Ketogenic Diets & Physical Performance

I've been experimenting with low carb eating for several months now, and there have definitely been a few bumps in the road. Whenever I attempt an intense CrossFit workout during the first few days of low carbing, I tank. The reason seems clear: I'm not eating enough carbs. Afterall, carbs are what supply the fuel for intense exercise, so it seems foolish to try to workout without them. Fortunately, there's some hope. Thanks to Robb Wolf over at The Performance Menu, I stumbled across this jewel of a study:

Ketogenic diets and physical performance

Introduction

The study is a discussion of the juxtaposition of clinical research results favoring carbohydrate against observed functional well-being in traditional cultures consuming none. It begins by giving a brief history of how carbohydrates came to dominate our diet, then cites a few studies that seem to confirm the necessity of carbs for optimal physical performance.

The hunter's counterpoint – practical observations on ketogenic diets

The author begins to provide some insight into how ketogenic diets can sustain performance by citing a couple of real world examples in which explorers were forced into ketosis during their travels without any noticeable performance detriments after a period of adaptation.

Modern ketogenic diet performance studies

This is where most of the value in the study lies. The author details a couple of studies that he has performed investigating the effects of ketogenic diets on physical performance:

1st Study:

...a study of subjects given a very low calorie ketogenic diet for 6 weeks in a metabolic research ward. The protein for this diet, along with a modicum of inherent fat, was provided by lean meat, fish, and poultry providing 1.2 grams of protein per kg of reference ("ideal") body weight daily. In addition, mindful that the natriuresis of fasting could reduce circulating blood volume and cause secondary renal potassium wasting, the subjects were prescribed 3 grams of supplemental sodium as bouillion and 25 mEq (1 g) of potassium as bicarbonate daily.

Treadmill performance testing of these subjects included determinations of peak aerobic power (VO2max) after a 2-week weight maintenance baseline diet, and again after 6 weeks of the ketogenic weight loss diet. Endurance time to exhaustion was quantitated at 75% of the baseline VO2max. This endurance test was repeated again after one week of weight loss and finally after 6 weeks of weight loss. Other than these tests, the subjects did no training exercise during their participation in this study. To compensate for the fact that the average subject had lost over10 kg, the final endurance treadmill test was performed with the subject carrying a backpack equivalent in weight to the amount lost.

The energy expenditure data (expressed as oxygen consumption) and exercise times across this 8-week inpatient study are shown in Table 1 (I was unable to link to the table, but you can link to it directly from the study via the link that I provided above). That these subjects'peak aerobic power did not decline despite 6 weeks of a carbohydrate-free, severely hypocaloric diet implies that the protein and mineral contents of the diet were adequate to preserve functional tissue. As can be noted, endurance time to exhaustion was reduced after one week of the ketogenic diet, but it was significantly increased over the baseline value by the 6-week time point. However the interpretation of this endurance test is confounded by the fact that the oxygen cost (ie, energy cost) of the treadmill exercise had significantly decreased following the weight loss, and this occurred despite the subjects being made to carry a backpack loaded to bring them back to their initial exercise test weight.

This question of improved efficiency notwithstanding, it is clear that our subjects experienced a delayed adaptation to the ketogenic diet, having reduced endurance performance after one week followed by a recovery to or above baseline in the period between one and six weeks. Given the reduced energy cost of the exercise despite the backpack, the extent of this adaptation cannot be determined from this study. To explain this improved exercise efficiency, we can speculate that humans are more efficient carrying weight in a modern backpack than under their skin as excess body fat. It is also possible that these untrained subjects became more comfortable with prolonged treadmill walking by their third test, and therefore improving their overall efficiency.

2nd Study

...study utilized competitive bicycle racers as subjects, confined to a metabolic ward for 5 weeks. In the first week, subjects ate a weight maintenance (eucaloric) diet providing 67% of non-protein energy as carbohydrate, during which time baseline performance studies were performed. This was followed by 4 weeks of a eucaloric ketogenic diet (EKD) providing 83% of energy as fat, 15% as protein, and less than 3% as carbohydrate. The meat, fish, and poultry that provided this diets protein, also provided 1.5 g/d of potassium and was prepared to contain 2 g/d of sodium. These inherent minerals were supplemented daily with an additional 1 g of potassium as bicarbonate, 3 grams of sodium as bouillon, 600 mg of calcium, 300 mg of magnesium, and a standard multivitamin.

The bicyclist subjects of this study noted a modest decline in their energy level while on training rides during the first week of the Inuit diet, after which subjective performance was reasonably restored except for their sprint capability, which remained constrained during the period of carbohydrate restriction. On average, subjects lost 0.7 kg in the first week of the EKD, after which their weight remained stable. Total body potassium (by 40K counting) revealed a 2% reduction in the first 2 weeks (commensurate with the muscle glycogen depletion documented by biopsy), after which it remained stable in the 4th week of the EKD. These results are consistent with the observed reduction in body glycogen stores but otherwise excellent preservation of lean body mass during the EKD.

The results of physical performance testing are presented in Table 2 (I was unable to link to the table, but you can link to it directly from the study via the link that I provided above). What is remarkable about these data is the lack of change in aerobic performance parameters across the 4-week adaptation period of the EKD. The endurance exercise test on the cycle ergometer was performed at 65% of VO2max, which translates in these highly trained athletes into a rate of energy expenditure of 960 kcal/hr. At this high level of energy expenditure, it is notable that the second test was performed at a mean respiratory quotient of 0.72, indicating that virtually all of the substrate for this high energy output was coming from fat. This is consistent with measures before and after exercise of muscle glycogen and blood glucose oxidation (data not shown), which revealed marked reductions in the use of these carbohydrate-derived substrates after adaptation to the EKD.

What is most interesting about these studies, particularly the second, is that sprinting capability (CrossFit Workouts) was the only performance parameter that wasn't restored after the keto-adaptation period. This is what I have observed from my own experience and through talking with others. Also, the keto-adaptation period must be strictly low carb, as the author points out:

There are to date no studies that carefully examine the optimum length of this keto-adapataion period, but it is clearly longer than one week and likely well advanced within 3–4 weeks. The process does not appear to happen any faster in highly trained athletes than in overweight or untrained individuals. This adaptation process also appears to require consistent adherence to carbohydrate restriction, as people who intermittently consume carbohydrates while attempting a ketogenic diet report subjectively reduced exercise tolerance.

This is where I've screwed up several times in the past. I can successfully go 5 days (M-F) strictly adhering to low carb eating, but somehow manage to indulge on the weekends. It's a vicious cycle in which I never become keto-adapted, and have to constantly supplement my diet with carbs in order to maintain high levels of performance. Even after becoming keto-adapted, unless I keep my exercise intensity low by focusing on strength routines and steady-state cardio, my performance will suffer, as the author notes in his conclusion:

Therapeutic use of ketogenic diets should not require constraint of most forms of physical labor or recreational activity, with the one caveat that anaerobic (ie, weight lifting or sprint) performance is limited by the low muscle glycogen levels induced by a ketogenic diet, and this would strongly discourage its use under most conditions of competitive athletics.

The question now becomes: Can you STAY keto-adapted while adding in some post-workout carbs to replenish your glycogen stores? I'll be sure to write a post on that as soon as I figure it out.