Attention Uphill Athletes: The information in these articles provides outdated, incorrect, and potentially harmful information. Scientific knowledge evolves as new studies are done and we are on the forefront of tracking and keeping you updated on the current best practices. Since this article was published new scientific and experiential findings directly and definitively contradict the information provided in this article. Uphill Athlete’s long-time registered dietician, Rebecca Dent, is working on updating our community on the new best practices, including what the latest research and coaching experience indicates to be best practices, and why. In the meantime, we want you to fuel all of your training sessions appropriately, to make sure you have enough energy to train and recover ready for your next training session and so you can cope with the training load of the week. This will help to ensure you are eating enough energy day to day to support your health and enable you to reach your full fitness potential ultimately helping you achieve your goal of summit success or crossing that finish line. In the meantime, please make sure you adequately fuel your training with a source of carbohydrate.

Sincerely, Rebecca Dent, MSc Sport Nutrition – Sports Nutrition Diploma – International Olympic Committee and Steve House, Uphill Athlete founder.

Nutrition strategies play an important role in your ability to train and perform well. They optimize training adaptations and aid recovery, helping you reach your full fitness potential. This is the second article in a series about nutrition and fat adaptation. Be sure to read the first, “Nutrition and Fat Adaptation,” as well as the third installment, “High-Fat Diets and Ultra-Endurance Performance.” It is important to highlight that this article is about the influence of specific dietary strategies on optimizing performance for endurance exercise and is not in relation to health.

In the first article of this series, “Nutrition and Fat Adaptation,” we highlighted that fat adaption training has two purposes:

  1. To enhance physiological adaptations to endurance training, enabling you to go farther and faster for longer.
  2. To enhance the body’s ability to use fat as a fuel source during endurance exercise (your endurance training), reducing your reliance on carbohydrates during endurance performance (a summit attempt, ultra race, alpine expedition, etc.).

Note that the term fat adaptation denotes enhancing the body’s ability to burn fat; however, the term fat adaptation training is often used to encompass both of the above points (1 and 2).

Specific Strategies for Fat Adaptation

Nutrition for endurance training is about optimizing fuel efficiency—being able to utilize both carbohydrates and fat as fuel sources. To encourage the body to optimize fat as a fuel source, there are two main strategies an athlete can pursue: doing fasted training sessions at low to moderate intensity and/or following a carbohydrate-restricted diet (a low-carbohydrate, high-fat diet).

Because it takes time for the body to get better at utilizing fat as fuel source, anyone who is new to endurance training will need to introduce fasted training slowly while at the same time making sure to take on board a source of carbohydrates to fuel higher-intensity (Zone 3–4) strength training or interval-type sessions. There are only a few situations where a high-fat diet OR a high-carbohydrate diet may be advised. The potential role of a high-fat diet for endurance is discussed in the next article in this series.

“Training Low”

Fat adaptation–specific training sessions involve carrying out training with low carbohydrate availability in the bloodstream, liver, and/or muscles. This has recently been defined as “training low.”

To “train low” entails dietary strategies that deliberately withhold carbohydrates before, during, and after carefully selected training sessions—i.e., low-to-moderate-intensity (Zone 1 and 2) sessions. (2)

There are several dietary strategies to “training low,” but we are only going to outline the strategies as advised here at Uphill Athlete, which are perhaps the simplest to apply.

Fasted Sessions

Fasted sessions take two forms:

  1. Training after an overnight fast: The dietary strategy here is to avoid eating from your last meal in the evening until after your morning training session. Only water, black tea, coffee, and sugar-free drinks are allowed.
  1. Training after a minimum of a 4-hour period without eating: If you intend to carry out your fat adaptation session later in the day, you need to allow a minimum of 4 hours (ideally 6 hours) without eating. Again, only water, black tea, coffee, and sugar-free drinks are allowed.
A Note on Caffeine

In both of the above fasted sessions, drinking black coffee before training (or ingesting 200 mg of an alternate sugar-free caffeine product—e.g.. gels, gum, tablet) is often advised. Caffeine ingestion before this type of training has been shown to help reduce the perceived intensity and effort of training (3), quite literally giving you a boost.

Fat Intake During Fasted Sessions

Dietary fat alone is not recommended during fasted training due to the risk of gastrointestinal upset.

Risk of Illness with Training Low

Training with low carbohydrate availability places additional stresses on the body and has been shown to reduce immune function and increase the risk of illness (2). It is therefore vital that adequate recovery takes place.

Fat Adaptation Strategies Summary

What is key to remember is that the above dietary strategies are designed to maximize the adaptive response to endurance training. If you are new to these fat adaptation strategies, training fasted will initially feel harder to do and your performance may likely be reduced during the early stages. It is also important to combine fat adaptation sessions with more performance-based ‘‘quality’’ sessions, which require an intake of carbohydrates to fuel the session (1).

Be sure to read the other articles in this series:

References/Links to Further Reading

  1. Burke, Louise M. “Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon?” Sports Medicine 2015;45(Suppl 1):S33–S49.
  2. Bartlett, Jonathan D., John A. Hawley, and James P. Morton. “Carbohydrate availability and exercise training adaptation: Too much of a good thing?” European Journal of Sport Science 2015;15(1):3–12

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