Component

Fasting / abstention from energy intake

Fasting is a physiological state: the body shifts fuel use, keeps making glucose, produces and uses ketones, and changes hormone and nutrient-sensing signals. This chapter connects those steps to specific enzymes and nutrient dependencies, including magnesium, thiamine, riboflavin, niacin, biotin, choline and copper. Human fasting, cell-starvation experiments and refeeding retain their distinct settings. Open the preserved fasting source for the full readable pathway overview and discovery questions.

20 recorded relationships. Experimental role, claim status and evidence remain attached to each record.

Read recorded mechanisms Open recursive mind map

How nutrients influence it

Every nutrient with a recorded effect on this component, credited to the nutrient that acted rather than the chapter that recorded it. Open a nutrient to see the findings and the conditions they were measured under.

How nutrients reach it in more than one step

Chains of two or more recorded steps that end here, grouped by the nutrient they start from. Each step is a separate finding, so a chain is a route a mechanism could take, not proof that it does.

Tracing routes…

What it does

Every recorded relationship this component is part of, grouped by its role. Plain wording comes first; the technical statement follows.

Recorded relationships

What it acts on

  1. Adipose G0S2 transcript levels decreased after fasting, independent of GH blockade.

    Fasting / abstention from energy intake → Human G0/G1 switch protein 2 / G0S2 source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary full-text Results: Regulation of lipolysis, DOI 10.1210/jc.2016-3835
    experimental_model
    Same human adipose biopsy study.
    limitations
    Expression alone does not establish which lipase step controlled whole-body flux.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    A second fat-release regulator changed.
    primary_references
    Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28324055/ · DOI 10.1210/jc.2016-3835

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 232–238

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Same human adipose biopsy study. · source_derived_draft · unverified_draft

    ## fast-adipose-g0s2 A second fat-release regulator changed. Adipose G0S2 transcript levels decreased after fasting, independent of GH blockade. Model: Same human adipose biopsy study. Limitations: Expression alone does not establish which lipase step controlled whole-body flux. Evidence access: Primary full-text Results: Regulation of lipolysis, DOI 10.1210/jc.2016-3835 Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28324055/ · DOI 10.1210/jc.2016-3835
    Complete structured claim and evidence

  2. Adipose PDE3B transcript levels decreased after fasting, with and without GH blockade.

    Fasting / abstention from energy intake → Human phosphodiesterase 3B / PDE3B source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary full-text Results: Regulation of lipolysis, DOI 10.1210/jc.2016-3835
    experimental_model
    Nine obese men; adipose biopsy after 72-hour fast.
    limitations
    Transcript level is not direct PDE3B enzyme activity.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    A molecular brake on fat release changed.
    primary_references
    Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28324055/ · DOI 10.1210/jc.2016-3835

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 224–230

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Nine obese men; adipose biopsy after 72-hour fast. · source_derived_draft · unverified_draft

    ## fast-adipose-pde3b A molecular brake on fat release changed. Adipose PDE3B transcript levels decreased after fasting, with and without GH blockade. Model: Nine obese men; adipose biopsy after 72-hour fast. Limitations: Transcript level is not direct PDE3B enzyme activity. Evidence access: Primary full-text Results: Regulation of lipolysis, DOI 10.1210/jc.2016-3835 Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28324055/ · DOI 10.1210/jc.2016-3835
    Complete structured claim and evidence

  3. Beta-hydroxybutyrate and acetoacetate became predominant cerebral fuels after prolonged starvation.

    Fasting / abstention from energy intake → Cerebral ketone-body utilization source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Three obese patients; cerebral catheterization after 5–6 weeks of starvation.
    limitations
    This prolonged, small historical study does not establish a 16-hour switch.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    The brain can use ketones while retaining a glucose requirement.
    primary_references
    Brain metabolism during fasting. · 1967 · https://pubmed.ncbi.nlm.nih.gov/6061736/ · DOI 10.1172/JCI105650

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 88–94

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Three obese patients; cerebral catheterization after 5–6 weeks of starvation. · source_derived_draft · unverified_draft

