Keto Diet: Friend Or Foe For Muscle Retention?

The ketogenic diet is a high-fat, adequate-protein, very-low-carbohydrate diet. It forces the body to use fat instead of sugar as fuel. While it has been used to treat metabolic disorders, obesity, cardiovascular disease, and type 2 diabetes, its effects on muscle mass are less understood.

Some studies have found that ketogenic diets lead to muscle atrophy, while others have found that they preserve muscle mass. It is suggested that the former may be due to the larger caloric deficit that tends to accompany ketogenic diets.

Ketogenic diets have been found to decrease muscle protein synthesis and increase muscle protein breakdown. They also tend to decrease insulin levels, which is linked to muscle growth.

However, ketogenic diets have also been found to improve and preserve grip strength during aging and to increase muscle protein synthesis despite a dramatic reduction in insulin levels.

Overall, the available evidence suggests that ketogenic diets may cause muscle loss, especially when compared to non-ketogenic diets. However, the effects seem to vary between individuals, and ketogenic diets do not necessarily impair strength performance.

Ketogenic diets and muscle hypertrophy

The ketogenic diet (KD) is a popular nutritional strategy that involves a drastic reduction in carbohydrates, specifically to less than 50 g per day or 10% of total caloric intake, accompanied by a substantial increase in fat, and sometimes protein. The KD has been proposed as an alternative for athletic performance, improving different pathologies, and optimising body composition.

Muscle Hypertrophy

Hypertrophy is defined as an increase in muscle mass and volume, where the contractile elements enlarge and the extracellular matrix expands. To achieve this, it is necessary to manipulate the diet and programming variables in strength training.

Reviews have shown that the KD can be an alternative for increasing muscle mass, as long as an energy surplus is generated. However, the KD's satiating effect and lack of adherence when maintained continuously for eight weeks or more do not seem to make it an optimal nutritional strategy for muscle hypertrophy.

A meta-analysis of KD effects on body composition and muscle performance with exercise endurance in humans with a particular focus on randomised controlled trials did not clearly support a major beneficial effect of KD on the muscle/fat ratio or performance in strength-trained individuals.

Studies on the Effects of KD on Muscle Hypertrophy

A study by Vargas-Molina et al. found no significant differences between groups in fat-free mass (FFM) variables, and more research is needed to perform studies with similar KD and control diet interventions.

Another study by Vargas et al. showed that a KD might be an alternative dietary approach to decrease fat mass and visceral adipose tissue without decreasing lean body mass; however, it might not be useful to increase muscle mass during a positive energy balance in men undergoing resistance training for eight weeks.

Paoli et al. found that a KD led to a significant reduction in fat mass and visceral adipose tissue without decreasing lean body mass; however, it did not increase muscle mass.

Nakao et al. found that a KD induced skeletal muscle atrophy via reducing muscle protein synthesis and possibly activating proteolysis in mice.

The KD's main influence on the muscle is reduced to changes in energy metabolism, particularly decreased carbohydrate and increased fat oxidation. The problem lies in contradictory data from studies of KD effects, starting from its influence on muscle weight to mitochondrial quantity, oxidative metabolism, antioxidant capacity, and activity of enzymes.

Although many studies demonstrate beneficial effects of KD on skeletal or cardiac muscle, these diets should be used carefully because there is data suggesting that such nutritional manipulations can have negative, including long-term, consequences.

Ketogenic diets and muscle protein synthesis

Ketogenic diets are high-fat, adequate-protein, and very low-carbohydrate diets that force the body to use fat as fuel instead of sugar. This shift in metabolism leads to the production of ketone bodies in the liver, which are then used as an energy source by extra-hepatic tissues such as the brain and muscles.

The ketogenic diet has been studied for its potential therapeutic effects on various diseases, including neurological disorders, obesity, cardiovascular disease, and type 2 diabetes. However, its impact on skeletal muscle hypertrophy is less understood.

Skeletal muscle mass is regulated by the balance between muscle protein synthesis and breakdown, which can be influenced by factors such as nutrition and resistance training. The ketogenic diet's effect on muscle mass control pathways is still unclear, but it appears to maintain or conserve muscle mass rather than induce net hypertrophy.

