Effects of high protein intake
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High Protein Intake and Body Weight, Fat Mass, and Satiety
Several studies show that high protein intake can help reduce body weight and fat mass, especially when combined with calorie restriction or resistance training. High-protein diets increase satiety, leading to reduced food intake, and help preserve fat-free mass during weight loss, which can prevent a decrease in resting energy expenditure. These effects are supported by changes in appetite-regulating hormones and increased diet-induced thermogenesis, making high-protein diets effective for weight loss and maintenance in healthy adults and resistance-trained individuals Antonio2016Moon2020Cuenca-Sánchez2015.
However, some long-term studies in populations at high cardiovascular risk have found that higher protein intake is associated with increased body weight and a higher risk of all-cause mortality, particularly when protein replaces carbohydrates or fat in the diet. Animal protein, in particular, is linked to greater risks of fatal and non-fatal outcomes .
High Protein Intake and Kidney Health
The impact of high protein intake on kidney health is debated. In healthy adults, most studies do not show harmful effects on kidney function, even with prolonged high protein consumption Antonio2016Moon2020Cuenca-Sánchez2015. However, there is evidence that high protein intake can worsen renal function in people with existing kidney disease and may increase the risk of developing chronic kidney disease (CKD) in the general population, especially with long-term intake of animal protein. The source of protein matters: red meat is associated with higher CKD risk, while plant and dairy proteins are less concerning or may even be protective. Because of conflicting evidence and the lack of long-term randomized trials, caution is advised, especially for those at risk for kidney disease Ko2020Kamper2017.
High Protein Intake and Metabolic Health
High protein diets can improve glucose homeostasis and reduce intrahepatocellular lipid accumulation, which may benefit liver health. However, in some cases, such as in obese postmenopausal women, high protein intake during weight loss can eliminate the usual improvement in insulin sensitivity that comes with weight loss, potentially having negative effects on metabolic function Smith2016Bortolotti2009.
High Protein Intake in Children, Adolescents, and Preterm Infants
The effects of high protein intake vary by age group. In children and adolescents, high protein intake is often above recommendations and is linked to increased BMI, mainly due to increased fat-free mass rather than fat mass. The long-term health impact in this age group is still unclear and needs more research .
For preterm infants, high protein intake (≥3.5 g/kg/d) may have short-term benefits for growth but is associated with increased risks of metabolic disturbances, neurodisability, and does not improve long-term growth outcomes. Therefore, very high protein intake is not recommended for this group .
Conclusion
High protein intake can support weight loss, preserve lean mass, and increase satiety in healthy adults, with little evidence of harm to kidney or bone health in this population. However, risks may exist for those with or at risk for kidney disease, and long-term high protein intake—especially from animal sources—may be linked to increased mortality and weight gain in some populations. In children, adolescents, and especially preterm infants, high protein intake should be approached with caution due to potential risks. More long-term studies are needed to clarify the safety and optimal levels of protein intake for different groups.
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