{
  "_meta": {
    "site": "https://dexaexplained.com",
    "endpoint": "https://dexaexplained.com/api/reference.json",
    "description": "The reference machinery behind the results interpreter: NHANES percentile parameters (Kelly 2009 LMS method), FFMI and ALMI formulas, and published interpretive cut-points — each with its primary citation.",
    "license": "Free to cite with attribution to DexaExplained and a link to https://dexaexplained.com.",
    "methodology": "https://dexaexplained.com/methodology/",
    "generated": "2026-08-17",
    "dataVerified": "2026-08-15",
    "disclaimer": "Educational body-composition information, not medical advice. Nothing here diagnoses, treats, or prevents any condition, and this site does not interpret bone-density results. Talk to your clinician about anything on a scan report that concerns you."
  },
  "boundary": "Body-composition education only. This site deliberately publishes nothing about interpreting bone-density results — that belongs to physicians.",
  "percentiles": {
    "citation": {
      "reference": "Kelly TL, Wilson KE, Heymsfield SB. Dual energy X-ray absorptiometry body composition reference values from NHANES. PLoS ONE 2009;4(9):e7038.",
      "pmid": "19753111",
      "pmcid": "PMC2737140"
    },
    "dataset": "NHANES 1999-2004 whole-body DXA (Hologic QDR-4500A), US adults aged 20-85.",
    "method": "The paper publishes smoothed LMS parameters (skew L, median M, population SD sigma) at 5-year age anchors, by sex — not percentile tables. Percentiles are computed with the paper's own equation from its published parameters (supplementary Table S2 for total-body %fat, Table S6 for appendicular lean mass / height^2), stored verbatim below.",
    "equations": {
      "zScore": "z = M * ((X/M)^L - 1) / (L * sigma); when L = 0, z = M * ln(X/M) / sigma",
      "percentile": "percentile = Phi(z), the standard normal CDF",
      "inverse": "X = M * (1 + L * sigma * z / M)^(1/L) (value at a given z, for reference rows)"
    },
    "interpolation": "L, M and sigma are interpolated linearly between the 5-year age anchors; ages outside 20-85 clamp to the nearest anchor and are flagged.",
    "referencePopulation": "The paper reports separate curves for White, Black, and Mexican-American participants and no pooled column; it notes the White curves rest on the most observations. The site uses those as its single general-population reference — an honest simplification, disclosed on /methodology. Treat percentiles as population context, not a personal grade.",
    "ageRange": {
      "min": 20,
      "max": 85
    },
    "displayPercentiles": [
      {
        "p": 5,
        "z": -1.645
      },
      {
        "p": 25,
        "z": -0.674
      },
      {
        "p": 50,
        "z": 0
      },
      {
        "p": 75,
        "z": 0.674
      },
      {
        "p": 95,
        "z": 1.645
      }
    ],
    "lmsParameters": {
      "columns": {
        "age": "years (5-year anchor)",
        "L": "skew",
        "M": "median (%fat, or ALMI in kg/m^2)",
        "S": "population SD sigma"
      },
      "totalBodyFatPct": {
        "male": [
          {
            "age": 20,
            "L": 0.221,
            "M": 23.4,
            "S": 6.68
          },
          {
            "age": 25,
            "L": 0.325,
            "M": 24.6,
            "S": 6.49
          },
          {
            "age": 30,
            "L": 0.428,
            "M": 25.7,
            "S": 6.25
          },
          {
            "age": 35,
            "L": 0.53,
            "M": 26.6,
            "S": 5.97
          },
          {
            "age": 40,
            "L": 0.631,
            "M": 27.5,
            "S": 5.68
          },
          {
            "age": 45,
            "L": 0.732,
            "M": 28.2,
            "S": 5.44
          },
          {
            "age": 50,
            "L": 0.831,
            "M": 29,
            "S": 5.3
          },
          {
            "age": 55,
            "L": 0.93,
            "M": 29.8,
            "S": 5.23
          },
          {
            "age": 60,
            "L": 1.028,
            "M": 30.5,
            "S": 5.19
          },
          {
            "age": 65,
            "L": 1.126,
            "M": 31.1,
            "S": 5.16
          },
          {
            "age": 70,
