top of page

Onetrack Paper

Are Carbs Bad? Truths, Myths and Misinformation

Nutrition is a minefield with more information than ever before in a heady mix of truth, myth, and self-serving misinformation. Add into the mix anecdotal evidence from everybody you’ve ever met, and it would be easy to scream.

Hopefully, I can clear up a little of the confusion, help you to understand why these suggestions are here, and give you the confidence to explore & experiment yourself.

There is, of course, a caveat on general advice… ‘IT DEPENDS’

I don’t know the exact situation you find yourself in or your dietary requirements. Working from these guidelines should allow you to understand how to find the best fit.

To answer the question, "Are carbs bad?", let’s start with why carbohydrates have got a bad rep recently…

The rise of Ketogenic or Low Carb High Fat (LCHF) diets has been swift in recent years. Fat adaptation for performance and a seemingly faster rate of weight loss mean these diets have gained traction. The phrase ‘carbs don’t agree with me’ has been uttered more than once, what does that mean?

There’s a little bit of science to understand here:

Carbohydrates are broken down and either used as glucose or stored as glycogen in the muscle or the liver. When we store Glycogen, we also store water. 1 Molecule Glycogen + 3 Molecules of water. Therefore 100G stored glycogen can = 400G on the scales.

Hopefully, now you can see why reducing carbohydrates can lead to a faster rate of weight loss. When people re-introduce them into their diet, they see their weight return on at a similar pace.

From a weight-loss perspective low carb isn’t the magic bullet it may seem to be. That is unless you’re maintaining a calorie deficit or planning on being low carb forever. Which brings us to the world of Fasted Cardio, Fat Adaptation & The Keto Diet.

Fat Oxidation ≠ Fat Burning

For a long time, the reasoning ‘I work out fasted; therefore, I will burn more fat because that’s all I have in the tank’ prevailed. There is nothing wrong with working out fasted; but Increased Fat Oxidation does not equal Increased Fat Burning.

Research has demonstrated that we oxidise more fat when working out fasted; however, it has gone on to show that over 24 hours following the fasted workout our body adjusts. James Krieger summarises it neatly below:

“There is no compelling evidence that fasted cardio will enhance body fat loss, despite the temporary increase in fat oxidation. If anything, fasted cardio will improve your utilisation of intramuscular triglycerides and dietary fat for fuel.

While fasted cardio may enhance 24-hour fat oxidation as shown below, it does so by sparing carbohydrates – not protein or lean mass.

What is happening is that, when you do fasted cardio, you reduce your muscle glycogen (carbohydrate stored in your muscle tissue) by around 18% (this amount will vary depending upon the duration and intensity of the cardio). Any carbs that you consume over the rest of the day will go to replenishing that muscle glycogen rather than being burned (that's why you burn fewer carbs over 24 hours as shown in the above graph).”

Energy Systems & Intensity

If we look at the relative intensity of a Onetrack session, we can see that our work rate is going to be well above the 75-84% Vo2 Max of Marathon Pace. Track Workouts operate between 85 -95% vo2 Max, a form of (mostly) aerobic HIIT training aimed at middle and long-distance runners. You can see where Long & Short Intervals sit on the scale below (Blue Arrow Ranges) compared to Repeated Sprint Training & Sprint Interval Training (Green & Yellow Arrows)

Justin Reid-Simms is a Certified Nutritionist, Running Coach & Personal Trainer. Find out more about him at or get in touch @alamerathletic / @houseofcardinal

Figure 2.5 Intensity range used for the various HIIT formats. ASR: anaerobic speed reserve; APR: anaerobic power reserve; MLSS: maximal lactate steady state; MSS: maximal sprinting speed; RST: repeated-sprint training; SIT: sprint interval training; V̇O2max: maximal oxygen uptake; vV̇O2max: minimal running speed required to elicit V̇O2max, V∆50: speed halfway between vV̇O2max and MLSS; Vcrit: critical velocity; VIFT: peak speed reached at the end of the 30-15 intermittent fitness test; VIncTest: peak incremental test speed.

Adapted by permission of Springer Nature from M. Buchheit and P.B. Laursen, “High-Intensity Interval Training, Solutions to the Programming Puzzle: Part I: Cardiopulmonary Emphasis,” Sports Medicine 43 no. 5 (2013): 313-338.

67 views0 comments

Related Posts

See All


bottom of page