    ## fast-brain-ketones The brain can use ketones while retaining a glucose requirement. Beta-hydroxybutyrate and acetoacetate became predominant cerebral fuels after prolonged starvation. Model: Three obese patients; cerebral catheterization after 5–6 weeks of starvation. Limitations: This prolonged, small historical study does not establish a 16-hour switch. Evidence access: Primary abstract Brain metabolism during fasting. · 1967 · https://pubmed.ncbi.nlm.nih.gov/6061736/ · DOI 10.1172/JCI105650
    Complete structured claim and evidence

  4. Peak oxygen uptake fell 13% and endurance declined; maximal strength was unchanged.

    Fasting / abstention from energy intake → Exercise endurance capacity source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Thirteen adults; seven-day fast, muscle biopsies and exercise testing.
    limitations
    Measured lean-mass loss also includes water and glycogen; it is not all muscle protein.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Strength and endurance did not respond identically.
    primary_references
    Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 192–198

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Thirteen adults; seven-day fast, muscle biopsies and exercise testing. · source_derived_draft · unverified_draft

    ## fast-exercise Strength and endurance did not respond identically. Peak oxygen uptake fell 13% and endurance declined; maximal strength was unchanged. Model: Thirteen adults; seven-day fast, muscle biopsies and exercise testing. Limitations: Measured lean-mass loss also includes water and glycogen; it is not all muscle protein. Evidence access: Primary abstract Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0
    Complete structured claim and evidence

  5. Fat oxidation supplied about 75% of resting energy requirements at 60 hours.

    Fasting / abstention from energy intake → Whole-body fat oxidation source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Six men; isotope tracers and indirect calorimetry during a 60-hour fast.
    limitations
    Protocol-specific fluxes; no universal hour-by-hour threshold.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Fuel use shifted toward fat.
    primary_references
    Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 40–46

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Six men; isotope tracers and indirect calorimetry during a 60-hour fast. · source_derived_draft · unverified_draft

    ## fast-fat-use Fuel use shifted toward fat. Fat oxidation supplied about 75% of resting energy requirements at 60 hours. Model: Six men; isotope tracers and indirect calorimetry during a 60-hour fast. Limitations: Protocol-specific fluxes; no universal hour-by-hour threshold. Evidence access: Primary abstract Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29
    Complete structured claim and evidence

  6. Growth-hormone levels increased after 72 hours of fasting.

    Fasting / abstention from energy intake → Human growth hormone source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Nine obese men; randomized crossover with overnight fast, 72-hour fast, and fast plus GH blockade.
    limitations
    Hormone concentration is not a direct measure of anabolic flux.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Fasting changed hormone signaling without proving muscle growth.
    primary_references
    Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28324055/ · DOI 10.1210/jc.2016-3835

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 208–214

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Nine obese men; randomized crossover with overnight fast, 72-hour fast, and fast plus GH blockade. · source_derived_draft · unverified_draft

    ## fast-gh-rise Fasting changed hormone signaling without proving muscle growth. Growth-hormone levels increased after 72 hours of fasting. Model: Nine obese men; randomized crossover with overnight fast, 72-hour fast, and fast plus GH blockade. Limitations: Hormone concentration is not a direct measure of anabolic flux. Evidence access: Primary abstract Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28324055/ · DOI 10.1210/jc.2016-3835
    Complete structured claim and evidence

  7. The estimated gluconeogenic fraction of glucose production increased from 36% overnight to 78% after 60 hours.

    Fasting / abstention from energy intake → Hepatic gluconeogenic flux source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Human stable-isotope study of fasting and hepatic UDP-glucose flux.
    limitations
    Tracer duration and glycogen cycling affect fractional estimates; a percentage is not an absolute production rate.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    New glucose production increasingly replaced stored carbohydrate.
    primary_references
    Hepatic gluconeogenic fluxes and glycogen turnover during fasting in humans. A stable isotope study. · 1997 · https://pubmed.ncbi.nlm.nih.gov/9276749/ · DOI 10.1172/JCI119644

