David Spence is a professor of neurology and clinical pharmacology at Western University and a director at the Stroke Prevention & Atherosclerosis Research Centre, Robarts Research Institute in London, Ont. David Jenkins is the Canada Research Chair in the department of Nutritional Sciences, Faculty of Medicine, University of Toronto. He has consulted and received research funds from industry to explore the effects of plant food components and plant-based diets on health.
This is the time of year we tend to consider a change in diet. There has been a lot of confusion in recent years about what constitutes a healthy diet, with many people advocating and espousing a ketogenic diet, similar to the Atkins diet: a low-carbohydrate, high-fat/high-cholesterol diet (HF/HC). Since most North Americans will die of a heart attack or stroke if they don't die young from another cause, this is a big mistake.
In 2016, there were large headlines trumpeting that "we can eat cholesterol now; the new U.S. guideline says so." But that's not what the guideline said. It said that there were insufficient data on which to base a specific limit to daily cholesterol intake, as in the past, but the intake of cholesterol should be as low as possible within the recommended eating pattern.
That a high fat/high cholesterol (HF/HC) diet increases coronary risk has been known for many years. The low-fat diet was dreamed up by a committee designing a diet to reduce fasting levels of cholesterol because in those days "fat" was considered to be "saturated fat." Fasting lipid levels are not just about diet – they are determined mainly by how much cholesterol your liver makes overnight. For approximately four hours after a HF/HC meal, there is a state of oxidative stress, and that damages your arteries. In the Seven Countries Study, which studied men in several regions since 1958, it was recognized that in Crete the coronary risk was 1/15th what it was in Finland, and only 40 per cent of that in Japan. The percentage of calories from fat was 40 per cent in Crete, 38 per cent in Finland and 10 per cent in Japan. The difference was that in Crete the fat was mainly olive oil, whereas in Finland it was animal fat.
Although a vegan diet may possibly be as good or even better than the Mediterranean diet for preventing strokes and heart attacks, that theory has yet to be tested. The best current evidence for prevention of heart attacks is for the Mediterranean diet, which is high in beneficial oils (olive and canola), high in whole grains, fruits, vegetables and legumes (beans, lentils, peas, nuts etc.), and much lower in cholesterol, saturated fat and trans fats than the traditional Western diet. In a retrospective article in 1995, Ancel Keys, the leader of the Seven Countries Study, described the Mediterranean diet as follows: "The heart of this diet is mainly vegetarian, and differs from American and northern European diets in that it is much lower in meat and dairy products and uses fruit for dessert."
A study that clarifies what is the best diet for weight loss and diabetes was done among overweight residents of a nuclear facility in Israel, who were randomized to a low-fat versus a low-carb HF/HC (Atkins) diet, versus the Mediterranean diet. Weight loss was identical on the Mediterranean diet and the low-carb HF/HC diet, and both were better than the low-fat diet. The key finding, though, was that the Mediterranean diet was clearly the best for lowering blood sugar, fasting insulin levels and something called insulin resistance (a prediabetic state).
Most importantly, the evidence from two studies done in the 1990s shows that the Mediterranean diet reduces the risk of heart attacks and strokes. In the Lyon Diet Heart Study, in patients who had survived a heart attack, the Mediterranean diet reduced recurrent heart attacks by more than 60 per cent in four years compared with a low-fat diet. This was twice the effect of simvastatin (a 40-per-cent reduction of heart attacks in six years) in the Scandinavian Simvastatin Survival Study, a contemporaneous study also in survivors of heart attacks. In the 2003-2011 Spanish PREDIMED study, a Mediterranean diet reduced cardiovascular events by 30 per cent in five years, among patients who had not yet experienced a heart attack or other cardiovascular event. The Mediterranean diet supplemented with nuts reduced stroke by 47 per cent in five years.
So the healthiest diet is the Mediterranean diet – a high-fat/low-glycemic index diet. This is why recent guidelines – the 2016 U.S. guideline, and the Canadian guideline now in development – are moving toward a more plant-based pattern of eating. We should limit red meat, avoid egg yolks and have three vegetarian days a week.