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Fats/Carbohydrates PURE Study Refuted by AHA
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Download the PDF here
published PURE Study below
The AHA issued a statementA in response to the PURE data stating "a nutrition study of PURE's scale and scope is extremely challenging" and suggesting the PURE results "be interpreted with significant caution."
ADirectly Contradictory to Recent AHA Advisory
The saturated-fat findings will be particularly controversial, especially in the cardiology community, which has traditionally held the mantra that saturated fat is the number-one dietary enemy.
Indeed, just a few weeks ago, the American Heart Association issued a new "advisory" recommending minimizing intake of saturated fat and replacing it with polyunsaturated fat or carbohydrate. The PURE findings appear to be in direct contradiction to this advice.
Commenting on this at her hotline presentation, PURE co-lead author Dr Mahshid Dehghan (McMaster University) said: "The upper levels of saturated fat intake in our study (mean 10%-13% of dietary energy) was associated with a significantly reduced mortality compared with low levels of saturated fat, and very low saturated-fat intake appears harmful. Current guidelines that recommend total fat below 30% and saturated fat below 10% of energy intake are not supported by our data."
Yusuf commented further: "The AHA guidelines are not based on the best evidence—saturated fat was labeled as a villain years ago, and the traditional church has kept on preaching that message. They have been resistant to change."
The AHA issued a statement in response to the PURE data stating "a nutrition study of PURE's scale and scope is extremely challenging" and suggesting the PURE results "be interpreted with significant caution."
The AHA says the self-reported food frequency questionnaire used as the study tool "poses some limitations." Specifically, "Individuals tend to over- or underrecall food intake, in general. In addition, the tool may not fully account for cultural differences in food patterns and may underrepresent locally relevant foods."
But the AHA added: "While we feel it's important to pay attention to saturated fats and refined carbohydrates, they are just part of the puzzle. Consumers should focus on an overall balanced diet." Medscape -
http://www.medscape.com/viewarticle/884937?src=WNL_confalert_170830_MSCPEDIT&uac=27194HK#vp_2
PURE Study Findings on fat & carbohydrates
During follow-up, we documented 5796 deaths and 4784 major cardiovascular disease events. Higher carbohydrate intake was associated with an increased risk of total mortality (highest [quintile 5] vs lowest quintile [quintile 1] category, HR 1⋅28 [95% CI 1⋅12-1⋅46], ptrend=0⋅0001) but not with the risk of cardiovascular disease or cardiovascular disease mortality. Intake of total fat and each type of fat was associated with lower risk of total mortality (quintile 5 vs quintile 1, total fat: HR 0⋅77 [95% CI 0⋅67-0⋅87], ptrend<0⋅0001; saturated fat, HR 0⋅86 [0⋅76-0⋅99], ptrend=0⋅0088; monounsaturated fat: HR 0⋅81 [0⋅71-0⋅92], ptrend<0⋅0001; and polyunsaturated fat: HR 0⋅80 [0⋅71-0⋅89], ptrend<0⋅0001). Higher saturated fat intake was associated with lower risk of stroke (quintile 5 vs quintile 1, HR 0⋅79 [95% CI 0⋅64-0⋅98], ptrend=0⋅0498). Total fat and saturated and unsaturated fats were not significantly associated with risk of myocardial infarction or cardiovascular disease mortality……"Our findings do not support the current recommendation to limit total fat intake to less than 30% of energy and saturated fat intake to less than 10% of energy. Individuals with high carbohydrate intake might benefit from a reduction in carbohydrate intake and increase in the consumption of fats."…..in our study most participants from low-income and middle-income countries consumed a very high carbohydrate diet (at least 60% of energy), especially from refined sources (such as white rice and white bread), which have been shown to be associated with increased risk of total mortality and cardiovascular events…..Therefore, recommending lowering carbohydrate might be particularly applicable to such settings if replacement foods from fats and protein are available and affordable. It is also noteworthy that the spline plots showed a non-linear increasing trend in total mortality with a carbohydrate intake and the rise seems to occur among those who consumed more than 60% of energy from carbohydrate (ie, based on the midpoint of the estimate, with the lower CI showing an HR >0⋅1 when more than 70% of energy came from carbohydrates). Additionally, higher carbohydrate intakes increase some forms of dyslipidaemia (ie, higher triglycerides and lower HDL cholesterol), apolipoprotein B (ApoB)-to-apolipoprotein A1 (ApoA1) ratios and increased small dense LDL (the most atherogenic particles)43, 44 and increased blood pressure45 (see Mente and colleagues45). However, the absence of association between low carbohydrate intake (eg, <50% of energy) and health outcomes does not provide support for very low carbohydrate diets. Importantly, a certain amount of carbohydrate is necessary to meet short-term energy demands during physical activity and so moderate intakes (eg, 50-55% of energy) are likely to be more appropriate than either very high or very low carbohydrate intakes.
