Am I consuming too much protein, and is that bad for my kidneys?
For people with healthy kidneys there is little reason to worry about a generous protein intake, but anyone who has kidney disease or was born with one kidney would be wise to limit their intake and consult a dietitian.
Whether a high-protein diet is bad for your kidneys depends primarily on whether your kidneys are healthy. In people with normally functioning kidneys, there is little evidence that a generous protein intake is harmful. The concern applies mainly to people who already have a kidney problem.
One mechanism that can occur with high protein intake is glomerular hyperfiltration: the small filtering units in your kidneys start working harder than normal. In healthy people this appears to be temporary and probably harmless. However, someone who already has fewer functioning filtering units, for example due to an existing kidney disease or a congenital abnormality, may over time sustain kidney damage from that extra strain.
In people with chronic kidney disease (CKD), a high-protein diet is indeed a risk. It has been linked to accelerated decline in kidney function, accumulation of nitrogen waste products in the blood, metabolic acidosis (acidification of the blood), inflammation and bone problems. In addition, excessive protein intake in this group also increases the risk of cardiovascular disease, oxidative cell damage, elevated phosphate levels in the blood and disruption of the gut microbiome.
Phosphate deserves separate attention: a high-protein diet often brings a high phosphate load with it, through meat, dairy and ultra-processed products. Chronically high phosphate intake has been linked to loss of kidney function and increased cardiovascular risk, even in people without pre-existing kidney disease.
The opposite is equally a pitfall. Too little protein in kidney patients leads to loss of muscle mass and a worse overall prognosis. The recommendation is therefore not an extreme choice in either direction, but an individually tailored diet, preferably with a predominance of plant-based protein sources, under the guidance of a dietitian or doctor. A specific at-risk group is children born with only one kidney: for them, excessive protein and salt intake is explicitly discouraged.
The claims are based on multiple studies (PMID 25979491, 35409969, 31728497, 40739997, 37394104, 35365815, 35511366, 35713730). The strength of evidence ranges from limited (for healthy individuals) to moderate (for CKD patients). There are few large randomised trials; much of the evidence is observational or mechanistic.
Do older adults need more protein than younger people?
Older adults likely need more protein than the standard guideline of 0.8 grams per kilogram suggests. As a healthy older adult, aim for 1.0 to 1.2 grams per kilogram per day, spread well across meals, and combine this with resistance training where possible.
Does extra protein help with losing weight without losing muscle?
Extra protein helps preserve muscle mass while losing weight, but works best in combination with resistance training. Aim for 1.6-2.4 g per kilogram of body weight per day, and make sure to train alongside it.
Is too much zinc harmful?
Too much zinc is certainly harmful: as an adult, stay below 25 mg per day (the EFSA limit) and be cautious with high-dose zinc supplements, because even moderate over-supplementation can disrupt copper balance.
Can you get too much vitamin D?
Too much vitamin D is genuinely harmful, but that risk only arises at blood levels far above the recommended values. Stick to the dosage on the packaging, and unsure about your level? Have it measured by your GP.
How much protein can your body use in a single meal?
Your body can use more than 20-25 grams of protein per meal, especially when that protein is combined with carbohydrates and fats. Spread your intake across four meals of approximately 0.4 grams per kilogram of body weight for the best results.
Does it matter what kind of protein I eat, or does only the total amount count?
The type of protein matters: animal proteins and well-combined plant-based sources provide more building material for muscles than collagen or single soy products. The total amount counts too, but it is not the whole story.