The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation

Phinney SD, Bistrian BR, Evans WJ, Gervino E, Blackburn GL · 1983 · Metabolism

DOI: 10.1016/0026-0495(83)90106-3View source ↗

“VO2max remained unchanged between the control week and week 3 of the ketogenic diet.”

Summary

Five well-trained cyclists ate their usual mixed diet for one week, then switched to a ketogenic diet — under 20 grams of carbohydrate per day — for four weeks. Calories and protein were matched between both diets; only the fuel source changed. After four weeks of ketosis, the cyclists could ride to exhaustion just as long as before (about 150 minutes), and their peak aerobic capacity (VO2max) was unchanged. What did change was where the energy came from. At the same exercise intensity, the body burned roughly three times less glucose and four times less muscle glycogen. The respiratory quotient — the ratio that tells you whether you're burning carbs or fat — dropped from 0.83 (mostly carbs) to 0.72 (almost entirely fat). The study was an early demonstration that humans can stay in ketosis for weeks and still perform endurance work, drawing energy almost entirely from fat and ketones.

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References cited by this entry

ExtendsEffects of Intermittent Fasting on Health, Aging, and Diseasede Cabo R & Mattson MP · 2019
The de Cabo & Mattson 2019 NEJM review cites this body of work when describing the metabolic switch to fat- and ketone-derived energy.

Entries that reference this one

ExtendsMetabolic characteristics of keto-adapted ultra-endurance runnersVolek JS et al. · 2016
Phinney 1983 first demonstrated that keto-adapted athletes can preserve submaximal exercise capacity; the FASTER study (Volek/Phinney 2016) extended that finding to elite ultra-endurance athletes adapted for an average of 20 months and documented record-high fat oxidation rates.
ExtendsStarvation in ManCahill GF · 1970
Cahill 1970 established the metabolic adaptations to fasting in healthy adults; Phinney 1983 extended the work into endurance athletes during chronic dietary ketosis.
ExtendsKetone bodies as signaling metabolitesNewman JC & Verdin E · 2014
Phinney 1983 showed humans use ketones as muscle fuel; Newman/Verdin 2014 reframes ketone bodies as signaling molecules with effects beyond fuel substitution — HDAC inhibition, gene expression, and longevity-relevant pathways.
ExtendsCarbohydrate restriction regulates the adaptive response to fastingKlein S & Wolfe RR · 1992
Klein & Wolfe identified carbohydrate restriction as the active driver of the fasting metabolic response; Phinney 1983 demonstrated this metabolic state can be induced and sustained dietarily without calorie deficit.
ContradictsLow carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkersBurke LM et al. · 2017
Phinney 1983 reported preserved submaximal exercise capacity in keto-adapted cyclists; Burke 2017 found impaired race-walking economy at race-relevant velocities. Phinney's protocol was much longer and the exercise intensity submaximal; Burke's intervention was 3 weeks and tested race-pace performance.
ExtendsCalorie restriction increases muscle mitochondrial biogenesis in healthy humansCivitarese AE et al. · 2007
Phinney 1983 demonstrated metabolic flexibility shifts under ketosis; Civitarese 2007 documents the mitochondrial substrate-level response (mitochondrial biogenesis, PGC-1α expression) that supports those metabolic shifts.
ExtendsCarbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat dietVolek JS et al. · 2009
Phinney 1983 established that humans tolerate ketosis without performance loss; Volek 2009 (with Phinney as senior author) extends this to a metabolic-syndrome population and shows ketosis improves the syndrome more than the conventional low-fat alternative.
ExtendsThe therapeutic implications of ketone bodies: the effects of ketone bodies in pathological conditions: ketosis, ketogenic diet, redox states, insulin resistance, and mitochondrial metabolismVeech RL · 2004
Phinney 1983 established that ketosis preserves submaximal exercise capacity in trained athletes; Veech 2004 explains the mitochondrial energetics — D-β-hydroxybutyrate has higher inherent energy content than pyruvate, the normal mitochondrial fuel from glycolysis.
ExtendsCalorie restriction induces mitochondrial biogenesis and bioenergetic efficiencyLópez-Lluch G et al. · 2006
Phinney 1983 demonstrated substrate flexibility under chronic ketosis; Lopez-Lluch 2006 explains the mitochondrial-level adaptations that support that flexibility.