Massive International Study Suggests to Consume Less Carbs and More Fats

It is well established that diet is one of the most important modifiable risk factors for cardiovascular disease and other non-transmittable diseases. Current dietary guidelines recommend a low-fat diet (<30% of energy) and limiting saturated fatty acids to less than 10% of energy intake by replacing them with unsaturated fatty acids, while consuming 45-65% of of total calories from carbohydrates. However, results from an international study, spanning more than a decade, are prompting experts to reconsider global dietary guidelines.

Image from Well-being Secrets

The Prospective Urban Rural Epidemiology (PURE) study is a large, epidemiological study that included more than 135,000 individuals between the ages of 35–70 years across 18 countries. Regions included Canada, Sweden, United Arab Emirates, Argentina, Brazil, Chile, China, Colombia, Iran, Malaysia, occupied Palestinian territory, Poland, South Africa, Turkey, Bangladesh, India, Pakistan, and Zimbabwe.

Overall, the researchers found that high carbohydrate intake (more than 60% of energy) 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.

For decades, dietary guidelines have focused on reducing total fat and saturated fatty acid intake, based on the presumption that replacing saturated fatty acids with carbohydrate and unsaturated fats will lower LDL cholesterol and should therefore reduce cardiovascular disease events. This focus is largely based on selective emphasis on some observational and clinical data, despite the existence of several randomized trials and observational studies that do not support these conclusions.

Results of the Study

After documenting 5796 deaths and 4784 major cardiovascular disease events and running statistical analyses, the researchers observed:

• Individuals who consumed a very high carbohydrate diet (at least 60% of energy), especially from refined sources (such as white rice and white bread), were associated with increased risk of total mortality and cardiovascular events.
• An inverse association between total fat and total mortality.
• Individuals consuming a higher glycemic load, such as refined carbohydrates, were associated with a higher risk of stroke
  
• An inverse association between saturated fatty acid intake, total mortality, non-
  cardiovascular disease mortality, and stroke risk without any evidence of an increase in major cardiovascular disease, myocardial infarction, and cardiovascular disease mortality.
  
• An inverse association between monounsaturated fatty acid intake and total mortality.
  

Association between estimated percentage energy from nutrients and total mortality and major cardiovascular disease (n=135335). Image from (Dehghan et al., 2017)

Recommendations and Take Away

The results of this study do not suggest a low-carbohydrate diet, but rather that a total fat intake of about 35% of energy while lowering carbohydrate intake might lower risk of total mortality. Collectively, the data does not support the recommendation to limit saturated fatty acids to less than 10% of intake and that a very low intake (ie, below about 7% of energy) might even be harmful.

Limitations of the Study

1. The researchers used food frequency questionnaires (FFQs) to estimate participants’ dietary intake which is not a measure of absolute intake, but is suited for classifying individuals into intake categories and is the most commonly used approach for assessing intake in epidemiological studies.
   
2. Dietary intakes were measured only at baseline, and it is possible that dietary changes might have occurred during the follow-up period. Even if major dietary changes occurred after the baseline assessment, they probably would have weakened the observed associations.
3. There is potential for social desirability bias and individuals who are health conscious might also adopt other healthy lifestyles. However, if this were the case, the researchers would not expect to see different associations for the different outcomes.
4. As with any observational cohort study, observed associations might be in part due to residual confounding (eg, differences in the ability to afford fats and animal proteins, which are more expensive than carbohydrates) despite extensive adjustment for known confounding factors.
   
5. The researchers were unable to measure trans-fat intake which might affect our results, especially our replacement analyses.
   
6. FFQ assessed polyunsaturated fatty acid intake mainly from foods, rather than from vegetable oils, which might have different health effects than those observed in the study.
   

The researchers declare no conflicts of interests

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References

Brown, E. (2017). More Evidence That Everything the Government Teaches Us About Eating Is Wrong. [online] Reason.com. Available at: http://reason.com/blog/2017/08/30/pure-study-challenges-dietary-dogma [Accessed 20 Sep. 2017].

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