This is the perfect example of a news release that cries out for deeper explanation of the study it’s based on, but ends up being given short shrift by the journal publishing the research. The possibility that an overall healthy diet could lead to significantly better health outcomes for people suffering from chronic kidney disease is an important contribution to the science around diet, and yet we are not given quite enough facts or context about the study to know how to evaluate the power of the findings.
The published report is an analysis of seven previously completed studies. The analysis set out to look for any associations between dietary patterns and kidney failure or mortality among adults with chronic kidney disease. As we keep reminding readers when news releases and news articles don’t mention it: association does not equal causation. The release would also have benefited from a mention of possible harms, and a discussion of cost, alternatives and what makes the finding novel.
Outcomes in chronic kidney disease are exceptionally poor, and any potential lifestyle modification that can attenuate this risk has significant public health implications.
The release could have explored two aspects of costs: the costs on a per-patient or per-month basis of treating chronic kidney disease and also the costs of eating healthy the way the people in this study did, but we suspect there is little data available on the latter.
The news release does provide some numbers around the benefits, but they are mostly in relative terms, not allowing reporters or other readers to assess how many people really ended up benefiting from the healthy diets. It says, for example, “In 6 studies, healthy dietary patterns were consistently associated with a 20% to 30% lower rate of mortality, with 46 fewer deaths per 1000 people over 5 years.” It’s hard to understand from this sentence what this means. If it is a range from 20% to 30% lower mortality rates, does this mean that “46 fewer deaths per 1,000 people” is the average reduction in mortality? And this is 46 fewer deaths than what? Than 100? Than 900? Precision would have helped here.
The release does not discuss any harms. Some of the “classic” dietary recommendations have a small harm profile (potassium, protein), and this is also not discussed.
The release does not provide any caveats around this type of retrospective meta-analysis of observational studies, specifically that such studies are incapable of proving that healthy diets caused better outcomes. Nor does it give any qualifications on any of the studies that were included as part of the meta-analysis. Instead, it provides the impressive statement that the researchers “analyzed the medical literature, finding seven relevant studies that included a total of 15,285 participants.” That seems like a lot of people, but the facts around the specific studies that were included matter. What types of people? How long were they were studied? What, if any, controls were there around what they ate, medications they took, the way they exercised, etc.? They also discuss the findings from six studies showing improved outcomes, but do not address the findings of the seventh study. Was it left out due to an absence of effect or some other reason?
There is no disease mongering in the release.
The release says that the authors had no financial conflicts of interest.
The release alludes to the standard dietary recommendations for people with chronic kidney disease and how hard those recommendations are to follow. But it does not provide us enough information to feel like a true comparison, nor does it discuss the controversies surrounding those recommendations.
The availability of healthy dietary options is one of the main points of the release.
The release does state reasonably that “In the absence of randomized trials and large individual cohort studies, this study is the best available evidence to drive clinical decision-making by patients and doctors on whole dietary approaches in chronic kidney disease.”
There is no unjustifiable language in the release.