Historically, societies that were able to support non-nomadic lifestyles and increased population density through agriculture – i.e., grain production – were actually more successful (1). Proof of concept comes from the fact that agriculture forms the base for most modern day populations, whereas hunter-gather societies are few. Of course, we do acknowledge that many people develop health problems linked to this modern-day diet and lifestyle, so we clearly haven’t perfected the system yet! But why is the backlash directed against previously-glorified grains and not just against sodium-laden, processed foods, which are not part of the hunter-gather diet either?
Somehow this “against the grain” mindset has become entrenched in the mythology of healthy eating. There have been numerous low-carb diets proposed overtime (many popular in the ’70s) and the ketogenic diet seems to be resurfacing. Is there any evidence to support ketogenic diets for physical performance or weight loss?
Ketogenic diets are ultra-low carbohydrate, high in fat and generally moderate-to-high in protein. The goal is to induce ketosis, forcing the body to shift from burning carbohydrates to fats; physiologically, this is a mechanism to adapt to starvation. Early studies using low-calorie ketogenic diets found side effects including fatigue, cardiac dysfunction, and in some cases, sudden death (1)… however, some populations, particularly those living or traveling in the Arctic, have been able to survive on diets consisting primarily of walrus blubber. Maybe researchers are missing something?
Ketogenic Diets and Physical Performance
Phinney et al (2) fed a low-calorie, ketogenic diet consisting of lean meat, fish and poultry to subjects for 6 weeks. The participants lost approximately 10 kg. When they underwent physical testing their peak aerobic power was maintained and their endurance increased. Importantly, however, the fact that their body weight decreased could explain why their endurance increased. Also these participant were not athletes nor were they completing any exercise or training during the 6 weeks except for the testing. They also reported that it took sometime for the participants to adjust with a decrease in performance in the first week and then improvements after six weeks.
To eliminate the possible effects of weight loss, the same author used a ketogenic diet – similar to the traditional Inuit diet – that would not promote weight loss (83% fat) in competitive cyclists. Here there was a decline in energy levels initially and their ability to sprint remained lower throughout the study. They found the cyclist could adapt and use more fat as an energy source and with no declines in performance. The caveat? In both cases, they had to use electrolyte and vitamin and mineral supplements to ensure health and all the participants were closely supervised. In our minds, this does not suggest that this is appropriate for the lay person. Furthermore, although there were no declines in aerobic performance nor were there improvements (3, 4). Both of these studies were performed thirty years ago; however, in the review published in 2004 the author notes that more recent human studies of similar quality do not exist (1).
“Key”togenic Points for Athletes
- Adaptation takes at least 3-4 weeks. Taking a “cheat day” will likely reduce your exercise tolerance to fats.
- At best performance is maintained and certainly not improved.
- The Inuit diet (the inspiration for these studies) contained caribou blood and soup made with salt water (delicious?) – suggesting that this is why they were able to maintain electrolyte levels. The modern version of this diet could be dangerous without monitoring vitamin and mineral intakes.
- Studies are short-term and use a small sample size so the long-term effects are unknown; particularly in those with health problems.
- In contrast to many popular body building websites, anaerobic (weight lifting and sprints) performance is generally reduced with a ketogenic diet and as such it would not be recommended for these athletes. Studies in endurance athletes again suggest no benefits with a high carbohydrate diet having the slight edge (5)
- Ketogenic diets may reduce the feeling of fatigue, cause mood disturbances and reduce the desire to exercise (6)
Ketogenic Diets and Weight Loss
The debate about whether it is a low carb, low fat, or high protein diet that is best for weight loss continues to rage with really no end in sight; however, some carbohydrate and fat restriction and increased protein intake may be helpful (7). We want to emphasize that it is creating an overall caloric deficit that is essential for weight loss as recently seen in the video of the school teacher that ate McDondald’s for 3 months but kept the calories low and and started exercising. The second consideration is that body composition can play a role in weight loss in the sense that muscle requires more energy to maintain and can therefore increase a person’s metabolic rate. Hence the importance of exercise (both cardio and strength) during weight loss.
Keeping the above points in mind, can a ketogenic diet be more effective for weight loss? Jabekk et al (8) evaluated the effects of exercise in combination with either a regular or ketogenic diet on weight loss in 16 overweight, untrained women. The women lifted weights and followed the ketogenic or regular diet for 10 weeks. Overall the ketogenic group consumed fewer, although not statistically significant, calories and more protein and fat than the regular diet group. Of course, this was based on only two self-reported food records. Those on the ketogenic diet lost ~5.6 kg as compared to 0.8 kg in the regular diet group and they found that the weight loss in the ketogenic diet group was fat mass and no change in muscle mass. They also suggest that hunger and insulin levels are reduced with a low-carbohydrate diet.
For weight loss, a recent review (9) suggests a ketogenic diet may be beneficial BUT it could be due to the increased protein intake that usually occurs with increased fat intake. They also note that the weight loss could just be because people consumed fewer calories on the diet. Here are a few potential reasons ways the diet may work; none of which have been conclusively proven.
- Reduction in appetite because of the higher protein intakes and possibly the keytone bodies suppressing appetite
- Reduced storage of fat and increased fat burning
- Increased metabolism of fats
- Increased energy use by the body when it converts glucose to proteins
No Baloney’s advice? We are not promoting a return to the diets of old (see our post Paleolithic Prescription?), nor is there any evidence to support the idea that healthy carb0hydrates promote disease. Ketogenic diets don’t seem to be beneficial for physical performance and are not generally recommended. Ketogenic diets may help with weight loss BUT the jury is still out and the risks are undetermined. Definitely talk to your doctor if you are considering trying it out and have a plan to monitor blood levels for glucose, ketone bodies, lipids, etc. for safety.
If you have any medical problems, DO NOT try this diet unless your doctor recommends it and is supervising its use (it can sometime be prescribed for epilepsy).