Daily Food Unit (DFU)
The Daily Food Unit (DFU) is Eaternity's standardized functional unit for comparing the environmental impact of different foods fairly.
Why DFU?
Different foods provide different nutritional value. Comparing 100g of beef to 100g of lettuce wouldn't be fair because they serve different nutritional purposes. The DFU solves this by normalizing environmental impacts to a comparable nutritional basis.
Definition
The DFU represents the amount of food that covers ⅓ of the normal daily requirement across multiple nutritional dimensions:
| Nutrient | Daily Requirement | DFU Target (⅓) |
|---|---|---|
| Proteins | 50 g | 16.7 g |
| Fats | 66 g | 22 g |
| Energy | 2200 kcal (~6000 kJ for carbs) | 733 kcal |
| Water | 2500 g | 833 g |
| Dry Weight | 600 g | 200 g |
The energy component uses kilojoules (kJ), not kilocalories. The 6000 kJ divisor represents the daily carbohydrate energy requirement after subtracting energy from proteins (~17 kJ/g) and fats (~37 kJ/g).
Calculation Formula
The DFU for any food is calculated as the average contribution across all nutritional dimensions:
DFU = (protein_ratio + fat_ratio + energy_ratio + water_ratio + dry_weight_ratio) / 5
Where each ratio is calculated as:
protein_ratio = g_protein / 50fat_ratio = g_fat / 66energy_ratio = (kJ_energy - 17×g_protein - 37×g_fat) / 6000water_ratio = g_water / 2500dry_weight_ratio = g_dry_weight / 600
Energy must be in kilojoules (kJ), not kilocalories. The coefficients 17 and 37 represent the energy content per gram of protein and fat in kJ respectively. To convert kcal to kJ, multiply by 4.184.
Example Calculation
100g whole-grain cereals:
- Proteins: 10g
- Fats: 7g
- Energy: 1434 kJ
- Water: 16g
- Dry weight: 84g
DFU = (10/50 + 7/66 + (1434 - 17×10 - 37×7)/6000 + 16/2500 + 84/600) / 5
DFU = (0.20 + 0.106 + 0.166 + 0.006 + 0.14) / 5
DFU = 0.122 (12.2% of daily requirement)
With a CO₂ value of 85g CO₂/100g, the normalized impact is:
85g / 0.122 = 697 g CO₂/DFU
Compared to the global average of 3894g CO₂/DFU, this is 82% better than average (Rating A - climate friendly).
Rating System
Foods are rated by comparing their CO₂/DFU against the global average of 3894g CO₂eq per DFU. The rating is based on the improvement percentage:
| Rating | CO₂eq/DFU Threshold | Improvement % | Meaning |
|---|---|---|---|
| A | < 1,947g | ≥ 50% better | Climate friendly |
| B | < 3,894g | > 0% better | Better than average |
| C | < 7,787g | > -100% | Up to 2× the average |
| D | < 15,574g | > -300% | Up to 4× the average |
| E | > 15,574g | ≤ -300% | More than 4× the average |
Rating A (≥50% improvement) indicates climate-friendly food, aligned with the IPCC and Eat-Lancet recommendations for reducing food emissions by 50% to meet climate targets.
Benefits of DFU
- Fair Comparison: Compare apples to beef fairly
- Nutritional Context: Impact relative to what you get nutritionally
- Consumer Clarity: Easy-to-understand ratings
- Scientific Basis: Grounded in nutritional science
Detailed Derivation
For the full scientific derivation of the Daily Food Unit methodology, see the technical paper:
Derivation of the Daily Food Unit (PDF)
See Also
- Benchmark Calculations — How ratings are determined
- Climate Score — Understanding CO₂ ratings
- Methodology Overview — LCA methodology