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Are keto diets good for losing weight?

Ketogenic diets, most commonly known as ‘Keto diets’, have become popular in sport, especially in combat sports due to the effectiveness of utilising fat stores and losing weight FAST!

However, there are some considerations to take before implementing any diet, especially for sports as complex and as intense as boxing.

In this article, nutritionist Lee Rickards shares the science, benefits and potential limitations of using a Keto diet to lose weight.

Keto Diets for Boxing – A Summary

A Ketogenic diet requires less than 10% of energy from carbohydrates. This means that the diet is predominantly made up of protein and fat.

Keto diets are effective at reducing body mass, however research suggests that a ketogenic diet impairs high-intensity performance.

Rapid weight loss in athletes can be detrimental to performance and increase injury risk.

Keto diets are associated with losses of lean muscle mass. Something we want to preserve when making weight.

What is a ketogenic diet?

A ketogenic diet consists mainly of protein, fat and vegetable sources, whereby the aim is to increase fat oxidation. This is achieved by restricting carbohydrate intake to <10% of total energy intake, this can be less than 50 g carbohydrates per day.  

Popular food sources on a Keto diet;

  • Steak, Chicken, Fish, Beef Jerky
  • Cheese, Cream, Butter and Oils
  • Avocado
  • Salads and Vegetables

The keto diet has been popular for many years in helping to treat illnesses and diseases such as obesity and epilepsy. However, the diet is now popular with athletes, especially boxers because it can aid rapid weight-loss.

A keto diet is often used at the start of a training camp for this very reason However, it can be detrimental to high-intensity performance.

4 x Weight Loss

Athletes typically lose 4 times the amount of body mass loss in the initial stages of Keto diet in comparison to a regular diet.

How does the Keto Diet Work?

Decreasing the amount of carbohydrate in the diet makes it easier to release free fatty acids from adipose tissue.

The primary reason being that carbohydrate induced increase in plasma insulin concentration exerts a powerful inhibitory effect on adipose tissue triacylglycerol lipase and hormone-sensitive lipase, reducing the breakdown of triacylglycerol and decreasing the circulating plasma free fatty acid concentration (Spriet 2014).

Once a person is in a ketogenic state, ketone bodies are produced in the liver due to gluconeogenesis which is the production of glucose from non-carbohydrate sources.

Glucose is the primary fuel used by the brain and muscles and once glucose is low, the brain and muscles use ketone bodies for energy. An assumption is that a ketogenic diet may be superior to other diets due to increased fatty acid oxidation from adipose tissue. 

Rapid Weight Loss

A ketogenic diet accelerates weight loss in the initial stages primarily due to a loss of water.

1 g of carbohydrate is stored with 3 g of water.

Muscle glycogen stores will slowly deplete on a keto diet, along with the water stored with them.

This is mainly why Keto diets appear to be effective as changes on the scales occur quickly. However, this is not going to beneficial in the long-term for body composition.

The Research

Some studies have found positive effects of a ketogenic diet on reducing fat mass compared to an isocaloric diet. 

Jabekk et al. (2010) reported a greater fat mass loss in the low carbohydrate ketogenic group 5.6 ± 2.9 kg compared to the non-ketogenic group 0.6  ±  0.8 kg after 10 weeks of resistance training.

However, a limitation of the study by Jabekk et al. (2010) was that protein intake wasn’t matched between groups. Greene et al. (2018) investigated the effects of a 12-week ketogenic diet on body mass and performance in 14 intermediate and elite level powerlifters and Olympic weightlifters compared to a usual diet with protein and calories equal between groups. The study found that there was no difference in performance (1RM of clean and jerk, snatch, deadlift, squat and bench press) between the ketogenic diet and the usual diet.

The ketogenic diet group lost significantly more body mass -1.7 kg compared to a usual diet group that gained body mass +1.6 kg. However, the ketogenic diet group lost 1.7 kg of lean mass compared to the usual diet group that increased lean mass by 0.52 kg.

This study suggests a ketogenic diet does not have adverse effects on strength performance when performance is low volume and high-intensity. In addition, the ketogenic diet group lost lean muscle mass compared to the usual diet group. However, there is potential for this loss to be attributed to changes in total body water because the method of analysis they used to assess body composition is dependent upon equations applied after assessing body water content.

It is known that leaner individuals are at higher risk of losing muscle mass compared to overweight obese individuals. Chappell and Colleagues (2018) observed that bodybuilders who consumed a higher amount of carbohydrates during the start of a preparatory training phase (5.7 g/kg vs 3.1 g/kg) had higher placings as well as greater amounts of lean muscle mass compared to those who consumed a low amount of carbohydrates.

This study has relevance because these athletes strive to reduce body fat to a similar level as combat sport athletes. Carbohydrate intake could spare muscle loss by promoting insulin (a storage hormone) whilst maintaining energy levels for high-intensity training sessions (Burke et al. 2011).

At Boxing Science, we place a strong emphasis on increasing lean muscle mass as it has been shown to be correlated to increasing punch force. Further research is needed on ketogenic diet studies investigating body mass loss in elite athletes rather than comparing current obesity and metabolic disorder studies in order to be more informed on the positive/ negative effects of a ketogenic diet.

Keto Diet Effects on High-Intensity Performance

Anecdotal research has stated that a ketogenic diet can improve aerobic and anaerobic performance. Yet, this has often been wrongly interpreted. Adaptation to a ketogenic diet during aerobic exercise causes a shift in fat oxidation from around 40% VO2max towards 70% VO2max meaning that carbohydrate stores are likely to be preserved during low-intensity exercise (Burke et al. 2017).  

Zajac et al. (2014) investigated the effects of a ketogenic diet on exercise metabolism and physical performance during a 105 minute in male off-road cyclists.

The study found that the ketogenic diet favoured positive exercise metabolism changes as described above as well as improved VO2 max and body mass loss compared to the non-ketogenic diet. However, the non-ketogenic diet group had a higher power output at maximal intensity as well as at lactate during the last 15 minutes of the trial providing evidence that a ketogenic diet is inferior at improving performance at near-maximal intensity.

Havemann et al. (2005) investigated the effects of a ketogenic diet compared to a high carbohydrate diet on 100 km time trial performance in well-trained cyclists. The study design ensured that both groups had a high carbohydrate diet before the start of the 100 km time trial. The study found that there was no difference between a ketogenic diet and a non-ketogenic diet on the 100 km time trial performance. But the non-ketogenic diet had a higher 1 km sprint power output. Providing evidence that the ketogenic diet can compromise high-intensity exercise possibly due to reduced glycolytic enzymes content and function.

The main takeaway point is that keto-adaptation may impair the muscles’ ability to use glycogen, compromising the use of glucose, the more economical energy source, when the oxygen supply is limited during high-intensity exercise (Burke, 2021).


In summary, to lose body fat and weight you must be in a negative energy balance and consume a high protein (1.6 g/kg+) diet to limit muscle mass loss. If protein and calories are equal in a ketogenic and an isocaloric diet, then the difference in body fat will be little if any, but the weight loss may be slightly more.

A review on fat-free mass change during ketogenic diets by Tinsley and Willoughby (2016) quoted that the average weight lost as fat-free mass was approximately 27% in ketogenic diet groups and 23% in nonketogenic diet groups.

It appears that ketogenic diets impair the ability to sustain and perform maximal intensity exercise. Therefore, a ketogenic diet might not be appropriate for combat sport athletes, who require lean muscle mass as well as high levels of aerobic and anaerobic fitness.


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