Why protein needs are expressed per kilogram of body weight
Protein requirements scale with body size, not with total calorie intake — a heavier person's body has more lean tissue to maintain, and needs proportionally more protein regardless of how many total calories they eat. This is why protein recommendations are expressed in grams per kilogram of body weight (g/kg), rather than as a flat number or a percentage of total calories the way some other nutrition guidance is framed.
The four activity-level ranges
Sedentary: 0.8-1.0 g/kg. Moderate activity: 1.2-1.6 g/kg. Active: 1.6-2.0 g/kg. Athlete (high training volume): 2.0-2.2 g/kg. Each range reflects commonly cited nutrition science guidance for how much additional protein higher training volumes require for muscle repair, recovery, and maintenance, on top of baseline bodily needs.
A worked example across all four levels
For a 70 kg person: sedentary recommendation is 56-70g/day (63g midpoint). Moderate activity: 84-112g/day (98g midpoint). Active: 112-140g/day (126g midpoint). Athlete: 140-154g/day (147g midpoint). The athlete's midpoint recommendation (147g) is more than double the sedentary person's (63g) — for the identical 70 kg body weight, purely from the difference in activity level.
Why the range narrows at higher activity levels
Notice the sedentary and moderate ranges span a wider gap (0.8-1.0 and 1.2-1.6 g/kg respectively) than the athlete range (2.0-2.2 g/kg, a narrower band). This reflects greater scientific consensus at the high end — athletes and heavily training individuals have been studied more extensively for protein needs specifically because muscle-protein synthesis and recovery are central concerns in that population, narrowing the range of commonly recommended values.
Why exceeding the range isn't necessarily harmful, but also isn't necessarily beneficial
These ranges represent commonly cited targets sufficient for muscle maintenance and growth at each activity level — consuming meaningfully more protein than the upper end of your range doesn't generally provide additional muscle-building benefit beyond a certain point, since the body can only use so much protein for tissue repair and synthesis at once. The range exists precisely to identify a sufficient target, not a "more is always better" minimum floor.