in this diet with runners is fairly straightforward. The average person has enough carbohydrate stored to fuel activity for approximately 2hrs, or 15 miles (give or take 10 miles). To compare, the same person has enough fat to fuel activity for 500-700miles. We reserve and store fat very efficiently, and can readily use it when needed. As you reflect on the pre-, during- and post- training protocols from the last 3 weeks, it becomes obvious that our body does not have a great deal of carbohydrate stores. You are constantly taking in glucose from food during the entire training and event to keep stores available. Runners on the ketogenic diet don’t use carbohydrate, and therefore do not have to eat anything before or during their event unless they choose to (except water and electrolytes). For an avid athlete running long distances on a regular basis, this has a great deal of appeal. It becomes more enticing when they learn that not only are feedings surrounding exercise optional, there is no need to time meals or eat every 3 hours. Since your body is not using sugar, no insulin is being produced, and blood sugar levels are stabilized by a compound called glycerol, which is abundant as a result of breaking down triglycerides into fatty acids for oxidation. With no need to manage blood glucose, and muscle glycogen out of the conversation, keto-dieters can eat when they please with no impact on performance.
In addition to endurance athletes, this diet has potential application with individuals who have compromised glucose utilization. For pre-diabetics, non-insulin dependent diabetics, and others deemed insulin resistant, the ketogenic diet has the potential to serve as an alternative to carb management and medication. As noted above, the body does not use insulin, and blood glucose is maintained with glycerol. Instead of trying to manage the compromised system, many diabetics are choosing a different energy path, one that “skips using what is broken”. In the short-term this seems to have success in many individuals. Unfortunately, we have never witnessed individuals in our culture and time maintain ketosis for a life time. More research and time is needed to better understand what the long-term effects of this diet are. My personal interest lies within extreme endurance athletes and diabetics. Extreme endurance athletes are often training so intensely their body must rely on an enormous amount of sugar, which strains the pancreas. Any organ used in this fashion will wear down over time. Just from observation I have noticed many endurance athletes in their 60’s are pre-diabetic. Low body fat, great muscle mass, but struggling with this issue despite it all. What if instead of demanding such constant insulin production, they were able to use fat. While fat also demands function from the pancreas, the amount of fat needed for caloric balance is less than half that of carbohydrate. All of this is speculation, but I look forward to watching this area of science grow.
At this point it seems like this diet would have great application to the populations discussed. With all this potential, what is the catch? Why isn’t everyone doing this? Are there any concerns? While there is a tremendous amount of potential, there are certainly a number of issues that complicate the ketogenic diet as a viable option for many individuals.
The first obstacle for most is the transition into ketosis. Our body does not like to switch to fat as our primary fuel source. Traditionally this switch implied starvation. Our body stores energy very efficiently, and body fat is meant to be a reserve kept for dire circumstances. As our body reaches the end of its carbohydrate reserves, most experience extreme fatigue, dizziness, headaches, changes in bowel regularity and consistency, shakiness, muscle cramping, disruptions in sleep, a temporary dip in thyroid hormones, and even an increase in kidney stone formation. That long list of symptoms is intimidating to type let alone experience, so it comes as no surprise many cannot handle this during training, working and activities of daily life. It is important to note that these are temporary, often lasting from 1-3 weeks depending on rate of carbohydrate depletion.
Once in ketosis, the biggest issue becomes the sustainability of the diet. Maintaining nutritional ketosis for extended periods is a very different diet than we are used to, and does not resemble most other low carb diets. Carbohydrate intake is supposed to be nonexistent, so it is essentially restricted to the 2.5 cups of dark green, non-starchy vegetables per day, and 1-2 servings of nuts. The rest of the diet is protein and fat. The most difficult part of this plan is the protein limitation. As mentioned before excess protein will be turned into carbohydrate, so protein has a restriction in ketosis, which is the main way this diet differs from an Atkins or South Beach. This results in a plan that has a lot more fat than protein, which means foods that are exclusively fat must take a leading role. Things such as grass-fed butter, vegetable oils, coconut oil and MCT oil are often consumed at every meal. An example meal plan for a 5’9” 155lb male triathlete is below:
Example Day: 2400 kcal 200g Fat 120g Protein 30g CHO
Meal 1: (60g Fat, 30g Protein)
4 slices Bacon (14g Fat, 12g Protein) Pan fried in 1 Tbsp Coconut Oil (14g Fat)
3 eggs (18g Protein, 12g Fat) cooked in 1.5 Tbsp Grass-fed Butter (18g Fat)
8oz Unsweetened Almond Milk (2.5g Fat, 1g CHO, 1g Protein) *For Calcium
Meal 2: (49g Fat, 33g Protein, 10g CHO)
6oz 75/25 Grassfed Ground Beef (42g Fat, 26g Protein)
1oz Cheese (7g Protein, 7g Fat)
2 cups mixed Greens (lettuce, romaine, spinach etc) (10g CHO)
Meal 3: (35g Fat, 15g Protein, 15g CHO)
½ cup Almonds
Meal 4: (56g Fat, 38g Protein, 5g CHO)
6oz Salmon Filet (22g Fat, 35g Protein) cooked in 1 Tbsp Olive Oil (14g Fat)
1 cup Asparagus (5g CHO, 3g Protein) add 1.5 Tbsp Grass-fed Butter (18g Fat)
8oz Unsweetened Almond Milk (2.5g Fat, 1g CHO, 1g Protein) *For Calcium
*Use ¾ teaspoon of Himalayan Sea Salt with food daily (Sodium and trace minerals)
*Use ¾ teaspoon of Salt Substitute with food daily (Potassium)
*Drink 130 ounces of fluids daily before accounting for exercise
Notice how much pure fat there is in the diet? While some enjoy it, others find it unappealing and cannot stick with it. In addition to fat as a barrier, vitamins and minerals pose a problem. Many of our micronutrients come from fruits, vegetables, dairy and grains. While we can do our best to maximize some of them in the 2 servings of vegetables and serving of nuts, we are still left without adequate micronutrients. To achieve balance many keto-dieters will use bone broth. It is very hard to assure adequate intake with broth, so supplements are commonly used. As noted above, this individual used unsweetened almond milk as a calcium supplement, salt for sodium, and salt substitute for potassium. This individual also consumes a mineral and vitamin complex that is spread throughout the day to maximize absorption and provide key vitamins and minerals that are lacking.
