Short answer: 1 g of protein ≈ 4 kcal. Whether it comes from chicken, eggs, lentils, or whey isolate. The same number on a Polish quark label, a Brazilian açaí bowl, and an American protein shake. Why doesn't this value change? Because it isn't a dietetic convention — it's combustion physics combined with intestinal digestibility.
In BiteNote you get a confidence range for the whole meal ("248–262 kcal, confidence: high"), but the 4 kcal/g coefficient for protein itself is fixed. Worth knowing why.
| Protein source | Energy from protein (kcal/g) | Total energy (kcal/100g) | Protein (g/100g) |
|---|---|---|---|
| Chicken breast, raw | 4.0 | 120 | 22.5 |
| Whole egg, raw | 4.0 | 143 | 12.6 |
| Cottage cheese | 4.0 | 130 | 18.5 |
| Lentils, dry | 4.0 | 353 | 24.6 |
| Whey protein isolate 80% | 4.0 | 380 | 80 |
The 4 kcal/g coefficient was introduced by Wilbur Atwater at the turn of the 20th century. He burned food samples in a bomb calorimeter, measured released energy, and subtracted losses (indigestible portion + urea excreted in urine). For protein, the net value came out to ~4 kcal/g — and that number has been in USDA tables since 1899. It has held for over 120 years because it rests on physics, not on a dietary trend.
Two important notes:
Gross vs net value. The bomb calorimeter burns the sample completely and shows ~5.65 kcal/g for protein. Your body doesn't burn protein completely — part of the nitrogen is excreted as urea (~1.25 kcal/g of potential energy). Atwater's 4 kcal/g already accounts for these metabolic losses. That's the relevant figure for your diet, not 5.65.
Thermic effect of protein (TEF). Digesting protein costs the body ~20–30% of its energy value. Out of 100 kcal of net protein, ~70–80 kcal are "available." Compare that to fat (~3% TEF) and carbs (~5–10% TEF). That's why high-protein diets feel more satiating at the same calorie count. The label doesn't reflect this — you always see 4 kcal/g gross.
From a calorie perspective — identical 4 kcal/g. The only difference is digestibility (absorbability): egg and whey ~95–98%, soy ~92%, rice ~88%, wheat ~80%. For strict nitrogen control (competitive sports, clinical protein diets) this matters. For everyday calorie counting: 1 g of protein = 4 kcal. Period.
📸 → BiteNote: grilled chicken breast, 150g, ~248 kcal (235–262). Protein ~33g = 132 kcal from protein. Confidence: high.
Want a daily macro breakdown? Ask /today.
📸 → BiteNote: 2 fried eggs + 5g butter, ~210 kcal (195–225). Protein ~12g = 48 kcal from protein. Confidence: medium.
Yes. 1 g of egg protein = 1 g of chicken protein = 4 kcal. The difference between products is in the amount of protein (egg 12.6 g/100g, chicken 22.5 g/100g), not the calories per gram.
No. 1 g of whey protein = 4 kcal. A 30 g whey scoop with 24 g of protein = ~96 kcal from protein, plus residual lactose/lecithin → typically ~110–125 kcal per scoop.
Thermic effect of food (TEF). Digesting protein costs the body ~20–30% of its energy vs ~5% for carbs. From 100 kcal of protein you actually use ~75 kcal. The label doesn't account for this — it shows the gross 4 kcal/g.
RDA is 0.8 g/kg of body mass; athletes need 1.6–2.2 g/kg. For an active 70 kg person that's 112–154 g of protein = 448–616 kcal from protein alone. If your target is 2200 kcal/day, protein covers ~20–28% of energy. BiteNote breaks this down in /today.
No — 4 is 4. Cooking only changes the amount of protein in the cooked product through water loss (raw chicken 22.5 g/100g → grilled ~31 g/100g — water evaporated, protein stayed the same, mass dropped).
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