HEART UK dietary fat recommendations for cholesterol management and the evidence behind them
Read about the different types of dietary fats and their effects on CVD, including saturated fat, omega 3s, cholesterol, plus current intakes in the uk.
- Cut down on foods containing a lot of saturated fat and replace them with foods that contain more unsaturated fat
- Watch the quantities of fat consumed, as all fats, whether saturated or unsaturated, are high in calories
- Avoid foods made with partially hydrogenated fats
- Eat 2 portions of fish a week, one of which should be oily
- Dietary cholesterol intakes of no more than 300mg/ day for people with FH or individuals at high risk of CVD
The evidence for reductions in saturated fat and replacement with unsaturated fats
Dietary fat recommendations for heart health have been reviewed by a number of expert bodies and professional organisations[1],[2],[3],[4],[5],[6] with consistent findings:
- Saturated Fatty Acids (SFA) are the dietary factor with the greatest impact on Low Density Lipoprotein Cholesterol (LDL-C).
- SFA should be substituted with unsaturated fatty acids (UFA) – polyunsaturated (PUFA) and monounsaturated (MUFA).
- Reducing SFA per se, or substituting with PUFA, MUFA, or a mixture of the two reduces total and LDL-C.
- Substituting SFA with UFA has no adverse effect on HDL, but simply reducing SFA or substituting with carbohydrate, reduces High Density Lipoprotein Cholesterol (HDL-C).
- Trans fatty acids (TFA) have a similar effect on LDL-C, however, while SFA increase HDL-C), TFA decreases it.
- TFA can be produced industrially by the partial hydrogenation of vegetable and fish oils, but also occur naturally in meat and dairy products from ruminant animals (e.g. cattle, sheep, goats, camels). Industrially-produced TFA can be found in baked and fried foods, pre-packaged snacks and food. TFA from ruminant animals are considered to be of less concern at the typical levels consumed in the diet [7],[8].
- In the UK, voluntary measures by the food industry have resulted in mean TFA intakes in adults and children significantly decreasing. Current intake at 0.5%[9] of food energy is below the recommended maximum for both the UK (<2% of dietary energy)[10] and internationally (<1% of dietary energy)[11].
In their recent review of the evidence examining the impact of saturated fat on health, the Scientific Advisory Committee on Nutrition (SACN) concluded that reducing saturated fat lowers the risk of cardiovascular disease (CVD) and coronary heart disease (CHD), lowers total, LDL-C and HDL-C and improves indicators of glycaemic control. Reducing population averages of SFA from current intake to no more than about 10% of total dietary energy would result in health benefits to the population [3].
Mechanism of action
Research suggests that eating too much SFA impacts the LDL receptors, preventing them from taking up LDL-C from the blood and into the liver to be broken down. The resulting effect is a build-up of LDL-C in the blood[12].
Why the confusion?
Despite the universal consensus, the question of fat around CVD risk is hotly debated with claims suggesting dietary recommendations to reduce SFA intake have been over exaggerated. Are fats the villains, neutral or the heroes? And which fats have different effects?
The recent controversy has arisen following a couple of recent analyses failing to find an association between SFA and CHD risk[13],[14]. However, these findings can be explained by:
- A lack of control over the replacement calories. When saturated fat is reduced, it’s important to consider the substitute nutrient. A Cochrane systematic review of 15 randomised controlled trials, involving almost 60 000 participants, found greater reductions (27%) in CVD events in studies that replaced SFA with PUFA than in studies where SFA was replaced with carbohydrate or protein, where there was little evidence of any effect[4]. Replacing SFA with UFA, and especially PUFA, leads to a reduction in serum LDL-C levels[15].
- The inclusion of older studies using spreads with higher TFA content. Other limitations of these types of meta-analyses include the use of cohort studies (which show associations but not cause and effect); the differing effects of individual SFA on LDL-C; and the effects of SFA from different foods - the food matrix and nutrients may interact with SFA resulting in different outcomes.
[1] François Mach, Colin Baigent, Alberico L Catapano, et al, ESC Scientific Document Group, 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk: The Task Force for the management of dyslipidaemias of the European Society of Cardiology (ESC) and European Atherosclerosis Society (EAS), European Heart Journal, , ehz455, https://doi.org/10.1093/eurheartj/ehz455
[2] NICE guidance (CG181), Cardiovascular disease: risk assessment and reduction, including lipid modification
[3] SACN. 2019 At: https://www.gov.uk/government/publications/saturated-fats-and-health-sacn-report
[4] WHO. 2018. Draft guidelines on saturated fatty acid and trans-fatty acid intake for adults and children. At: https://extranet.who.int/dataform/upload/surveys/666752/files/Draft%20WHO%20SFA-TFA%20guidelines_04052018%20Public%20Consultation(1).pdf
[5] Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association Circulation. 2017; 136:e1–e23. DOI: 10.1161/CIR.0000000000000510
[6] NICE guidance (CG71) Familial hypercholesterolaemia: identification and management
[7] Gayet-Boyer C, Tenenhaus-Aziza F, Prunet C et al. (2014) Is there a linear relationship between the dose of ruminant trans-fatty acids and cardiovascular risk markers in healthy subjects: results from a systematic review and meta-regression of randomised clinical trials. British Journal of Nutrition 112: 1914–22.
[8] de Souza RJ, Mente A, Maroleanu A et al. (2015) Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. British Medical Journal 351: h3978.
