{
  "format_version": 3,
  "claim_formal": {
    "subject": "human brain (adult)",
    "sub_claims": {
      "SC1": {
        "property": "brain mass as fraction of total adult human body weight",
        "operator": "within \u00b10.5pp of 2.0",
        "threshold_pct": 2.0,
        "operator_note": "The claim states '2%' \u2014 an explicitly rounded figure used throughout the neuroscience literature. Proof checks whether cited sources report a value within \u00b10.5 percentage points of 2.0%. This is the conservative interpretation: a value of 1.5% or 2.5% would still satisfy the claim; a value of 1.0% or 3.0% would not. Both sources in fact report exactly 2%."
      },
      "SC2": {
        "property": "brain share of resting whole-body O2 consumption",
        "operator": "within \u00b12pp of 20.0",
        "threshold_pct": 20.0,
        "operator_note": "The claim states '20%' \u2014 a well-established rounded figure. Proof checks whether cited sources report a value within \u00b12 percentage points of 20%. This is generous enough to accommodate natural rounding (e.g., 18-22%), while being narrow enough to distinguish '~20%' from competing claims like '25%' or '15%'. Both sources in fact report exactly 20%."
      }
    },
    "condition": "at rest (basal metabolic state)"
  },
  "claim_natural": "The human brain accounts for 2% of body weight but uses 20% of the body's oxygen at rest.",
  "evidence": {
    "B1": {
      "type": "empirical",
      "label": "PNAS 2002: brain = ~2% of body weight",
      "sub_claim": null,
      "source": {
        "name": "Raichle & Gusnard 2002 'Appraising the brain's energy budget' PNAS (via PMC)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC124895/",
        "quote": "In the average adult human, the brain represents about 2% of the body weight."
      },
      "verification": {
        "status": "verified",
        "method": "full_quote",
        "coverage_pct": null,
        "fetch_mode": "live",
        "credibility": {
          "domain": "nih.gov",
          "source_type": "government",
          "tier": 5,
          "flags": [],
          "note": "Government domain (.gov)"
        }
      },
      "extraction": {
        "value": "2.0",
        "value_in_quote": true,
        "quote_snippet": "In the average adult human, the brain represents about 2% of the body weight."
      }
    },
    "B2": {
      "type": "empirical",
      "label": "PNAS 2002: brain = ~20% of resting O2",
      "sub_claim": null,
      "source": {
        "name": "Raichle & Gusnard 2002 'Appraising the brain's energy budget' PNAS (via PMC)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC124895/",
        "quote": "the brain accounts for about 20% of the oxygen and, hence, calories consumed by the body"
      },
      "verification": {
        "status": "verified",
        "method": "full_quote",
        "coverage_pct": null,
        "fetch_mode": "live",
        "credibility": {
          "domain": "nih.gov",
          "source_type": "government",
          "tier": 5,
          "flags": [],
          "note": "Government domain (.gov)"
        }
      },
      "extraction": {
        "value": "20.0",
        "value_in_quote": true,
        "quote_snippet": "the brain accounts for about 20% of the oxygen and, hence, calories consumed by "
      }
    },
    "B3": {
      "type": "empirical",
      "label": "NCBI Basic Neurochemistry: brain = ~2% body weight",
      "sub_claim": null,
      "source": {
        "name": "Basic Neurochemistry (NCBI Bookshelf): Regulation of Cerebral Metabolic Rate",
        "url": "https://www.ncbi.nlm.nih.gov/books/NBK28194/",
        "quote": "the brain, which represents only about 2% of total body weight"
      },
      "verification": {
        "status": "verified",
        "method": "full_quote",
        "coverage_pct": null,
        "fetch_mode": "live",
        "credibility": {
          "domain": "nih.gov",
          "source_type": "government",
          "tier": 5,
          "flags": [],
          "note": "Government domain (.gov)"
        }
      },
      "extraction": {
        "value": "2.0",
        "value_in_quote": true,
        "quote_snippet": "the brain, which represents only about 2% of total body weight"
      }
    },
    "B4": {
      "type": "empirical",
      "label": "NCBI Basic Neurochemistry: brain = 20% resting O2",
      "sub_claim": null,
      "source": {
        "name": "Basic Neurochemistry (NCBI Bookshelf): Regulation of Cerebral Metabolic Rate",
        "url": "https://www.ncbi.nlm.nih.gov/books/NBK28194/",
        "quote": "accounts for 20% of the resting total body O2 consumption"
      },
      "verification": {
        "status": "verified",
        "method": "full_quote",