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Comment
PURE study challenges the definition of a healthy diet: but key questions remain
Lancet Aug 29 2017 - *Christopher E Ramsden, Anthony F Domenichiello, Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA (CER, AFD); and Intramural Program of the National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, USA (CER)
The relationships between diet, cardiovascular disease, and death are topics of major public health importance, and subjects of great controversy.1, 2 In European and North American countries, the most enduring and consistent diet advice is to restrict saturated fatty acids, by replacing animal fats with vegetable oils and complex carbohydrates (and more recently whole grains).1, 3 In The Lancet, Mahshid Dehghan and colleagues4 echo the views of a growing number of scientists by stating that advice to restrict saturated fatty acids "is largely based on selective emphasis on some observational and clinical data, despite the existence of several randomised trials and observational studies that do not support these conclusions". This lack of definitive evidence has left clinicians, scientists, and the public uncertain about the best foods to advise and to eat.2
Dehghan and colleagues4 add to this uncertainty by publishing the initial results of the Prospective Urban Rural Epidemiology (PURE) study, an ambitious undertaking involving over 200 investigators who collected data on more than 135 000 individuals from 18 countries across five continents for an average of 7⋅4 years. As the largest prospective observational study to assess the association of nutrients (estimated by food frequency questionnaires) with cardiovascular disease and mortality in low-income and middle-income populations, the PURE findings make an important contribution to the field. The PURE team report that higher intakes of fats (including saturated fatty acids, monounsaturated fatty acids, and total polyunsaturated fatty acids) and animal protein were each associated with lower mortality, whereas carbohydrate intake was associated with increased mortality.4 Here we provide context and highlight questions that need to be answered to move the field forward.
Do meats and dairy reduce mortality? Animal products (including beef, lamb, and dairy) are the major sources of saturated fatty acids and monounsaturated fatty acids in most populations studied in PURE. Since saturated fatty acids, monounsaturated fatty acids, and animal protein were all inversely associated with mortality, is the real finding simply that meat and dairy intakes were associated with increased survival? To answer this question, the PURE team needs to complete a thorough analysis relating intakes of different animal products to mortality.
Micronutrient malnutrition is an important problem in many of the countries included in PURE. Animal products are rich sources of zinc, bioavailable iron, vitamin K2, and vitamin B12, which might be suboptimal in populations consuming high carbohydrate diets. Therefore, one potential explanation for the PURE results is that nutrient-dense meats corrected one or more nutrient deficiencies. Since the PURE study collected blood for lipoprotein analyses,5 this potential role of micronutrient deficiency in PURE could be investigated further.
Which carbohydrates are associated with increased mortality? Dehghan and colleagues4 report that high intake of total carbohydrates was associated with increased mortality. In a concurrent Lancet Article,6 the PURE group reports that intakes of fruits, legumes, and raw vegetables (three major carbohydrate sources) were associated with lower mortality. This discrepancy suggests that processed carbohydrates, including added sugars and refined grains, are likely driving this association. In a future paper, the PURE group should report associations between added sugars, refined grains, whole grains, and mortality.
