Raw vs Cooked Weight

The raw vs cooked weight distinction is the single most common source of systematic dietary-logging error among users who weigh their food but log against the wrong database entry. A chicken breast weighed at 200 g raw, cooked, and logged as "chicken breast, cooked (200 g)" will be substantially overcounted in calories, because cooked chicken breast has higher calorie density per gram (the water left). The same 200 g raw breast, cooked, weighs roughly 150 g; the database "cooked" entry is per-gram calibrated to the cooked state.

The moisture-loss arithmetic

Nearly all proteins lose moisture during cooking. Typical losses by method and food:

• Chicken breast, grilled or baked: 25 per cent mass loss.
• Chicken thigh, roasted: 30 per cent.
• Ground beef (80/20), pan-fried: 25 per cent mass loss, of which roughly 40 per cent is rendered fat and 60 per cent is water.
• Lean beef steak, grilled medium: 15 to 20 per cent.
• Salmon fillet, baked: 20 per cent.
• Bacon: 60 to 70 per cent mass loss (water plus rendered fat).

Grains and starches move the other direction — they absorb cooking water:

• White rice: +150 to +200 per cent mass (one cup dry becomes roughly three cups cooked).
• Pasta: +100 to +150 per cent.
• Oatmeal: +200 per cent.
• Dry beans: +100 per cent.

Why it produces systematic error

The USDA FoodData Central database includes both raw and cooked entries for most foods, appropriately calibrated. A "Chicken breast, skinless, cooked, roasted" entry at 165 kcal per 100 g and a "Chicken breast, skinless, raw" entry at 120 kcal per 100 g describe the same food in different physical states, and the per-gram figures are both correct for their respective states. The error arises when a user weighs the food in one state and logs the entry for the other — weighing the raw breast (200 g raw) and logging 200 g of the cooked entry, or weighing the cooked (150 g) and logging the raw entry for 150 g. Either mismatch produces a systematic miss, direction depending on which way the mismatch runs.

Consistent-convention solution

The methodological fix is to adopt a single weighing convention and stick to it. Two common conventions work:

• Raw-always. Weigh before cooking, log against the raw entry. Most accurate because raw weights are typically well-characterised in USDA. Requires weighing in kitchen mise-en-place workflow.
• Cooked-always. Weigh on the plate, log against the cooked entry. More convenient but requires the cooked database entries to exist and to match the actual cooking method closely.

Research-grade dietary-assessment tools (NCI's Automated Self-Administered 24-hour Dietary Assessment Tool, for example) use the cooked-always convention because the user is recalling the meal after the fact, when the raw weight is no longer accessible. Consumer weight-based logging in performance-nutrition contexts tends to use raw-always, because the athlete is weighing at preparation time anyway.

Cooking-yield factors in FNDDS

FNDDS handles the raw-to-cooked transition via published cooking-yield factors. The USDA's Table of Cooking Yields provides multipliers (typical yield for roasted chicken breast: 0.75; for pan-fried ground beef: 0.73) that allow conversion between states at the database level. Users of research-grade tools rarely interact with these factors directly; they are applied behind the scenes.