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 64–70

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Human stable-isotope study of fasting and hepatic UDP-glucose flux. · source_derived_draft · unverified_draft

    ## fast-gluconeogenesis New glucose production increasingly replaced stored carbohydrate. The estimated gluconeogenic fraction of glucose production increased from 36% overnight to 78% after 60 hours. Model: Human stable-isotope study of fasting and hepatic UDP-glucose flux. Limitations: Tracer duration and glycogen cycling affect fractional estimates; a percentage is not an absolute production rate. Evidence access: Primary abstract Hepatic gluconeogenic fluxes and glycogen turnover during fasting in humans. A stable isotope study. · 1997 · https://pubmed.ncbi.nlm.nih.gov/9276749/ · DOI 10.1172/JCI119644
    Complete structured claim and evidence

  8. Glucose oxidation decreased approximately 85%.

    Fasting / abstention from energy intake → Whole-body glucose oxidation source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Six men; isotope tracers and indirect calorimetry during a 60-hour fast.
    limitations
    Protocol-specific fluxes; no universal hour-by-hour threshold.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    The body conserved glucose by burning less of it.
    primary_references
    Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 48–54

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Six men; isotope tracers and indirect calorimetry during a 60-hour fast. · source_derived_draft · unverified_draft

    ## fast-glucose-use The body conserved glucose by burning less of it. Glucose oxidation decreased approximately 85%. Model: Six men; isotope tracers and indirect calorimetry during a 60-hour fast. Limitations: Protocol-specific fluxes; no universal hour-by-hour threshold. Evidence access: Primary abstract Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29
    Complete structured claim and evidence

  9. At 60 hours, glycogen-derived plasma glucose flux of 0.32 mg/kg/min was balanced by 0.31 mg/kg/min retained gluconeogenic carbon.

    Fasting / abstention from energy intake → Hepatic glycogen turnover source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Human isotope model; 60-hour fast.
    limitations
    Does not support a fixed time when all glycogen becomes empty.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    The liver still cycled carbon through glycogen.
    primary_references
    Hepatic gluconeogenic fluxes and glycogen turnover during fasting in humans. A stable isotope study. · 1997 · https://pubmed.ncbi.nlm.nih.gov/9276749/ · DOI 10.1172/JCI119644

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 72–78

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Human isotope model; 60-hour fast. · source_derived_draft · unverified_draft

    ## fast-glycogen-cycle The liver still cycled carbon through glycogen. At 60 hours, glycogen-derived plasma glucose flux of 0.32 mg/kg/min was balanced by 0.31 mg/kg/min retained gluconeogenic carbon. Model: Human isotope model; 60-hour fast. Limitations: Does not support a fixed time when all glycogen becomes empty. Evidence access: Primary abstract Hepatic gluconeogenic fluxes and glycogen turnover during fasting in humans. A stable isotope study. · 1997 · https://pubmed.ncbi.nlm.nih.gov/9276749/ · DOI 10.1172/JCI119644
    Complete structured claim and evidence

  10. Muscle glycogen content was approximately halved.

    Fasting / abstention from energy intake → Skeletal-muscle glycogen content source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Thirteen adults; seven-day fast, muscle biopsies and exercise testing.
    limitations
    This is muscle glycogen, not a measurement of hepatic glycogen.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Muscle retained some carbohydrate reserve.
    primary_references
    Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 200–206

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Thirteen adults; seven-day fast, muscle biopsies and exercise testing. · source_derived_draft · unverified_draft

    ## fast-glycogen-muscle Muscle retained some carbohydrate reserve. Muscle glycogen content was approximately halved. Model: Thirteen adults; seven-day fast, muscle biopsies and exercise testing. Limitations: This is muscle glycogen, not a measurement of hepatic glycogen. Evidence access: Primary abstract Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0
    Complete structured claim and evidence

