How evidence-based are dietary advice guidelines

Introduction

Is nutritional science evidence-based? Smith concludes that ‘from low fat to Atkins and beyond, diets that are based on poor nutrition science are a type of global, uncontrolled experiment that may lead to bad outcomes [Ref]. Mayer says that ‘prescribing a diet restricted in carbohydrates to the public was “equivalent to mass murder”[Ref]. Nina Teicholz’s book, The Big Fat Surprise chronicled the bad fat saga.[Ref]. The recent 2015-2020 dietary  for Americans have introduced significant changes in recommendations especially for dietary fat [Ref].

Ancel Keys who established the link between cholesterol and heart disease in the 1960s with the ‘seven-country study’ advocated a low-fat, low cholesterol diet to prevent heart disease. However Keys’s study was flawed because he omitted contradictory data from fifteen countries which he had gathered, leading to criticism of its findings at the time. Nonetheless, the American Heart Association strongly promoted a low-fat diet, which included advocating margarine instead of butter and avoidance of eggs.

Next came the sugar scandal. Sugar is in three-fourths of all packaged foods. Since the 1950s, the sugar industry has promoted the idea that a calorie is a calorie, and that eating a calorie’s worth of sweets is no more likely to make someone obese than any other food. The sugar trade association put the blame for heart disease on saturated fat. For decades, the sugar industry has been commissioning researchers, including the influential Ancel Keys, to echo these claims. The three Harvard scientists who published the classic review paper indicting dietary fats for heart disease in the New England Journal of Medicine in 1967 were paid by the Sugar Association. The trade association also opposed new labels on food that would disclose how much sugar had been added to packaged foods. That problem continues in the present day. In 2015, we learned that Coca-Cola worked with scientists to squash the notion that sugar had anything to do with obesity. This is not a problem only with the sugar industry. 

Marion Nestle has shown that, in nearly two hundred food studies, those funded by industry (compared to no industry support) had a positive ratio of thirteen to one. Food “science” is not only compromised by a dearth of hard evidence but also colored by bias.

Nobody really questioned ‘Salt reduction’ until and it was associated with hypertension and heart attacks. Less maybe good for weight loss because the food becomes so tasteless that Sir George Pickering once said, “To stay on it requires the asceticism of a religious zealot.”  A 2018 study of more than 95,000 people in eighteen countries, while verifying a modest increase of blood pressure (with increasing sodium ingested as reflected by urine measurement), showed that the bad outcomes only occurred when sodium intake exceeded 5 grams per day. The average American takes in about 3.5 grams of sodium per day. In fact, for less than 5 grams per day of sodium, there was an inverse correlation between sodium intake and heart attack and death.

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