Study in Lancet Challenges Diet Wisdom About Fat, Vegetables

That BLT you had for lunch? Turns out it’s not the bacon that should worry you. The lettuce and tomato? No, they’ve always been OK. The culprit? Let’s hope you had it on whole wheat, and just a regular sandwich. The club with the extra bread slice—there’s carbohydrates you don’t need.

Maybe you know this already, but researchers reporting in The Lancet have confirmed it after poring over data from 135,000 adults in 18 countries. And not just the usual places like the United States and Europe, but also far-flung places in the Middle East and Southeast Asia, offering a rich mix of ethnic backgrounds and incomes, education levels, and lifestyles. The study, called PURE (Prospective Urban Rural Epidemiology), followed people for an average of 7.4 years to see what people ate and who developed cardiovascular disease and later died.

In short, the results point to the adage, “everything in moderation.” The lowest risk of death was among those with 3 to 4 servings (or 375 to 500 grams) of fruits and vegetables and legumes a day. Adding more than that offered little benefit. By contrast, there were great differences between high fat and low fat, and high carb and low carb.

The study found that those with the highest intake of dietary fat—35% of daily calories—were 23% less likely to have died than those who consumed just 10% of daily calories from fat. What accounts for this? Those with diets top-heavy in carbohydrates (77%) were more likely to have died than those with low-carb diets (46% of calories). However, this was not necessarily accompanied by a higher risk of cardiovascular disease.

The PURE study was produced by researchers from the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences in Hamilton, Canada. Results were presented Tuesday at the European Society of Cardiology in Barcelona, Spain.

The researchers said the results are consistent with observational results about certain populations. They are sure to add to the ongoing controversy about the US Dietary Guidelines for Americans. Critics have argued for years that lobbyists for the grain industries helped create the now-discarded “food pyramid," which recommended lopsided servings of breads and cereals, at the expense of fats.

In fact, a collaboration between Virta Health and Indiana University Health has shown that a nutritional intervention that focuses on decreasing carbohydrates can help patients with type 2 diabetes reduce their glycated hemoglobin by improving insulin resistance.

Mahshid Dehghan, the study’s lead author for the study and an investigator at PHRI, said that guidelines developed in Western countries more than 40 years ago, when fat was nearly 45% of the diet, sought to drive down fat’s share of the calories without thinking about what would replace it. While guidelines often recommended 5 or more servings of fruits or vegetables, for many this proved too expensive or unrealistic, and people ended up eating more starches, including potatoes and breads. The consumption of fat is now around 31% and saturated fat is about 11%, the authors said.

Andrew Mente, an investigator at PHRI and an associate professor of the Department of Health Research Methods, Evidence and Impact at McMaster, said in a statement, "Most people in the world consume 3 to 4 servings of fruits, vegetables and legumes a day. This target is likely more affordable and achievable, especially in low and middle income countries where the costs of fruits and vegetables are relatively high."

"The findings of these studies are robust, globally applicable and provide evidence to inform nutrition policies. This is relevant because in some parts of the world nutritional inadequacy is a problem, whereas in other parts of the world nutritional excesses may be the problem," he said.

Reference

Miller V, Mente A, Dehghan M, et al. Fruit, vegetable, and legume intake, and cardiovascular disease and deaths in 18 countries (PURE): a prospective cohort study [published online August 29, 2017]. Lancet. DOI: http://dx.doi.org/10.1016/S0140-6736(17)32253-5.