  11. FGF21 rose notably on days 7–10, after ketone concentrations had already increased.

    Fasting / abstention from energy intake → Human fibroblast growth factor 21 / FGF21 source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract; protocol checked in PMC4665770
    experimental_model
    Eleven volunteers; ten-day fast with daily multivitamin, 20 mEq potassium chloride and 200 mg allopurinol.
    limitations
    Small supported protocol; timing does not exclude every possible FGF21 contribution.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    This hormone did not precede initial human ketogenesis.
    primary_references
    FGF21 and the late adaptive response to starvation in humans. · 2015 · https://pubmed.ncbi.nlm.nih.gov/26529252/ · DOI 10.1172/JCI83349

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 280–286

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Eleven volunteers; ten-day fast with daily multivitamin, 20 mEq potassium chloride and 200 mg allopurinol. · source_derived_draft · unverified_draft

    ## fast-human-fgf-delay This hormone did not precede initial human ketogenesis. FGF21 rose notably on days 7–10, after ketone concentrations had already increased. Model: Eleven volunteers; ten-day fast with daily multivitamin, 20 mEq potassium chloride and 200 mg allopurinol. Limitations: Small supported protocol; timing does not exclude every possible FGF21 contribution. Evidence access: Primary abstract; protocol checked in PMC4665770 FGF21 and the late adaptive response to starvation in humans. · 2015 · https://pubmed.ncbi.nlm.nih.gov/26529252/ · DOI 10.1172/JCI83349
    Complete structured claim and evidence

  12. CRP, hepcidin, midkine and IL-8 increased during prolonged fasting.

    Fasting / abstention from energy intake → Acute inflammatory markers during prolonged fasting source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Twenty adults; supervised water fast averaging 9.8 days, then guided refeeding.
    limitations
    Not proof that every fast increases inflammation; cellular NLRP3 results measure something different.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Whole-body inflammatory measurements did not simply follow the anti-inflammatory ketone story.
    primary_references
    Prolonged fasting promotes systemic inflammation and platelet activation in humans: A medically supervised, water-only fasting and refeeding study. · 2025 · https://pubmed.ncbi.nlm.nih.gov/40268190/ · DOI 10.1016/j.molmet.2025.102152

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 432–438

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Twenty adults; supervised water fast averaging 9.8 days, then guided refeeding. · source_derived_draft · unverified_draft

    ## fast-inflammation Whole-body inflammatory measurements did not simply follow the anti-inflammatory ketone story. CRP, hepcidin, midkine and IL-8 increased during prolonged fasting. Model: Twenty adults; supervised water fast averaging 9.8 days, then guided refeeding. Limitations: Not proof that every fast increases inflammation; cellular NLRP3 results measure something different. Evidence access: Primary abstract Prolonged fasting promotes systemic inflammation and platelet activation in humans: A medically supervised, water-only fasting and refeeding study. · 2025 · https://pubmed.ncbi.nlm.nih.gov/40268190/ · DOI 10.1016/j.molmet.2025.102152
    Complete structured claim and evidence

  13. Estimated renal contribution to whole-body glucose production increased from 5 ± 2% postabsorptively to 24 ± 3% after 60 hours.

    Fasting / abstention from energy intake → Renal glucose production source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Healthy humans; renal/hepatic exchange and isotope measurements.
    limitations
    Study-specific estimates, not a universal organ split.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    The kidney helped make glucose, alongside the liver.
    primary_references
    Contributions by kidney and liver to glucose production in the postabsorptive state and after 60 h of fasting. · 1999 · https://pubmed.ncbi.nlm.nih.gov/10334304/ · DOI 10.2337/diabetes.48.2.292

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 80–86

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Healthy humans; renal/hepatic exchange and isotope measurements. · source_derived_draft · unverified_draft

    ## fast-kidney-glucose The kidney helped make glucose, alongside the liver. Estimated renal contribution to whole-body glucose production increased from 5 ± 2% postabsorptively to 24 ± 3% after 60 hours. Model: Healthy humans; renal/hepatic exchange and isotope measurements. Limitations: Study-specific estimates, not a universal organ split. Evidence access: Primary abstract Contributions by kidney and liver to glucose production in the postabsorptive state and after 60 h of fasting. · 1999 · https://pubmed.ncbi.nlm.nih.gov/10334304/ · DOI 10.2337/diabetes.48.2.292
    Complete structured claim and evidence

