Quick Summary tl;dr
The interest of the ketogenic diet within strength-based sports is increasing. However, there is a significant lack of well-designed studies that have properly looked at this.
Whilst some studies would highlight that a ketogenic diet coupled with resistance training can promote a more favourable body composition, there is a lack of understanding on its long-term use in this category.
We also lack the complete understanding on how well the diet can stimulate significant muscle mass growth. That being said, we can see that this type of diet does not appear to impact on overall strength or power performance.
The use of the ketogenic diet within endurance sports is gaining in popularity as we better understand how ketones can be used as an alternative fuel source. However, the use of the diet within strength or power sports is still not fully understood.
As within the world of endurance sports where the idea that people need to carb load for optimal performance, similar beliefs around how to grow and maintain muscle mass also exist.
What is Strength Performance?
Strength performance includes events or sports that require muscular strength and power such as weight lifting, CrossFit and team games including rugby or American football.
Ketogenic Diets and Body Composition
Whilst most people talk about ‘losing weight’ when they follow a dietary regime, the real goal of most is to be able to reduce body fat percentage and maintain or grow lean body mass.
This goal is especially true for many strength athletes as the reduction in fat mass and increase in muscle mass is important for enhancing power production and mechanical efficiency.
Likewise, many strength athletes have a period of ‘cutting’ before an event whereby they are aiming to get to a desired or set body composition for their chosen sport.
Fat Loss and Muscle Sparing Effects of the Ketogenic Diet
Many calorie-controlled or low-fat diets though, often result in a loss of both fat and muscle mass.
One of the most interesting discoveries about the ketogenic diet has been its perceived ability to positively impact an individual’s body composition. Some early studies showed that the ketogenic diet resulted in a preferential loss of body fat whilst preserving lean body mass, independent of the level of exercise that they were doing ( 1, 2, 3).
One study directly compared the impact of a ketogenic diet vs a low fat diet on body composition in overweight men and women ( 4). A novel finding of this study was that those in the ketogenic group had a three-fold greater reduction in fat within the abdominal area, compared to those in the low fat group.
Keto Combined with Resistance Exercise
Although some studies show that the ketogenic diet alone can promote favourable changes in body composition, others have reported different results.
A meta-regression analysis looked at the effects of variation in protein and carbohydrate intakes on body mass and composition. The study showed that those who ate the lowest carbohydrate intake, had the greatest loss in fat mass but also appeared to lose more muscle mass ( 5).
Can Keto Help You Lose Weight and Preserve Muscle at the Same Time?
If we know that the ketogenic diet can promote a greater loss in fat mass and we know that resistance or strength training is the most effective tool for maintaining or increasing muscle mass, then the two combined may be an effective strategy.
One study which tested this strategy looked at the effects of 10 weeks of resistance training in combination with either a regular diet or a low carbohydrate diet in overweight women ( 6). The women performed between 60-100 minutes of resistance exercise (which included weighted exercises such as seated leg press, shoulder press, leg curls, bicep curls and chest press) twice per week. Those in the lower carbohydrate group ate 6% of total calories from carbohydrates. Compared to those in the regular group, the low carbohydrate group experienced a greater loss in fat mass and overall weight loss.
The low carbohydrate group not only had the greatest loss in fat mass, but also maintained their level of muscle mass. Indicating that the combination of a low carbohydrate diet and resistance training may indeed be the best strategy for achieving an ideal body composition.
These results are further highlighted by two similar studies that also looked at the effects of low carbohydrate diets combined with resistance training ( 7, 8). Both studies (one conducted in females and the other in males) confirm the hypothesis that a low carbohydrate diet alone can promote favourable losses in fat mass. However, when combined with resistance exercise, there is not only a greater loss in fat mass, but also a preservation or gain in muscle mass ( see figure 1).
The Role of Insulin in Building and Preserving Muscle
One of the arguments that people have for a low carbohydrate diet not working within resistance training, is due to the hormone insulin.
Insulin is known as an anabolic hormone which means it inhibits the breakdown and promotes the storage of nutrients in the body. When the levels of insulin are lowered in the body, it can switch on the process of fat burning as insulin is directly involved in lipogenesis (the building of fat in the body).
The main macronutrient that stimulates insulin and therefore lipolysis is carbohydrates. As well as an effect on fat mass, insulin also has an anabolic effect on muscle by increasing protein synthesis and inhibiting protein breakdown (9).
If Insulin Stimulates Muscle Growth, How Can You Preserve Muscle on Keto?
Due to carbohydrates being the biggest stimulator for insulin release, it is therefore believed that having a lack of carbohydrates in the diet will mean that the body cannot maintain or grow muscle mass.
However, insulin is a stimulator of protein synthesis only when adequate amino acids are available (amino acids are the building blocks of all tissues in the body), meaning that it is not only carbohydrates that can stimulate protein synthesis ( 10). Whilst ingestion of carbohydrates after exercise has been shown to stimulate protein synthesis, the effects are often very small and delayed in comparison to just consuming protein after exercise ( 11).
Ketogenic Diet in Strength Athletes
For a lot of competitive strength athletes, their events often require them to meet weight categories, where weight loss without negative changes in body composition and performance is often needed.
Many of the studies that have been discussed so far have looked at the effect of the ketogenic diet coupled with resistance exercise in untrained individuals. Whilst these studies have shown that the ketogenic diet coupled with resistance exercise can induce a greater fat loss whilst maintaining muscle mass, the question remains on the use of this type of diet in highly trained individuals partaking in strength activities.
One of the first studies that looked at the effects of the ketogenic diet on strength performance and explosive strength performance was carried out in a group of elite gymnasts ( 12). Body composition and various strength performance activities were measured before and after 30 days of a modified ketogenic diet. The athletes then acted as their own controls, meaning after three months the same tests were carried out before and after 30 days of the athlete's usual diet (which was a standard American diet).
Overall the results showed no significant difference between the ketogenic diet group and the standard American diet group in all strength tests. With regards to body composition, the ketogenic group had a significant reduction in fat mass and body weight whilst increasing muscle mass.
Similar results were also found in a study that tested the effects of a low carbohydrate diet on body composition and performance in CrossFit athletes (13).
Potential Pitfalls of the Ketogenic Diet and Its Effects on Strength Performance
Whilst all of these studies demonstrate that a low carbohydrate diet can maintain or even improve strength performance, there is a lack of data on how well the diet can contribute to significant muscle mass growth.
When the ketogenic diet was compared to a standard American diet in resistance-trained athletes, although there was a significant increase in muscle mass at 10 weeks (2.4%) for the ketogenic group, those in the standard American diet group experienced a greater increase of 4.4% ( 14).
It has been proposed that a long-term ketogenic diet can interfere with some muscle hypertrophy mechanisms ( 15). Therefore, if the aim of the athlete is to grow a substantial amount of muscle, the ketogenic diet may be slighter counterproductive.
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