The Saturated Fat and Heart Disease Debate

I enjoyed writing this article about the very topical issue of saturated fat, which was first published in the December 2017 edition of NHD Magazine.


Saturated fats contain single bonds between carbon atoms which causes the fat to be ‘saturated’, or to be linked to as many hydrogen atoms as possible. Sources of saturated fat include: butter, coconut oil, palm oil, lard, full fat dairy products, pies, pastries, cakes and biscuits and the visible fat on meat1.  

Due to the association between saturated fat and increased LDL cholesterol levels, most public health bodies recommend limiting saturated fat intake in order to reduce the risk of heart disease1,2.

As there has been a lot of recent debate surrounding this topic, this article will examine some of the common arguments put forward by those who challenge the link between saturated fat intake and heart disease.

Argument One: “Studies have found that saturated fat intake is not associated with heart disease”

A large meta-analysis by Chowdhury et al. (2014) is often quoted to support this argument, as this study did not find a significant association between saturated fat intake and cardiovascular disease (CVD)3. However, there have several criticisms of this study, such as: errors in some of the data, omitting relevant studies, a lack of consistency (for example whether saturated fat was substituted for refined carbohydrates), and the fact that data representing monounsaturated fats was taken from meat and dairy rather than more relevant sources such as nuts and olive oil4.

Furthermore, numerous other large meta-analysis’ have found that lowering saturated fat intake is associated with a reduced risk of heart disease5-7.

These studies also found that neither a lower total fat intake or replacing saturated fat with refined carbohydrates was associated with a lower risk of heart disease, but that replacing saturated fat with unsaturated versions or wholegrains was associated with a reduced risk of CVD5-7. For example, a large systematic review by Hopper et al. (2015) found that a reduced saturated fat intake was associated with a 17% reduced risk of CVD7. A more recent large prospective cohort study, called the PURE study, found that there were no significant differences between the type of fat consumed and the risk of cardiovascular events, and that lower intakes of saturated fat were associated with an increased risk of stroke8. Although these are interesting results it is important to remember that no causal relationship can be assumed due to the observational design of this study. Another limitation is the potential confounding effect of socio-economic status. Although education status was corrected for, the PURE study was predominantly carried out in low and middle income countries, and the researchers themselves state that “high-carbohydrate and low-fat diets might be a proxy for poverty or access to healthcare”8.  

 

Argument Two: “The initial research about saturated fat intake and heart disease is flawed”

The Seven Countries Study (SCS) by Ancel Keys et al. which started in 1958 was one of the first large studies to identify an association between saturated fat intake and heart disease. A recent white paper report which was issued by the ‘The True Health Initiative’ addressed the numerous recent criticisms related to the SCS which mainly focus on reported issues with the study methods 9. This paper concluded that as with every scientific study the SCS had limitations, especially as it was an observational study10.

Therefore, the SCS should be viewed within the wider context of epidemiological evidence10.

However the overall body of evidence which has emerged since the SCS was published, including the famous Framingham Heart Study and the studies discussed above, supports the link between saturated fat intake and heart disease risk5-7,10.

 

Argument Three: “The French eat high levels of saturated fat, yet have low levels of heart disease”

Shortly after this “French Paradox” theory was suggested in the 1980s, it was proposed that this may have been caused by the under-classification of CVD in France and the time-lag between the increased consumption of saturated fat in France (which was relatively recent at the time) and the subsequent increase in CVD levels11.

Based on recent statistics, the average intake of saturated fat in France remains high at 14.6% of total energy intake12.

However, France does not have a low prevalence of heart disease anymore13.

The age-adjusted average prevalence of CVD in France in 2015 was 6101 per 100,000 for males and 4666 per 100,000 for females, which was close to the EU average and was also very similar to the UK average; despite the higher obesity levels found in the UK13. There are currently many other countries with a lower prevalence of CVD in Europe, including countries which have a lower average saturated fat intake than France, such as: Italy, Portugal, Switzerland, Ireland, Spain etc13-14.

 

Argument Four: “Sugar and carbohydrates are the problem, not saturated fat”

There is a grain of truth to this argument, as recent studies have shown that replacing fats with refined carbohydrates does not have a cardio-protective effect (as discussed above)3,5-8.

However, vilifying carbohydrates as a whole ignores the numerous health benefits of wholegrains and fibre which includes a reduced risk of: cardiovascular disease, diabetes and colorectal cancer15. In the UK we currently consume more free sugars and less fibre than recommended levels, therefore current public health guidelines advise that “a greater proportion of total dietary energy from foods that are lower in free sugars and higher in dietary fibre whilst continuing to derive approximately 50% of total dietary energy from carbohydrates”15. As with argument number two, there can often a conspiracy theory element to the ‘sugar vs. fat’ argument which may blame certain governments and the sugar industry. Drastic claims such as these should be assessed critically as to whether this could have occurred on such a large scale, considering the knock on effect this would have on health care systems and taxpaying workforces. Furthermore, sugar has never been promoted in public health guidelines, and there has been a recent emphasis on reducing sugar intake worldwide15-16.

Overall this argument creates a false dichotomy, as it suggests that a diet which has a lower saturated fat intake will result in an increased intake of refined carbohydrates.

