Ketogenic diets are superior for fat loss short term, but long term there are identical fat losses when calories are matched. Ketogenic diets don’t affect muscle strength but can result in reductions in performance for anaerobic exercise. Ketogenic diets maintain lean mass but few studies have found a ketogenic diet to be able to increase lean mass compared to a carbohydrate control diet.
THE PROS AND CONS OF GOING KETO FOR LOSING FAT KEY POINTS:
- Going keto for losing fat results in faster short term fat loss.
- Ketogenic diets are superior for short-term fat loss, but there are identical fat losses when calories are matched in the long term.
- Ketogenic diets don’t affect muscle strength but can result in reductions in performance for anaerobic exercise.
- Ketogenic diets maintain lean mass, but few studies have found a ketogenic diet to increase lean mass compared to a carbohydrate control diet.
INTRODUCTION TO KETO FOR LOSING FAT AND GAINING MUSCLE
There has never been a more controversial subject than keto diets and muscle loss. Ketogenic diets are characterized by high-fat and moderate to high protein content but of an insufficient level of carbohydrates (usually 20 g-50 g per day), thus forcing the body to primarily use fat as a fuel source. The ketogenic diet mimics metabolic starvation, resulting in large increases in the body’s use of fat as an energy source. The reduction of dietary carbohydrates decreases plasma insulin and increases glucagon; this state promotes liver glycogen breakdown and gluconeogenesis (i.e., creation of glucose from non-carbohydrate sources) and lipolysis of adipose tissue through the increase of HSL (hormone-sensitive lipase).(1)
This process of shifting from carbohydrates as a fuel source to fat is known as ketosis. Ketogenic diets increase the concentration of ketone bodies in the blood, usually above >0.5 mmol/L, indicating nutritional ketosis.(2) As the brain depends on glucose when following a ketogenic diet, the brain depends on ketone bodies as an energy source.(3) Ketone bodies are present under fed states; however, ketones increase with fasting, prolonged exercise, and reduced carbohydrate availability.
KETO FOR LOSING FAT STUDIES
Ketogenic diets are effective for weight loss by increasing satiety and reducing appetite. In a systemic review of the literature, the keto diet resulted in a negative energy balance of -339 kcals per day compared to a control diet.(4) A large number of studies in which subjects were not restricted by calories showed ketogenic diets resulted in lower calorie intake.(5, 6)
When calories are matched, there are no significant differences in losing body weight or body fat over a year.(7-9) Based on the evidence, ketogenic diets result in more weight loss short term; however, there are no differences in fat loss or bodyweight long term compared to a high carbohydrate, low-fat diets.(10) There is no evidence that a ketogenic diet is superior for fat loss to a high carbohydrate, low-fat diet in the long term when calories are equal.
KETO FOR LOSING FAT AND APPETITE
The decreases in appetite have been attributed to the high protein consumed on ketogenic diets and increased appetite-suppressing hormones (i.e., decreased leptin, ghrelin, etc.), resulting in a lower caloric intake. Others have suggested the increased fiber from consuming more vegetables also contributes to the reduced caloric intake. Thus, keto causes a substantial reduction in caloric intake compared to control diets.
Some have touted that ketogenic diets result in a “metabolic advantage” resulting in increased energy expenditure, but this was disproven by Kevin Hall. He showed that a ketogenic diet resulted in about a 100 kcal increase in energy expenditure after adjusting for body mass and composition.(11) The data from several studies suggest that the metabolic advantage of a ketogenic diet would be small, certainly not enough to make it superior to that of a carbohydrate-matched diet.
KETO FOR LOSING FAT AND KETONE BODIES
Ketogenic diets also increase circulating ketones. Several studies have shown that exogenous administrations of ketone metabolites that increase ketones without carbohydrate restriction demonstrate anti-catabolic and anti-inflammatory properties. (12, 13) In endurance athletes, administration of ketone esters has been found to increase markers of recovery by preventing overtraining and overreaching.(14)
Despite symptoms of overreaching, the ketone supplemented group improved their overall work output and endurance performance test by 15% compared to the control group. In animal models, cancer-induced muscle wasting can be prevented with supplemental ketones.(15) Others have found that ketone esters could increase anabolic signaling pathways in muscle (i.e., mTOR). (16)
Despite these properties of ketones, most of the studies that have compared ketogenic diets to isocaloric diets with resistance exercise have found either decreases(17-20), similar changes(19, 21-26), or increases(25, 27) in lean muscle mass. In Wilson et al. study, the ketogenic diet was followed with a carbohydrate refeed in the post-evaluation period, likely enhancing glycogen and positively influencing the final lean mass results.(25)
KETO FOR LOSING FAT AND MUSCLE MASS
Most of the earlier studies on ketogenic diets used low protein diets; however, the studies in elite athletes found that a high protein (i.e., 30-40% protein) ketogenic diet maintained muscle mass.(28, 29) In sum, ketogenic diets can maintain lean mass but do not seem to be productive for increasing muscle mass. Most of the research suggests that combining a ketogenic diet with resistance training can favor a fat mass reduction in healthy and trained individuals. However, muscle mass may also be compromised.(30)
