A review of issues of dietary protein intake in humans.
Level 5 - mechanism / opinion, no new human data
Narrative review based on physiological mechanisms and theoretical calculations without systematic review methodology
PubMed 16779921 · doi:10.1123/ijsnem.16.2.129
What was done
Narrative review analyzing the physiological constraints and safety parameters of human dietary protein intake, focusing on gastrointestinal amino acid absorption rates and hepatic capacity for urea synthesis.
What was found
Intestinal amino acid absorption rates range from 1.3 to 10 g/h. The accepted baseline intake of 0.8 g/kg/d reflects structural requirements only, whereas high-protein diets advocating 200 to 400 g/d (approximately 5 g/kg/d) may exceed hepatic capacity to convert nitrogen to urea. Intakes exceeding 35% of total energy intake risk toxicity, including hyperaminoacidemia, hyperammonemia, hyperinsulinemia, nausea, diarrhea, and death. The proposed safe maximum intake is approximately 25% of energy requirements (2 to 2.5 g/kg/d, or 176 g/d for an 80 kg individual on a 12,000 kJ/d diet), below the theoretical maximum safe range of 285 to 365 g/d for an 80 kg adult.
Why it matters
Provides quantitative, mechanism-based physiological boundaries for dietary protein intake to help evaluate the safety of high-protein diets against hepatic deamination limits.
Limits
Based on theoretical physiological modeling and narrative synthesis rather than a systematic review or primary clinical trial. The abstract provides no participant counts, empirical trial outcomes, or direct safety data in specific clinical or athletic sub-populations.
Cited by
- supports Consuming pure protein without sufficient fat or carbohydrates creates a dangerous metabolic imbalance because the human body can only use a limited amount of protein for fuel.