Just what the wellness community needed—yet another study questioning what we thought we knew about nutrition and health.
When results of the massive, multicontinent “PURE” (Prospective Urban Rural Epidemiology) nutrition study were published, headlines blared:
- “Huge new study casts doubt on conventional wisdom about fat and carbs” (PBS).
- “Massive food study puts current nutrition standards into question” (Mother Nature Network).
But not so fast. A closer inspection shows the study’s findings support what we already know.
PURE researchers explored global nutrition factors associated with cardiovascular disease, heart attack and stroke, and cardiac and all-cause mortality.
To do that, the scientists collected self-reported food-frequency questionnaires from 135,335 people in 18 countries across five continents, representing low-, middle- and high-income countries. They followed the participants for a median of 7.4 years and probed the relationship between reported nutrition intake and health outcomes.
The researchers then published three studies in The Lancet in August 2017:
- The first looked at the relationship between cardiovascular disease and eating fruits, vegetables and legumes. They concluded that “higher fruit, vegetable and legume consumption was associated with a lower risk of non-cardiovascular and total mortality. Benefits appear to be maximum for both non-cardiovascular mortality and total mortality at 3–4 servings per day.”
- The second looked at the association of fat and carbohydrate intake and cardiovascular disease and mortality. It concluded that “high carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to total mortality . . . [and] were not associated with cardiovascular disease, myocardial infarction or cardiovascular disease mortality, whereas saturated fat [had] an inverse association with stroke.”
- The third looked at the relationship of macronutrient intake and blood lipids. It concluded that “reducing saturated fatty-acid intake and replacing it with carbohydrates has an adverse effect on blood lipids. Substituting saturated fatty acids with unsaturated fats might improve some risk markers, but might worsen others.”
It is difficult to draw globally applicable conclusions from these studies, at least in part because of questionable accuracy of the dietary data collected. As David Katz, MD, MPH, FACP, FACPM, FACLM, director of the Yale University Prevention Research Center, pointed out in his review of the study, there was marginal correlation between the food-frequency questionnaire that all participants completed and the 24-hour dietary recall completed by a subgroup of participants (HuffPost 2017). The Harvard T.H. Chan School of Public Health’s response noted that participants from China, who accounted for almost one-third of the total study participants, reported nearly 18% of total calories from fat, while other surveys have found that the typical Chinese person consumes about 30% of calories from fat.
In addition, there is massive variability in the types of foods eaten around the world, especially in low- versus high-income countries. Researchers did not differentiate between types of carbohydrates, though clearly fruits, vegetables and legumes (which are mostly carbohydrate) have substantial nutritional differences from white rice, a low-nutrient staple in many of the low-income countries studied. The health benefits of fruits, vegetables and legumes are well recognized, yet these foods continue to be underconsumed in the U.S.
The researchers did break down components of fat (though not trans fat, the most lethal of them all) and found data consistent with what we already know—replacing saturated fat with carbohydrate does not make people healthier. However, randomized trials have shown that replacing saturated fat with polyunsaturated fat does improve health, but the PURE researchers did not do that analysis. Also, participants who ate the most total and saturated fat still consumed less than the typical American, negating any suggestion that Americans should eat more of these fats to improve their health.
In sum, U.S. nutrition recommendations should not change in light of the PURE study. Indeed, the standard advice still echoes Michael Pollan’s simple, three-sentence edict: “Eat food. Not too much. Mostly plants.”