Hearth health

Lower intake of saturated fat coupled with higher intake of polyunsaturated fat helps to lower low density lipoprotein (LDL) cholesterol and supports a healthy heart. The recommended shift from saturated to unsaturated fats should occur without increasing total energy intake. One effective way to achieve this is by altering the overall dietary pattern by eating more nutrient-dense plant-based foods.

Heart disease in the UK. Over 2.3million people are living with coronary heart disease (CHD) in the UK and it is one of the leading causes of mortality with an average 180 deaths each day.  

Raised blood cholesterol levels are a known modifiable risk factor for coronary heart disease (CHD). The evidence is substantial and consistently demonstrate a dose-dependent relationship between low density lipoprotein (LDL) cholesterol and the risk of CHD. Additionally, the evidence shows that lowering LDL-C reduces CHD events. The lower the LDL-C level attained, and the longer time period the reduction is maintained, the greater the clinical benefit accrued. 

Over half the UK adult population have high cholesterol levels – above 5mmol/L.

Causes of elevated serum LDL cholesterol.

A main cause of elevated cholesterol levels is unhealthy dietary habits and, in particular, a high intake of saturated fatty acids. Other causes of CHD beyond genetics are also dietary related: type 2 diabetes, central obesity and metabolic syndrome.

Replacing saturated fat with unsaturated fat in the diet is central to lowering LDL cholesterol

Despite the current debate about saturated fats, 2018 saw the publication of two extensive reviews of the totality of high quality scientific evidence by the Scientific Advisory Committee on Nutrition (SACN) and the World Health Organisation (WHO). Both have concluded that lowering saturated fat and replacing with unsaturated fat will lower cholesterol levels and thus support heart health. The SACN’s and the WHO’s conclusions were in line with the earlier findings from the American Heart Association (AHA): all confirmed that saturated fat intake should be reduced but also emphasised that in order to reduce the CHD risk, saturated fat should be replaced with unsaturated fat, and especially, with polyunsaturated fat.

These findings are in agreement with the earlier conclusions of the European Food Safety Authority (EFSA) who authorised the health claim, “replacing saturated fats with unsaturated fats in the diet has been shown to lower/reduce blood cholesterol. High cholesterol is a risk factor in the development of coronary heart disease.” EFSA is responsible for assessing the scientific credibility of nutrition and health claims communicated to consumers.

The relationship between saturated fat (SFA) and CHD events is indirect, and mediated through the LDL cholesterol raising effects of dietary SFA.

Poorly designed studies have fueled the saturated fat controversy.

Studies claiming that saturated fat intakes and serum cholesterol and or CHD events are not related, have failed to take into consideration the numerous limitations of studies they have included in their review and meta-analysis process which would make any findings null and void. 

• Common limitations of studies overlooked:
  • Statistical power.
• The macronutrient used to replace saturated fat in the diets:
  • Type of carbohydrate used to replace saturates e.g. sugars, refined carbohydrates or wholegrains. It is now well established that replacement of SFA with refined carbohydrates has no impact on CHD events or cholesterol and may even result in a negative effect.
• Confounding factors:
• Use of trans fat, particularly in older studies e.g. the Sydney Heart Study used in many of the meta-analysis fuelling the saturated fat controversy.
• Sufficient data on the range of intakes of saturated fats.
• The complexity of dietary and other changes made during interventions e.g. PUFA intakes in some studies were exceptionally high and significantly above recommendations.
• Changes in body weight when iso-energetic diets were not used between intervention groups.
• Dietary intake methodology.
• Pharmaceutical treatments (e.g. statins) in studies published after 1990.

Replacing SFA with refined carbohydrate, as many Westerners have done in an attempt to lower their total and SFA intake, has little if any impact CHD risk. Population studies failing to show lower SFA intake is associated with a lower CHD risk have failed to consider the impact of the macronutrient that replaces SFA. 

The beneficial fat profile of plant-based foods (low in saturated fat, high in unsaturated fat) has been associated with lower blood LDL-C .

Beyond saturated fat for lowering cholesterol: there are other plant-based foods which have been associated with lowering serum cholesterol levels: soya protein, nuts, beta-glucans found in oats and barley as well as foods fortified with stanols and sterols.

Direct cholesterol-lowering effect of soya protein

Several meta-analysis have shown the cholesterol-lowering effect of soya protein. Soya protein seems to be capable of directly lowering LDL-C by approximately 4 to 5%. The greater the initial cholesterol level, the larger the drop in cholesterol. 

Meta-analysis of clinical studies evaluating the effects of soya protein on lipid levels:

Source: Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soya protein intake on serum lipids. N Engl J Med 1995;333:276-82

One proposed explanation for the hypo-cholesterolaemic effect is that peptides formed from the digestion of soya protein upregulate LDL receptors in the liver allowing cholesterol to be removed from the bloodstream more efficiently.

This benefit of soya protein was first formally recognised by the US Food and Drug Administration (FDA) in 1999. The FDA allowed a health claim on soya foods stating that “daily consumption of 25 grams of soya protein, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease”.

In 2015, Health Canada’s Food Directorate also approved a ‘Health claim about Soya Protein and Cholesterol Lowering’. According to Health Canada’s Food Directorate, scientific evidence exists to support the health claim that consumption of soya protein helps to lower blood cholesterol levels. The Health Canada’s Food Directorate based its decision on literature research covering a period from 1980 to March 2010. All foods containing soya protein such as isolated soya protein, soya protein concentrate, textured soya protein and soya flour but also foods made from the whole soya bean are eligible for the health claim. Food containing at least 6g of soya protein per reference amount and per serving as well as complying with a list of conditions regarding the presence of recommended nutrients, maximum levels of cholesterol, alcohol, etc., are allowed to bear the health claim.