Some studies have shown that a ketogenic diet can lead to muscle atrophy, with a decrease in muscle weight, fiber area, and grip strength. This atrophy may be related to hypercorticosteronemia, hypoinsulinemia, reduced insulin-like growth factor 1 (IGF-1), and oxidative stress.

On the other hand, a ketogenic diet may have a protective effect against muscle mass loss during aging or low-calorie diets. It can also improve and preserve grip strength during aging.

The effects of a ketogenic diet on muscle mass seem to depend on factors such as the duration of the diet, the amount of protein intake, and the fitness level of the individuals. More research is needed to fully understand the impact of ketogenic diets on muscle hypertrophy, especially in resistance-trained individuals.

Ketogenic diets and muscle atrophy

The ketogenic diet is a nutritional approach that involves a high-fat and adequate-protein content, but a very low level of carbohydrates (less than 20g per day or 5% of total daily energy intake). This diet forces the body to use fat, instead of sugar, as its primary fuel source.

Skeletal muscle constitutes 40% of total body mass and is one of the major sites of glucose disposal. The ketogenic diet is a well-defined approach to induce weight loss, but its role in muscle adaptation and muscle atrophy is less understood.

Muscle Atrophy

Muscle atrophy is the accretion of muscle fibre size that may occur in response to resistance exercise. Muscle atrophy can also be caused by a variety of pathological conditions, such as disuse, cancer, denervation injury, and ageing.

There is conflicting evidence about the effect of ketogenic diets on muscle atrophy. Some studies have found that ketogenic diets lead to muscle atrophy, while others have found that ketogenic diets preserve muscle mass compared to low-fat diets in the absence of training.

Mechanisms of Muscle Atrophy

Insulin

The ketogenic diet dramatically reduces insulin levels, which can have a negative impact on muscle growth. Insulin stimulates muscle protein synthesis and has anabolic effects on skeletal muscle.

Testosterone

Ketogenic diets have been found to have negligible effects on testosterone levels. However, caloric restriction and fasting, which share many mechanisms with ketogenic diets, reduce testosterone levels.

Ketone Bodies

Ketone bodies, such as beta-hydroxybutyrate (BHB), have been found to inhibit Akt, a protein involved in cell growth and glucose metabolism. BHB has also been found to inhibit histone deacetylase (HDAC) activity, which may help maintain muscle mass.

Muscle Glycogen

Glycogen is an important component of muscle mass, and each gram of glycogen is bound to 3 grams of water. However, research has indicated that ketosis reduces glycogen breakdown at rest and during exercise, which may preserve muscle performance.

In conclusion, there is conflicting evidence about the effect of ketogenic diets on muscle atrophy. While some studies have found that ketogenic diets lead to muscle atrophy, others have found that ketogenic diets preserve muscle mass compared to low-fat diets. More research is needed to fully understand the effects of ketogenic diets on muscle atrophy.

Ketogenic diets and muscle glycogen

The ketogenic diet is a nutritional approach that involves a high-fat and adequate protein content, with a very low level of carbohydrates (less than 20 g per day or 5% of total daily energy intake). This forces the body to use fat as its primary fuel source instead of sugar.

Muscle glycogen is an important component of muscle mass, and each gram of glycogen is bound to 3 grams of water. During endurance exercise, nutritional ketosis reduces glycolysis and preserves glycogen resources, enhancing muscle performance.

Ketogenic diets have been shown to decrease muscle glycogen breakdown at rest and during exercise. This is due to a shift in substrate competition, where the body uses fat and ketone bodies as an alternative source of energy.

Ketosis, characterised by an increase in ketone bodies in the blood, occurs when the body's glycogen stores are depleted, and can be induced by fasting or a ketogenic diet.

Ketogenic diets have been found to have a protective effect on muscle mass, particularly during aging or low-calorie diets. However, there is conflicting data on the effect of ketogenic diets on muscle hypertrophy, with some studies showing an increase in muscle mass and others showing no significant changes.

The impact of ketogenic diets on muscle mass control pathways is still not fully understood, but it appears that ketogenic diets may exert a protective effect against muscle mass loss rather than inducing net hypertrophic effects.

Mechanisms of Ketogenic Diets on Muscle Glycogen

Ketogenic diets induce a metabolic shift, decreasing plasma insulin and increasing glucagon. This promotes hepatic glycogenolysis and gluconeogenesis, as well as lipolysis of adipose tissue.

