Suche
Relation
M. Dhghan, A. Mente, X. Zhang et al. Associations of fat and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study.lancet. 2017;S0140-6736(17):1-13.
Objective
The present study examines whether a high-fat or high-carbohydrate diet is associated with an increase in both cardiovascular disease (CVD) and all-cause mortality.
Draft
Epidemiological cohort study
Participant
Participants included 135,335 adults aged 35 to 70 years who enrolled between January 1, 2003 and March 31, 2013 and were followed for a median of 7.4 years. Since the study aimed to include populations differing in traditional diets and socioeconomic factors, participants were selected from 18 countries (from 5 continents): Canada, Switzerland, United Arab Emirates, Argentina, Brazil, Chile, Cuba, Colombia, Iran, Malaysia, Occupied Palestinian Territories, Poland, South Africa, Turkey, Bangladesh, India, Pakistan and Zimbabwe.
The study authors excluded participants whose follow-up information was unavailable or who already had CVD.
Study parameters assessed
Standardized questionnaires were used to collect information on demographic factors, socioeconomic status (education, income and employment), lifestyle (smoking, alcohol consumption and physical activity), health history and medication use.
For decades, the conventional medical community has recommended that people eat a low-fat, high-carbohydrate diet to prevent cardiovascular disease and early death.
Participants' regular dietary intake was recorded using country- or region-specific validated food frequency questionnaires (FFQs) at baseline and included multiple 24-hour dietary recalls in 60 to 250 individuals from each country as reference for validated FFQs.
Primary outcome measures
The primary endpoints were all-cause mortality and major cardiovascular events (fatal CVD, non-fatal myocardial infarction). [MI], stroke and heart failure). Secondary outcomes included all myocardial infarction, stroke, CVD mortality, and non-CVD mortality.
Key insights
During follow-up, investigators documented 5,796 deaths and 4,784 major cardiovascular events.
The highest quintile of carbohydrate intake (>60% of total calories) was associated with a higher risk of all-cause mortality than the lowest quintile of carbohydrate intake (hazard ratio [HR]: 1.28;P=0.0001). Carbohydrate intake was not associated with an increased risk of cardiovascular disease or mortality.
The highest quintile of total fat intake (>35% of total calories) correlated with 23% lower all-cause mortality compared to the lowest quintile (P=0.0001). Additionally, the individual types of fats consumed were also associated with a lower risk of all-cause mortality. For example, diets containing 10% to 15% saturated fat were correlated with a 14% lower risk of all-cause mortality than those containing the lowest amount of saturated fat (P=0.0088). Diets highest in polyunsaturated and monounsaturated fats were also found to contain 20% (P=0.0001) and 19% (P=0.001) lower overall mortality risk compared to the lowest intake quintiles.
Higher levels of saturated fat were associated with a lower risk of stroke. However, fat intake (total, saturated, or unsaturated) was not significantly associated with the risk of myocardial infarction or cardiovascular mortality.
When 5% of carbohydrate calorie intake was replaced with polyunsaturated fats, an 11% reduction in all-cause mortality and a 16% reduction in non-cardiovascular mortality risk were observed. Replacing carbohydrates with saturated fats was associated with a 20% lower risk of stroke, while intake of polyunsaturated and monounsaturated fats did not appear to affect stroke risk.
Practice implications
Cardiovascular diseases have become a global epidemic. For decades, the conventional medical community has recommended that people eat a low-fat, high-carbohydrate diet to prevent cardiovascular disease and early death. This idea originated primarily from the 1980 study by Ancel Keys, who examined the diet and incidence of CVD in 7 countries. His data suggest that elevated blood cholesterol and dietary saturated fat intake are a major factor in the occurrence of coronary heart disease and the risk of stroke.1These results assume that elevated cholesterol levels and dietary saturated fat intake are the causative factors in the risk of heart disease, without taking into account other parameters influenced by saturated fat intake, such as: which, when elevated, have been shown to protect against heart disease.2
The present study is inspired by recent meta-analyses of randomized trials and prospective cohort studies that showed either no association or even a lower risk of all-cause mortality and CVD events with higher saturated fat consumption.3In addition, various socioeconomic factors were considered, hypothesizing that countries in Europe and North America may have access to more dietary fat and higher total calorie intake compared to regions with less access to expensive, fatty foods and, in contrast, may be malnourished and overnutrition. Most observational studies linking high saturated fat intake to all-cause mortality have been conducted in wealthier countries, where saturated fat intake can range from 7% to 15% of total calories.4and one of the authors' goals in the present study was to determine whether these results could be extrapolated to regions of the world where food is more scarce and the diet consists primarily of cheaper carbohydrates.
Consistent with these recent studies, the authors found that participants who consumed more fat, including more saturated fat, and fewer carbohydrates generally had lower all-cause mortality, while no increase in major cardiovascular disease was observed. Not surprisingly, higher intakes of polyunsaturated and monounsaturated fats were also associated with a lower risk of all-cause mortality and were not associated with an increase in CVD events or mortality. These results were consistent between Asian and non-Asian countries, notable because it is often cited that people in Asia live longer than people in other parts of the world because of their low-fat, high-carbohydrate diets.5
The current recommendation to limit total fat intake to less than 30% and saturated fats to less than 10% of total calories consumed is not supported by the results of this study, and individuals who eat a high-carbohydrate diet may actually benefit from replacing some of these carbohydrates with fats. The lowest mortality rates were observed when total carbohydrate intake was less than 60% of total calories consumed; However, diets that were less than 50% of the daily total were not associated with increased benefit. Furthermore, according to these findings, 35% of daily calorie intake from fats, of which 10% to 15% (and not less than 7%) should be saturated, appears to be the optimal range.
One of the main limitations of this study is that the authors did not differentiate between the sources or types of carbohydrates consumed. We cannot determine whether participants consumed refined white flour, whole, unprocessed grains, starchy root vegetables, or any combination thereof. Fruits and non-starchy vegetables were undoubtedly included in the “carbohydrate” category, but there is no way to know which and how much of them were consumed by each population studied.
(For more on the health effects of carbohydrates, see "Bread and the Microbiome: A Personal Matter" in this month's issue.)
Diets containing large amounts of refined grains and foods with a high glycemic index are associated with an increased risk of cardiovascular disease.6Diabetes,7and several types of cancer.8Conversely, a diet rich in fiber, such as that found in unprocessed grains, fruits and vegetables, is correlated with a reduced risk of heart disease, cancer and diabetes.9
In addition, it is well known that a diet rich in antioxidants, found in many fruits and vegetables, protects against many health conditions, including cardiovascular disease.10,11This is particularly important in the presence of lipids that can accumulate in the blood vessels, as these phytonutrients prevent lipid peroxidation and endothelial inflammation, major factors in the development of CVD.12
Without information about the source of carbohydrates in participants' diets, it is difficult to conclude exactly which factors contribute to the results of the present study. Overall, however, current evidence suggests that dietary fats, even saturated fats, are not the enemy that conventional medicine has proclaimed for so many years, and reducing total carbohydrates is likely to be beneficial for most people.