Starting at an early age, I had already begun internally challenging nutritional rhetoric. As a kid, breakfast cereal was my jam, but I still remember that while I sat at the table, slurping down all that soggy goodness that is unique to breakfast cereal, I would read the cereal box and ironically wonder about the validity of the food guide pyramid.
Yes, the now-regrettable food guide pyramid. I would think, “11 servings of bread?!” or, “only 2 servings of meat/eggs?!” Needless to say, I was destined to be a muscle-head. Although, it did not occur to me at the time, my enjoyment of drinking half-and-half, licking mayonnaise off the knife after making a sandwich, or eating the individually-wrapped butters at the diner while waiting for our food would come to help me realize the full-extent of our errors in the nutritional guidelines.
Obviously, I am a supporter of high-fat, high-protein diets, and at this point, nearly all nutrition professionals agree that dietary fat was inappropriately demonized in our recent history. While evidence mounts for carbohydrate-restricted diets for health outcomes, there are still those who are not convinced and continue to support the fat-restriction model. Neither is “wrong.” Both diets “work.” However, while someone like myself very much likes dietary fat but does not really like foods that predominately contain carbohydrate (sugary stuff aside), there are those who love potatoes even if they’re devoid of all the fixin’s. The point here is, if you can’t follow the diet, don’t bother. That being said, “good” diets should contain 1) appropriate total calories, 2) moderate to high protein, 3) plenty of vegetables, and 4) inverse intakes of fat and carbohydrate. The last criterion there has to do with something called the Randle cycle.
Essentially, the Randle cycle states that fats inhibit carbohydrate metabolism while carbohydrates inhibit fat metabolism. In part, this is why eating high amounts of fat and carbohydrate leads to increased body fat. Moreover, high amounts of either fat or carbohydrate in isolation, will also slow the metabolism of these substrates and lead to the accumulation of body fat. From an evolutionary standpoint, this was advantageous in case the person could not find food for a few days. In today’s society, this is almost never the case, highlighting the first criterion – appropriate total calories.
In the low-carbohydrate realms, it is often said that calories don’t matter, as if once low-carb dieters reach their daily caloric needs, all the extra calories disappear. This is absolutely false. In trying to popularize low-carb diets, I think we made a mistake with this statement, as too many subscribers to carbohydrate-restriction now say this as if it is validated fact, and it deters the rational from giving the diet a chance. The statement was initially made to highlight a believed metabolic advantage and satiety advantages of fat and protein over carbohydrate. Here’s what we actually know.
The touted “metabolic advantage,” is not so robust that it can make up for eating far too many calories, but it does certainly exist, as energy is lost in various metabolic endpoints of protein and in gluconeogenesis. In 5 studies currently available comparing low-carbohydrate diets to standard diets under conditions of equal protein intake, 4 seem to support minor beneficial effects of carbohydrate restriction on body composition. As a brief overview, Noakes [cite] found greater lean mass retention of Mediterranean-style carbohydrate restriction versus both high saturated fat carb-restricted and high-carbohydrate diets. Paniagua et al. [cite] reported a seemingly beneficial redistribution of fat mass with high unsaturated fat carbohydrate restriction compared to a high-carbohydrate diet, but changes in total fat mass were not different. Shai et al. [cite] observed a 2kg greater loss of weight with Mediterranean carbohydrate-restriction versus a high-carbohydrate diet. In this study, a third group followed a ketogenic diet and also lost more weight, but they had a higher protein intake (criterion 2!). Gardner [cite] found no differences between high- or low-carbohydrate diets. Finally, Douris et al. [cite] found that mice eating a carbohydrate-restricted diet over the lifespan had a leaner body composition than mice eating a carbohydrate-rich diet, but the low-carb mice also ate low-protein, and while the mice were allowed to eat as much as they wanted, it is possible that calories differed between groups. Collectively, it would appear that carbohydrate restriction either produces favorable changes in body composition or no changes compared to diets with higher carbohydrate intakes.
Finally, the third criterion, eat plenty of vegetables, is not in contention in any circles, so we need not discuss the matter at length. Fiber is good for you for a multitude of reasons, and the same holds true for the micronutrients and phytonutrients found in plants. Actually, about half of ingested fiber becomes short-chain fatty acids through fermentation in the gut, so if you’re low-carb and trying to reconcile with fiber counting as carbohydrate, don’t worry about it.
When it comes to carbohydrate counting, traditional ketogenic diets limit total carbohydrate intake to 30-50g. I have an issue with this for several reasons, one of which concerning net carbohydrate and vegetable consumption. Although, the most pressing issue is that this does not account for activity level or fueling requirements of exercise because nearly all research on ketogenic diets has been conducted in clinical population samples with individuals who are typically sedentary and only moderately active at best.
Keto diets are popular for weight loss and endurance performance, and we’ve discussed weight loss a bit already. Endurance performance absolutely can be enhanced with the assumption of a ketogenic diet. However, this doesn’t really kick in until the duration of exercise begins to exceed about 15-25 miles of running depending on fitness level. That is about the time that muscle glycogen is significantly depleted (even with loading), and that is one reason why the diet is most popular with ultra-endurance athletes, but let’s take a closer look.