  14. Lipolysis increased approximately 2.5-fold over 60 hours.

    Fasting / abstention from energy intake → Whole-body lipolytic flux source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Six men; isotope tracers and indirect calorimetry during a 60-hour fast.
    limitations
    Protocol-specific fluxes; no universal hour-by-hour threshold.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Stored fat supplied more circulating fuel.
    primary_references
    Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 24–30

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Six men; isotope tracers and indirect calorimetry during a 60-hour fast. · source_derived_draft · unverified_draft

    ## fast-lipolysis Stored fat supplied more circulating fuel. Lipolysis increased approximately 2.5-fold over 60 hours. Model: Six men; isotope tracers and indirect calorimetry during a 60-hour fast. Limitations: Protocol-specific fluxes; no universal hour-by-hour threshold. Evidence access: Primary abstract Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29
    Complete structured claim and evidence

  15. Measured muscle AMPK activity was unchanged.

    Fasting / abstention from energy intake → Skeletal-muscle AMPK activity source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Thirteen adults; seven-day fast, muscle biopsies and exercise testing.
    limitations
    Not proof that AMPK is unchanged in every tissue or at every time point.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    A popular fasting signal did not rise in this tissue and protocol.
    primary_references
    Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 184–190

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Thirteen adults; seven-day fast, muscle biopsies and exercise testing. · source_derived_draft · unverified_draft

    ## fast-muscle-ampk A popular fasting signal did not rise in this tissue and protocol. Measured muscle AMPK activity was unchanged. Model: Thirteen adults; seven-day fast, muscle biopsies and exercise testing. Limitations: Not proof that AMPK is unchanged in every tissue or at every time point. Evidence access: Primary abstract Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0
    Complete structured claim and evidence

  16. Muscle PDK4 expression increased 13-fold, alongside greater inhibitory PDH phosphorylation.

    Fasting / abstention from energy intake → Human pyruvate dehydrogenase kinase 4 / PDK4 source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Thirteen adults; seven-day fast, muscle biopsies and exercise testing.
    limitations
    Co-occurrence supports the pathway interpretation but does not isolate causality.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Muscle reduced access from carbohydrate into oxidation.
    primary_references
    Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 176–182

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Thirteen adults; seven-day fast, muscle biopsies and exercise testing. · source_derived_draft · unverified_draft

    ## fast-pdk4 Muscle reduced access from carbohydrate into oxidation. Muscle PDK4 expression increased 13-fold, alongside greater inhibitory PDH phosphorylation. Model: Thirteen adults; seven-day fast, muscle biopsies and exercise testing. Limitations: Co-occurrence supports the pathway interpretation but does not isolate causality. Evidence access: Primary abstract Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans. · 2025 · https://pubmed.ncbi.nlm.nih.gov/39747857/ · DOI 10.1038/s41467-024-55418-0
    Complete structured claim and evidence

  17. Proteomic analyses and follow-up assays indicated platelet degranulation and complement/coagulation-associated changes.

    Fasting / abstention from energy intake → Platelet degranulation and coagulation-associated readouts source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Same prolonged-fasting cohort.
    limitations
    Pathway readouts do not prove that participants developed thrombosis or cardiovascular disease.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    The response included blood and vascular pathways.
    primary_references
    Prolonged fasting promotes systemic inflammation and platelet activation in humans: A medically supervised, water-only fasting and refeeding study. · 2025 · https://pubmed.ncbi.nlm.nih.gov/40268190/ · DOI 10.1016/j.molmet.2025.102152

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 440–446

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Same prolonged-fasting cohort. · source_derived_draft · unverified_draft

