For decades, the standard dietary advice for preventing or managing high blood pressure (hypertension) has been simple: eat less salt. This recommendation has been codified in medical guidelines and public health campaigns worldwide, leading millions to meticulously track their sodium intake. However, according to nephrologist Dr. Jason Fung, the scientific foundation for this low-salt mandate is far weaker than most people realize.
In his analysis, Dr. Fung argues that a close examination of the evidence reveals significant biases, flawed interpretations of landmark studies, and contradictions from real-world data, suggesting that salt is not the villain it has been made out to be.
The Initial Cracks in the Low-Sodium Doctrine
The idea that reducing salt is a panacea for hypertension has been taught to physicians, dietitians, and the general public for nearly half a century. Yet, a crucial challenge to this consensus came from a surprising source: the U.S. Institute of Medicine (IOM).
When evaluating the comprehensive body of evidence, the IOM concluded that there was a “lack of evidence of benefit and concern for harm” for recommending very low sodium intakes. This statement suggested that a dogmatic approach to extreme salt restriction was not only unsupported by robust science but could potentially carry its own risks.
While some meta-analyses of clinical trials do show that a low-salt diet can result in a modest reduction in blood pressure (e.g., a drop of about 5.4 mmHg systolic), Dr. Fung highlights that these summaries often fail to account for a critical issue: publication bias.
The Skewed Funnel of Evidence
When looking at the collective data on salt reduction, researchers must use statistical tools like a funnel plot to check for bias. A clean funnel plot shows symmetry, where both small and large trials show a similar average effect.
However, Dr. Fung points to analysis showing that the salt and blood pressure data is asymmetric. Small trials that showed a significant blood-pressure-lowering effect were likely to be published, while small trials that showed no effect often languished unpublished. This creates a systemic bias, leading the total body of evidence to appear more positive than it truly is, fostering the belief that salt restriction is universally effective when the largest, most reliable studies show little or no impact.
Revisiting the Intersalt Study
The fear of salt largely stemmed from the Intersalt study, a massive 1988 investigation that measured salt consumption and blood pressure across 52 groups in 32 countries. Its initial conclusion—that blood pressure rises steadily with salt intake—cemented the low-sodium movement.
However, the study contained a major analytical flaw: the inclusion of four isolated, indigenous populations (like the Yanomami and Zingu Indians) who lived as hunter-gatherers.
- Extreme Outliers: These groups ate extraordinarily little salt (sometimes less than a few millimoles per day) and had exceptionally low blood pressure that did not rise with age.
- Unfair Comparison: Critically, their lifestyles were completely different from modern society (diet, activity level, stress, processed foods). Comparing them to an average person living in New York or London is scientifically questionable.
The Reversal
When the Intersalt data was re-analyzed in 2015, excluding these four outlier populations, the initial conclusion dramatically reversed. For the general, modern populations studied, the link between salt and blood pressure virtually disappeared. In some analyses, as salt intake increased, blood pressure slightly decreased. This re-evaluation demonstrated that the entire paradigm of salt restriction was built on data skewed by a handful of unrepresentative groups.
The True Culprit: The Processed Food Hypothesis
If salt isn’t the primary driver of hypertension for most people, what is?
Dr. Fung suggests that salt is likely just a marker for a much larger dietary problem: ultra-processed foods.
Processed foods are designed to be hyper-palatable and long-lasting, meaning they are loaded with several unhealthy components: - High Salt: Used for preservation and flavor.
- High Sugar/Refined Carbs: Contributes to insulin resistance, a known driver of hypertension.
- Artificial Ingredients and Preservatives: Used for shelf stability and texture.
In this context, high salt intake is merely an indicator that a person is eating a diet dominated by packaged snacks, fast food, and ready-made meals—a diet where the combination of sugar, refined seed oils, and low nutrient density may be the true cause of poor metabolic health and rising blood pressure.
The Japanese Paradox
Global evidence further supports this distinction. Dr. Fung notes that Japan consistently has one of the highest salt intakes in the world, largely due to a diet rich in traditional foods preserved with soy sauce, miso, and sea salt. If the low-sodium hypothesis were correct, Japan should have an epidemic of hypertension.
In reality, Japan has a lower rate of hypertension than countries like the United States. This “paradox” suggests that when salt is consumed in the context of a traditional diet with whole foods, its effects on blood pressure are benign, or at least heavily mitigated.
The overall takeaway is that the decades-old mandate to restrict salt must be approached with skepticism. The focus for lowering blood pressure should arguably shift away from salt shakers and toward eliminating ultra-processed foods and embracing a whole-food diet, regardless of the sodium content.
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