Over the past few years, the medical community have been working hard to reduce the rate of heart and blood vessel disease, which is also called cardiovascular disease (CVD). The death rate in the UK due to CVD has decreased by more than 75% over the past 57 years (1), but heart disease is still the most common cause of death worldwide (1), so it’s important to keep fighting it.
What is Cardiovascular Disease
What exactly do we mean when we talk about cardiovascular disease? The main culprit is atherosclerosis, which is the build-up of fatty material and inflammation inside our arteries. Although it can be tempting to describe atherosclerosis as fat clogging the arteries, this is not a very accurate way to describe what happens (4,5). It develops initially as an accumulation of fat and inflammation under the lining of the artery that grows and thickens. This fat accumulation is called an atherosclerotic plaque (6). This plaque can lead to chest pain (a.k.a. angina) by narrowing our blood vessels, a heart attack or cause a stroke, if a piece breaks off or if it triggers a clot to form, blocking important vessels (6).
Cardiovascular disease Risk
While a single cause is almost impossible to pinpoint (except for certain rare genetic disorders), there are things which make developing CVD more likely, especially when we start adding them up. We have no control over some of these risk factors, such as increasing age, a history of heart disease in the family, South Asian or African Caribbean ethnicity, and being male (2). But we do have some control over other risk factors, like obesity, diabetes, smoking, alcohol intake, high blood pressure, high cholesterol, inflammation, and certain diet and exercise habits (2).
It’s important to tackle the CVD risk factors which we can do something about. Currently, cardiovascular disease prevention includes lifestyle measures and medication to reduce the risk, e.g. aspirin, to prevent clots; statins, to reduce cholesterol; and blood pressure tablets, among other possible medicines (3). The lifestyle changes that help include alcohol reduction, stopping smoking, maintaining a healthy weight, exercise, and adopting a healthy diet (3). These changes should reduce someone’s chances of developing heart disease, or of dying from it.
What Does “High Cholesterol” Mean?
Cholesterol plays a part in the process of atherosclerosis. There are two types of cholesterol: LDL (often called the ‘bad’ cholesterol) and HDL (the ‘good’ cholesterol). LDL takes fat to our cells, where it carries out its role in the body, but it is also involved in the build-up of fat in the arteries (i.e. atherosclerosis). HDL, on the other hand, takes the fat that accumulates around the body to the liver, where it can be broken down and either used or removed from the body. HDL is really important in preventing and assessing the risk of heart disease (7).
Cholesterol isn’t the only fat circulating in our blood. We also have another kind of fat, called triglycerides. While cholesterol has a role in the structure of our cells and some hormones, triglycerides store energy that we can use (16). They also play a role in the stiffening of our arteries (16, 17).
Saturated Fat and Cardiovascular Disease
Reducing how much saturated fat (which is often called “bad fat”) we eat helps to reduce LDL cholesterol (8,9). Although we should note that a diet high in saturated fat may also increase HDL cholesterol (10), this occurs to a lesser degree than the increase in LDL cholesterol, meaning there is more LDL to the HDL in the blood (11). Saturated fat is found mainly in animal products like meat, whereas unsaturated fats (also known as “good” fats) are found mainly in vegetable oils (like sunflower and soybean oil) and oily fish (12).
It seems logical that if we eat less fat, then there won’t be as much of it to build up inside the arteries, right? Not so fast! Some researchers say that the evidence for saturated fat reduction as a method for preventing CVD is not very clear-cut (4,5). Studies have found that it isn’t good enough to just reduce saturated fat intake – it depends on what we replace it with (4,9,13).
There is evidence to show that only reducing saturated fat, or replacing this with refined carbohydrates or protein, may not reduce the risk of CVD or cardiovascular events (i.e. heart attacks, stroke, heart failure, an irregular heartbeat or unplanned heart surgeries) (8, 14). But this is not the case when saturated fats are replaced with unsaturated fats, as this is seen to reduce the risk of CVD (8,14). This is why current guidelines suggest we reduce our intake of saturated fats and replace some of it with unsaturated fats – which is more effective than simply reducing how much fat we eat in total (14).
Take Home Message
So – do so-called “bad” fats clog up our arteries? Yes and no.
A build-up of LDL cholesterol in our arteries does increase the risk of CVD, as does consuming too much saturated fat on a regular basis. But as the British Nutrition Foundation puts it, this topic is a lot more complicated than labelling saturated fats as “bad” (15). No single food or nutrient is either “good” or “bad”, as it depends on the context – it’s the overall balance of diet which matters. This is the reason why so many health professionals are moving away from calling saturated fat “bad fat”.
Talking about clogged arteries oversimplifies the role of saturated fats in heart disease; but it is important to keep in mind that replacing saturated fat with unsaturated fat is a key step to reducing our risk of heart disease.