[9] Roberts C, Steer T, Maplethorpe N et al. (2018) National Diet and Nutrition Survey Results from Years 7 and 8 (combined) of the Rolling Programme (2014/2015 to 2015/2016). Public Health England: London.
[10] SACN (Scientific Advisory Committee on Nutrition) (2018) Update on Trans Fatty Acids and Health. Available at: www.gov.uk/government/publications/sacn-update-on-trans-fatty-acids-2007
[11] WHO (World Health Organization) (2018) REPLACE Trans Fat: An Action Package to Eliminate Industrially‐Produced Trans‐Fatty Acids. World Health Organization: Geneva. Available at: www.who.int/nutrition/topics/replace-transfat
[12] Maria Luz Fernandez, Kristy L. West, Mechanisms by which Dietary Fatty Acids Modulate Plasma Lipids, The Journal of Nutrition, Volume 135, Issue 9, September 2005, Pages 2075–2078, https://doi.org/10.1093/jn/135.9.2075
[13] Siri-Tarino PW, Sun Q, Hu FB et al. (2010) Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. American Journal of Clinical Nutrition 91: 535–46.
[14] Chowdhury R, Warnakula S, Kunutsor S et al. (2014) Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Annals of Internal Medicine 160: 398–406.
[15] Hooper L, Martin N, Abdelhamid A et al. (2015) Reduction in saturated fat intake for cardiovascular disease. Cochrane Database of Systematic Reviews 10: CD011737.
Individual SFA and their effects on lipid markers
Not all SFA raise cholesterol – Lauric (12:0), Myristic (14:0) and Palmitic (16:0) Acids raise total, LDL-C and HDL-C, while stearic acid (18:0) is considered to have a neutral affect. However replacing stearic acid with unsaturated fat lowers LDL-C. Read the WHO's detailed overview of the impacts of different SFA on cholesterol.
Foods containing SFA usually comprise a combination of SFA (see right), and so their individual differences on serum cholesterol should not affect dietary recommendations to lower overall saturated fat intake and replace with unsaturated fat.
Recommendations for omega-3 fatty acids
PUFA exist in the n-3 or n-6 isomeric configuration. Both isomers are essential nutrients and have different biological effects. α-Linolenic acid, a dietary n-3 PUFA, is present in soybean and rapeseed oil, walnuts and in very small amounts in some green vegetables. Fish oil contains the very-long-chain n-3 PUFA, eicosapentaenoic acid and docosahexaenoic acid.
Observational evidence indicates that consumption of fish (at least twice a week) and vegetable foods rich in n-3 fatty acids is associated with lower risk of CVD death and stroke but has no major effects on plasma lipoprotein metabolism at this intake[1],[2]. However high-dose prescription n-3 supplemental forms may be used to treat hypertriglyceridaemia.
Public health guidance is to eat two portion of fish a week, one of which should be oily, to achieve the SACN recommendations of 0.45g of long chain Omega 3 fatty acids a day[2]. While a recent Cochrane review has questioned the heart health benefits of fish oil supplements[3], the dietary advice for fish consumption remains.
[1] Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association Circulation. 2017; 136:e1–e23. DOI: 10.1161/CIR.0000000000000510
[2] Public Health England (20014) SACN Advice on Fish Consumption https://www.gov.uk/government/publications/sacn-advice-on-fish-consumption
[3] Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega‐3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2018, Issue 7. Art. No.: CD003177. DOI: 10.1002/14651858.CD003177.pub3.
Recommendations for dietary cholesterol
Although there is a positive dose-dependent relationship between the intake of dietary cholesterol with blood LDL-C concentrations, the main dietary determinant of blood LDL-C concentrations is SFA intake. As such, public health recommendations do not provide guidance on dietary cholesterol intakes. A good overview on the effects of dietary cholesterol on lipids can be found here.
NICE guidance for both ‘Familial Hypercholesterolaemia management’ and for ‘Cardiovascular disease: risk assessment and reduction, including lipid modification’, do provide advice for high risk individuals, recommending an intake of dietary cholesterol less than 300 mg/day. As a nation our average intake of dietary cholesterol is below this threshold[1].
All animal foods contain some cholesterol, so by cutting down on animal foods high in saturated fat, cholesterol intakes will also be reduced.
A Science Advisory from the American Heart Association [2] recently reviewed the evidence examining the relationship between dietary cholesterol and blood lipids, lipoproteins and cardiovascular disease risk. Meta-analyses of intervention studies generally find associations between cholesterol intakes that exceed current average levels with elevated total and LDL-C. However, the available evidence suggests that, within the context of healthy eating patterns, replacing SFA with UFA is expected to produce greater reductions in LDL-C than reducing dietary cholesterol alone. Rather than provide a specific dietary cholesterol target, it is recommended to promote healthy eating patterns which emphasise fruit and vegetables, whole grains, low fat dairy foods, lean protein sources, nuts, seeds and liquid vegetable oils. These eating patterns are inherently low in cholesterol.
[1] EFSA Panel on Dietetic Products, Nutrition and Allergies (2010) Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol
https://doi.org/10.2903/j.efsa.2010.1461
[2] Jo Ann S. Carson, Alice H. Lichtenstein, Cheryl A.M. Anderson, et al. (2019) Dietary Cholesterol and Cardiovascular Risk: A Science Advisory From the American Heart Association Circulation 140:00–00. DOI: 10.1161/CIR.0000000000000743
