Q2 High Fat

Question 1

Mechanism

Answer 1

In endurance sports of over 3 hours glycogen depletion is main concern and cause of fatigue

The utilization of fatty acids occurs in submaximal exercise intensities of between 45 and 65% of VO2max

fat is essentially an infinite substrate, a person with between 7-14% body fat will have over 30,000cals of energy reserves

Most research suggests to increase the body’s ability to oxidize fats the best strategy is to reduce the availability of CHO for a number of weeks whilst increasing dietary fats to induce dietary ketosis.

muscle glycogen content acts as a signal for adaptation and so training in a glycogen depleted state (or overnight fasted) gives the additional stress to derive cellular signalling for adaptation

This combination of low carb and high fat is thought to give ‘keto-adaptation’ where the body is able to utilise fats at higher intensities of exercise as opposed to carbs

Question 2

Dose/ Timing

Answer 2

Adaptations can occur in as little as 5 days

However over 2-3 weeks of little dietary carbs blood ketone levels will be very high

Carb intake of no more than 50g per day but ideally <20g
Fat becoming predominant macro

Emerging area of research is into exogenous keto- supplementation

• Instead of altering diet long term, ingesting ketones can raise blood ketone levels
• This has the potential for athletes to still use CHO to fuel trainings
• However there has been issues with gastrointestinal discomfort and this negatively impacting performance

Question 3

Positives

Answer 3

Enhanced rates of fat oxidation

Increased glycogen sparing

Decreases central fatigue as it provides an alternative fuel
source for the brain

Improved H+ ion removal from muscles

Potential for body recompositions (decrease fat) which can
improve power to weight ratio

Athlete claims of improved recovery

Question 4

Negatives

Answer 4

A study of high fat diets on ironman triathletes found increases in their ability to oxidise fat, but no positive effect on performance of elite athletes

highest rates of fat oxidation are not enough to sustain the energy required by elite ironmen and supplementation with exogenous carbs is required

Plausible to think that low carb/keto diets may elicit enough adaptations to fat oxidation to support the rate of energy expenditure for the event (but not for a competitive time)

Increased perception of effort