    ## fast-platelet-readouts The response included blood and vascular pathways. Proteomic analyses and follow-up assays indicated platelet degranulation and complement/coagulation-associated changes. Model: Same prolonged-fasting cohort. Limitations: Pathway readouts do not prove that participants developed thrombosis or cardiovascular disease. Evidence access: Primary abstract Prolonged fasting promotes systemic inflammation and platelet activation in humans: A medically supervised, water-only fasting and refeeding study. · 2025 · https://pubmed.ncbi.nlm.nih.gov/40268190/ · DOI 10.1016/j.molmet.2025.102152
    Complete structured claim and evidence

  18. Proteolysis and protein oxidation increased approximately 50%.

    Fasting / abstention from energy intake → Whole-body protein oxidation source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Six men; isotope tracers and indirect calorimetry during a 60-hour fast.
    limitations
    Protocol-specific fluxes; no universal hour-by-hour threshold.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    This protocol did not preserve all body protein.
    primary_references
    Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 56–62

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Six men; isotope tracers and indirect calorimetry during a 60-hour fast. · source_derived_draft · unverified_draft

    ## fast-protein-use This protocol did not preserve all body protein. Proteolysis and protein oxidation increased approximately 50%. Model: Six men; isotope tracers and indirect calorimetry during a 60-hour fast. Limitations: Protocol-specific fluxes; no universal hour-by-hour threshold. Evidence access: Primary abstract Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29
    Complete structured claim and evidence

  19. A seven-day fast changed more than 1,000 measured plasma proteins; broad changes became evident after about three days.

    Fasting / abstention from energy intake → Plasma proteome changes during fasting source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Twelve volunteers; approximately 3,000 plasma proteins profiled.
    limitations
    Three days is not an autophagy-onset threshold. Proteogenomic disease predictions are not observed clinical outcomes.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Many circulating proteins adapted, on different schedules.
    primary_references
    Systemic proteome adaptions to 7-day complete caloric restriction in humans. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38429390/ · DOI 10.1038/s42255-024-01008-9

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 416–422

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Twelve volunteers; approximately 3,000 plasma proteins profiled. · source_derived_draft · unverified_draft

    ## fast-proteome Many circulating proteins adapted, on different schedules. A seven-day fast changed more than 1,000 measured plasma proteins; broad changes became evident after about three days. Model: Twelve volunteers; approximately 3,000 plasma proteins profiled. Limitations: Three days is not an autophagy-onset threshold. Proteogenomic disease predictions are not observed clinical outcomes. Evidence access: Primary abstract Systemic proteome adaptions to 7-day complete caloric restriction in humans. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38429390/ · DOI 10.1038/s42255-024-01008-9
    Complete structured claim and evidence

  20. Intra-adipocyte fatty-acid re-esterification also increased approximately 2.5-fold.

    Fasting / abstention from energy intake → Adipose fatty-acid re-esterification source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Six men; isotope tracers and indirect calorimetry during a 60-hour fast.
    limitations
    Protocol-specific fluxes; no universal hour-by-hour threshold.
    nutrient_topic
    Fasting physiological-state collection; human protocols, cellular deprivation and refeeding are distinguished. · Fasting / abstention from energy intake
    plain_language
    Some released fat was recycled rather than burned.
    primary_references
    Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29

    Fasting: fuel switching, nutrient sensing, ketone signaling, nutrient dependencies and refeeding (2026-09-18) · lines 32–38

    AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Six men; isotope tracers and indirect calorimetry during a 60-hour fast. · source_derived_draft · unverified_draft

    ## fast-reesterification Some released fat was recycled rather than burned. Intra-adipocyte fatty-acid re-esterification also increased approximately 2.5-fold. Model: Six men; isotope tracers and indirect calorimetry during a 60-hour fast. Limitations: Protocol-specific fluxes; no universal hour-by-hour threshold. Evidence access: Primary abstract Fuel and energy metabolism in fasting humans. · 1994 · https://pubmed.ncbi.nlm.nih.gov/8017334/ · DOI 10.1093/ajcn/60.1.29
    Complete structured claim and evidence

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