Fat Adaptation Questions

Debate on high-fat diets and fat adaptation have been ubiquitous in the endurance community over the past several years. In addition it seems like this subject in particular generates the most passion and emotion from a select few. Calm down, you can eat however you want to, but here are my thoughts on the subject.

Full disclaimer: I am not telling anyone to eat a particular way and I'm not a nutrition expert. I did, however, do my masters thesis on this topic so I have a fair bit of knowledge about it.

There are a few things to consider when it comes to high-fat diets and fat adaptation. They are:

-Race distance

-Point in the Race Season

-Individual Goals

When you are in race season and your goal is to race as fast as possible, I see no reason to cut carbs if you're competing in anything shorter than an Ironman distance event (or the equivalent race length in another sport). The first reason is that any distance shorter than the full ironman can be covered 100% on energy provided by body fat, stored glycogen, and exogenous carbohydrate (food). You will not run out of glycogen in a half ironman if you are fueling properly (assuming your stomach can tolerate 60-90g of carbohydrate per hour). In addition, effective race-season training for a half ironman race will include a fair dose of moderately intense work that cannot be done effectively if carbohydrate stores are low. This includes anything shorter than a 70.3 as the training intensity will be skewed even more toward high-end aerobic and even anaerobic work.

Key point: Training and racing for the 70.3 and shorter distances requires substantial amounts of carbohydrates.

However, training and racing for an ironman event is very different. When racing longer than 6-7 hours at a "moderate" intensity, your body will gradually deplete glycogen levels no matter how quickly you try to replace them by eating. If you do not burn fat effectively your body will run out of glycogen towards the end of the race and you will hit a wall. This is why one's ability to burn fat at higher and higher intensities is paramount for the ultra-endurance athlete. Now there are a few different ways to go about doing this, and some are easier than others. They include:

-High-fat low-carb diet- This means eating a diet that contains under 50-100g of carbohydrate per day and around 70% of one's calories from fat. The basis for this is it forces your body to become more efficient at burning fat because there is simply not enough carbohydrate available for it to use. The drawbacks of cutting carbs almost entirely from your diet are adherence and loss of high-end power. It's very hard to maintain this diet consistently and studies show that maximal power will be decreased. But for the ironman this loss of aerobic power is less important.

-High volume training- Training with a high volume will increase one's ability to utilize fat as a fuel source no matter what diet they follow. Loads of low intensity work will make fat burning more efficient, and some see the high-fat low-carb diet as explained above as a way to help fat burning for athletes that are training at lower volumes.

-Fasted training- Thoughtfully timed fasted training means undergoing a percentage of one's training in a fasted, glycogen-depleted state while performing harder sessions with ample carbohydrate. This can also be explained as "fueling for the work required" as demonstrated by a study performed by Marquet and associates in 2017 (https://www.ncbi.nlm.nih.gov/pubmed/26741119). Put simply it means eating carbohydrates when the intensity is high and restricting them when they are not needed. Much more research needs to be done on this topic but initial results are promising.

Any of these three approaches can be taken to increase an athlete's ability to utilize fat as a fuel and spare glycogen and they will work to varying degrees in different people. It is up to the athlete and coach to determine which approach they may take if any. I believe as an athlete and coach that for ironman distance races and any other race that exceeds 6-7 hours that fat utilization should be a predominant focus in day-to-day training.

Time of year is also a factor to take into account when considering diet. There are some examples of athletes utilizing a high-fat diet during the winter to improve body composition and fat utilization while intensity is traditionally low. Then more carbohydrates are introduced into the diet as training intensity increases. Nutrition can be periodized just like training, so different foods can be eaten when there is a different training focus.

For beginner athletes who want to lose weight or simply finish their first race a high-fat diet can be a great tool. Studies show that body composition is improved on a consistent basis when reducing carbohydrates. So if a person's main goal is to lose weight in order to finish a race and they're not as worried about a slight reduction in high-end aerobic power this diet may be right for them.

Again, this topic is very complicated and I'm not a nutrition expert, but I believe there is much to be gained when it comes to diet and nutrient timing for every athlete. It's up to the athlete and coach to discuss what is optimal for them individually, because nutrition is highly individual and isn't something to generalize for everyone. And most importantly, if you're following a high fat diet, don't feel the need to tell everyone :)