Whey Protein, the Liver and the Kidneys: Is It Safe?
"Protein shakes will wreck your kidneys" is one of the most persistent gym myths, usually repeated with a mixture of concern and folklore. Our editorial team reviewed the clinical evidence on higher protein intakes in healthy adults and separated the genuine risks — which do exist for certain people — from the scare stories.
Where the concern comes from
Whey protein is simply a concentrated fraction of milk protein. It contains nothing exotic — just the same amino acids found in a chicken breast, an egg or a glass of milk. The worry is not about whey as such, but about high protein intakes in general.
When we eat protein, the nitrogen from amino acids is converted into urea in the liver and excreted by the kidneys. Higher protein intakes increase this workload and raise the glomerular filtration rate (GFR) — the speed at which the kidneys filter blood. In people with existing kidney disease, this "hyperfiltration" can accelerate damage, which is why renal patients are often advised to moderate protein.
The leap from "harmful in kidney disease" to "harmful for everyone" is where the myth was born. A narrative review by Martin, Armstrong and Rodriguez (2005) found no convincing evidence that protein intakes typical of athletes damage healthy kidneys, and noted that increased GFR is a normal adaptive response.
The liver concern is even more speculative. It mostly arises from case reports involving contaminated or adulterated "protein" products, or from people combining supplements with anabolic steroids and other hepatotoxic substances.
Kidneys: what the trials say
The best summary to date comes from a systematic review and meta-analysis by Devries and colleagues (2018), which pooled data from 28 studies. Healthy adults eating higher-protein diets showed a small rise in GFR but no meaningful difference in markers of kidney function compared with those eating normal or lower protein intakes.
Antonio and co-workers (2016) conducted a one-year crossover study in resistance-trained men consuming very high protein intakes, well above typical recommendations. They found no harmful effects on blood lipids, liver enzymes or markers of renal function over the study period.
It is important to be honest about limitations. Most trials last months rather than decades, and very long-term data in healthy people consuming extreme intakes are limited. However, there is currently no good evidence that ordinary use of whey protein — one or two servings a day within a sensible total protein intake — harms healthy kidneys.
Hydration matters more than many realise. Higher protein intakes increase urea production and therefore urine output. Drinking enough fluid is a simple, sensible habit, especially in hot weather or during heavy training.
The liver and whey protein
The liver processes amino acids from every protein you eat, regardless of whether it comes from a shaker or a steak. There is no plausible mechanism by which whey, at normal intakes, would be uniquely toxic to a healthy liver.
Some research has even explored whey in metabolic liver disease, given its role in supporting glutathione synthesis and helping weight management, though findings are preliminary and not a reason to self-treat.
Where liver injury does occur, the culprit is usually something else. The US Drug-Induced Liver Injury Network found that bodybuilding supplements accounted for a notable share of supplement-related liver injury, but these were overwhelmingly products containing anabolic steroids or other undeclared compounds rather than plain protein (Navarro et al., 2014).
| Situation | Liver or kidney risk from whey | Comment |
|---|---|---|
| Healthy adult, normal intake | No evidence of harm | Total protein matters more than its source |
| Chronic kidney disease | Potentially relevant | Protein targets set by the renal team |
| Advanced liver disease | Individual | Protein needs are specific; specialist advice required |
| Use with AAS or oral hormones | Risk comes from the drugs | Hepatotoxicity and kidney injury are documented with AAS |
| Unverified "protein" with additives | Unknown | Contamination risk; choose tested products |
Who should be cautious
Although the picture is reassuring for healthy people, there are groups who should not simply add protein shakes without advice.
- People with diagnosed chronic kidney disease, a single kidney, or a history of kidney stones.
- Those with diabetes or long-standing high blood pressure, both common causes of kidney damage that may be unrecognised.
- People with cirrhosis or other significant liver disease.
- Anyone taking medication that affects the kidneys, such as regular high-dose anti-inflammatories.
For these groups, NICE guidance and the international KDIGO guidelines emphasise individual assessment. Protein restriction is not automatically required in every case, but intake should be planned with a doctor or renal dietitian.
It is also worth noting that frequent use of non-steroidal anti-inflammatories in athletes poses a more realistic threat to the kidneys than protein powder, particularly when combined with dehydration during endurance events.
Blood tests: avoiding false alarms
Many gym-goers panic when a routine blood test shows raised creatinine or liver enzymes. In athletes, both are frequently explained by training rather than organ damage.
Creatinine is a breakdown product of creatine in muscle. Muscular individuals, people using creatine supplements, and anyone who had a large meat meal or a hard session the day before may show higher values. Because eGFR is calculated from creatinine, it may appear artificially low. Cystatin C is a useful alternative marker in such cases.
Similarly, ALT and AST — often called "liver enzymes" — are also present in muscle. Heavy resistance training can raise them for several days, which can be mistaken for liver injury if the clinician is not told about recent exercise.
If a result is abnormal, a repeat test after 48–72 hours without strenuous exercise, with normal hydration and with your supplements disclosed to the doctor, is usually the most informative next step.
Conclusions of the editorial team
For healthy adults, current evidence does not show that whey protein at normal intakes damages the kidneys or liver. The body adapts to higher protein loads, and short- to medium-term studies are consistently reassuring.
The real risks lie with pre-existing organ disease, undiagnosed conditions such as diabetes and hypertension, contaminated products, and the concurrent use of hepatotoxic or nephrotoxic drugs.
Sensible practice is simple: keep total protein within a reasonable range for your goals, drink enough fluids, choose independently tested products and share supplement use with your doctor when you have blood tests.
You may also be interested in our articles on preparing for a creatinine test, on how much protein athletes really need, and on liver enzymes after training.
References
- Martin WF, Armstrong LE, Rodriguez NR. Dietary protein intake and renal function. Nutr Metab (Lond). 2005;2:25.
- Devries MC, Sithamparapillai A, Brimble KS, et al. Changes in kidney function do not differ between healthy adults consuming higher- compared with lower- or normal-protein diets: a systematic review and meta-analysis. J Nutr. 2018;148(11):1760–1775.
- Antonio J, Ellerbroek A, Silver T, et al. A high protein diet has no harmful effects: a one-year crossover study in resistance-trained males. J Nutr Metab. 2016;2016:9104792.
- Navarro VJ, Barnhart H, Bonkovsky HL, et al. Liver injury from herbal and dietary supplements in the U.S. Drug-Induced Liver Injury Network. Hepatology. 2014;60(4):1399–1408.
- Kalantar-Zadeh K, Fouque D. Nutritional management of chronic kidney disease. N Engl J Med. 2017;377(18):1765–1776.
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
