Dietary Dogma: Tested and Failed

There were two recent studies that looked at diets. One compared the 2010 Dietary Guidelines against the typical American diet. The other compared multiple dietary interventions: Mediterranean diet, low-fat diet, and low-salt diet. This covers the main diets advocated most often by doctors, nutritionists, dieticians, and health officials. Yet neither study found a significant overall benefit to any of the recommended diets. That is shocking, when one considers how official experts and major institutions have pushed these diets for decades. The low-fat diet has been a favorite among dietary technocrats for about a half century (The Creed of Ancel Keys).

What these studies didn’t bother to consider is the benefits of traditional foods diet (Weston A. Price & Sally Fallon Morrell), paleo/hunter-gatherer diet, low-carb high-fat diet, ketogenic diet, carnivore diet, etc. Nor any of the related but less well known diets like ketotarian, pegan, etc. Nor related dietary strategies such as fasting, either intermittent or extended, along with calorie restriction. With a narrow focus, the comparisons were limited. Still, it is a powerful judgment that none of the diets that were tested stood out as being all that impressive. What is being brought under doubt represents the key message of authoritative opinion on diet and nutrition. These diets tested (official Dietary Recommendations, Mediterranean diet, low-fat diet, and low-salt diet) are among the best that the collective wisdom of mainstream thought has to offer.

Here is an intriguing point. The first study looked at the 2010 Dietary Guidelines as separate from weight loss, to determine what were the results of the diet itself (besides, even including weight loss, the low-fat diet is one of the worst, as studies show few people drop body fat when adhering to it — see meta-analysis by UK Public Health Collaboration, Eat Fat, Cut The Carbs and Avoid Snacking To Reverse Obesity and Type 2 Diabetes). This officially trumpeted dietary regime, a fad diet that hasn’t been around long by the way, had no noticeable affect on glucose homeostasis, fasting lipids, or type 2 diabetes. Let’s consider another study, as a comparison and to clarify a point (Parker N. Hyde et al, Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss). As with the above mentioned study, body weight was carefully maintained so as to control for that potentially confounding factor. What were the results?

“Despite maintaining body mass, low-carbohydrate (LC) intake enhanced fat oxidation and was more effective in reversing MetS [metabolic syndrome, including type 2 diabetes], especially high triglycerides, low HDL-C, and the small LDL subclass phenotype. Carbohydrate restriction also improved abnormal fatty acid composition, an emerging MetS feature. Despite containing 2.5 times more saturated fat than the high-carbohydrate diet, an LC diet decreased plasma total saturated fat and palmitoleate and increased arachidonate.”

Interestingly, these particular two studies demonstrate that obesity by itself is not necessarily the problem. Rather, it is a symptom of the problem. Obesity can even be an attempt by the body to compensate in preventing something even worse (Coping Mechanisms of Health). The fundamental problem is the metabolic syndrome itself and the insulin resistance behind it, and any diet that doesn’t directly deal with that will be ineffective. Only some variation of a low-carb diet can accomplish that end.

It’s time to rethink dietary recommendations and guidelines. There are signs this is already happening. The public is already turning toward low-carb diets (Low-Carb Diets On The Rise). And slowly but surely the official position is shifting in this direction (Obese Military?, Weight Watchers’ Paleo Diet, American Diabetes Association Changes Its Tune, Official Guidelines For Low-Carb Diet, & Slow, Quiet, and Reluctant Changes to Official Dietary Guidelines). The evidence keeps accumulating. These recent two studies add to the growing pile. It’s getting harder and harder to ignore the obvious.

* * *

A randomized controlled-feeding trial based on the Dietary Guidelines for Americans on cardiometabolic health indexes
by Sridevi Krishnan et al

To our knowledge, this is the first controlled-feeding trial to test the effect of a food-based dietary pattern following recommendations of the DGA [2010 Dietary Guidelines for Americans]. We measured cardiometabolic disease risk factors in an at-risk female cohort, while maintaining body weight, with the use of foods that are accessible and acceptable to the consumer. The higher quality of the DGA diet relative to the TAD [typical American diet] was confirmed by HEI scores of 98 and 62, respectively. We found that, in the absence of weight loss, consuming a diet based on recommendations of the DGA did not change glucose homeostasis or fasting lipids in our cohort. The 2015 DGA Advisory Committee report concluded that there was moderate evidence for reduction in type 2 diabetes risk associated with nutrient-dense diets (2); however, the results from our short-term intervention trial did not align with this evidence. By design, the intervention did not lead to significant weight loss, and because changes in body weight and body fat can play a role in the pathogenesis of type 2 diabetes (31), this may also explain why improvements in blood sugar control were not observed despite the improvement in diet quality.

Supplements and Diets for Heart Health Show Limited Proof of Benefit
by Anahad O’Connor

When Dr. Khan and his co-authors looked at various diets recommended for cardiovascular prevention, they found a similar lack of solid evidence.

That was certainly the case for low-fat diets, which health authorities have recommended for decades as a way to lower cholesterol and heart disease risk. Dr. Khan and his colleagues found that the most rigorous randomized trials provided no evidence that eating less fat, including saturated fat, had an impact on mortality or cardiovascular outcomes. Low-fat diets have largely fallen out of favor among health authorities in recent years, though the federal government’s dietary guidelines still encourage people to limit their intake of foods rich in saturated fat, such as butter, meat and cheese.

One diet that remains highly touted by health authorities is the Mediterranean diet, with its abundance of whole grains, beans, nuts, fruits and vegetables and olive oil. While clinical trials have found that it reduces cardiovascular risk, some of the major ones have been flawed, and experts who have scrutinized the evidence for the diet have urged caution.

One of the largest and most publicized Mediterranean diet trials, called Predimed and published in 2013, found that it reduced heart attacks and strokes. But last year it was retracted because of methodological problems. The Predimed authors published a new analysis of their data, claiming their conclusions had not changed. But other Mediterranean diet trials have been embroiled in similar controversies. After analyzing data from all the relevant trials, Dr. Khan and his colleagues found that “the totality of evidence did not favor the Mediterranean diet for cardiovascular outcomes.”

“It’s not favorable or harmful,” he added. “It’s just a neutral diet from a cardiovascular perspective.”

The one dietary intervention that seemed to have the most support from randomized trials was lowering salt intake, though the researchers graded the evidence only as having “moderate certainty.” And there was nuance. Low-salt diets reduced mortality from all causes only in people with normal blood pressure. Among people with hypertension, lowering salt intake reduced deaths from heart disease but not from other causes.

Dr. Topol said that in his own clinic he sees a wide range of responses to salt intake. Some people are very sensitive to salt: A small increase in salty foods can have a pronounced effect on their blood pressure. But others can eat salt-laden meals and their blood pressure will hardly budge.

Dr. Topol said he finds diet studies hard to interpret because they rarely take into account the unique way that different people can have markedly different responses to dietary changes, whether it is cutting back on salt or avoiding fat or carbohydrates.

“The problem we have here is that all these studies essentially treat all people as one,” he said. “I think that all these things are going to turn out to be quite heterogeneous. Maybe salt restriction really is beneficial for some, but we haven’t defined the people yet that would drive that.”

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