Is PURE less confounded by conscientiousness than observational studies done in European and North American countries? Conscientiousness is among the best predictors of longevity.7 For example, in a Japanese population, highly and moderately conscientious individuals had 54% and 50% lower mortality, respectively, compared with the least conscientious tertile.8 Conscientious individuals exhibit numerous health-related behaviours ranging from adherence to physicians' recommendations and medication regimens,9 to better sleep habits,10 to less alcohol and substance misuse.11 Importantly, conscientious individuals tend to eat more recommended foods and fewer restricted foods.12 Since individuals in European and North American populations have, for many decades, received influential diet recommendations, protective associations attributed to nutrients in studies of these populations are likely confounded by numerous other healthy behaviours. Because many of the populations included in PURE are less exposed to influential diet recommendations, the present findings are perhaps less likely to be confounded by conscientiousness.
The PURE study is an impressive undertaking that will contribute to public health for years to come. Initial PURE findings challenge conventional diet-disease tenets that are largely based on observational associations in European and North American populations, adding to the uncertainty about what constitutes a healthy diet. This uncertainty is likely to prevail until well designed randomised controlled trials are done. Until then, the best medicine for the nutrition field is a healthy dose of humility.
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Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study
Summary
Background
The relationship between macronutrients and cardiovascular disease and mortality is controversial. Most available data are from European and North American populations where nutrition excess is more likely, so their applicability to other populations is unclear.
Methods
The Prospective Urban Rural Epidemiology (PURE) study is a large, epidemiological cohort study of individuals aged 35-70 years (enrolled between Jan 1, 2003, and March 31, 2013) in 18 countries with a median follow-up of 7⋅4 years (IQR 5⋅3-9⋅3). Dietary intake of 135 335 individuals was recorded using validated food frequency questionnaires. The primary outcomes were total mortality and major cardiovascular events (fatal cardiovascular disease, non-fatal myocardial infarction, stroke, and heart failure). Secondary outcomes were all myocardial infarctions, stroke, cardiovascular disease mortality, and non-cardiovascular disease mortality. Participants were categorised into quintiles of nutrient intake (carbohydrate, fats, and protein) based on percentage of energy provided by nutrients. We assessed the associations between consumption of carbohydrate, total fat, and each type of fat with cardiovascular disease and total mortality. We calculated hazard ratios (HRs) using a multivariable Cox frailty model with random intercepts to account for centre clustering.
Findings
During follow-up, we documented 5796 deaths and 4784 major cardiovascular disease events. Higher carbohydrate intake was associated with an increased risk of total mortality (highest [quintile 5] vs lowest quintile [quintile 1] category, HR 1⋅28 [95% CI 1⋅12-1⋅46], ptrend=0⋅0001) but not with the risk of cardiovascular disease or cardiovascular disease mortality. Intake of total fat and each type of fat was associated with lower risk of total mortality (quintile 5 vs quintile 1, total fat: HR 0⋅77 [95% CI 0⋅67-0⋅87], ptrend<0⋅0001; saturated fat, HR 0⋅86 [0⋅76-0⋅99], ptrend=0⋅0088; monounsaturated fat: HR 0⋅81 [0⋅71-0⋅92], ptrend<0⋅0001; and polyunsaturated fat: HR 0⋅80 [0⋅71-0⋅89], ptrend<0⋅0001). Higher saturated fat intake was associated with lower risk of stroke (quintile 5 vs quintile 1, HR 0⋅79 [95% CI 0⋅64-0⋅98], ptrend=0⋅0498). Total fat and saturated and unsaturated fats were not significantly associated with risk of myocardial infarction or cardiovascular disease mortality.
Interpretation
High carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to lower total mortality. Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke. Global dietary guidelines should be reconsidered in light of these findings.
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