Ketogenic diets or low carbohydrate diets routinely appear in the media with stories ranging from the negative health implications they can have including reduced bone health to the benefits they have on weight loss, diabetes and performance in elite athletes. With such conflicting information out there, let’s turn to the literature to see what the truth is about ketogenic diets and performance.

What Is Keto?

For a diet to be considered ketogenic it needs to contain less than 50g of carbohydrates (CHO) per day, be high in fats 70-80%, with the remaining 15-25% coming from protein. For athletes, especially endurance athletes CHO’s are the preferred fuel source for enhancing performance therefore by restricting CHO intake it forces the body into ketosis. In a ketosis state, ketone bodies (fat molecules) are released from the liver, producing an alternative fuel source to CHO’s.

Why Athletes Choose a Keto Diet

The utlization of fats as fuel becomes one of the primary reasons endurance athletes are attracted to ketogenic diets. This attraction occurs because fats provide a better source of energy than carbohydrates and there is an abundance of fat stores compared to the limited glycogen (CHO) stores in the muscles. Other reasons athletes are attracted to ketogenic diets include, the feeling of enhanced recovery, improvements in body composition and reduced post exercise inflammation.

It is well documented that ketogenic and low CHO diets are beneficial for body composition changes, namely weight reduction through decreases in adipose (fat) tissue. This isn’t surprising considering fat oxidation (fats being burned for fuel) becomes the primary energy source in a ketogenic diet.

Keto Diets and Athletic Performance

In terms of athletic performance the evidence is less clear. Majority of the current studies looking at athletic performance and ketogenic diets routinely involve small sample sizes of elite athletes and over a short time frame (3-10 weeks). As a result, any findings from these studies need to be interpreted and considered with other available literature. With such a specific cohort (study population) transferability of the results to other non-elite athletes becomes difficult.

Exercise Capacity

In terms of endurance performance, there appears to be a reduction in performance during high intensity bouts above 70% of VO2Max when on a short term (3-10 week) ketogenic diet. The postulated causes include; fats require greater oxygen uptake and energy to be broken down compared to CHO, possible impaired glycogen metabolism at higher intensities. However, one study which looked at endurance athletes who were on ketogenic diets for longer than 6 month showed no changes in muscle glycogen stores.

Resistance Training

For resistance training and lean muscle mass it appears that ketogenic diets result in reduced body mass, with conflicting evidence on whether it impacts on lean muscle mass. Regardless, it doesn’t appear to negatively impact strength.

Bone Health

Bone health is an interesting area. An Australian study published early this year revealed that bone resorption (break down of bone) increased and bone formation (new bone formation) decreased in elite athletes (race walkers) while on a short term (3 – 3.5 week) ketogenic diet. This study received a lot of press because the implications are potentially serious; ketogenic diets leading to reduced bone mineral density and bone injuries in elite athletes. However, this study needs to be put into context. It looked at elite race walkers, predominantly males who were on short term ketogenic diets. This is a very specific subgroup of people. As the study rightly points out, further research is needed to understand these findings further before any definitive answer is known about ketogenic diets (short and long term) and bone health in elite athletes and in the general population.

The Wash Up

When it comes to athletic performance ketogenic diets improve fat oxidation and reduce body mass, which is important in endurance sports and weight-class based sports such as boxing, weight lifting, martial arts etc. They don’t negatively affect exercise capacity at submaximal workloads below 70% VO2Max but they do appear to reduce exercise capacity at high intensities. They may also reduce endurance capacity but this appears to be individual, with some athletes being affected and others not. At present, finding the right balance of lower CHO levels which are higher enough not to impact performance at higher intensities is the best approach to maximize athletic performance through a ketogenic diet. One final note, even though CHO intake levels are low, this does not mean an athlete will be running a negative energy balance; energy expenditure should always match energy intake.

[Click Through To Read About Plant-Based Diets]

The Game Changers, a movie promoting the benefits of a plant-based diet on athlete performance has been gaining a lot of traction. With big sports stars involved like Lewis Hamilton, Novak Djokovic, Arnold Schwarzenegger, Jackie Chan and backed by Hollywood heavy weight director and producer James Cameron one can see why. However, for the uninitiated majority of those involved with this production including the chief science advisor are supporters of plant-based diets, leading to a somewhat biased slant. Therefore, the question needs to be asked “what does the research really say about plant-based diets and athletic performance”.

“love to put Viagra out of business, just by spreading the word on plant-based eating.”

