We know from research findings that carbohydrate is necessary for enhancing both high intensity and endurance performance. But recently this theory has been challenged by a true number of endurance athletes and researchers.
In this first part of a two-part series, Joe Alan and McQuillan McCubbin introduce us to high-fat, low-carb diets, discuss the advantages of such diets and look at how you can try one for yourself. Some athletes claim that following a low carbohydrate diet – with a greater proportion of energy coming from fat – has allowed them to consume less carbs during exercise with no loss of performance.
I was never hungry. In fact, it seemed like the more fat I ate, the more weight I lost. These suggestions stem from research showing that the reliance on carbohydrate as opposed to fat to provide energy increases with the intensity of the exercise. Studies have proven that beginning endurance exercise with more carbohydrate kept as glycogen in muscles and the liver increases performance when the duration is more than 2 hours long and when the exercise is performed at a moderate-high intensity.
Consuming additional carbohydrate during exercise further increases performance by adding to the total amount of carbohydrate available to the muscles. A recent study showed that increasing the amount of carbohydrate consumed during endurance exercise 2 hours of continuous moderate intensity cycling followed by a 20km time trial improved performance see Table 1, right above.
The need for such volumes of carbohydrate stems from the need to avoid running out of muscle glycogen during periods of high-intensity training or racing. When this occurs without additional carbs coming in from food the muscles draw on blood glucose as the only remaining source of carbs in the body.
If the body draws much then blood glucose levels fall too, resulting in hypoglycaemia. Low-carb diets and energy production At lower-intensity exercise our body requires very little energy to move the bike forwards. When the physical body can keep up with demand for oxygen, fat can be utilized as the major energy source. This makes fat a more weight-efficient way of carrying kept energy in the body far. If we could better access this pool of energy at higher exercise intensities we could be able to reduce our dependence on carbohydrate dietary and kept and prevent bonking during a race.
In both cases the athletes rode for 20 minutes at watts; thereafter the wattage increased by 25W every 5 minutes with heart rate and blood lactate measurements taken at the end of each 5 minute stage. The minute warm-up was used to allow the athlete to increase their reliance on fat as a fuel. As you can see in figure 1, the first athlete preferentially used greater relative amounts of carbs over fat even at low intensities, despite not eating for four hours to the test prior.
It is fair to say that Athlete 1 is carb dependant even at lower intensity exercise heavily. Figure 1: Percentage fat and carbohydrate use during incremental cycling exercise in Athlete 1.different findings are seen with Athlete 2
Very, tested under the same protocols figure 2. Figure 2: Percentage fat and carbohydrate use during incremental cycling exercise in Athlete 2. As well as Athlete 2 having a 50W higher peak power output, it is apparent that they use a far greater percentage of fat as an energy source compared to Athlete 1. Figure 3 left : Percentage of fat utilisation vs VO2max. Figure 4 right : Percentage of carbohydrate utilisation vs VO2max.
Why would low carb diets be beneficial for endurance athletes? Being dependent on carbohydrate as the major energy source during exercise has some apparent limitations limited supply, depletion results in hypoglycaemiaand therefore adapting the body to utilise more of our body fat stores to fuel exercise makes practical sense.
While the concept of fat adaptation and low carb diets for athletes has only risen to prominence recently, research in this area goes almost two decades back. Several papers followed in the next few years, all showing the same result.
They also found that athletes struggled to perform high intensity training intervals after a period of high fat, low carb eating. These studies found evidence of fat adaptation Again, but no difference in performance at the final end of the training block. They also noticed that athletes who undertook every second session carb-depleted actually performed less work in training, but interestingly performed as well at the end of the training block just.
What it has improved is getting to and staying at race weight without calorie counting or hunger. In part 2 in this series Alan and Joe show how the two test subjects responded to high-fat, low-carb diets, discuss what a high-fat, low-carb diet may look like, and describe what you can do if you would like to try such a diet for yourself. Click to read part 2 here. Having said that, EPO shall reduce your reliance on carbohydrate at any given power output, meaning you can go harder for before you run out longer.