Positive Health Online

Synopsis

The vilification of fat began around 50 years ago on the back of an epidemiological study by Ancel Keys[1], which showed a relationship between fat consumption and incidence of coronary heart disease.  This has formed the basis of dietary guidelines on fat intake ever since. However, in a report published earlier this year in the medical journal BMJ Open Heart[2], Dr James DiNicolantonio, a cardiovascular research scientist, suggests that it is our switch from saturated fat to a diet high in carbohydrates (in particular sugar and refined  carbohydrates) that has, paradoxically, increased our risk of heart disease. Could it be, perhaps, that fat has been wrongly made the ‘bad guy’ ? This article will discuss the evidence.

Introduction

For the past 50 years we’ve been led to believe that saturated fat causes heart disease. Healthy eating has become synonymous with a low-fat diet.  In fact, up until recently, this has been such a deeply ingrained belief in our society, that few people have even questioned it. Bacon, eggs and sausage, washed back with a mug of milky coffee, we jest, ‘heart attack on a plate’! But there have always been some experts who have fiercely contested the science on which this theory was originally based.  And with recent research putting into doubt the validity of the early ‘pivotal’ studies that led to this, it seems that the voices of these experts are starting to become both heard, and listened to.  

Saturated Fat, the Enemy?

The vilification of saturated fat began in the early 1970s on the back of findings from an epidemiological study by Dr Ancel Keys[1]; which showed an association between fat calories as a percentage of total calories, and death from degenerative heart disease. This was based on data from 7 countries, but what has since emerged is that Keys excluded data from 16 countries that did not fit his hypothesis.[3] In fact, some claim that the full set of data suggested the opposite - that those eating the most saturated fat tend to have a lower incidence of heart disease. What others have also been quick to point out is that ‘association’ does not equal causation. However, in 1977 what followed this study was a set of dietary guidelines from the American government (titled Dietary Goals for Americans) that recommended increasing carbohydrates and decreasing saturated fat and cholesterol in the diet.[4] This was based on the theory that since saturated fats increase total cholesterol, they must increase the risk of heart disease.

The Shift to Low-Fat

What succeeded this was a sharp increase in carbohydrate intake, and the ‘low-fat’ industry revolution was born. Dietary guidelines stated that no more than 30% of total calorie intake should come from fat, with no more than 10% from saturated fat.[5] The public were advised to eschew foods such as butter and dairy products in favour of vegetable oils, soya and margarine. Low-fat, diet products filled the supermarket shelves. But in replacement of the fat removed from many foods (which provided much of the flavour and texture), sugar was added, and as a result consumption of the white stuff, in all its different forms, vastly increased and has continued to do so.

Questioning the Evidence

Science writer Gary Taubes wrote an article back in 2001 The soft science of dietary fat questioning the evidence that led to these recommendations, stating that “despite decades of research, it is still a debatable proposition whether the consumption of saturated fats above recommended levels by anyone who is not already at high risk of heart disease will increase the likelihood of untimely death”.[6]  In this piece he also discusses the potential health implications of this huge dietary shift to a high-carbohydrate diet, describing the sharp rise in both obesity and diabetes (both of which increase heart disease risk) that have occurred concurrently to these changes in recommendations.[6] He is by no means alone in his scrutiny of the facts, nor is he in his assertion that an increase in sugar has had devastating consequences to public health. Most recently, in an editorial in the British Medical Journal Dr Aseem Malhotra, interventional cardiology specialist registrar, discusses how the avoidance of saturated fat has paradoxically increased our cardiovascular risk.[7] He discusses mounting scientific evidence that sugar may be an independent risk factor for metabolic syndrome (a combination of hypertension, dysglycaemia, raised triglycerides, low HDL cholesterol, and increased waist circumference), which is known to lead to diabetes and increased risk of cardiovascular disease.[7]

Part of the demonization of dietary fat is on the basis that its energy (calorie) content per gram is over double that of both protein and carbohydrate. However, there is an argument to oppose the theory that all calories are equal; with scientists showing evidence that the body does not metabolise different macronutrients in the same way. In fact, a review of 23 studies of low-carbohydrate versus low-fat diets found that the low- carbohydrate diet consistently produced better weight loss results.[8] We also know that adequate dietary fat is essential for the absorption of fat-soluble vitamins A, D, E and K, all of which are important for cardiovascular health. There is strong evidence of a link between vitamin D deficiency and significantly increased risk of cardiovascular mortality.[9]

Is Cholesterol the Culprit?

Further to this, it has now been suggested by some experts that taking a low-fat approach to lower cholesterol levels does not translate to a positive outcome in reduced risk of cardiovascular disease. This is discussed by cardiovascular research scientist Dr James DiNiicolantonio in the medical journal BMJ Open Heart earlier this year.[2] Dr DiNiicolantonio explains how LDL cholesterol (the so-called ‘bad’ cholesterol) consists of two subtypes - large type (type A) particles and small dense (type B) particles.[10] Saturated fat increases levels of the type A LDL particles and yet, he explains, it’s the type B LDL particles that negatively impact on cardiovascular health. Replacing fat with carbohydrate may actually increase type B LDL particles. Not only this but omega-6 fatty acids (found in margarines and vegetable oils such as sunflower, corn or safflower oil), the recommended ‘heart-healthy’ replacements to saturated fat, have also been shown to increase levels of the type B LDL particles.