Ketogenic diets make perfect sense for ultra-endurance athletes because they just run or cycle somewhat slowly for hours on end – there is no real sprinting or intermittent high intensity activity that would be common in pretty much any other sport. Higher intensity activity can only utilize carbohydrate to create the energy needed to perform, and without that carbohydrate, an athlete will be unable to maintain high-intensity activity for very long. That is just how our metabolism is set up. However, our “normal” diets are so plentiful that we are always able to use carbohydrate as fuel (it is the preferred energy source), so the body “forgets” how to efficiently metabolize fat – we lose metabolic duality. This is evidenced by an unpleasant adaptation phase to ketogenic diets due to the withdrawal-like symptoms after nearly eliminating dietary carbohydrate.
Obviously, you can see that performance can be negatively impacted without sufficient carbohydrate. Conversely, being unable to tap into our fat storage can also limit performance, as we may need to do so as glycogen decreases and using fat at lower intensities preserves muscle glycogen. In a study published earlier this year, Dr. Volek found that keto-adapted endurance athletes can maintain higher intensity activity using fat instead of carbohydrate [cite]. While this can certainly aid in glycogen sparing, it only extends benefit up to a certain point. Specifically, ~70% VO2Max vs. ~55% VO2Max in carb-based athletes. Thus, exercise intensities exceeding 70% VO2Max in keto-adapted athletes might be impaired due to inadequate carbohydrate availability.
Although, this study also found equal levels of muscle glycogen and glycogen changes in response to exercise. This might be due to an extended period of assuming the diet (20 months) permitting a greater degree of adaptation, but the fact that their diets contained double the carbohydrate content of a traditional ketogenic diet must be at least partially responsible for these effects. Despite carbohydrate composing 10.4% (82g) of the athletes’ total energy intake, these athletes maintained nutritional ketosis.
This is not unexpected – active individuals have greater carbohydrate tolerance than sedentary individuals. Moreover, recent work from our laboratory has found professional MMA athletes to maintain ketosis until the diet is composed of 9-11% carbohydrate [cite]. Even the sedentary models indirectly support greater carbohydrate allowance in ketogenic athletes. A limit of 30g carbohydrate on a 1,500 Calorie diet corresponds to 8% of energy from carbohydrate. Therefore, we can conclude that athletes need not adhere to the strict confines of traditional ketogenic diets.
So what should a ketogenic athlete do, exactly? First, get keto adapted. During this phase, it is still a good idea to keep carbohydrate intake sufficiently low, in the <30-50g range for 4 weeks. Then, begin working in more carbohydrates. It is highly unlikely that this amount will exceed 15% of total energy [cite], although it may be possible with high activity levels and/or proper carbohydrate timing. With moderate activity levels, a safe bet is 8%. To accurately determine how much carbohydrate an individual can tolerate will require playing with carbohydrate levels and frequent testing of blood and/or urine ketone levels. Blood ketones should be greater than 0.3mmol/L.
Low-carbohydrate performance may best be enhanced with a targeted ketogenic approach. This is purely anecdotal, but it makes sense to increase blood glucose when glucose is needed most – before and during exercise. This can help to increase exercise volume for greater lean mass adaptations to resistance exercise and benefit overall athletic performance, which likely features some high intensity work. Even the ultra-endurance athlete can benefit from a carbohydrate gel taken a few minutes before an uphill section of the course. Our observations of a ketogenic diet in recreational bodybuilders found that for some athletic adaptations, such as anaerobic power output, the ketogenic athletes made the adaptation, but without having the carbohydrates available, they were unable to realize their potential [cite]. Once given carbohydrate, their performance increased. However, if the main goal is fat loss, fat oxidation may be interrupted by increasing blood glucose just before or during exercise (remember the Randle cycle?). In sum, carbohydrate content of the diet may need to be adjusted after weighing the relative importance of each athletes’ individual goals.
I know if you’ve made it this far, you must be interested in low-carb dieting, and I’m very passionate on the subject myself, but we can’t let that override a few existing principals. Right now we can say with some confidence that there are health benefits to low-carbohydrate diets. There is little we can say with confidence about low-carbohydrate athletics. Personally, I do well with a ketogenic diet and, as a powerlifter, perform great. There are similar anecdotal reports, but it’s not science. It’s also not exactly scientific that I know I can eat 75-100g of carbs/day and maintain ketosis, but science does say with certainty that carbohydrates aid athletic performance, and I am not about to deny that, nor should anybody else at this juncture.
About the Author
Jordan M. Joy, MS, CSCS, CISSN
Jordan M. Joy MS, CSCS, CISSN is currently a Graduate Research Assistant at Texas Woman’s University and the Founder of InnovaSolutions LLC Consulting Services. He has his BS in Exercise Science from the University of Tampa, an MS in Applied Nutrition with a focus in Sport Nutrition from Northeastern University, and he is currently pursuing his PhD in Nutrition with a minor in Kinesiology. Jordan has worked principally as a scientist for both academia and industry while notching over 100 publications on topics pertaining to human performance Finally, Jordan is also a record-holding powerlifter.