While quite a few websites now boast recipes and options for keto-dieters, many people still struggle with the lack of variety, and miss certain foods. As a Dietitian, my job is to help people maximize their health. For me, health is a balance of quality and quantity of life. It varies for most individuals, and that is our right. The clients I have who maintain the ketogenic diet are those who do not have strong social and emotional ties to food. While in many ways this is a positive attribute, it is a rare one in our culture. The ability to look at food as simply “energy to perform and sustain life”, will usually result in successful ketosis, but may also restrict certain social ties to food that many would argue impact quality of life.
A large barrier in the world of performance is application to certain athletes. While many view the ability to fuel on fat through endurance races as an advantage, there is one lingering disadvantage. Our body’s anaerobic systems, the energy systems that function when there is not enough oxygen, are exclusively reliant on carbohydrate. In simpler terms this means that when you are exerting yourself at maximum intensity, you rely exclusively on carbohydrate for fuel. In ketogenic dieting, there is no carb, so there is no true max performance. Endurance athletes are rarely concerned with this, as their push to the finish is often not going to be at max performance, but many athletes rely on anaerobic systems to compete. Sprinters and those athletes who rely on short bursts of high intensity will not see a performance benefit from this diet. Most of the studies investigating performance in ketosis note an increase in perceived rate of exertion, and an inability to reach max effort (White 2007), meaning they felt like they were working harder compared to when they were eating carbs for the same intensity, and they were unable to achieve max intensity. This is why the diet is most popular in endurance sports and why Lebron James only went “low-carb” in his offseason.
Aside from the daily life and performance concerns that many will find discouraging, we also have a lack of vision for the long-term impact of the diet on health. There are quite a few personal testimonials of individuals feeling great at a healthy body weight with encouraging clinical indicators of health for 5 and even 10 years in ketosis. This is quite encouraging, but we need much longer and better controlled trials. While it is true that diets with too much carbohydrate, particularly refined and processed carbs, can cause a host of problems in very little time, we have abundant data proving a eucaloric diet containing carbohydrate is able to propel humans well into their 80’s and 90’s with similar values. The inflammation and metabolic disturbances linked to carbohydrate largely stem from excessive intake and a large calorie surplus. It is much more difficult to over consume calories on the ketogenic diet, but there are still potential issues only time will tell us. As a practitioner, I am most concerned with the long-term impact of a high fat diet on the digestive tract and accessory organs. We know too much sugar wears on our pancreas and causes insulin resistance. Is it possible that a diet with high levels of fat will wear in our production of pancreatic lipase and lead to pancreatitis? I am also concerned with the effects on the gallbladder, liver and our lymphatic system. Finally, while short-term observations suggest no adverse effects on lipid profile, we simply do not know the long-term impact on lipid levels or the cardiovascular system.
Overall, it becomes clear that while this diet has great promise in certain populations, there are severe barriers to sustainability, as well as large gaps in our understanding of the long-term impact on the body. Until more research is presented, the scope of this diet is fairly limited. Personally, I am most excited about the potential application in non-insulin dependent diabetics, as well as in ultra-endurance athletes during their training and competitive seasons. For the general population I still promote the idea of carbohydrate management as opposed to elimination, but there is always a need for Case Specific Nutrition™!
Below are some links to the most comprehensive materials I know of. Much of the research on ketogenic dieting and performance was done by Dr. Jeff Volek & Dr. Stephen D. Phinney, and can be accessed at.
Dr. Peter Attia is a fascinating man with a great understanding of the physiology and potential in ketogenic dieting. For a great explanation of how our body runs on fat, I recommend his post “Keto 101”
For any other questions or concerns, fell free to contact me at casespecificnutrition.com or Pittsburgh-dietitian.com
Well written article Andrew! I love how objective you are when giving the reader all this information. I agree that this type of eating style is not for everyone. Unfortunately, there is no long term data available; its too bad we weren’t running randomized controlled studies back in the paleolithic era, when our ancestors ate nothing but fat and meat. I work with alot of type 2 diabetic patients, and although I have them on a low carb plan, i am not pushing the fat until maintenance. At our clinic, we have successfully got clients off of all diabetic meds like insulin and metformin, even blood pressure medications. I personally follow a semi-keto, low carb plan that helps me with weight maintenance, as I down about 40lbs and have kept it off for the past 7 years or so. I have only been keto style for the past year, and it makes weight maintenance almost effortless!