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Metabolic Efficiency - Don’t try and become fat adapted, just get fitter.

Metabolic efficiency - Don’t try and become fat adapted, just get fitter.

Teach the body to use fat. Sounds pretty cool right? But are we oversimplifying things and forgetting the bigger picture?

Metabolic efficiency is a strategy designed to help you become better adept at tapping into fat stores (an almost infinite supply) as a fuel source to help spare muscle glycogen (a limited supply). If we can run off fat instead of carbohydrates we theoretically can go for longer. During longer distance events (ultra/ironman) where fat is often the preferred fuel source it makes sense, however, because of fat being a particularly inefficient fuel (1) (produces less speed/power from the same amount of oxygen compared to carbohydrates), it would be a poor choice for shorter, faster events (5k- marathon, sprint-Olympic tri, maybe ½ iron).

But what about the recreational sportsman or woman, does striving to become more ‘fat adapted’ really help us improve?

Although nothing new, biohacking our physiology in attempt to use more body fat seems like a win win, however, placing more emphasis on becoming fat adapted can often miss the mark of what’s really important. Getting fitter and faster.

Being able to use more fatty acids at a given intensity is a welcome benefit, however the real goal should be to increase your VO2 max, your lactate/anaerobic threshold and running/cycling economy, as these are the key factors to develop your endurance performance (2).

There are clearly some real benefits of being able to use more fatty acids as a fuel source: -

Spare muscle glycogen - we need this for higher intensities

Reduce lactate accumulation that will eventually slow you down.

But what about (body) fat loss?

Just by increasing the use of using fatty acids as a fuel source may does not necessarily equate to a drop in body fat, you still need to be in an overall energy deficit (more on that here) for this to happen. Any excess kcals that aren’t used will simply be popped back into your stores (re-esterification) with no net loss in body fat.

So forget it?

Not necessarily. We just need to shift our mindset from exercising to ‘burn’ fat, to instead becoming more efficient, as this is what will ultimately lead to better changes in health and body composition.

Adapting your nutrition and exercise to increase metabolic efficiency

A key determinant of your VO2 max is your ability to use oxygen and covert it to energy. Those with higher VO2 max’s will be able to take more oxygen into the muscles which slows down the point at which you fatigue.

One of the reasons for this is because of mitochondria. Mitochondria are the energy powerhouse of the muscle cell and the more we have, the more oxygen you can use to generate energy, whilst reducing the amount of waste products (hydrogen ions/lactic acid from lactate) you accumulate when you exercise.

See the two examples below. Athlete A's crossover point from fat to carbohydrates appears far later than athlete B's, indicating better fat oxidation at a given intensity.

Athlete A metabolic efficiency
Athlete B Metabolic efficiency

Through training and some dietary interventions (3), increasing the number and density of the mitochondria reduces how much glycogen you use and lactate produced at a given intensity, meaning your lactate threshold will increase, allowing you to exercise for longer durations and at greater percentages of your VO2max. This also means you are able to use more fatty acids at this same intensity rather than having to rely on carbohydrates.

In simple terms, this means that exercise will feel easier at the same work rate (watts or speed), you won’t fatigue as quickly and you can recover faster (4). You’re not becoming fat adapted, you’re just getting fitter.

How can you test your efficiency?

Through metabolic testing and VO2Max Testing we are able to measure what % of fat and carbohydrates you are using at different intensities, however we can also look at other metrics such as VO2 peak, anaerobic threshold and how much oxygen you can extract (FeO2) to paint a better overall picture of what’s really going on under the good.

  • Which areas are you poor at?

  • Which areas of your training do you need to develop?

  • How can you fuel accordingly?

We can learn a lot more than just trying to burn more fat.

Interested to take your performance up another and become more efficient with your training? Find out more about testing here



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