During ketosis, the body produces ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) in the liver, which are then used as an energy source by extrahepatic tissues such as the brain, heart, and skeletal muscle.

Ketone bodies can act as signalling molecules, regulating gene expression and adaptive responses. They can also inhibit histone deacetylase activity, leading to reduced oxidative damage and potentially helping to maintain muscle mass.

Ketogenic diets have been shown to decrease muscle glycogen breakdown and preserve glycogen resources, particularly during endurance exercise. While the impact on muscle mass control pathways is not fully understood, ketogenic diets appear to have a protective effect on muscle mass rather than inducing net hypertrophic effects.

Ketogenic diets and muscle strength

The ketogenic diet is a nutritional regimen characterised by a high-fat and adequate protein content, with very low carbohydrate levels (less than 20g per day or 5% of total daily energy intake). The insufficient level of carbohydrates forces the body to use fat instead of sugar as its primary fuel source.

Skeletal muscle constitutes 40% of total body mass and is one of the major sites of glucose disposal. The ketogenic diet is a well-defined approach to induce weight loss, with its role in muscle adaptation and muscle hypertrophy less understood.

Muscle Hypertrophy

Skeletal muscle tissue plays a key role in the regulation of whole-body metabolism, functional work capacity and exercise performance. Muscle hypertrophy is the accretion of muscle fibre size that may occur in response to resistance exercise. Understanding the molecular mechanisms of this muscle adaptation is important to counteract the opposite mechanism of muscle atrophy, which is related to many pathological conditions such as disuse, cancer, denervation injury and ageing.

Muscle mass is the result of the balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). The algebraic sum of MPS and MPB results in the net protein balance (NPB). Only with a positive NPB is it possible to achieve muscle protein accretion and, consequently, growth of muscle fibre size.

Ketogenic Diets and Muscle Mass Control Pathways

Nutrition and resistance training play a pivotal role in influencing rates of MPS and MPB, and ultimately, the NPB. The regulation of skeletal muscle mass reflects changes in protein synthesis and protein degradation, and several stimuli lead to protein synthesis and subsequent muscle hypertrophy.

The question that should be addressed is whether a diet in which one of the macronutrients is restricted, i.e. carbohydrates in KD, may affect skeletal muscle hypertrophy.

KD theoretically may affect skeletal muscle mass control pathways in several ways, but data provided by scientific literature suggests a negligible or no effect of KD on muscle mass with concomitant resistance training. KD may instead exert a protective effect against muscle mass loss during ageing or during low-calorie diets. The total effect seems to consist in the maintenance of muscle mass rather than a net hypertrophic effect.

Ketogenic Diets and Muscle Glycogen

One important component of muscle mass is glycogen. Glycogen is stored in skeletal muscles at a rate of 500g, and each gram of glycogen is bound to 3 grams of water, thus glycogen and associated water may significantly contribute to the whole muscle mass in athletes, especially in activities such as competitive bodybuilding.

Research has indicated that during endurance exercise, nutritional ketosis alters substrate competition and reduces glycolysis, promoting the preservation of glycogen resources to enhance muscle performance. More generally, ketosis related to both chronic high-fat, low-carbohydrate diet, or KE intake, decreases glycogen breakdown at rest as well as during exercise.

Histone Acetylation Mechanisms

Histone acetylation plays numerous roles in muscle control and different classes of histone deactylase have different effects on skeletal muscle, such as control of contracting proteins, calcium channels and, in general, muscle health. BHB mediates inhibition of histone deacetylase (HDAC) activity in vivo. HDAC inhibitors increased the lifespan by a still not very well known mechanism, yet associated with hyperacetylation of histones and a large number of other proteins. Moreover, KD inhibits HDAC activity, modifying related gene transcription and leading to reduced oxidative damage, which could help the maintenance of muscle mass.

Ketogenic Diets and Muscle Mass

There are conflicting data about the effect of chronic very low-carbohydrate (ketogenic) diets on lean body mass, muscle mass and exercise. Some studies have shown an increase in muscle mass after a ketogenic diet and resistance training, while others have found a general conservation of muscle mass with no significant increases.

One confounding factor might be the amount of daily protein intake expressed as grams of protein per kilogram of body mass.

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