Keto diets for endurance athletes

by ir. Yvana van den Hork

Many of us will have heard of the advantages of very low carb diets for obese patients and more specifically for diabetics. Going very low carb results in not having as much hunger and much healthier blood glucose levels. Another group that often goes on a keto diet are those who want to prevent tumour growth.

But how about endurance runners or cyclists that experience running out of glycogen, the carb fuel a body runs on. Can trying a  keto diet result in better endurance capacity and prevent 'running into a wall' ?
In theory, running/cycling in ketosis is a marvelous concept, because the body would be adapted to rely on fat instead of carbohydrate. Others say that it is not possible.

From experimenting with both a high-carb and low-carb strategy it appears you may be able to achieve similar performance levels. It does take quite a long period of time in order to get fat adapted, up to almost 2 years. Even after that period, there will be a higher requirement for oxygen in order to burn fatty acids stored in the body, which normally isn't too problematic unless you are at a very high altitude.

The main problem with going totally without carbohydrates during competitions is that there is very little energy left for short, high-intensity efforts. Every competitive long-distance endurance events will have periods in which short bursts of very high-intensity efforts are needed.

One major advantage of a keto diet for endurance athletes over using carbohydrates is that being reliant on carbs will not only have logistic problems, but also may cause gastric distress.
During prolonged exercise, especially in warm weather, gut motility can come to a grinding halt. Even when somene has had no problems during training events, an actual competition can raise heart rate so much that consuming food can become very problematic. The resulting gas, bloating, and nausea make athletes drop out of races. GI problems are the leading cause of DNFs in ultra events, so prevention of gastric distress could potentially going keto a reasonable solution for some ultradistance athletes.

However, when you transition to a keto diet and have never followed a low carb diet before, your body needs at least 2-3 weeks to adapt and produce enough ketones, unless external ketones are are absorbed.
During this period, training performance will suffer and everything you do may feel like a struggle, while recovery will be slower too.
Once you are adapted to fueling yourself primarily on ketones for day-to-day living, you still need to adapt to performing optimally as an athlete fueled by ketones. This can take months, during which time your only progress will be in fat adaptation, not aerobic development, the ability to produce power, or the ability to achieve faster paces.
If you are going to try ketosis as an athlete, the best time to experiment would be a period of general aerobic endurance training. For athletes who reach their peak in summertime, this typically means they should start to experiment in autumn or winter. It would be a mistake to try making this transition in spring.
Another advantage of going on a keto diet in winter will be that cutting out carbs prevents you from gaining too much surplus weight off-season while becoming keto-adapted will be at your advantage in spring when building up mileage and starting on lower intensity training.  
Exercise studies of athletes who have adapted to ketosis show they burn more fat at a given exercise intensity than when they were carbohydrate-fueled, but not that they can go faster.
When athletes get faster after adapting to ketosis, or even after a period of ketosis followed by a return to an “all fuels” strategy, weight loss is often a big contributing factor to the increase in speed. These athletes lost weight, because diets that eliminate food groups cause people to pay a lot of attention to all food choices. This dramatically reduces mindless eating, and the consumption of junk food, alcohol, and excess sugar. It typically leads to increased consumption of fresh, whole foods. In the case of ketosis, it leads to increased consumption of whole food sources of protein, fat, and vegetables. Low-fat diets on the other hand can be much trickier as generally more hunger is experienced and even more foods are restricted.
Just remember, the driving factor for weight loss is calorie reduction, so don't go looking for replacement foods. While we were fooled with tons of low-fat junkfood, you can bet your life on it, now keto diets become more popular, keto cookies will appear too.. don't be fooled into buying those thinking you will also lose weight when eating these.

Weight loss will increase VO2 max (milliliters of oxygen/kilogram/minute), improve power-to-weight ratio, and lower the effort needed to move forwards. Even if power utput doesn't improve, you will still go faster.

Advocates of keto diets paint a picture of a glorious lifestyle where you’re not hungry as often and don’t suffer from energy fluctuations. From a health perspective, claims include decreased triglycerides, increased insulin sensitivity and reduced symptoms of Type II diabetes, lower blood pressure, slower growth in cancerous tumors, improved cognitive function, and many more.

Compliance to a keto diet is a major problem. Nearly everyone who has had good results with either high fat or low fat diets, will gradually move back toward a higher carb and moderate fat diet within two years.

Going on a keto diet requires almost complete abstinence from carbs, limiting intake to less than 50 grams for most people. Overconsumption of carbs, even as simple as a banana will immediately kick yourself out of ketosis!
People who have gotten used to a ketodiet but occasionally indulge a high carb treat, often report feeling terrible afterward. For some, this negative feedback provides greater motivation to avoid temptations that knocked them out of previous diets. For the vast majority of people, even with good results the restrictive nature of the dietary strategy is too high a barrier for long-term compliance.

The best prepared athletes are those who are the most adaptable. To be a successful athlete you have to be able to perform using whatever fuel that is available. Circumstances may change during events and your special food may not be available. If you can’t immediately change your strategy, you are at a competitive disadvantage.

From a sports science perspective, exogenous ketone supplementation is most promising development. Ketone esters have made it possible to consume ketones in a drink or food and significantly reduce the time necessary to achieve dietary ketosis. Dual fuels may become an interesting option. An athlete can supplement with exogenous ketones and thereby conserve limited carbohydrate stores for high-intensity efforts.

Matching carbohydrate availability to training goals is a strategy that has been used successfully by athletes for a long time. There are various protocols but the basic idea is to complete high-intensity intervals and important competitions with high carbohydrate availability.
During endurance or general fitness training, exercising with low carbohydrate availability can enhance weight loss and improve the body’s ability to metabolize fat for energy.

If you want to lose weight, (very) low carb diets work. If you want to train effectively, a mixed diet with high carbohydrate availability for important workouts and competitions is your best bet.


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