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“Available evidence suggests that carbohydrate restriction and ketosis afford benefits to kidney function.” (Athinarayanan et al., 2024)
Dietary carbohydrate restriction is well established to be beneficial for reversing metabolic syndrome and other conditions related to insulin resistance, such as polycystic ovarian syndrome (PCOS) and nonalcoholic fatty liver disease (NAFLD). However, there are still some pervasive myths about ketogenic diets that make patients and practitioners alike wary to try this low-carb, higher fat way of eating.
One of the myths that persists despite mounting evidence to the contrary is that keto is harmful for the kidneys. But recent research indicates that not only is carbohydrate restriction not harmful for kidney function, but rather, it appears to be beneficial. Let’s take a closer look.
Diabetes and hypertension are the two biggest causes of chronic kidney disease (CKD) and kidney failure. According to the American Kidney Fund, diabetes and hypertension are responsible for 47% and 27% of new cases of kidney failure, respectively. Among adults with diabetes, type 2 accounts for 90-95% of cases, so, taken together, type 2 diabetes and hypertension are responsible for nearly 75% of all cases of kidney failure.
Considering that carbohydrate restriction has been shown to put type 2 diabetes into remission and improve hypertension (including leading to discontinuing of antihypertensive medication), keto diets may support healthy kidney function by improving or completely reversing the two biggest causes of CKD.
At best, conventional treatment for CKD slows the disease progression. Kidney function continues to decline; it just declines more slowly. On the contrary, a very low-calorie ketogenic diet was shown to actually restore healthy kidney function in 27% of subjects with mild CKD. The study diet consisted partially of meal replacements and calorie intake was very low for part of the intervention, so this may not be reflective of a more standard keto diet where people choose their own food, but this still demonstrates that being in a ketogenic state didn’t only stop the disease from getting worse – it actually made it better.
Fortunately, kidney function has been studied in subjects following more “real world” approaches to low-carb and keto, and ad lib low-carb diets show a beneficial effect on the kidneys. Compared to low-fat and Mediterranean diets that both called for calorie restriction, a low-carb diet unrestricted in calories was shown to have the biggest beneficial effect on kidney function.
In patients with moderately to severely reduced kidney function, a low-carb diet resulted in either no change to eGFR or an improvement. In patients with type 2 diabetes and normal kidney function or mild CKD, markers of kidney function improved after following a low-carb diet.
Keto diets shine even for kidney disease driven primarily by genetic mutations. In a study of keto for autosomal-dominant polycystic kidney disease – the most common genetic cause of kidney failure – keto resulted in improved kidney function while subjects following their usual diet or doing periodic fasting (fasting three days per month) continued to experience a decline in kidney function.
A review published earlier this year in Clinical Kidney Journal made a strong case in favor of ketogenic diets as an intervention for patients with CKD. Having reviewed the evidence, they stated:
“Altogether, the available clinical studies and experience to date suggest that KMT [ketogenic metabolic therapy] is feasible in patients with CKD and does not harm the kidneys but rather has beneficial effects including CKD remission.”
Despite the evidence supporting the use of keto diets in patients with kidney disease, there may still be lingering questions about protein intake.
It’s important to note that keto is not a high-protein diet. The fundamental principle of a ketogenic diet is maintaining a very low carbohydrate intake – not gorging on protein. But even among individuals who consume higher protein diets, there’s no evidence that high-protein diets increase risk for CKD. In a paper that covered 13 risk factors for CKD, there was no mention of a high protein intake.
The U.S. Centers for Disease Control and Prevention (CDC) recommends keeping the kidneys healthy by managing blood sugar and blood pressure. There is no suggestion to limit dietary protein. High protein intake is also absent from the National Kidney Foundation’s list of causes of CKD.
If high protein intakes don’t cause kidney disease, what about people who already have CKD? Here, too, the conventional guidelines appear to be based on weak evidence. As we covered in a previous article, calls are growing to rethink protein restriction for individuals with CKD because this has little effect on disease progression.
On the other hand, carbohydrate restriction has been shown to be beneficial for slowing disease progression or improving CKD even when protein intake is generous. In a study of people with type 2 diabetes and diabetic nephropathy, a low-carb diet with 25-30% of calories from protein – much more than is typically recommended for individuals with compromised kidney function – was more effective for slowing disease progression and reducing deaths compared to a low-protein, high-carb diet. Higher protein approaches have been employed in several other studies looking at low-carb or ketogenic diets for CKD and benefits were still observed, even if the protein sources were predominantly animal foods rather than plant foods.
The authors of a paper published earlier this year in BMJ Open Diabetes Research & Care concluded:
“There is a considerable body of research suggesting that a very low carbohydrate ketogenic diet is safe in individuals with moderately diminished kidney function, even in studies that had higher protein intake than what is recommended for kidney disease and diets that are not plant-based. The diet can be safely prescribed in patients with T2D for treating and remitting diabetes even if they have underlying stage 2 or 3 CKD or reduced kidney function.” (Athinarayanan et al., 2024)
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