Agriculture & Future Food Systems · Article
Define the stage before reporting food loss
A useful food-loss or waste measurement states where material was measured, what was included and which destinations count.
Preparation and related reading
Shared Foundations
Related articles
This article helps you
- Set an explicit production, retail, service or household boundary.
- Avoid adding percentages with different stage inputs.
- Separate food transfers and retained stock from discarded material.
Two reports can describe different parts of the same supply
A grower records material removed during packing, while a shop records food discarded after arrival. Both observations can help improve a food system, but they cover different stages. Comparing their percentages without checking the input quantities can hide where material left the chain.
Begin with the question: a particular crop's post-harvest loss, a shop's discarded stock, a meal service's remaining food or household disposal. Specify the site, period, material and route. A useful number needs those definitions as much as it needs a unit.
Use named definitions with their boundaries
In the SDG monitoring framework described by FAO, the Food Loss Index covers stages from harvest up to, but excluding, retail. UNEP's Food Waste Index concerns retail, food service and households. This is a named statistical distinction, not a rule that every organisation must use identical everyday vocabulary.
The FLW Protocol instead helps inventories state which material types and destinations they include. A discarded-food-only study and a study including associated inedible parts answer different questions. Record the chosen definition before calling either result the total for a food system.
Follow one cohort through consecutive stages
In an invented chain, 100 kg of the same food enters stage A. Ten kilograms are removed to the defined waste destination, leaving 90 kg for stage B. Stage B removes 9 kg to that destination and passes on 81 kg. Assume no added material, water-mass change, other exit or stock change.
Each stage removes 10% of its own incoming mass, but the combined removal is 19 kg out of the original 100 kg: 19%. The diagram follows the cohort. Adding the two 10% stage figures gives 20%, which uses incompatible denominators and overstates this result.
| Stage | Incoming food | Removed to waste | Passed onward |
|---|---|---|---|
| A | 100 kg | 10 kg | 90 kg |
| B | 90 kg | 9 kg | 81 kg |
Follow a 100 kg cohort without double counting
Read the diagram as text
Stage A removes 10 kg from 100 kg, leaving 90 kg. Stage B removes 9 kg from that 90 kg, leaving 81 kg. Combined removal is 19 kg, or 19% of the original input.
Parts
- 100 kg into A
- Initial food mass; no other inputs or stock change.
- 90 kg into B
- After the 10 kg removal in stage A.
- 81 kg passed onward
- After the 9 kg removal in stage B.
- 10 kg removed at A
- 10% of A's 100 kg input.
- 9 kg removed at B
- 10% of B's 90 kg input.
Connections
- 100 kg into A → 90 kg into B: remaining
- 90 kg into B → 81 kg passed onward: remaining
- 100 kg into A → 10 kg removed at A: removed
- 90 kg into B → 9 kg removed at B: removed
Keep stocks and transfers distinct
Food retained for later use is not yet discarded. Food moved from a shop to another human-food service is a transfer, whose later destination still needs checking. The FLW Protocol keeps food continuing to human consumption separate from removal from that supply chain.
A combined inventory must avoid recording the same material twice at collection and final treatment. Connect records with a material identity and handover time. Measuring a bin at a service and the same bin at a treatment facility describes two observations of one flow, not two newly generated quantities.
Record food state and destination
Fresh, dried and cooked masses can differ because water was removed or added. A mass decrease is therefore not automatically food discarded. A coherent balance includes known water changes, other outputs and inventory changes before attributing an unexplained difference to waste.
Destination also matters: material retained in human-food use, sent for treatment or disposed of is not interchangeable. A narrow landfill inventory can decrease when material moves to another treatment route, even if the quantity leaving human-food use is unchanged. State whether the question concerns generation or one destination.
Make the result useful for a comparison
Report the amount alongside its stage, reference input and period. Keep methods and material definitions consistent across observations. If the boundary changes, separate its effect from a change in practice; a larger measured scope can produce a larger total without worse performance.
Use the meal-flow articles and shared conservation and measurement Foundations for the accounting logic. Compare nutrient loss, economic value or environmental effects only with the additional information those questions require. Kilograms alone do not establish the importance or cause of a loss.
Worked examples
Two 10% stages are not 20% of the original
Calculate the combined removal for the 100 kg cohort when stages A and B remove 10 kg and 9 kg respectively.
- Stage A: 10/100 × 100 = 10%.
- Stage B: 9/90 × 100 = 10%.
- Combined: (10 + 9)/100 × 100 = 19%; 100 − 10 − 9 = 81 kg passed onward.
The total is 19 kg, or 19% of the original input, under the explicit no-other-flow assumptions.
A gap is not all waste
An invented service receives 150 kg, serves 120 kg, retains 20 kg and sends 10 kg to its stated waste route. There are no other flows or stock changes. Is the 30 kg difference between receipts and service all waste?
- Reconcile 150 = 120 + 20 + 10 kg.
- The receipt-to-service difference is 150 − 120 = 30 kg.
- It contains 20 kg retained and 10 kg sent to waste.
No. Only 10 kg has the stated waste destination; the other 20 kg is retained stock.
Check your understanding
Does FAO's named Food Loss Index boundary include retail?
Show answer and reasoning
No.
The inspected SDG framing ends before retail; retail is included in the Food Waste Index framework.
Can the same 10 kg bin measured at a kitchen and its treatment facility be added as 20 kg of newly generated waste?
Show answer and reasoning
No.
The records concern the same material flow.
Does a food's mass decrease after drying prove it was discarded?
Show answer and reasoning
No.
Water removal changes mass and must be accounted for separately.
Key ideas
- Attach stage, material, destination and period to the measurement.
- Use a common initial input when combining sequential-stage results.
- Keep water changes, stocks, transfers and repeated observations separate.
References
Sources supporting the explanations and examples in this article.