James Cameron – The Independent 25/04/2018

Diets for athletic performance are extremely individualised and are geared towards the specific demands of the athlete and sport the individual competes in. In a very simplistic manner, it requires a balance of protein, carbohydrates and fats to aid with the development of lean muscle mass, energy production and recovery matched against energy expenditure or calories burned throughout the day.

Gluten Free Diets

Athletes are always looking to find that extra edge over their competitors and diet is one area that can be utilized to good effect however, all that glitters may not actually be gold. A few years ago with the explosion of gluten and wheat intolerances and celiac disease a few athletes decided to go gluten free and claimed it was responsible for improving their athletic performance, even though they hadn’t been diagnosed as celiac. Interestingly though these claims aren’t currently supported by the research, with a study in 2015 that took 13 competitive endurance cyclists with no history of celiac disease and compared their time trial performance while on a short term gluten containing diet and on a gluten free diet. The study showed athletic performance didn’t improve for the athletes on a gluten free diet with no history of celiac disease. Given, this study had a small sample size of 13 athletes and was conducted over a short time period (7-day diets) it is however currently the only study comparing gluten free and gluten containing diets on athletic performance in non-celiacs.

Ketogenic Diets

Ketogenic diets have been another diet trend amongst athletes, especially in the world of sports like CrossFit. Ketogenic diets are low in carbohydrates and high in fats, which at first glance seems counterproductive to athletic performance when carbohydrates are an athlete’s main source of energy. In the non athletic population Ketogenic diets or low carbohydrate diets have been shown to be beneficial with weight-loss and reductions in the risk of diabetes. One could argue that reducing body mass might be an important goal in endurance and weight based sports however, the current limited literature looking at ketogenic diets and athletic performance does not support the use of ketogenic diets for athletic performance. Although ketogenic diets do not negatively impact performance, they may lead to unwanted decreases in lean body mass or a drop off in skeletal muscle hypertrophy.

Plant-Based Diets

As it is becoming quickly evident the current literature investigating diet and athletic performance is sparse and generally low in quality. This trend continues when comparing plant-based diets versus omnivore (animal and plant) diets and athletic performance, especially in the elite athletic population which is the premise of The Game Changers documentary. A search of PubMed found only one review paper which systematically reviewed the current literature comparing vegetarian and omnivore diets with physical performance. The paper included 8 studies, 7 randomised controlled trials and 1 cross-sectional study and found there were no differences in athletic performance between a vegetarian-based diet and omnivore diet.

“As someone who follows a plant-based diet, I believe we need a healthier high street option that tastes amazing but also offers something exciting to those who want to be meat-free every now and again.”

Lewis Hamilton on his Neat Burger company – The Sun 29/08/2019

With such limited and low-quality evidence currently available comparing diets and athletic performance, it is extremely important in this commercial and marketing driven age that we step back and ask questions to understand where the truth lies, rather than letting a documentary “inform” us. Plant-based diets and reducing animal meat intake has been associated with health benefits, with a large section of the research on plant-based diets focusing on its potential risk reduction in chronic preventable diseases such as cardiovascular disease. At present there is limited research available analysing its effects on athletic performance with no known larger scale multi-arm studies comparing a variety of diets on athletic performance. Currently the evidence does not show a positive association between a plant-based diet and athletic performance compared to other animal meat with plant based diets.

Diets for athletes, especially elite athletes are extremely individualised and what works for one athlete might not necessarily work for another. Whatever diet is chosen, plant-based or omnivore it should be driven by a nutritionist, dietitian or health professional with sports nutrition training and be grounded in the best evidence available.  

Cardiovascular disease is a preventable chronic disease responsible for 17 million deaths worldwide. It effects both men and women and results in coronary artery disease, stroke and heart failure. This article highlights the modifiable risk factors associated with cardiovascular disease and the simple steps people can take to reduce their risk profile.

What you eat and drink pre and post workout are vitally important for performance optimization and recovery. This article provides an overview of the types of fuels and amounts needed to help fuel your body for optimal performance and recovery.

Fueling your body for optimal performance.


Obesity is an epidemic in the USA, Britain and Australia, placing huge strains on the health system. It is associated with diseases like Type II Diabetes, Heart Disease, musculoskeletal pain and depression. There was a recent article in the New York Times, which suggested that eating less was a more effective strategy to lose weight then exercise. The link below is a response to that article which offers a more sound way to lose weight, through an overall lifestyle shift involving, controlling food portion sizes, the nutritional value of what is eaten and exercise.

Responding to a NY Times Article That Missed the Point – “To Lose Weight, Eating Less is Far More Important Than Exercising More”