Note: This article is supporting content to the Optimum Nutrition for Health and Performance course.
Author: Dr. Crionna Tobin, PhD
At this time of year the majority of people are focused on diets, detoxes and cleanses or any means possible to try to shed the Christmas excess. There are so many different diets on trend that it is important to understand the pros and cons of each one and which one may suit your client depending on their health and performance goals and lifestyle. One of the most popular diets in the mainstream and fitness media over the past several years is the ketogenic diet. Big name celebrities claim the keto diet has gave them their chiseled lean physiques, while testimonials from formerly overweight or obese individuals attribute their 100+ pound weight loss to this diet. Other claims include enhanced endurance and improved cognition to name a few. But what should you believe? Is it all hype and anecdotes or has the keto diet been shown to be effective?
The ketogenic diet is an extremely restrictive, extremely low carbohydrate, high fat diet. It has taken on many forms, but generally consists of ~60-75% of your calories coming from fat, 20-30% from protein, and only 5-10% from carbs. This is quite different than the general recommendations for fat (~20-35% of calories) and carbs (~45-65% of calories). The original ketogenic diet was not meant to be accompanied by calorie restriction, but given the restrictive nature of this diet most people end up reducing their calorie intake.
The goal of the keto diet is to put your body into Ketosis. Ketosis is the body’s response to starvation and/or low carb availability. Glucose (i.e., carbohydrate) is the preferred fuel source for most cells; however, during carbohydrate restriction, both protein and fat can be utilized as an alternative fuel source. The body converts fat to ketone bodies, which cells can use for fuel. Be careful not to beef up the protein too much. High protein intake actually hampers ketone production as they can be converted to glucose, which would then be used as the body’s fuel source instead of ketones.
Keto and Weight Loss
Individuals seeking weight loss significantly reduce carbohydrates with the hope of utilizing fat stores for energy instead of glucose (carbs). Although the keto diet will lead to enhanced fat oxidation this does not translate to a greater loss of body weight/fat unless accompanied by a calorie deficit. The weight loss experienced with this diet is likely driven by the reduced calorie intake (Remember: weight loss = calories in < calories out). So while it may lead to calorie restriction and weight loss in the short-term (weeks to months), people may gain some or all of the weight back if they find it difficult to adhere to. To date, the most successful weight loss diets are those that fit the lifestyle of the person and that they can stick to more easily over the long-term (i.e., years). Weight loss is not a one size fits all strategy!
Keto and Performance
Many types of athletes, especially endurance, rely heavily on carbohydrates to sustain performance. Once carbohydrate stores in the body are low or depleted, performance intensity suffers greatly. The keto diet has been proposed to enhance endurance performance by increasing fat oxidation and reducing carbohydrate oxidation during exercise, thus sparing your stored carbohydrates (i.e., glycogen)2. However, studies have not supported an enhanced endurance performance with the keto diet. In fact, it has been shown to impair sprint performance2.
Keto and Cognition
While the keto diet is being explored in patients with cognitive diseases, there is no evidence to suggest it enhances cognitive function in healthy adults. People may actually experience adverse effects on attention and focus since the brain prefers glucose for fuel.
Is it worth the hype?
There certainly may be people who enjoy eating a ketogenic diet and find it easier to stick to which may be due to their personal food preference and/or the appetite suppressing effect of ketones3. However, there may also be some that find it difficult to stick to making their weight loss journey even more challenging. As with every fitness and health strategy there is more than one option for everyone and the challenge for you as a coach is to advise on the one that is best suited to set you and your client up for success. Are you a PT, coach or fitness professional and want to better your overall nutrition knowledge? Sign up to our online nutrition course today! The course consists of ten online modules and on completion of these you will receive an accredited certificate in Nutrition by the Association for Nutrition (AfN) and earn CPD points from your professional body.
- Kirkpatrick et al., 2019. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. Journal of clinical Lipidol
- Evans et al., 2017. Metabolism of ketone bodies during exercise and training:physiological basis for exogenous supplementation. J Physiol
- Stubbs et al., 2018. A Ketone Ester Drink Lowers Human Ghrelin and Appetite. Obesity (Sliver Spring)