# Another Study Validates Athletic Carnivore: Metabolic Flexibility Over Permanent Ketosis!
**by Laurent Glatz – for Athletic Carnivore**
Is it absolutely necessary to remain in ketosis to achieve a high-performing metabolism? What if this fixation prevents some athletes from fully tapping into their muscular potential?
For years, Athletic Carnivore has championed a simple principle: **our body must be able to utilize fats, glucose, or both, depending on its energy demands.**
A new study published on October 6, 2026, in the prestigious scientific journal *PNAS* reinforces the physiological mechanisms underpinning this approach.
A Study Putting Muscle Function Back at the Heart of the Debate
Researchers Jeffrey Rothschild, Anna Katharina Dunst, Jessie Axsom, Henning Wackerhage, and Hermann Heck investigated how muscles generate their energy.
Using a mathematical model developed in 1984 by Alois Mader, they created software called *MetaboliSim* that simulates the interactions between different muscular energy systems.
Their simulations were tested against ten well-known physiological phenomena, including fat utilization, lactate fluctuations, and the effects of exercise intensity on energy production.
**Result: all ten phenomena were qualitatively reproduced.**
The principle is clear: at low intensity, muscles can rely heavily on fats. As effort intensifies, they increasingly draw on glucose and glycogen stores. Multiple energy systems operate simultaneously.
Our body does not depend on a single fuel source. It adapts fuel use according to demand.
Why Insist on Staying in Ketosis All the Time?
This is where some ketogenic narratives become questionable.
Ketosis corresponds to a state of ketone body production and availability. It does not, by itself, represent our full capacity for energy adaptation.
Our body can enter ketosis, exit it, and return depending on physiological conditions. However, using more glucose during exercise does not automatically mean leaving ketosis.
**True metabolic flexibility is not about maintaining ketones at maximum levels but about efficiently mobilizing the various available fuels.**
This distinction is especially crucial for athletes.
Why Athletic Carnivore Now Recommends Dextrose in Certain Sports
Consider an athlete training intensively four, five, or six times a week.
Each demanding session consumes part of their muscle glycogen reserves. When workouts are frequent and energy recovery insufficient, these reserves can gradually deplete.
The body can produce glucose without direct dietary intake, notably through gluconeogenesis. It can thus replenish glycogen even on a very low-carb diet.
**But this capacity does not guarantee rapid enough replenishment when efforts are particularly intense, long, or closely spaced.**
This is precisely why Athletic Carnivore now views dextrose as a relevant tool for certain athletic profiles.
Dextrose is simply D-glucose. It provides a directly absorbable glucose source without needing prior digestion of complex carbohydrates.
Taken during prolonged or demanding exercise, it can supply immediately usable glucose, support energy availability, and partially spare glycogen reserves.
A meta-analysis published in January 2026 in the *Journal of Applied Physiology*, led in part by Jeffrey Rothschild, compiled 31 studies. It found a modest but statistically significant glycogen-sparing effect when carbohydrates were consumed during prolonged exercise.
**The goal is not to consume glucose all day but to provide it when muscular demand justifies it.**
What About Insulin?
Here lies a particularly interesting mechanism.
At rest, insulin plays a major role in glucose uptake into muscles.
But during exercise, muscle contractions also activate glucose transport, notably via GLUT4 transporters, through mechanisms that do not directly require increased insulin.
Active muscles can thus absorb much more glucose than at rest.
This does not mean dextrose causes no insulin response. It means **the physiological context in which glucose is consumed drastically changes its utilization.**
That’s why targeted intake during training can be more relevant than consumption unrelated to energy needs.
However, dextrose during exercise does not automatically replace the need for adequate nutritional recovery after training.
Performance Over Dietary Dogma
At Athletic Carnivore, we do not consider dextrose essential for all athletes.
A short session, a walk, or moderate training does not impose the same demands as an endurance competition, a particularly high-volume bodybuilding session, or multiple intense workouts close together.
Strategy must therefore depend on the sport, intensity, duration, available reserves, and recovery.
**Glucose is not the enemy of fats. Ketosis is not a mandatory goal. And dextrose is not contradictory to our metabolic approach.**
This PNAS publication does not directly demonstrate the effects of dextrose or ketosis variations. However, it supports the central principle: muscle metabolism is dynamic and adapts its energy pathways to effort.
This logic precisely guides our thinking.
The real objective is not to remain locked in a metabolic state but to enable the body to respond effectively to its needs.
**And you, are you truly aiming to optimize your metabolism, or just to stay in ketosis at all costs?**
**Understand Your Metabolic Terrain — Athletic Carnivore Premium Report**
Scientific References
**Rothschild et al. (2026).** *The Mader model of muscle energy metabolism simulates key metabolic exercise phenomena.* PNAS, 123(40).
https://doi.org/10.1073/pnas.2525555123
**Rothschild et al. (2026).** *Carbohydrate ingestion during prolonged exercise and net skeletal muscle glycogen utilization: a meta-analysis.* Journal of Applied Physiology, 140(1), 76–87.
https://doi.org/10.1152/japplphysiol.00861.2025
**Richter, Bilan, and Klip (2025).** *A comprehensive view of muscle glucose uptake: regulation by insulin, contractile activity, and exercise.* Physiological Reviews.
https://doi.org/10.1152/physrev.00033.2024
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