            "L": 1.223,
            "M": 31.4,
            "S": 5.11
          },
          {
            "age": 75,
            "L": 1.32,
            "M": 31.6,
            "S": 5.02
          },
          {
            "age": 80,
            "L": 1.418,
            "M": 31.6,
            "S": 4.88
          },
          {
            "age": 85,
            "L": 1.515,
            "M": 31.6,
            "S": 4.73
          }
        ],
        "female": [
          {
            "age": 20,
            "L": 0.361,
            "M": 35.1,
            "S": 7.22
          },
          {
            "age": 25,
            "L": 0.573,
            "M": 36,
            "S": 7.23
          },
          {
            "age": 30,
            "L": 0.785,
            "M": 37,
            "S": 7.21
          },
          {
            "age": 35,
            "L": 0.996,
            "M": 38,
            "S": 7.12
          },
          {
            "age": 40,
            "L": 1.207,
            "M": 38.9,
            "S": 6.96
          },
          {
            "age": 45,
            "L": 1.417,
            "M": 39.8,
            "S": 6.73
          },
          {
            "age": 50,
            "L": 1.626,
            "M": 40.8,
            "S": 6.46
          },
          {
            "age": 55,
            "L": 1.833,
            "M": 41.7,
            "S": 6.16
          },
          {
            "age": 60,
            "L": 2.041,
            "M": 42.5,
            "S": 5.86
          },
          {
            "age": 65,
            "L": 2.247,
            "M": 43,
            "S": 5.58
          },
          {
            "age": 70,
            "L": 2.453,
            "M": 43,
            "S": 5.37
          },
          {
            "age": 75,
            "L": 2.66,
            "M": 42.9,
            "S": 5.24
          },
          {
            "age": 80,
            "L": 2.866,
            "M": 42.5,
            "S": 5.14
          },
          {
            "age": 85,
            "L": 3.072,
            "M": 42.1,
            "S": 5.08
          }
        ]
      },
      "almiKgM2": {
        "male": [
          {
            "age": 20,
            "L": -0.708,
            "M": 8.87,
            "S": 1.34
          },
          {
            "age": 25,
            "L": -0.616,
            "M": 8.94,
            "S": 1.32
          },
          {
            "age": 30,
            "L": -0.524,
            "M": 9.02,
            "S": 1.31
          },
          {
            "age": 35,
            "L": -0.432,
            "M": 9.09,
            "S": 1.3
          },
          {
            "age": 40,
            "L": -0.341,
            "M": 9.12,
            "S": 1.29
          },
          {
            "age": 45,
            "L": -0.249,
            "M": 9.11,
            "S": 1.27
          },
          {
            "age": 50,
            "L": -0.157,
            "M": 9.05,
            "S": 1.25
          },
          {
            "age": 55,
            "L": -0.065,
            "M": 8.95,
            "S": 1.22
          },
          {
            "age": 60,
            "L": 0.027,
            "M": 8.81,
            "S": 1.18
          },
          {
            "age": 65,
            "L": 0.118,
            "M": 8.64,
            "S": 1.14
          },
          {
            "age": 70,
            "L": 0.21,
            "M": 8.44,
            "S": 1.09
          },
          {
            "age": 75,
            "L": 0.302,
            "M": 8.21,
            "S": 1.03
          },
          {
            "age": 80,
            "L": 0.394,
            "M": 7.97,
            "S": 0.97
          },
          {
            "age": 85,
            "L": 0.486,
            "M": 7.72,
            "S": 0.91
          }
        ],
        "female": [
          {
            "age": 20,
            "L": -0.818,
            "M": 6.81,
            "S": 1.04
          },
          {
            "age": 25,
            "L": -0.818,
            "M": 6.86,
            "S": 1.08
          },
          {
            "age": 30,
            "L": -0.817,
            "M": 6.9,
            "S": 1.11
          },
          {
            "age": 35,
            "L": -0.817,
            "M": 6.93,
            "S": 1.15
          },
          {
            "age": 40,
            "L": -0.816,