Analysing the Studies

A meta-analysis in 2010 of 21 prospective epidemiologic studies, concluded that there is no significant evidence that dietary saturated fat is associated with an increased risk of cardiovascular disease.[11] This was then further verified by a review from the University of Cambridge, published in the journal Annals of Internal Medicine, which similarly concluded a lack of evidence linking saturated fat consumption to heart disease.[12] The meta-analysis of 76 studies called into question all standard nutritional guidelines relating to heart health, with the authors stating: "current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats." Dr DiNicolantonio cites several studies whose findings suggest advice to replace saturated fats with polyunsaturated (omega-6) fatty acids may increase the risk of coronary heart disease, cardiovascular events, death due to coronary heart disease and overall mortality.[2] On this basis, he urges that the dietary recommendations to replace saturated fats with vegetable oils and carbohydrates are urgently reassessed.

Plant Sterols

There is also a level of controversy surrounding the widely advocated use of plant sterols as a cholesterol-lowering approach. Sterol enriched foodstuffs, such as Flora Pro-Active, work by partially blocking the absorption of cholesterol from the gut, and can therefore reduce overall blood cholesterol levels. Their use is recommended by the British Heart Foundation[13] and other heart health organizations, despite guidelines from NICE (National Institute for Health and Care Excellence) which advise explicitly against their routine use on the basis that “plant sterols and stanols have been shown to reduce cholesterol levels, but it is not known whether the consumption of plant sterols as part of a low-fat diet will provide worthwhile additional benefit and whether they reduce CVD events”.[14] This once again reiterates the question that many others are asking - is the dietary reduction of cholesterol to lower heart disease risk actually an evidence-based approach?

Trans-Fats

Where there is unanimous agreement amongst the experts is in the link between industrially produced trans-fats and increased risk of heart disease. Trans-fats are formed when liquid vegetable oils are converted into solids through an industrial process called hydrogenation, used to increase the shelf life and improve texture of foods. They are commonly found in fried foods, margarines, baked goods, biscuits, crackers and crisps. Numerous studies have shown a link between trans-fat intake and heart disease. In an article on this topic, Dr John Briffa cites three studies which found that consuming just 2% of our calories from trans-fats is associated with an increased risk of heart disease of 28-93%.[15]

Conclusion

To conclude, by looking at the literature it can be seen that there is still a huge amount of controversy surrounding the link between dietary fat intake, cholesterol and heart disease. However, there does seem to be a compelling argument for the general lack of evidence in support of a low-fat diet (with the exception of trans-fats). It is likely that this most recent analysis will have prompted much further study in this area, so in time we will learn whether guidelines with regards to dietary fat intake will be modified as a result.[12]

References

1. Keys A (Ed). Seven Countries: A multivariate analysis of death and coronary heart disease. Harvard University Press. Cambridge, Massachusetts. ISBN 0-674-80237-3. 1980.

2. BMJ Open Heart. The cardiometabolic consequences of replacing saturated fats with carbohdrates or Ω-6 polyunsaturated fats: Do the dietary guidelines have it wrong? Journal of BMJ Open Heart. http://openheart.bmj.com/content/1/1/e000032.full

3. Perry S. It’s time to stop vilifying saturated fat, heart-disease researcher says. MinnPost. 2014. www.minnpost.com/second-opinion/2014/03/its-time-stop-vilifying-saturated-fat-heart-disease-researcher-says )

4. DGAC. History of the Dietary Guidelines for Americans. 2010. www.cnpp.usda.gov/Publications/DietaryGuidelines/2010/DGAC/Report/E-Appendix-E-4-History.pdf

5. Kraus R M (Ed). Dietary Guidelines for Healthy American Adults. American Heart Association. 1996. http://circ.ahajournals.org/content/94/7/1795.full

6. Taubes G. The soft science of dietary fat. Science 291:2536–45. 2001. www.sciencemag.org/content/291/5513/2536

7. Malhotra A. Saturated fat is not the major issue. BMJ 347:f6340. 2013 www.bmj.com/content/347/bmj.f6340

8. Gunnars K. 23 Studies on Low-Carb and Low-Fat Diets – Time to Retire The Fad. Authority Nutrition. http://authoritynutrition.com/23-studies-on-low-carb-and-low-fat-diets/  2013.

9. University of Copenhagen. Vitamin D deficiency increases risk of heart disease, Danish study finds. Science Daily. www.sciencedaily.com/releases/2012/09/120924102504.htm  2012.

10. DiNicolantonio J J. The cardiometabolic consequences of replacing saturated fats with carbohydrates or Ω-6 polyunsaturated fats: Do the dietary guidelines have it wrong? Open Heart;1. 2014.

11. Patty W Siri-Tarino, Qi Sun, Frank B Hu, and Ronald M Krauss. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. Mar;91(3):535-46. 2010. http://ajcn.nutrition.org/content/early/2010/01/13/ajcn.2009.27725.abstract

12. Chowdhury R, Warnakula S, Kunutsor S, Crowe F, Ward HA, Johnson L, Franco OH, Butterworth AS, Forouhi NG, Thompson SG, Khaw KT, Mozaffarian D, Danesh J, Di Angelantonio E. Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Ann Intern Med. 160(6):398-406. http://annals.org/article.aspx?articleid=1846638   March 18 2014.

13. British Heart Foundation. Flora pro.activ. British Heart Foundation. N.d. www.bhf.org.uk/get-involved/how-your-company-can-help/flora-proactiv.aspx

14. NHS. Lipid modification – Cardiovascular risk assessment and the modification of blood lipids for the primary and secondary prevention of cardiovascular disease. National Institute for Health and Care Excellence. 2010. www.nice.org.uk/nicemedia/pdf/CG67NICEguideline.pdf

15. Briffa J. Food companies that put trans fats in food may be breaking the law. Dr Briffa. 2010. www.drbriffa.com/2010/06/18/food-companies-that-put-trans-fats-in-food-may-be-breaking-the-law/  2010.