Protein: it’s the word on every fitness enthusiast’s lips and the centre of countless health debates. For years, a nagging claim has floated around—that eating too much protein can harm your kidneys. This belief has become so entrenched that many people shy away from high-protein diets out of fear for their kidney health. But here’s the kicker: not only is this myth outdated, but the latest research is revealing that protein might actually protect your kidneys in certain situations. Surprised? You’re not alone.
Dr Layne Norton breaks it down. In his words, “We’ve been telling people to eat low protein if they have CKD for years, but we might have been causing more harm than good.”
Dr Layne Norton is a scientist, pro natural bodybuilder, raw elite powerlifter, and physique coach, among other things. He received his BS in Biochemistry, and his PhD in Nutritional Sciences. Besides being a coach, he also commands his YouTube channel in which he talks about science and fitness intertwined, sometimes breaking down scientific studies that come out so people can make better-informed decisions in their fitness journey.
So, where did this myth come from, why does it persist, and what does science now say about protein’s role in kidney health? Let’s unravel the truth.
The Myth: Protein Damages Kidneys
For years, people with kidney problems were advised to cut back on protein. The rationale? Protein metabolism produces urea, which the kidneys filter out. More protein was thought to mean more stress on the kidneys. Sounds logical, right? Not quite.
This idea largely stems from mechanistic studies that showed protein consumption increased filtration rates in the kidneys. But as Layne points out, “Just because something is working harder doesn’t mean it’s being damaged.”
The Evidence: Protein and Kidney Health
A recent study in the Journal of Nutrition, Obesity and Exercise looked at 14,400 participants, including those with chronic kidney disease (CKD) stages 1–3. They measured mortality over ten years to see how protein intake affected kidney health. Here’s what they found:
- Higher protein intake didn’t harm kidneys in those with normal function.
- In people with CKD, more protein was associated with lower mortality rates. Yes, you read that right—protein was protective.
For every 0.2 grams of protein per kilogram of body weight increase, there was an 8% reduction in mortality risk for people with CKD. Those eating the highest protein amounts (up to 1.6 g/kg) had a 23% lower mortality risk compared to those with the lowest intake (0.8 g/kg).
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Why the Myth Persists
Despite mounting evidence to the contrary, the idea that protein harms kidneys still hangs around in medical and fitness circles. But why? To understand, we need to look back at how this misconception started.
The theory originates from early studies that found high-protein diets increased the workload of the kidneys. These studies noted an increase in something called the glomerular filtration rate (GFR)—essentially, the kidneys’ process of filtering blood. This led to the assumption that making the kidneys work harder might damage them over time. But here’s the flaw: just because an organ works harder doesn’t mean it’s being harmed. Think of it like your heart during exercise—it’s working more, but it’s not being damaged; in fact, it’s often getting stronger.
Another reason the myth endures is the reliance on epidemiological studies, which observe patterns in large populations. These studies sometimes show a correlation between high-protein diets and kidney issues, but correlation doesn’t equal causation. As Layne explains, “Epidemiology is messy. It’s full of confounding variables.” For example, someone eating a high-protein diet might also have other lifestyle habits that contribute to kidney problems, like poor hydration or excessive salt intake. Randomised controlled trials, which remove these confounders, consistently show no harm to healthy kidneys from high-protein diets.
The medical field also tends to err on the side of caution. For decades, doctors have recommended low-protein diets to patients with kidney disease to reduce urea production. While this may be appropriate for patients with advanced kidney failure (stages 4 or 5 CKD), there’s no evidence it benefits those with milder forms of CKD—or people with healthy kidneys. Yet, the advice persists, leaving many people needlessly cutting back on protein.
Animal vs Plant Protein: Does It Matter?
When it comes to protein, not all sources are created equal—or so the myth goes. There’s often a debate about whether plant proteins are healthier than animal proteins, particularly for kidney health. Let’s break it down.
The recent study that Layne discussed found that both plant and animal proteins have protective effects, but plant proteins showed a slightly stronger link to reduced mortality risk. For individuals with CKD, switching from the lowest to the highest intake of plant protein reduced mortality risk by an impressive 42%. Even in those without CKD, plant proteins were associated with a 39% reduction in mortality risk compared to 12% for animal proteins.
So, why might plant proteins come out ahead? It’s not necessarily the protein itself but the company it keeps. Plant-based foods are rich in other nutrients like fibre, antioxidants, and vitamins that contribute to overall health. They’re also lower in saturated fat, which can be beneficial for heart and kidney health.
That said, animal proteins are far from the villain they’re often made out to be. The study found that animal protein also had significant protective effects, particularly when sourced from lean meats or fish. Fish, in particular, stood out for its high omega-3 content, which offers anti-inflammatory benefits. As Layne put it, “I don’t think there’s anything magical about fish; it’s just that people who eat more fish tend to be more health-conscious overall.”
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Here’s the breakdown:
- Animal protein: 12% reduction in mortality risk per 0.2 g/kg increase.
- Plant protein: 20% reduction for people with CKD, and a staggering 39% for those without CKD.
Ultimately, the best approach is a balance. Incorporating both plant and animal proteins into your diet ensures you get a diverse range of nutrients. And as Layne emphasises, what really matters isn’t whether your protein comes from plants or animals but that you’re getting enough to support your health.
Protein Intake as We Age
Ageing changes everything—our metabolism, muscle mass, and even how our bodies process protein. This makes protein intake especially crucial as we get older, but the amount we need can vary depending on our age group.
For adults under 75 years old, the study found that protein’s benefits plateau around 1.2 grams per kilogram of body weight per day. Eating more than this doesn’t seem to offer additional benefits, likely because younger adults are generally better at synthesising protein for muscle repair and other bodily functions.
However, for those over 75 years old, the story is different. In this group, protein benefits continue to increase linearly up to 1.6 grams per kilogram per day. Why? Older adults face unique challenges, such as a natural decline in muscle mass (sarcopenia) and a less efficient muscle protein synthesis process. This means they require more protein to maintain muscle strength and overall health.
Layne also points out that older adults who consume more protein are often healthier overall. “It could be a bit of reverse causality,” he notes. “People in better shape are able to eat more protein.” Regardless, the data strongly suggest that maintaining or even increasing protein intake is a smart move as we age.
For older adults, the benefits of protein go beyond preserving muscle mass. It’s protective against age-related declines in physical function, supports immune health, and even reduces the risk of falls and fractures. So, if you’re over 75, don’t shy away from that extra serving of chicken or a hearty lentil stew—your body will thank you.
So, to make sure you got this right:
- Under 75 years: Protein benefits plateau at around 1.2 g/kg/day.
- Over 75 years: Protein benefits are linear up to 1.6 g/kg/day. Muscle loss (sarcopenia) and reduced protein synthesis in older adults likely make higher intake more beneficial.
The Takeaway: Rewriting the Narrative
Layne Norton sums it up perfectly: “We need to shift the framework of how we think about kidney disease away from this dogma that protein is bad.” The evidence is clear—protein doesn’t just not harm the kidneys; it may actually help protect them, even for those with CKD.
If you’re worried about your kidneys and protein intake:
- Consult a nephrologist for personalized advice.
- Don’t automatically jump to a low-protein diet—it might do more harm than good.
- Focus on a balanced diet with high-quality protein sources.
The bottom line? Protein is an essential nutrient with a protective edge, not a dietary villain. Let’s toast to that with a protein shake!
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