A keto diet is a low-carb, high-fat, moderate-protein diet. It was originally used in the treatment of epilepsy in children by increasing the level of ketone bodies in the blood.
Although the keto diet is a low-carb subtype, it deserves a separate discussion. While the non-ketogenic level of a low number of carbohydrates is determined subjectively, the ketogenic diet can be determined objectively by measuring circulating ketone bodies. A condition called ketosis, also known as physiological or food ketosis, should be fixed. In addition, to complete starvation, this condition is achieved by limiting carbohydrates to a maximum of ~ 50 g or ~ 10% of the total energy, while the protein remains moderate (1.2–1.5 g kg day) while maintaining the predominance of energy consumption from fats (~ 60–80 % or more, depending on the degree of displacement of proteins and carbohydrates).
The state of ketosis is relatively benign, which should not be confused with ketoacidosis, which is a pathological condition observed in type 1 diabetics, where dangerous overproduction of ketones occurs in the absence of exogenous insulin. The primary ketone produced by the liver is acetoacetate, and the primary circulating ketone is β-hydroxybutyrate. Under normal non-dietary conditions, circulating ketone levels are low (less than three mmol / L). Depending on the degree of restriction of carbohydrates or total energy, the keto diet can increase the level of circulating ketone to a range of ~ 0.5–3 mmol / L, while the level of physiological ketosis reaches a maximum at 7–8 mmol / L.
Increased energy consumption on a ketogenic diet
The perceived advantage of fat loss resulting from reduced carbohydrates compared to a simple reduction in total energy is mainly based on insulin-mediated inhibition of lipolysis and supposedly enhanced fat oxidation.
However, a study by Hall et al. studied the effect of 4 weeks on a low-fat diet (300 g carbohydrates), and then four weeks on the keto diet (31 g carbohydrates). The level of ketones in the blood reached ~ 1.5 mmol / L for two weeks in the keto diet. When switching to the keto diet, there was a short-term increase in energy consumption (~ 100 kcal/day), which lasted a little more than a week. This was accompanied by a short-term increase in nitrogen loss, which could potentially indicate a stress response, including increased gluconeogenesis.
Although insulin levels rapidly and significantly decreased during keto diet (consisting of 80% fat, 5% CHO), during the first half of the keto diet phase, there was a real slowdown in body fat loss during the first half of the keto diet phase, which coincided with increased protein use and loss mass without fat.
It has been suggested that the production and use of ketone bodies creates a unique metabolic state that, theoretically, should exceed non-ketogenic conditions for the purpose of fat loss. However, this claim is largely based on studies related to higher protein intake in experimental groups. Even small differences in the amount of protein can lead to significant advantages for higher energy consumption. A meta-analysis by Clifton et al. found that a difference in protein intake of 5% or more between diets at 12 months was associated with a threefold increase in the effect of fat loss.
Is keto diet safe?
Soenen et al. systematically demonstrated that higher protein content in low carbohydrate diets, rather than a lower carbohydrate content, was a decisive factor in contributing to greater weight loss in controlled hypocaloric conditions. This is not too surprising, given that protein is known to be the most saturating macronutrient. A striking example of the saturating effect of protein is a study by Weigle et al. showing that under ad libitum conditions, an increase in protein intake from 15 to 30% of total energy led to a spontaneous decrease in energy consumption by 441 kcal day. This led to a decrease in body weight of 4.9 kg in 12 weeks.
With the exception of one small study [Wilson J, Lowery R, Roberts M, Sharp M, Joy J, Shields K, et al. The effects of ketogenic dieting on body composition, strength, power, and hormonal profiles in resistance training males. J Strength Cond Res. 2017. doi: 10.1519 / JSC.0000000000001935.], To date, all controlled interventions that coincided with protein and energy consumption between the keto diet and non-keto diet conditions have not been able to demonstrate the benefits of keto diet in fat loss.
A fairly recent review by Hall (2017) summarizes: “There has not been a single study with stationary nutritional controls that tested the effects of low-calorie diets with equal protein content and that reported a significant increase in energy expenditure or greater loss of body fat with low-carb diets “. In addition, the author claims that the model of obesity, based on the carbohydrate-insulin theory, is too simplified. Several logical implications of this model of obesity have recently been investigated in a pair of carefully controlled studies in stationary nutrition, the results of which did not confirm the key model predictions.
In light of this and the previously discussed study, the “special effects” of the keto diet are not associated with their expected metabolic advantage, but with higher protein content. Perhaps the most convincing evidence against the alleged metabolic benefit of carbohydrate restriction is the recent pair of Hall & Guo meta-analyzes, which included only isocaloric, protein-controlled, food-controlled studies in which subjects were provided with all the food necessary for the experiment (as opposed to their own choice and self-esteem). A total of 32 studies were included in the analysis. Carbohydrates ranged from 1 to 83%, and dietary fat ranged from 4 to 84% of total energy. In low carbohydrate conditions, there was no benefit in energy consumption or fat loss. In fact, the opposite was discovered. Energy consumption and fat loss were slightly higher in conditions with a high carbohydrate and low-fat content (at 26 kcal a day, fat loss at 16 g a day); however, the authors acknowledged that these differences were too small to be considered practically significant.
