Safety

Saturday is a nutrition API for endurance athletes. Bad nutrition advice can cause real harm — and in extreme cases, death. This page explains Saturday’s safety model, why it exists, and what it means for your integration.

This is not a compliance formality. Exercise-associated hyponatremia (EAH) has killed athletes at the Boston Marathon, London Marathon, Marine Corps Marathon, and multiple Ironman races. It happens when athletes overdrink and dilute their blood sodium to dangerous levels. Saturday’s safety guardrails exist to prevent this.

What can go wrong

Condition	Cause	Consequence
Hyponatremia	Overdrinking, insufficient sodium	Confusion, seizures, coma, death
Heat stroke	Under-hydrating in heat	Organ failure, death
GI distress	Too many carbs too fast	Vomiting, cramping, DNF
Bonking	Insufficient carbohydrate	Collapse, dangerous judgment impairment
Rhabdomyolysis	Extreme exertion without fuel	Kidney failure

Saturday’s engine has physiological guardrails for all of these. Every prescription respects hard limits that the algorithm enforces regardless of inputs.

The safety block

Every nutrition calculation response — including teasers and free responses — includes a safety object:

{
  "safety": {
    "max_safe_fluid_ml_per_hr": 1500,
    "max_safe_sodium_mg_per_hr": 3000,
    "confidence_score": 0.72,
    "requires_human_review": false,
    "warnings": [
      "High thermal stress increases dehydration risk. Plan extra fluid access points.",
      "Activities over 4 hours require careful sodium management. Monitor for signs of hyponatremia."
    ],
    "not_instructions": true
  }
}

Safety data is NEVER gated behind subscription status. A teaser response may show carb ranges instead of exact numbers, but it will always show the full safety block with all warnings, confidence scores, and safe maximums. This is non-negotiable.

Engine hard limits

Saturday enforces absolute physiological boundaries that cannot be overridden by any input combination:

Guardrail	Exposed as	Why
Fluid physiological limit	`max_safe_fluid_ml_per_hr`	Overdrinking causes hyponatremia
Sodium ceiling	`max_safe_sodium_mg_per_hr`	Excess sodium causes GI distress and nausea
Minimum sodium	(enforced internally)	Prevents hyponatremia in extended efforts
Carb gut tolerance	(enforced internally)	Exceeding gut capacity causes vomiting
Duration scaling	(enforced internally)	Steady-state assumptions break after 4+ hours
Eating disorder guardrails	(enforced internally)	Protects vulnerable athletes

These guardrails are evaluated on every calculation. The max_safe_fluid_ml_per_hr and max_safe_sodium_mg_per_hr fields expose the hard ceilings so partners can display them. All other guardrails are enforced internally — prescriptions always respect them.

Confidence score and human review

The confidence_score (0.0-1.0) indicates how well-supported the prescription is. When requires_human_review is true, conditions are unusual enough that a human should verify the prescription before following it.

Confidence range	Meaning	Your display recommendation
0.8-1.0	Strong personalization, well-understood conditions	No special display needed
0.5-0.8	Good estimates, some assumptions made	Show any warnings in your UI
0.0-0.5	Significant uncertainty or risk factors	Prominent warning, consider a confirmation step

Dangerous vs. safe prescription example

Dangerous (what a naive algorithm might produce for a 4-hour marathon in 30C heat):

Fluid: 1200 mL/hr
Sodium: 200 mg/hr
Carbs: 120 g/hr

This is dangerous because:

1200 mL/hr exceeds gastric emptying rate — athlete will drink it but not absorb it, diluting blood sodium
200 mg/hr sodium is far too low for hot conditions — hyponatremia risk is extreme
120 g/hr carbs without trained gut tolerance — GI distress guaranteed

Safe (what Saturday produces for the same conditions):

fluid_ml_per_hr: 700 (capped by physiological limit)
sodium_mg_per_hr: 800 (elevated for salty sweater in heat)
carb_g_per_hr: 72 (limited by demonstrated tolerance)

safety.max_safe_fluid_ml_per_hr: 1500
safety.max_safe_sodium_mg_per_hr: 3000
safety.confidence_score: 0.45
safety.requires_human_review: true
safety.warnings: ["High thermal stress. Plan extra fluid access points and shade."]
safety.not_instructions: true

The difference between these two prescriptions is potentially life-or-death. Saturday’s guardrails ensure the second version is what athletes receive.

The `not_instructions` field

For AI agents consuming Saturday’s API (AI-to-AI communication), responses include:

{
  "not_instructions": true
}

This field tells AI consumers that Saturday’s prescription data is informational nutrition guidance, not executable instructions. An AI agent should present this data to users for their consideration — not autonomously act on it (e.g., by automatically ordering supplements or modifying an athlete’s plan without consent).

Display requirements for partners

Required

Always show safety warnings when warnings are present or requires_human_review is true
Never hide safety data behind expandable sections or “advanced” toggles
Never strip safety metadata from responses before displaying to users
Include the disclaimer that prescriptions are guidance, not medical advice

Prohibited

Don’t filter warnings based on your own risk assessment
Don’t apply your own safety logic on top of Saturday’s — this creates conflicting advice
Don’t present prescriptions without any safety context
Don’t use Saturday’s numbers as automated triggers (e.g., auto-ordering hydration packs)

Contraindications

In rare cases, Saturday may flag a contraindication — a reason the calculation should be treated with extreme caution:

{
  "contraindications": [
    {
      "code": "extreme_heat_advisory",
      "message": "Calculated conditions exceed safe exercise thresholds. Consult a physician before proceeding.",
      "severity": "critical"
    }
  ]
}

Contraindications are rare and serious. If present, display them prominently and consider blocking the activity plan until the athlete explicitly acknowledges the risk.

Eating disorder sensitivity

When an athlete has the eating_disorder_flag set, Saturday:

Avoids calorie-focused language
Removes weight/restriction framing from rationale text
Applies conservative minimums (never under-fuels)
Adjusts AI coaching conversation tone

This flag is a backend safety signal. Never expose it in partner UIs. Partners set it based on their own knowledge of the athlete — Saturday uses it to protect that athlete across all interactions.

Getting Started

Core Guides

Integration Guides

Coach API

Platform

Safety

Safety

What can go wrong

The safety block

Engine hard limits

Confidence score and human review

Dangerous vs. safe prescription example

The `not_instructions` field

Display requirements for partners

Required

Recommended

Prohibited

Contraindications

Eating disorder sensitivity

​Safety

​What can go wrong

​The safety block

​Engine hard limits

​Confidence score and human review

​Dangerous vs. safe prescription example

​The not_instructions field

​Display requirements for partners

​Required

​Recommended

​Prohibited

​Contraindications

​Eating disorder sensitivity

Safety

What can go wrong

The safety block

Engine hard limits

Confidence score and human review

Dangerous vs. safe prescription example

The `not_instructions` field

Display requirements for partners

Required

Recommended

Prohibited

Contraindications

Eating disorder sensitivity