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Thursday March 22, 2018

It's the kind of breathless nutrition journalism you've come to expect in today's 24-hour, always-on news cycle's thirst for sensation:

  • "Low-fat diet could kill you, major study shows," says the headline in London's Telegraph.
  • "Eating a low-fat diet increases your risk of dying young by 25%," according to The Sun.
  • "Everything we thought we knew is a lie," says one women-centric news website.

Hair-afire journalism aside, the findings of the new study just published in the medical journal The Lancet are contradictory to conventional wisdom on saturated fats, to say the least. Canadian medical epidimiologist Mahshid Dehghan and more than 200 other investigators from around the world undertook an "ambitious" study that collected data on more than 135,000 people from 18 countries across five continents, following their diet and health for an average of 7.4 years.

Here's what they found. On average, those people who got more than a third of their daily calories in the form of fat demonstrated a reduced risk of dying vs. those who got the lowest amount from fat, or about 11 per cent. And as you'd expect—since the only other meaningful dietary source of calories is carbohydrates—people who obtained more than three-quarters of their daily calories from carbohydrates had a 30 per cent higher risk of dying than people who got less than half their energy from carbs.

"Once again," write the Lancet editors in a commentary on the study, "This lack of definitive evidence has left clinicians, scientists, and the public uncertain about the best foods to [recommend] and to eat."

Why this abrupt reversal in thinking about saturated fats, flying in the face of, in the editors' words, "the most enduring and consistent diet restrict saturated fatty acids, by replacing animal fats with vegetable oils and complex carbohydrates (and more recently whole grains)?"

Because it really wasn't a reversal, at least as far as the science is concerned.

In The Lancet article, Dehghan echoes the opinion of a growing number of scientists: The common advice to restrict saturated fatty acids, which has even been incorporated into USDA's dietary guidelines, “is largely based on selective emphasis on some observational and clinical data, despite the existence of several randomised trials and observational studies that do not support these conclusions.” The Dehghan study only reinforces what common-sense nutritional recommendations have long understood. An extremely low-fat, high-carb diet is at least associated with, if not a cause of, an increased risk of death from something other than heart disease, but moderate fat and carbohydrate intakes were not associated with increased risks. In a separate Lancet article, the same group reports that eating specific carbohydrate groups—fruits, legumes and raw vegetables—was associated with a lower risk of death. So the bottom line: Once again, it's likely processed carbohydrates, including added sugars and refined grains, that may be driving the increase in risk.

When it comes to the common sources of saturated fats, the case has never been closed on their relative value vs. their risk of contributing to heart disease. Here's what we know:

Eggs: Eggs have one of the lowest ratios of energy to nutrients as any food, writes British nutritionist Bruce Griffin, and a protein quality that's as good as dairy and better than steak. That must certainly qualify them as good, so the burden of proof has been to settle the question of whether their high cholesterol offsets that good. What we're now coming to understand about the difference between dietary and blood cholesterol has tipped the question in eggs' favor. "After 60 years of research," he says, "a general consensus has now been reached that dietary cholesterol, chiefly from eggs, exerts a relatively small effect on serum LDL-cholesterol and [heart-disease] risk, in comparison with other diet and lifestyle factors. Although some question may still remain about their risk in people who are diabetic, it's likely other dietary components have unfairly clouded that picture against eggs.

Milk and dairy. Despite milk and dairy foods contributing about a quarter of saturated fat intake in western diets, evidence from prospective cohort studies does not support a detrimental effect of milk and dairy foods on risk of heart disease, according to nutritional researcher Julie Lovegrove. The majority of prospective studies and meta-analyses examining the relationship between milk and dairy product consumption and risk of cardio-vascular disease show that milk and dairy products, excluding butter, are not associated with detrimental effects on dying or risk biomarkers that include serum LDL-cholesterol. In addition, there is increasing evidence that milk and dairy products are associated with lower blood pressure and arterial stiffness. These apparent benefits of milk and dairy foods have been attributed to their unique nutritional composition, and suggest that the elimination of milk and dairy may not be the optimum strategy for heart disease risk reduction.

Red meat? Scottish nutritionist Laura Wyness notes red meat has earned its spot in the evolution of the human diet by providing a rich source of not only protein, but protein that's easily available to the body to digest and use. It's micronutrients, particularly iron, are also more bio-available. But what of its notorious saturated fat? Dietary advice to limit red meat has gone too far, write nutritionists from Canada's beef and pork associations in the scientific journal Meat Science—even to the point of causing unintended health consequences. Even as dietary advice to limit red meat has remained standard in developed countries, energy intakes from processed foods have increased dramatically at the expense of nutrient-rich foods. They argue, as the Lancet authors suggest, that research implies the jump in obesity and associated disease in recent decades should be laid at the feet of carbs, not saturated fats in red meat. "It is time for dietary advice that emphasizes the value of unprocessed red meat as part of a healthy balanced diet," they say.

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