What to know about the Keto
This keto diet is a common source of questions, and so I thought it would be helpful to revisit the topic for new (and returning) members. This is a great prompt for me to revisit the research and see what’s new…
Keto stands for ketogenic – the ketogenic diet is one where the body is in ketosis. This state occurs when the body is starving or is severely restricted of carbohydrates. Essentially, when the body is depleted of dietary and stored carbohydrate, it breaks down fat energy (facilitated by lower levels of insulin that typically promote storage); a by-product of fat metabolism are ketone bodies (particularly acetoacetate and beta hydroxybutyrate). While the brain and central nervous system prefer glucose as an energy source and cannot use fat (there is a blood-brain barrier), the brain can use ketone bodies in the absence of sufficient carbohydrate.
Traditionally ketogenic diets were used in the treatment of epilepsy – for many individuals with this life-threatening medical condition, a ketogenic diet can all but ‘cure’ their epilepsy (as long as they remain on the diet). However, in more recent years, the ketogenic diet has been applied to a variety of other health conditions. Interestingly, ketogenic diets have shown quite favorable results regarding metabolic and cardiovascular health outcomes which includes the management of diabetes. To be clear, using the ketogenic diet for management of disease is outside of the scope of this blog and anyone with a metabolic or cardiac condition (including diabetes) should absolutely consult their physician before initiating this dietary approach.
However, we are also seeing the application of the ketogenic diet for weight loss and sports performance. Indeed, there is sufficient research to indicate the ketogenic diet can be quite helpful in facilitating weight loss while also supporting preservation of lean body mass (= muscle). What is still unclear is how it compares with other healthy, low calorie approaches (that is, moderately low, not excessively low) that can also facilitate weight loss and maintain muscle mass. That is, is the keto approach better than other healthy, moderate approaches to weight loss? Maybe, but the results are still inconclusive (some show keto is better, some do not).
There is also uncertainty regarding the application of the ketogenic diet in the performance arena. It is well established that even after just several days of following the keto diet that we see an upregulation of ‘fat burning’ machinery – that is, an increase in the enzymes and pathways that oxidize fat; over time, we see that adaptation to the ketogenic diet results in enhanced fat oxidation at higher exercise intensities. The benefit of this is that athletes can burn fat at higher intensities and thus are not limited by muscle and liver glycogen that otherwise would limit exercise performance.
What is interesting to see is that while indeed individuals on the keto diet do upregulate fat oxidation, and downregulate carbohydrate oxidation, there is actually very little research to indicate that this improves performance. Most research has been conducted on endurance and ultra-endurance athletes who adapt to the ketogenic diet. Indeed, these athletes are significantly more ‘efficient’ at burning fat at higher intensities, but it is important to keep in mind that this is relative – higher intensities may indicate they are burning more fat at, say, 70% of ones VO2 max, compared with 60% of ones VO2max. This is not considered to be ‘high intensity’. What is more, research does not actually show that this enhanced fat oxidation improves performance. Huh.
As it pertains to anaerobic performance (such as high intensity interval training that correlates best with most CrossFit workouts), a recent examination of the few studies that have been done concluded that a keto diet resulted in impaired performance in 4 of 7 studies, and did not improve or worsen performance in 2 of 7 studies, with the last study inconclusive. So yes, the majority of studies in this analysis demonstrated impaired anaerobic performance when following a ketogenic diet. This should be noteworthy. One of the two studies that showed performance was not worse (but not better) is a study commonly cited in this field looking at elite gymnasts. The authors (and other keto proponents) emphasize that these gymnasts were able to lower their body fat while maintaining (but not gaining) muscle mass. There is certainly some notable benefit to this, and the ketogenic might be a feasible approach for individuals looking to decrease fat mass while maintain strength. It is unlikely one will see increases or performance gains, but given one of the biggest risks of severely restricting calories to lose weight is loss of muscle mass, this is not insignificant.
So what is my take away from this? Here are my thoughts. First, when an athlete comes to me and asks if they should go keto, I ask a couple of follow-up questions. Are they aware of how restrictive the diet is? This approach only allows for net 20 grams of carbohydrates a day. That means no grains or starches, no legumes or soy, very, very little fruit, and small to moderate amounts of non-starchy vegetables. Considering that even a 1-ounce serving of almonds has 6 grams of carbohydrates (and 20 grams is the daily total), even nuts have to be limited to some degree. This is a very high-fat diet including oils, butter, and cheese. And, contrary to what many think, it is actually a moderate (and not high) protein diet. While meat and other high protein foods are quite low in carbohydrates, protein itself results in glucose production via gluconeogenesis and thus to be correctly done this diet is not high in protein (Atkins diet this is not). In fact, many ‘purists’ in the keto world recommend only .6-.8 grams of protein per kg of body weight – this is half of what is normally recommended for strength athletes. So really, it is just a really high fat diet, moderate in protein, and very limited carbohydrates.
I then ask if individuals would find this sustainable. Can beer-lovers give up beer? Even wine has about 4 grams of carbohydrates and is recommended to only be consumed sparingly. Seemingly healthful foods like fruits and yogurt need to be restricted. AND, perhaps the biggest challenge to this, is that there is no wiggle room. You can’t have your ‘cheat day’ or even your ‘cheat meal’ – even just a moderate amount of carbohydrate takes you out of ketosis and you have to start the process all over. And let’s just say entering ketosis – particularly for the first time – can be quite an unpleasant experience for many – individuals report feeling foggy, light-headed, dizzy, lethargic – and this can take up to 2 weeks to start feeling ‘normal’ again. Once in ketosis, most individuals report feeling great with good energy levels and easily managed hunger and fullness levels. However, most report that high-intensity exercise is very difficult and recovery can be quite slow.
I ask about lifestyle factors – are you okay to miss social events that revolve around food and celebration? Or are you okay to go to these events and pass on just about everything that is served? Going out to restaurants can be challenging (but doable). I know as a mother of 2 young girls, I could never role model this dietary approach because of the message I would be sending to them – I am not okay to start them thinking at age 5 and 6 that there are ‘good’ foods and ‘bad’ foods and that certain foods should be avoided at all costs. I see firsthand as a dietitian that specializes in eating disorders how this exposure can start a lifelong unhealthy relationship with food.
There is still a lot of research that needs to be done before we can provide more conclusive statements regarding the ketogenic diet. I would not call it a balanced approach by any means, but one that may promote fat loss and may have a performance beneit for ultra-endurance athletes (this has yet to be clearly shown. Otherwise I believe there are many other dietary approaches that have shown to enhance performance (and can still support weight loss if desired).