Is excessive protein intake harmful?

From the Guidelines

Consuming too much protein can be detrimental to one's health, particularly for individuals with pre-existing kidney disease, and healthy adults should generally not exceed 0.8 grams of protein per kilogram of body weight daily. When considering protein intake, it's essential to prioritize the recommended daily allowance (RDA) to avoid potential health risks.

• Excessive protein consumption may strain kidney function, potentially cause digestive discomfort, and could contribute to weight gain if total caloric intake exceeds needs.
• Very high protein diets might also lead to nutritional imbalances if they displace other important food groups.
• The body can only use a certain amount of protein at once for muscle building and other functions, with excess typically being converted to glucose or stored as fat. According to the most recent and highest quality study, 1, dietary protein intake should be approximately 0.8 g/kg body weight per day for people with nondialysis-dependent diabetic kidney disease.
• Higher levels of dietary protein intake (>20% of daily calories from protein or >1.3 g/kg/day) have been associated with increased albuminuria, more rapid kidney function loss, and CVD mortality and therefore should be avoided.
• Reducing the amount of dietary protein below the recommended daily allowance of 0.8 g/kg/day is not recommended because it does not alter glycemic measures, cardiovascular risk measures, or the course of GFR decline. It's also worth noting that the quality of protein consumed likely matters more than the actual quantity of protein, as suggested by 1, where substituting chicken or other non–red meat sources of protein in lieu of red meat strongly attenuated ESRD risk.
• Counseling patients to moderate animal protein intake, especially red meat intake, may have beneficial effects on GFR decline for some patients. Overall, focusing on a balanced diet with moderate protein from diverse sources (including plant-based options) is the healthiest approach, as supported by 1 and 1.

From the Research

Potential Risks of Excessive Protein Intake

• High protein intake (>2 g per kg BW per day for adults) may result in digestive, renal, and vascular abnormalities and should be avoided 2
• Long-term consumption of high protein/high meat intake is associated with adverse effects such as disorders of bone and calcium homeostasis, disorders of renal function, increased cancer risk, disorders of liver function, and precipitated progression of coronary artery disease 3
• The evidence suggests that there is currently no reasonable scientific basis to recommend protein consumption above the current RDA (high protein diet) for healthy adults due to its potential disease risks 3

Recommended Protein Intake

• The Recommended Dietary Allowance of protein for a healthy adult with minimal physical activity is currently 0.8 g protein per kg body weight (BW) per day 2
• Dietary intake of 1.0,1.3, and 1.6 g protein per kg BW per day is recommended for individuals with minimal, moderate, and intense physical activity, respectively 2
• Long-term consumption of protein at 2 g per kg BW per day is safe for healthy adults, and the tolerable upper limit is 3.5 g per kg BW per day for well-adapted subjects 2

Health Effects of Protein Intake

• The evidence is assessed as probable for an estimated average requirement of 0.66 g good-quality protein/kg body weight (BW)/day based on nitrogen balance studies 4
• Vegetable protein intake is associated with decreased risk in many studies, including inverse relationships between cardiovascular mortality and vegetable protein intake, and between blood pressure and vegetable protein 4
• High protein intake may have potentially adverse effects on cardiometabolic health, and the use of different units of protein intake (e.g. grams, percent energy, g/kg BW) can contribute to confusion about protein's effects on health 5