Two complementary papers based on a large cohort study show that fats - both saturated and unsaturated - may not be as harmful as previously thought. Carbohydrates can have a more damaging impact, but should still be consumed in moderation, and a stable intake of fruits and vegetables is a must.
A large cohort study, the Prospective Urban Rural Epidemiology (PURE) study, at the Population Health Research Institute of McMaster University in Canada, has paved the way for a better understanding of what makes healthful, balanced diets.
The study collected data from 135,335 people with ages between 35 and 70, from 18 different countries across five continents, covering regions from the Middle East, South America, Africa, China, North America, Europe, and South Asia.
Participants were asked to provide details about their socioeconomic situation, lifestyle, medical history, weight, and blood pressure, among others. They were followed up for a median period of 7.4 years, and relevant information regarding cardiovascular disease and death risk was collected periodically.
PURE data was recently used in two complementary studies, one looking at the effects of macronutrients, especially fats and carbohydrates, on people's health and life expectancy, and the other exploring the global importance of fruit and vegetable intake.
The first study, whose principal author is Dr. Mahshid Dehghan, from McMaster University, shows that diets that include a moderate fat intake and which avoid a high intake of carbohydrates are linked with a reduced risk of mortality. An
Moderate fat intake is beneficial
For the purpose of this study, data on the participants' daily dietary choices and habits were analyzed alongside other relevant information, to allow the researchers to calculate how much energy was provided by fat, carbohydrate, and protein intake in each individual's case.
A surprising finding, which appears to contradict existing beliefs about healthy dietary practices, was that a higher total fat intake - providing 35.3 percent of energy - was linked with a 23 percent lower risk of mortality than a lower fat consumption.
At the same time, a high intake of carbohydrates - providing 77 percent of energy - was found to correlate with a 28 percent higher mortality risk.
Total fat intake was not significantly associated with a risk of mortality linked with cardiovascular disease, and carbohydrate intake was not associated with cardiovascular disease at all.
These findings also have country-specific and cultural-specific implications, and may be related to the income level of each country, the researchers say.
"A decrease in fat intake automatically led to an increase in carbohydrate consumption and our findings may explain why certain populations such as South Asians, who do not consume much fat but consume a lot of carbohydrates, have higher mortality rates," suggests Dr. Dehghan.
Three to four a day
Based on relevant PURE data, Miller and her colleagues calculated how many servings of fruits, vegetables, and legumes the participants consumed on a regular basis.
The researchers defined "one serving" as 125 grams of fruits or vegetables, or 150 grams of cooked legumes, in accordance with recommendations from the United States Department of Agriculture.
Potatoes, other tuberous crops, legumes, and fruit and veg juices were not included as vegetables. The study took "legumes" to refer to beans, black beans, lentils, peas, chickpeas, and black-eyed peas.
The researchers found that three to four servings of fruits and vegetables per day correlated with the best health outcomes.
"Our study found the lowest risk of death in those who consumed three to four servings or the equivalent to 375 to 500 grams of fruits, vegetables and legumes per day, with little additional benefit for intake beyond that range. Additionally, fruit intake was more strongly associated with benefit than vegetables."
Miller and her team also noted that, on a global level, fruit, vegetable, and legume intake is of three to four servings per day, despite the fact that many state dietary guidelines recommend a "five-a-day" regime.
The researchers suggest, however, that eating five servings of fruits and vegetables per day may be unattainable in many middle- and low-income countries, where these foods are expensive for the general population. This appears to be the case in regions such as South Asia, China, Southeast Asia, and Africa.
The fact that the study was conducted with participants from across five continents, the researchers argue, gives extra credibility to research, showing that plant-based diets are more healthful.
"The PURE study includes populations from geographic regions which have not been studied before, and the diversity of populations adds considerable strength that these foods reduce disease risk," says Miller.
Another important finding of Miller and her team's study was that raw vegetables are more healthful than cooked ones, a distinction which is not usually made in dietary guidelines across the world. This "raw" versus "cooked" debate also taps into country-specific dietary practices, the researchers say.
"Raw vegetable intake was more strongly associated with a lower risk of death compared to cooked vegetable intake, but raw vegetables are rarely eaten in South Asia, Africa and Southeast Asia. Dietary guidelines do not differentiate between the benefits of raw versus cooked vegetables - our results indicate that recommendations should emphasize raw vegetable intake over cooked," explains Miller.
The findings of the two related studies add some important considerations regarding the effects of different diets on health outcomes, especially as they outline the global framework of dietary practices.
The researchers also presented the results of their studies yesterday, at the specialist Congress of the European Society of Cardiology in Barcelona, Spain.