A new rigorous research paper has just been published, which presents strong evidence for performance - more on that below.Before jumping in, lets first answer the question of what 'top-end intensity' is for endurance athletes, and take a look at a few recent performances from low-carb high-fat athletes.
Endurance racing: What is Top-End Intensity?Racing intensity for most endurance athletes' (even some pros) for a full Ironman is typically in the 77-82% (FTP) range, and upto 85% for 70.3 distances. Ironman.com, suggests that full Ironman racing is typically performed at ~70% of Vo2Max, 75% for 70.3 distances, upto 85% for Olympic distances, and likely higher for 5000m track racing.
So the first point is if the race duration is over 4 hours (i.e. Ironman, ultras, and 70.3s etc.) then realize, that your race intensity is mostly supported by the aerobic system, of which fat is the pre-dominant fuel source.
Can Low-Carb Athletes deliver?
This is kind of a tongue-in-cheek question these days, with so many world-class performances from low-carb high-fat athletes. Here's a few recent anecdotes from the SFuels stable -
- Zach Bitter's 100-mile treadmill world record, had him punching out 7.18-minute miles for over 12 hours. Zach's 2019, 100-mile track world record, had him running sub-6.50-minute miles, for over 11 hours.
- Dr. Dan Plews, 2018 Kona age-group course record, had him run a 2.50.56 marathon, which translates to a highly consistent sub-7-minute mile pace across the whole run leg.
- Matt Kerr's 2021 age-group Ironman World Championship victory in St George Utah, delivered the fastest run leg of all age-groupers, 2.57.57, on a course with 1400ft elevation gain, and temperatures in 80-90F through the bike-run legs.
2023 Research Paper - Findings
In a new paper (Feb, 2023), a group of highly reputable sports-science researchers, challenged the former premise, that athletic performance was superior via a high-carbohydrate diet and fueling regime.
What was most striking at first glance of the paper, was that the question of 'endurance performance' was tested at a very high intensity (@~85% vo2Max), shorter duration tests including 1mile, and 6 by 800m interval repeats. Traditional thought would consider such intensity-duration testing, as 'anaerobic' and by nature more dependent on carbohydrate oxidation, and less-so fat oxidation. But in a rigorous highly controlled testing protocol, and elegant research design, the team produced a set of findings that will certainly challenge traditional thinking. The study summarized four notable findings -
- High-Carb athletes had no superior (high-intensity) performance over LCHF (low-carb high-fat) athletes,
- Even at intensities at >85% Vo2Max, LCHF athletes were oxidizing fat at rates of 1.58gr/min (+/- 0.33gr/min).
- LCHF athletes had higher HDL, LDL, and total cholesterol,
- LCHF athletes, had reduced mean-median blood glucose levels. Conversely, 30% of the High-Carb athletes, had mean-median blood-glucose levels consistent with pre-diabetes.
SFuels: Perspective on the Research
It's great to see such a well-controlled set of factors (diet, training load, body composition, etc.) and high-intensity testing protocol, where the core, pre-dominant factor of difference was diet and fueling.
In this study, a 2018 paper on cross-country skiers and our own lab observations of low-carb high-fat athletes, we are seeing more consistent references to high-fat oxidation rates (>1.5gr/min) at high intensities >80% Vo2Max. This is supportive of the suggestion, that with such metabolic efficiency, the body could provide a glycogen-sparing effect when fat can be predominately used for fuel at these high intensities.
It is an important note, that aside from the athletic performance outcomes, a number of health markers were also tested, and reference was made to the complications (pre-diabetes) that were associated with high-carb diet athletes.
I guess from a balanced perspective, you would like to see more subjects in such a study, and also would like to have the study repeated for women. Nevertheless, the paper highlighted that prior studies that had less attention to study design controls (diet, fueling and training-load factors) drove different and non-repeatable findings.
Most critical to the metabolic and performance outcomes of this study, is the diet protocol used.
1) Carbohydrate volume, <50gr/day,
2) % calories from fat per day, 75-80%,
3) the duration of intervention, 31 days.
This is consistent with the guidance given by SFuels and Endure.IQ for an effective transition (~cold-keto phase) to efficient fat oxidation, and metabolic flexibility.
As published by Rothschild and team, a review of 125 studies, and over 1100 subjects, revealed that diet (fueling), and training duration are some of the most pre-determinate factors of substrate-fat oxidation efficiency.
In observing professional and age-group athletes' lab data, it's clear that training alone doesn't guarantee fat-oxidation efficiency and subsequent performance in endurance racing. Diet is critical.
Bottom-line: ensure you pay attention to the guidance (above 3 points in blue) for an effective low-carb high-fat diet transition period - in realizing the intended metabolic shift, and performance outcomes of a low-carb lifestyle.
To help you with this, download and read our -
1) SFuels LIFE Guide - giving you over 40 simple meal, snack, and shake ideas for a low-carb high-fat lifestyle - using SFuels TRANSFORM, SFuels Revivial, SFuels Keto3, SFuels TRAIN, SFuels LIFE Bars.
2) SFuels Fueling Guide - and noted research on the impact of Medium Chain Triglycerides in diet and fueling.