            "M": 6.95,
            "S": 1.17
          },
          {
            "age": 45,
            "L": -0.815,
            "M": 6.93,
            "S": 1.19
          },
          {
            "age": 50,
            "L": -0.813,
            "M": 6.9,
            "S": 1.18
          },
          {
            "age": 55,
            "L": -0.811,
            "M": 6.84,
            "S": 1.17
          },
          {
            "age": 60,
            "L": -0.81,
            "M": 6.76,
            "S": 1.14
          },
          {
            "age": 65,
            "L": -0.809,
            "M": 6.67,
            "S": 1.1
          },
          {
            "age": 70,
            "L": -0.808,
            "M": 6.57,
            "S": 1.06
          },
          {
            "age": 75,
            "L": -0.808,
            "M": 6.45,
            "S": 1.01
          },
          {
            "age": 80,
            "L": -0.808,
            "M": 6.33,
            "S": 0.96
          },
          {
            "age": 85,
            "L": -0.807,
            "M": 6.2,
            "S": 0.91
          }
        ]
      }
    }
  },
  "ffmi": {
    "formula": "FFMI = fat-free mass (kg) / height (m)^2",
    "formulaCitation": "VanItallie TB et al., Am J Clin Nutr 1990;52:953-9.",
    "normalized": "normalized FFMI = FFMI + 6.1 * (1.8 - height in m)",
    "normalizationCitation": "Kouri EM, Pope HG, Katz DL, Oliva P. Clin J Sport Med 1995;5:223-8 (PMID 7496846). The abstract prints a 6.3 slope; the paper's methods and the literature reproducing it use 6.1, which the site follows.",
    "landmark": {
      "value": 25,
      "meaning": "Kouri 1995's non-steroid-using athletes reached normalized FFMI values up to a well-defined limit of 25.0; pre-steroid-era Mr. America winners averaged 25.4."
    }
  },
  "almi": {
    "formula": "ALMI = appendicular lean mass (arms + legs, kg) / height (m)^2",
    "percentileSource": "Kelly 2009 Table S6 (LMS parameters above).",
    "cutPoints": [
      {
        "maleKgM2": 7.26,
        "femaleKgM2": 5.45,
        "citation": "Baumgartner RN et al., Am J Epidemiol 1998;147:755-63 (PMID 9554417) — 2 SD below a young reference group."
      },
      {
        "maleKgM2": 7,
        "femaleKgM2": 5.5,
        "citation": "Cruz-Jentoft AJ et al. (EWGSOP2), Age Ageing 2019;48:16-31 (PMID 30312372), Table 3."
      }
    ],
    "framing": "These are research definitions used in studies of low muscle mass, shown for context only. Falling under a cut-point is a reason to talk to a clinician, not a diagnosis."
  },
  "visceralFat": {
    "validation": "DXA visceral-fat estimates validated against CT: Kaul S et al., Obesity 2012;20:1313-8 (PMID 22282048; r^2 ~ 0.95 vs CT).",
    "thresholds": {
      "elevatedCm2": 100,
      "elevatedCitation": "Examination Committee of Criteria for \"Obesity Disease\" in Japan, Circ J 2002;66:987-92 (PMID 12419927), derived on CT.",
      "highCm2": 160,
      "highNote": "Common convention in DXA vendor reporting rather than a single primary paper; labeled that way by the interpreter."
    },
    "unitsNote": "Thresholds are CT-derived areas (cm^2) applied to DXA via the validated calibration; DXA also reports VAT as mass (g) and volume (cm^3), which are not interchangeable with area cut-points."
  },
  "aceBodyFatCategories": {
    "source": "American Council on Exercise body-fat norms (secondary interpretive scale).",
    "categories": [
      {
        "category": "Essential fat",
        "female": "10-13%",
        "male": "2-5%"
      },
      {
        "category": "Athletes",
        "female": "14-20%",
        "male": "6-13%"
      },
      {
        "category": "Fitness",
        "female": "21-24%",
        "male": "14-17%"
      },
      {
        "category": "Average",
        "female": "25-31%",
        "male": "18-24%"
      },
      {
        "category": "Obese",
        "female": "32%+",
        "male": "25%+"
      }
    ]
  },
  "compositionBandVisual": {
    "typicalBonePct": 4,
    "note": "When bone-mineral content isn't entered, the band visual draws bone at a typical 4% of body mass and labels it typical; no computed statistic uses it."
  },
  "tools": {
    "resultsInterpreter": "https://dexaexplained.com/tools/results/",
    "ffmiCalculator": "https://dexaexplained.com/tools/ffmi/"
  }
}