The other consequences of a low-carbohydrate diet are feeling of fatigue or what has been referred to as the “Keto-flu.”(31) Several meta-analyses have found that ketogenic diets are beneficial for losing body fat but are not favorable for increasing lean muscle mass.(4, 32, 33) A ketogenic diet can maintain lean muscle mass as long as the protein intake is sufficiently high ~1.7 g/kg/day, but the studies do not show its beneficial for increasing lean muscle mass. Others have found reductions in anabolic signaling pathways (i.e., mTOR, AMPK) and reduced anabolic hormones (i.e., testosterone and IGF-1), which could contribute to the reduced increases in lean mass.(20, 34-36)
GLYGOGEN LOSS
The large increases in lean mass on a ketogenic diet can be attributed to increased water loss as ketones increase water loss and large reductions in glycogen (i.e., every gram of glycogen holds 3 grams of water).(37-39) The larger increases in body weight losses with ketogenic diet over low-fat diets during short-term interventions are attributed to losses in body water. Well-hydrated muscles account for almost 75% of the water content. For example, a study of bodybuilders who underwent a carbohydrate loading protocol before a show increased the size of their chest, thighs, arms, calves, etc., compared to a group that did not carb load before a competition.(40)
Most studies measuring body composition using dual-energy X-ray absorptiometry or DEXA is heavily reliant on the measurement of body water content; thus, researchers don’t know whether there are true losses in lean body mass or just water weight. Therefore, the losses of lean muscle mass in studies can incorrectly assume its lean mass when it could just be water weight loss. DEXA is widely used for its ease of use, but DEXA has been found to have a 4% error and has been found to poorly accurately detect changes in lean mass in response to resistance exercise. DEXA does not have the accuracy to detect small to moderate increases in muscle size.(41)
DO KETOGENIC DIETS AFFECT MUSCULAR STRENGTH?
In terms of performance, most of the available studies have found that short, high-intensity exercise is not affected by ketogenic diets. The studies are defined as high-intensity, low-duration exercises that last less than 2 minutes. Energy demands for short-term high-intensity exercise are met by the ATP-PC and lactic acid system, which are highly dependent upon skeletal muscle glycogen.
Ketogenic diets have not been found to affect performance in gymnasts, powerlifters, and CrossFit athletes.(17, 25, 26, 42) A review of the literature found no clear performance benefit to athletes following a ketogenic diet. However, some athletes can perform better in short duration, vigorous-intensity tests when weight loss occurs on a ketogenic diet results in less body mass having to be moved. (43, 44)
KETO FOR LOSING FAT AND STRENGTH
A reduction in body fat and body weight will result in higher strength/power to body mass ratio. Another review of the literature on ketogenic diets found that ketogenic diets with high protein (~1.8 g/kg/day) have a “muscle-sparing” effect as ketogenic diets maintain muscle mass while having no harmful effects on strength or power.(45) The meta-analysis by Henselmans et al. found low carbohydrates diets did not impact strength gains. In the review of the literature, 15 out of 17 studies found no effects of carbohydrate intake on strength gains in which protein and calorie intake were matched between groups.(46)
DOES CARB CYCLING BUILD MORE MUSCLE THAN REGULAR DIETING?
The study by Wilson et al.(25) in which subjects who were following a ketogenic diet then switched to a high-carbohydrate diet gained more muscle mass than other ketogenic diet studies raised questions as to the efficacy of cycling in carbs on a carb-restricted diet to gain muscle mass. The cyclical ketogenic diet includes weekly periods of ketosis followed by high carbohydrate days. For example, Monday thru Friday would be low carbohydrate days, and Saturday and Sunday would be carbohydrate days.
KETO FOR LOSING FAT STUDIES ON CARB CYCLING
The theory behind this is the concept of fuel shifting. There are periods of high-fat utilization on low carb days, and high carbohydrates replenish glycogen stores for enhanced anabolism and restoration of high-intensity exercise with carbohydrates. For eight weeks, researchers assigned subjects to a cyclical ketogenic diet or a control diet with resistance exercise and cardio. The cyclical ketogenic diet consumed less than 30 grams of carbohydrates.
The weekends consisted of carbohydrates super-compensation days in which 8-10 g/kg/bw were consumed (70% carbohydrate intake; 15% protein; and 15% fat). The control diet consisted of 55% carbohydrates, 30% fat, and 15% protein. Both groups lost body weight and body fat at the end of eight weeks, but the cyclical ketogenic diet group lost more lean muscle mass.
The cyclical ketogenic diet had neutral effects on strength gains, whereas the regular diet had greater strength improvements than the cyclical ketogenic diet group.(47) Body composition was measured for bioelectrical impedance, which is highly inaccurate, so whether the true losses in muscle were due to actual muscle loss or just fluid loss was not determined.
KETO FOR LOSING FAT KEY POINTS:
- Ketogenic diets are superior for short-term fat loss, but there are identical fat losses when calories are matched in the long term.
- Ketogenic diets don’t affect muscle strength but can result in reductions in performance for anaerobic exercise.
- Ketogenic diets maintain lean mass, but few studies have found a ketogenic diet to increase lean mass compared to a carbohydrate control diet.
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