Lab 2 — The fat-vehicle gate

Question for students: a spinach salad's nutrition panel lists vitamin A. The dressing is fat-free. Does the vitamin A reach the student?

The pair

from biology_as_code.packets import get_packet

for packet_id in ("ex.spinach_salad.with_oil", "ex.spinach_salad.zero_fat"):
    packet = get_packet(packet_id)
    print(packet.common_name)
    print("  cargo :", packet.cargo_nutrients())
    print("  lipid :", packet.partner("dietary_lipid_g"), "g")

Same leaf matrix, same carotenoid cargo. One declares 6 g of dietary lipid, the other declares 0.

Audit the label's implied claim

from biology_as_code import Claim, audit_claim

claim = Claim(
    id="claim.spinach_vitA_no_fat",
    surface_claim="Eat fat-free spinach salad for vitamin A to prevent deficiency disease",
    verb_class="disease_claim",
    nutrient="beta_carotene",
    surface_verb="prevents",
)

for packet_id in ("ex.spinach_salad.zero_fat", "ex.spinach_salad.with_oil"):
    result = audit_claim(claim, get_packet(packet_id))
    print(f"\n--- {packet_id}")
    print("verdict        :", result.verdict)
    print("gate_check     :", result.gate_check)
    print("closed_through :", result.l1_to_l5.get("closed_through"))
    print("laws           :", result.law_refs)
    for level in ("L1", "L2", "L3", "L4", "L5"):
        if level in result.l1_to_l5:
            print(f"  {level}: {result.l1_to_l5[level]}")

Two teaching points, not one

First: the zero-fat salad returns Busted, closed through L3. The panel number is real — the carotenoid is in the leaf — but the micellar path needs a lipid phase (LAW-020), and the absorbed cargo leaves the enterocyte by chylomicron (LAW-045). No lipid, no path. This is a categorical failure, not a small number.

Second, and less obvious: adding the oil does not make the claim true.

result = audit_claim(claim, get_packet("ex.spinach_salad.with_oil"))
print(result.verdict, "at", result.l1_to_l5["closed_through"])
print(result.gate_note)

The gate now passes, but the verdict is UNEVALUABLE closed through L5. A single meal path cannot carry a disease-prevention endpoint. Fixing the mechanism earns you the mechanism, nothing further.

This is the anti-tunnel rule

The constitution forbids L1→L5 tunnelling — jumping from a food to a disease slogan without the intervening mechanism. Here it is enforced in code: even a mechanically sound meal returns UNEVALUABLE for a disease claim.

Reframe the claim and watch it change

Same packet, same food, weaker verb:

mechanism_claim = Claim(
    id="claim.spinach_carotenoid_mechanism",
    surface_claim="Adding oil to this salad raises carotenoid bioavailability",
    verb_class="bound_increase",
    nutrient="beta_carotene",
)
result = audit_claim(mechanism_claim, get_packet("ex.spinach_salad.with_oil"))
print(result.verdict, "|", result.gate_check, "|", [f.direction for f in result.bound_findings])

The mechanism claim is Plausible. The disease claim is not. The food did not change — the claim did. That is the whole lesson.

Exercise

1. What would the verdict be if a packet declared no lipid field at all? Try get_packet("ex.kale.raw"). Explain why the answer differs from 0 g.
2. LAW-045's gate text mentions abetalipoproteinemia. Should host genotype be a packet field, a persona field, or neither?
3. Find a marketed "fat-free" product whose panel advertises a fat-soluble vitamin.