References
(1) British Heart Foundation. CVD Statistics – BHF UK Factsheet. 2017;(Cvd):4–5. Available from: https://www.bhf.org.uk/research/heart-statistics
(2) Atherosclerosis | National Heart, Lung, and Blood Institute (NHLBI) [Internet]. NIH. 2018 [cited 2018 Jul 19]. Available from: https://www.nhlbi.nih.gov/health-topics/atherosclerosis
(3) Cardiovascular disease prevention [Internet]. NICE. [cited 2018 Jul 19]. Available from: https://pathways.nice.org.uk/pathways/cardiovascular-disease-prevention
(4) Rothberg MB. Coronary artery disease as clogged pipes: a misconceptual model. Circ Cardiovasc Qual Outcomes [Internet]. 2013 Jan 1 [cited 2018 Jul 16];6(1):129–32. Available from: http://www.ncbi.nlm.nih.gov/pubmed/23322809
(5) Malhotra A, Redberg RF, Meier P. Saturated fat does not clog the arteries: coronary heart disease is a chronic inflammatory condition, the risk of which can be effectively reduced from healthy lifestyle interventions. Br J Sports Med [Internet]. 2017 Aug 1 [cited 2018 Jul 16];51(15):1111–2. Available from: http://www.ncbi.nlm.nih.gov/pubmed/28442474
(6) Topol EJ. Textbook of Cardiovascular Medicine [Internet]. 3rd ed. Philadelphia: Lippincott Williams & Wilkins; 2007 [cited 2018 Jul 19]. 2-10 p. Available from: https://books.google.nl/books?id=35zSLWyEWbcC&pg=PA2#v=onepage&q&f=false
(7) Mensink RP, Zock PL, Kester AD, Katan MB. 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. Am J Clin Nutr [Internet]. 2003 May 1 [cited 2018 Aug 7];77(5):1146–55. Available from: https://academic.oup.com/ajcn/article/77/5/1146/4689813
(8) Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev [Internet]. 2015 Jun 10 [cited 2018 Jul 19]; Available from: http://doi.wiley.com/10.1002/14651858.CD011737
(9) Jakobsen MU, O’Reilly EJ, Heitmann BL, Pereira MA, Bälter K, Fraser GE, et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr [Internet]. 2009 May [cited 2018 Aug 7];89(5):1425–32. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19211817
(10) Hayek T, Ito Y, Azrolan N, Verdery RB, Aalto-Setmla K, Walsh A, et al. Dietary Fat Increases High Density Lipoprotein (HDL) Levels Both by Increasing the Transport Rates and Decreasing the Fractional Catabolic Rates of HDL Cholesterol Ester and Apolipoprotein (Apo) A-I. J Clin Invest [Internet]. 1993 [cited 2018 Aug 7];91:1665–71. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC288145/pdf/jcinvest00039-0409.pdf
(11) Müller H, Lindman AS, Brantsæter AL, Pedersen JI. The Serum LDL/HDL Cholesterol Ratio Is Influenced More Favorably by Exchanging Saturated with Unsaturated Fat Than by Reducing Saturated Fat in the Diet of Women. J Nutr [Internet]. 2003 Jan 1 [cited 2018 Aug 7];133(1):78–83. Available from: https://academic.oup.com/jn/article/133/1/78/4687701
(12) Fat [Internet]. British Nutrition Foundation. [cited 2018 Aug 8]. Available from: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/fat.html?start=5
(13) Astrup A, Dyerberg J, Elwood P, Hermansen K, Hu FB, Jakobsen MU, et al. The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: where does the evidence stand in 2010? Am J Clin Nutr [Internet]. 2011 Apr 1 [cited 2018 Jul 19];93(4):684–8. Available from: https://academic.oup.com/ajcn/article/93/4/684/4597646
(14) Hooper L, Summerbell CD, Thompson R, Sills D, Roberts FG, Moore HJ, et al. Reduced or modified dietary fat for preventing cardiovascular disease. Cochrane Database Syst Rev [Internet]. 2011 May 16 [cited 2018 Jul 19]; Available from: http://doi.wiley.com/10.1002/14651858.CD002137.pub3
(15) Saturated fat: good, bad or complex? [Internet]. British Nutrition Foundation. 2017 [cited 2018 Aug 6]. Available from: http://doi.wiley.com/10.1002/14651858.CD011737
(16) Triglycerides: Why do they matter? [Internet] Mayo Clinic. 2015. [cited 2018 Sep 6] Available from: https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/in-depth/triglycerides/art-20048186
(17) High cholesterol. [Internet] British Heart Foundation. [cited 2018 Sep 6] Available from: https://www.bhf.org.uk/informationsupport/risk-factors/high-cholesterol
feature image: Conner Wells via Unsplash