But this isn’t necessarily the case, as ideally some saturated fat should be replaced with heart healthy alternatives such as: wholegrains, unsaturated fats, fruit, vegetables and legumes.

 

Argument Five: “All saturated fats are not equal”

Saturated fats can be classified as odd-chain or even-chain depending on the number carbon atoms attached to the molecule.

There is some emerging research which has found that odd-chain saturated fatty acids (which are generally found in full fat dairy products) may have a protective effect against cardiometabolic disorders3,17-19.

However, it has also been suggested that the ‘whole food effect’ of dairy and other nutrients which it contains may contribute to this association, such as: CLA (a naturally occurring form of trans fat), protein, the numerous vitamins and minerals present and the fact that some sources also contain probiotics20.

Although this is a fascinating area, more randomised controlled trials are needed before it can be stated that there is a causal relationship between individual types of saturated fat and health outcomes.  

 

Argument Six: “Coconut oil is good for your heart”

Due to its high saturated fat content (82% compared to butter which is 63%, and olive oil which is 14%), the UK department of health advises to consume only small amounts of coconut oil21-22. Some argue that coconut oil is healthy because it contains medium chain tryglycerides (MCTs), however, less than 16% of the fats present in coconut oil are MCT as the main fat  present is lauric acid which is a long chain tryglyceride (LCT)23. There are some studies which have found that a high intake of coconuts was not associated with an increased risk of heart disease23. However no conclusions can be made about coconut oil based on this, as these studies were observational and were also based on the consumption of coconut flesh and coconut milk rather than the extracted oil. There is a lack of human research in relation to coconut oil and health, however the best available published evidence indicates that coconut oil consumption is associated with an increase in total and LDL cholesterol when compared to consumption of unsaturated vegetable oils22,24

Coconut oil is fine to have in small amounts as part of a balanced diet, but there is currently no good evidence that it adds any specific health benefits.

 

The Bottom Line:

Although moderate amounts of total fat in the diet should not be vilified, the current body of evidence in relation to heart disease risk supports limiting saturated fat intake and consuming the majority of fat from unsaturated sources25. It is also important to remember that on average in the UK we currently exceed the recommended intake of saturated fat which is <11% of total dietary energy25. Whilst there is some emerging research in relation to how individual types of saturated fat may affect the risk of heart disease in different ways, more high quality research is needed to investigate this. Although this is often an emotive debate, it is crucial to be guided by the best available evidence and to be wary of the potential appeal of conspiracy theories. It is also important to acknowledge that as with all areas of science, nutrition is a complex and constantly evolving area which rarely provides one black and white answer to a topic such as this. It will be interesting to see whether we gain more clarity about this when SACN publish its upcoming review of saturated fat26.


References:

  1. BDA (2014) Food Facts Sheet “Fats” 
  2. NICE (2010) “Cardiovascular Disease Prevention”
  3. Chowdhury et al (2014) “Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis”
  4. Annals of International Medicine (2014): http://wphna.org/wp-content/uploads/2014/08/2014-03_Annals_of_Int_Med_Chowdhury_et_al_Fat_and_CHD_+_responses.pdf
  5. Mensink et al (2003) “Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials”
  6. Mozaffarian et al (2010) “Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials”
  7. Hooper (2015) “Reduction in Saturated Fat Intake For Cardiovascular Disease”
  8. Deghan et al. (2017) “Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study”
  9. Pett et al. (2017) “Ancel Keys and the Seven Countries Study: An Evidence-based Response to Revisionist Histories”
  10. Kromhout et al. (2002) “Prevention of Coronary Heart Disease: Diet, Lifestyle and Risk Factors in the Seven Countries Study”
  11. Law (1999) “Why heart disease mortality is low in France: the time lag explanation”
  12. WHO (2013) “Nutrition, Physical Activity and Obesity – France” 
  13. Wilkins et al. (2017) “European Cardiovascular Disease Statistics 2017 edition” 
  14. Micha et al. (2014) “Global, regional and national consumption levels of dietary fats and oils in 1990 and 2010: a systematic analysis including 266 country-specific nutrition surveys” 
  15. SACN (2015) “Carbohydrates and Health”
  16. WHO (2016) “Report of the Commission on Ending Childhood Obesity”
  17. Forouhi et al. (2014) “Differences in the prospective association between individual plasma phospholipid saturated fatty acids and incident type 2 diabetes: the EPIC-InterAct case-cohort study” 
  18. Khaw et al. (2012) “Plasma phospholipid fatty acid concentration and incident coronary heart disease in men and women: the EPIC-Norfolk prospective study”
  19. De Oliveira et al. (2012) “Dietary intake of saturated fat by food source and incident cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis”
  20. Gebauer et al. (2011) “Effects of ruminant trans fatty acids on cardiovascular disease and cancer: A comprehensive review of epidemiological, clinical, and mechanistic studies”
  21. NHS Choices (2015) “Is saturated fat bad for me?”
  22. Sacks et al. (2017) “Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association”
  23. NZ Heart Foundation (2014) “Coconut Oil and The Heart”
  24. Eyres et al. (2016) “Coconut oil consumption and cardiovascular risk factors in humans“
  25. BNF website “Fat” (accessed September 2017 via: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/fat.html
  26. https://www.gov.uk/government/groups/scientific-advisory-committee-on-nutrition#saturated-fats-working-group

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