        "coverage_pct": null,
        "fetch_mode": "live",
        "credibility": {
          "domain": "nih.gov",
          "source_type": "government",
          "tier": 5,
          "flags": [],
          "note": "Government domain (.gov)"
        }
      },
      "extraction": {
        "value": "20.0",
        "value_in_quote": true,
        "quote_snippet": "accounts for 20% of the resting total body O2 consumption"
      }
    },
    "A1": {
      "type": "computed",
      "label": "SC1: extracted brain weight % lies within \u00b10.5pp of 2%",
      "sub_claim": "SC1",
      "method": "compare(weight_pct_pnas, within \u00b10.5pp of 2.0)",
      "result": "True",
      "depends_on": []
    },
    "A2": {
      "type": "computed",
      "label": "SC2: extracted brain O2 % lies within \u00b12pp of 20%",
      "sub_claim": "SC2",
      "method": "compare(oxygen_pct_pnas, within \u00b12pp of 20.0)",
      "result": "True",
      "depends_on": []
    }
  },
  "cross_checks": [
    {
      "description": "SC1: brain weight % \u2014 PNAS vs NCBI (independently sourced)",
      "values_compared": [
        "2.0",
        "2.0"
      ],
      "agreement": true,
      "fact_ids": []
    },
    {
      "description": "SC2: brain O2 % \u2014 PNAS vs NCBI (independently sourced)",
      "values_compared": [
        "20.0",
        "20.0"
      ],
      "agreement": true,
      "fact_ids": []
    }
  ],
  "adversarial_checks": [
    {
      "question": "Do any authoritative sources give a significantly different brain weight percentage (not ~2%)?",
      "verification_performed": "Searched web for 'human brain percentage body weight NOT 2 percent disputed alternative'. Also computed: adult brain ~1,400 g / reference body 70 kg = 2.0% exactly. Some sources note range 1.3-1.5 kg for brain mass and 60-80 kg for body weight, yielding 1.6-2.5% \u2014 always rounding to ~2%.",
      "finding": "No credible source disputes ~2%. Minor variation (1.6-2.5%) reflects different reference body weights and brain masses across sexes and ages, but all sources describe the rounded figure as 'about 2%'.",
      "breaks_proof": false
    },
    {
      "question": "Do any sources give a substantially different brain O2 percentage at rest (not ~20%)?",
      "verification_performed": "Searched web for 'human brain oxygen consumption NOT 20 percent disputed cerebral metabolic rate'. Independently verified via published CMRO2 data: normal CMRO2 = 3.5 mL O2/100g/min; for 1,400g brain = 49 mL O2/min. Average resting VO2 = ~250 mL/min. 49/250 = 19.6% \u2248 20%. Some sources say '20-25%' for active brain but consistently cite ~20% at rest.",
      "finding": "No credible counter-evidence found. Independent numerical derivation from CMRO2 values confirms ~20%: (3.5 mL/100g/min \u00d7 14 dL) / 250 mL/min \u2248 19.6%. Any variation (18-22%) rounds to '20%' as claimed.",
      "breaks_proof": false
    },
    {
      "question": "Does the '20% at rest' qualifier matter \u2014 would the claim be false if measuring during activity?",
      "verification_performed": "Searched for 'brain oxygen consumption increase during cognitive task vs rest'. Neuroimaging studies (fMRI/PET) show that local blood flow increases 30-50% during specific tasks, but whole-brain O2 consumption increases only ~1-5% above baseline. The claim explicitly says 'at rest', which matches the cited sources.",
      "finding": "The 'at rest' qualifier is accurate and important: during vigorous mental activity the brain's share remains near 20% because both brain and body metabolism increase. The claim is correctly qualified.",
      "breaks_proof": false
    }
  ],
  "verdict": {
    "value": "PROVED",
    "qualified": false,
    "qualifier": null,
    "reason": null
  },
  "key_results": {
    "sc1_brain_weight_pct_reported": 2.0,
    "sc1_threshold_pct": 2.0,
    "sc1_holds": true,
    "sc2_brain_oxygen_pct_reported": 20.0,
    "sc2_threshold_pct": 20.0,
    "sc2_holds": true,
    "sources_cross_checked": true,
    "claim_holds": true
  },
  "generator": {
    "name": "proof-engine",
    "version": "0.10.0",
    "repo": "https://github.com/yaniv-golan/proof-engine",
    "generated_at": "2026-03-28"
  },
  "proof_py_url": "/proofs/the-human-brain-accounts-for-2-of-body-weight-but/proof.py",
  "citation": {
    "doi": "10.5281/zenodo.19455660",
    "concept_doi": "10.5281/zenodo.19454368",
    "url": "https://proofengine.info/proofs/the-human-brain-accounts-for-2-of-body-weight-but/",
    "author": "Proof Engine",
    "cite_bib_url": "/proofs/the-human-brain-accounts-for-2-of-body-weight-but/cite.bib",
    "cite_ris_url": "/proofs/the-human-brain-accounts-for-2-of-body-weight-but/cite.ris"
  },
  "depends_on": []
}