Between 1990 and 2010, some of our leading causes of death and disability remained the same. Heart disease was the leading cause of loss of life and health then and remains the leading cause today. Some things got better, like HIV/AIDS, but others got worse, like chronic kidney disease. We saw a doubling in the tens of thousands of deaths and the hundreds of thousands of patients whose kidneys failed completely, requiring kidney transplants or lifelong dialysis.
About one in eight of us now has chronic kidney disease—and most don’t even know it: About three-quarters of the millions of people affected are unaware that their kidneys are starting to fail. This is “particularly worrisome given that early identification provides an opportunity to slow the progression and alter the course of disease.” So, what can we do about it?
In my video Which Type of Protein Is Better for Our Kidneys?, I discuss how the Western-style diet is a major risk factor for impaired kidney function and chronic kidney disease. Also known as “the meat-sweet diet or standard American diet,” it causes an impairment of kidney blood flow, inflammation, subsequent leakage of protein in the urine, and a rapid decrease in kidney function. Table sugar and high-fructose corn syrup are associated with increased blood pressure and uric acid levels, both of which can damage the kidney. The saturated fat, trans fat, and cholesterol found in animal fat and junk food negatively impact kidney function, as well.
The consumption of animal fat can actually alter the structure of the kidney, and animal protein can deliver an acid load to the kidneys, increase ammonia production, and damage the sensitive kidney cells. This is why restricting protein intake is recommended for preventing kidney function decline—though it may be animal protein in particular that may need restricting, not just protein in general. So, the source of the protein, plant versus animal, may be more important than the amount regarding adverse health consequences.
Animal protein intake profoundly affects normal human kidney function, inducing what’s called hyperfiltration, which increases the workload of the kidney. This may help explain why our kidneys fail so often. “Unlimited intake of protein-rich foods, now generally regarded as ‘normal,’ may be responsible for dramatic differences in renal function between modern human beings and their remote predecessors who hunted and scavenged for meat.” Indeed, our kidney reserves are continuously called upon by our sustained, rather than intermittent, excesses of protein. This causes a kind of unrelenting stress on our kidneys that can predispose even healthy people to progressive kidney scarring and deterioration of kidney function. It’s as if we’re always revving our engine into the red. Conversely, intake of an equal quantity of protein from plants doesn’t appear to have the same effects.
We saw in a study that eating meat increases the workload on the kidneys within hours of consumption, but, apparently, processing plant protein is a cinch. That particular study was done with beef, but any animal protein will do. If you eat a meal of tuna fish, pressure on the kidneys goes up within just hours of consumption. Then the researchers switched it up and found that if instead of having a tuna salad sandwich, you have a tofu salad sandwich (with the same amount of protein): no adverse effect.
The same thing happens with eggs and dairy protein—both in people with normal kidneys and people with diseased kidneys.
Short-term studies have indicated that “substituting soy protein for animal protein is associated with less hyperfiltration and [protein leakage]…therefore slowing deterioration of renal function.” However, the long-term effect had not been adequately studied, until 2014. A six-month double-blind, randomized, placebo-controlled trial compared the effects of soy and dairy protein on renal function and determined that “the consumption of whole soy tended to preserve renal function compared with milk placebo in individual with lowered renal function.” Similar results were reported in diabetics. Even just giving isolated soy protein appeared to make things better, compared to dairy protein which made things worse.
Once one’s kidneys have deteriorated to the point that they’re actively losing protein in the urine, a plant-based diet may help come to the rescue. Protein leakage on a standard low-sodium diet was compared to a special supplemented vegan diet. The researchers showed through diet alone, kidney dysfunction could be switched on and off like a light switch depending on what was going into their mouth. See the extraordinary graph in my video.
What is going on? Why does animal protein cause that overload reaction, but plant protein doesn’t? The renal reaction appears to be an inflammatory response triggered by the animal protein. We know this because administration of a powerful anti-inflammatory drug abolished the hyperfiltration, protein leakage response to meat ingestion. Kidney stress has been shown to escalate in response to a meat meal, but that stress level remains low during the meal when supplemented with an anti-inflammatory drug. This confirms the role of inflammation in the impact of animal protein on our kidneys.
This is part of a new, extended series of videos on kidney health, which includes:
I’ve compared plant and animal protein in a variety of ways. See, for example,
Perhaps the most dramatic demonstration was the study I featured in my 2015 annual presentation, Food as Medicine: Preventing and Treating the Most Dreaded Diseases with Diet.
Michael Greger, M.D.
PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: