Low carbohydrate high fat ketogenic diets on the exercise crossover point and glucose homeostasis.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing the authors' own prior human studies and mechanistic theories.
PubMed 37057184 · doi:10.3389/fphys.2023.1150265
What was done
This narrative review summarizes findings from a series of studies evaluating the metabolic and performance effects of adaptation to a low-carbohydrate, high-fat (LCHF/ketogenic) diet versus high-carbohydrate, low-fat (HCLF) diets during exercise, specifically assessing the exercise crossover point, maximal fat oxidation rates (FATMAX), high-intensity exercise metabolism, and glycemic homeostasis.
What was found
The authors report that LCHF adaptation shifted the substrate crossover point to >80% VO2max (compared to the classical model prediction of ≥60% VO2max) and increased FATMAX to >1.5 g/min (typical baseline: 0.3–0.6 g/min). During 6 × 800 m running intervals at 86.4 ± 6.2% VO2max, endurance athletes achieved peak fat oxidation rates of 1.58 ± 0.33 g/min, with 30% exceeding 1.85 g/min. Furthermore, 30% of middle-aged competitive athletes exhibited pre-diabetic glycemic values while consuming an HCLF diet, which reversed on the LCHF diet.
Why it matters
These data challenge the established physiological assumption that carbohydrate is obligatorily the dominant fuel during high-intensity exercise (>80%–85% VO2max) and suggest LCHF adaptation fundamentally alters fuel utilization and glycemic profiles in endurance athletes.
Limits
This publication is a narrative review focused on the authors' own selected prior studies rather than a systematic review or meta-analysis. The abstract does not report total sample sizes, blinding, control details, or overall athletic performance outcomes (e.g., time-to-exhaustion or race times). Long-term clinical and performance consequences remain unmeasured.
Cited by
- supports Studies of individuals habitually following a ketogenic diet show that their maximal fat oxidation occurs at approximately 85% of maximal exercise intensity.