The common criticism
A common criticism of the existing literature is that trials should last longer (several months instead of several weeks) to provide sufficient “keto-adaptation”, which represents a physiological shift towards increased fat oxidation and reduced glycogen utilization. The problem with this statement is that an increase in the level of fat oxidation, objectively measured by a reduced respiratory coefficient, reaches a plateau during the first week of the keto diet. The increased oxidation of free fatty acids, plasma triacylglycerol, and intramuscular triacylglycerol during exercise is a well-known reaction to diets rich in fats. However, this increase in fat oxidation is often misunderstood as a higher rate of decrease in fat mass. This assumption ignores the concomitant increase in fat intake and storage. As a result of fat adaptation, elevated intramuscular levels of triacylglycerol indicate increased fat synthesis compared to degradation during rest periods between workouts. To confirm the previous point of view, strictly controlled isocaloric studies with consistent protein content consistently demonstrate that keto-adaptation does not necessarily mean a net decrease in fat balance.
If the keto diet has any advantage over the non-keto diet in fat loss, it is potentially in the area of appetite regulation. Under unlimited caloric conditions, keto diet constantly led to a decrease in fat and or body weight.
This occurs due to a spontaneous decrease in energy consumption, which may be associated with increased satiety due to suppression of the production of the hormone that regulates hunger – ghrelin.
In addition, the keto diet demonstrated the effect of suppressing hunger, regardless of protein content. In a 4-week cross-sectional study, Johnstone et al. found that in the keto diet, ad libitum food intake (without a targeted calorie restriction) led to a 294 kcal decrease in energy intake. Recent results were obtained despite relatively high amounts of protein (30% of total energy), comparable between the conditions of the keto diet (4% carbohydrates) and non-keto diet (35% carbohydrates).
Further supporting this idea, a meta-analysis by Gibson et al. found that keto diet suppresses appetite more than a hyper-low-calorie diet. However, it remains unclear whether appetite suppression is associated with ketosis or other factors, such as increased protein or fat intake, or carbohydrate restriction.
Keto diet in sports
An area of growing interest is the influence of the keto diet on athletic performance. Since the ability to fully train can affect body composition, the effect of the keto diet on exercise requires discussion. Limiting carbohydrates in combination with high fat intake for adaptation to fat (or keto-adaptation) is a tactic aimed at improving performance by increasing the body’s dependence on fat as an energy source and, thereby, reducing glycogen consumption, which supposedly can improve sports results. However, unlike the perceived benefits in performance, Havemann et al. found that seven days of a high-fat diet (68%), followed by one day of a high-carb diet (90%), expectedly increased fat oxidation, but reduced the sprint power by 1 km for well-trained cyclists.
Stellingwerff et al. compared the use of the type of substrate for ATP synthesis, glycogenolysis (production of glucose by the liver from glycogen) and enzymatic activity on a 5-day diet high in fat (67%) or high in carbohydrates (70%), and then for one day with a high content carbohydrates without training and subsequent experimental tests on the seventh day. A high-fat diet increased fat oxidation, but also reduced the activity of the pyruvate dehydrogenase enzyme (characterizing glucose oxidation) and reduced glycogenolysis. These results provide a mechanistic explanation for the deterioration in high-intensity labor productivity as a result of a diet high in fat and low in carbohydrates.
Recently, the ergolytic effect of keto-adaptation is observed at lower intensities. Burke et al. reported that after three weeks on keto diets with a slight energy deficit, elite runners showed increased aerobic ability and fat oxidation. However, this was accompanied by an increased oxygen demand for a given speed, which leads to a slight decrease in productivity. At that time, both linear and non-linear diets high in carbohydrates led to a significant improvement in performance.
Notably, Paoli et al. did not find a decrease in strength indicators based on body weight in elite gymnasts within 30 days of the keto diet. In addition, the keto diet led to a significant loss of fat mass (1.9 kg) and a slight increase in muscle mass (0.3 kg). However, unlike a study by Burke et al., In which protein was at the same level between groups (~ 2.2 g kg), protein intake in Paoli et al. was distorted in favor of keto diet (2.9 versus 1.2 g / kg).
Wilson et al. reported a similar increase in strength and power, as well as changes in body composition when comparing the keto diet and a Western dietary model in conditions of energy deficiency. However, in the keto diet, total testosterone increased significantly from the beginning to the end of the 11-week experiment (118 ng/dl) compared to the Western diet (-36 ng/dl), while insulin did not change. It is noteworthy that despite such different changes in testosterone levels, this did not affect the growth of athletic performance, however, as in other similar studies.
Conclusions: Like other diets, ketogenic does not show obvious benefits for weight loss, except for its ability to reduce hunger, although this cannot be called an insignificant bonus since hunger is the main reason for the failure in losing weight.
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