This morning I read an article published in the New England Journal of Medicine. It is one of their clinical decision papers, where a patient case is presented and a clinical question is proposed. This is followed by a short discussion about the pros and cons of the clinical decision.
The case and clinical problem
The article provides a brief case history. Here are some of the key points I picked out:
- 63 year old Black man, history of well-controlled HTN, CAD and Stage 3B CKD
- Current eGFR 35ml/min, declining ~1ml/min per year
- No family history of kidney disease
- BMI 25
- Patient is asking if he should follow a low protein diet
The clinical problem: To recommend or not recommend a protein diet targeting less than 0.8g/kg
Pro Side: Recommend Low Protein Diet
The authors of the pro-side argument start off by highlighting that current nutrition practice guidelines recommend lowering protein. The specific recommendation is either 0.55-0.60g/kg body weight or 0.28-0.43g/kg body weight if supplemented with ketogenic amino acids. This has been found to reduce the risk of kidney failure, impaired quality of life and death.
Animal and clinical studies have reported that lower protein intake reduces pressure inside the glomerulus, which helps reduce kidney damage. Higher protein intake leads to hyperfiltration and increases kidney damage.
The authors specifically mention the Modification of Diet in Renal Disease (MDRD) study. The second analysis of the MDRD study showed that those eating a low protein diet had slower eGFR decline.
Nutritional adequacy is then discussed, and the authors note that 0.8g/kg is the RDA, and 0.66g/kg is the average requirement. Several studies are mentioned that have shown benefit from the low protein diets, without increased risk of malnutrition or hospitalization.
Con Side: Do Not Recommend Low Protein Diet
The author of the con side highlights that many of the studies demonstrating benefit for low protein diets were conducted before agents such as RAASi and SGLT-2 inhibitors were being used. New pharmalogical options mean it isn’t clear if low protein diets are indicated. Furthermore, the author points out that in this case, dialysis start may be more than 20 years away. So is following a restrictive diet for this length of time is worth the burden?
The author highlights that the original data published from MDRD found no benefit for dietary protein restriction (see below for why the same study appears to be saying 2 different things). And that a Cochrane review reported that low protein diets did not change how many people started dialysis, though may slow kidney function loss.
Just to give a quick background on what is happening with these conflicting descriptions of the MDRD Study:
The MDRD study was original analyzed with an INTEntion to treat. This means that everyone who was told to follow the low protein diet was assumed to be compliant with this recommendation. So even people who didn’t eat a low protein diet were part of the low protein group. When they went back into the data and sorted it, such that only people who followed the low protein diet were grouped into the low protein group, then the low protein diet showed benefit.
The other challenge with low protein diet is adherence and nutritional adequacy. It has been proposed that only 15% of standard clinic patients could comfortably follow a low protein diet. Additionally, the World Health Organization states that the required median protein intake for healthy adults is 0.66g/kg with 0.83g/kg considered the safe level.
What would you do?
As dietitians I think we are acutely aware of how difficult following diets is long term. And I think that we know that there are some patients where a low protein diet would likely be over-whelming and difficult to follow. But, I think we can also think of those patients who are well-resourced and super keen to make any change they possibly can for their health.
So I think it depends. For a patient who comes in explicitly asking about the low protein diet, I would do my best to give them a summary of what we know and don’t know about low protein diets and help them make an informed decision.
After I have given them as much information as I can, then I think it is my job to support them in the decision they make. So, if they are keen for low protein, my job becomes helping them identify what foods contain protein, setting up the right target and ensuring their diet is nutritionally adequate. If they aren’t interested in low protein diets, then my job is to look at other pieces of the diet that they may be willing to work on to meet their health goals.