In Europe the claim has been submitted, however has not been approved for use on food products containing soya.

Indirect cholesterol-lowering effect: food substitution effect

Soya foods potentially reduce cholesterol via a combination of the direct cholesterol-lowering effect of soya protein and the substitution or displacement of higher saturated fat foods (such as fatty meat and dairy products) with soya foods providing unsaturated fats.

When soya foods replace common sources of animal protein in Western diets, which are typically high in saturated fat, the favourable change in fatty acid intake can help lower LDL-C.

Jenkins et al. explored the extent to which the displacement of animal-derived foods (high in SFA) from the diet with a soya was responsible for the cholesterol lowering properties of soya foods. Using data from 11 interventions, he calculated that when comparable amounts of animal proteins were replaced with soya proteins there was a 3.6-6.0% reduction in LDL-C due to the displacement of SFA and cholesterol from the diet. 

WHO. Gaining health: The European strategy for the prevention and control of non-communicable diseases. 2006. 

Adult Treatment Panel II. National Cholesterol Education Program. Second Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel II). Circulation 1994;89:1333-445.

Adult Treatment Panel III. Executive Summary of The Third Report of The National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, And Treatment of High Blood Cholesterol In Adults (Adult Treatment Panel III). JAMA 2001;285:2486-97.

Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soya protein intake on serum lipids. N Engl J Med 1995;333:276-82.

Chiavaroli L, Nishi S, Khan T et al. Portfolio Dietary Pattern and Cardiovascular Disease: A Systematic Review and Meta-analysis of Controlled Trials. Prog Cardiovasc Dis.. 2018;61(1):43-53

Chowdhury R, Warnakula S, Kunutsor S et al. Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Ann Intern Med 2014;160:398-406.

FDA Approved claims: “Soya protein and risk of coronary heart disease”. Federal Register vol 64 no 206 Tuesday October 26 1999

FDA. FDA Approved claims: "Soya protein and risk of coronary heart disease". Federal Register vol 64 no 206 Tuesday October 26 1999. 26-10-1999. Ref Type: Report

Ference B, Ginsberg H, Graham I, et al. Low-density lipoproteins cause atherosclerotic cardiovascular disease. Evidence from genetic, epidemiologic, and clinical studies. A consensus statement from the European Atherosclerosis Society Consensus Panel. Eur Heart J. 2017;0:1–14.

Griffin BA. Serum low-density lipoprotein as a dietary responsive biomarker of cardiovascular disease risk: Consensus and confusion. Nutr Bull 2017;42:266-73.

Harland JI, Haffner TA. Systematic review, meta-analysis and regression of randomised controlled trials reporting an association between an intake of circa 25g soya protein per day and blood cholesterol. Atherosclerosis 2008;200:13-27.

Health Canada, Bureau of Nutritional Sciences, Food Directorate Health Products and Food Branch. Summary of Health Canada's Assessment of a Health Claim about Soya Protein and Cholesterol Lowering. March 2015 [Internet]. 2015 [cited 13th March 2018]. Available from: https://www.canada.ca/en/health-canada/services/food-nutrition/food-labelling/health-claims/assessments/summary-assessment-health-claim-about-protein-cholesterol-lowering.html

Hooper L, Kroon PA, Rimm EB et al. Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr 2008;88:38-50.

Jenkins DJ, Mirrahimi A, Srichaikul K et al. Soya Protein Reduces Serum Cholesterol by Both Intrinsic and Food Displacement Mechanisms. J Nutr 2010;140:2302S-11S.

Keys A, Parlin RW. Serum cholesterol response to changes in dietary lipids. Am J Clin Nutr 1966;19:175-81.

Keys A, ANDERSON JT, GRANDE F. Prediction of serum-cholesterol responses of man to changes in fats in the diet. Lancet 1957;273:959-66.

Law MR, Wald NJ, Thompson SG. By how much and how quickly does reduction in serum cholesterol concentration lower risk of ischaemic heart disease? BMJ 1994;308:367-72.

Li Y, Hruby A, Bernstein AM et al. Saturated Fats Compared With Unsaturated Fats and Sources of Carbohydrates in Relation to Risk of Coronary Heart Disease: A Prospective Cohort Study. J Am Coll Cardiol 2015;66:1538-48.

Reynolds K, Chin A, Lees KA, Nguyen A, Bujnowski D, He J. A meta-analysis of the effect of soya supplementation on serum lipids. Am J Cardiol 2006;98:633-40.

Sacks FM, Lichtenstein AH, Wu JHY et al. Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association. Circulation 2017;135.

SACN. Draft report: Saturated fats and health [Internet]. 2018 [cited Aug 2018]. Available from: https://www.gov.uk/government/consultations/saturated-fats-and-health-draft-sacn-report

Taku K, Umegaki K, Sato Y, Taki Y, Endoh K, Watanabe S. Soya isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials. Am J Clin Nutr 2007;85:1148-56.

Tokede OA, Onabanjo TA, Yansane A, Gaziano JM, Djousse L. Soya products and serum lipids: a meta-analysis of randomised controlled trials. Br J Nutr 2015;114:831-43. 

Weggemans RM, Trautwein EA. Relation between soya-associated isoflavones and LDL and HDL cholesterol concentrations in humans: a meta-analysis. Eur J Clin Nutr 2003;57:940-6.

WHO. Draft guidelines on saturated fatty acid and trans-fatty acid intake for adults and children [Internet]. 2018 Available from: https://extranet.who.int/dataform/upload/surveys/666752/files/Draft%20WHO%20SFA-TFA%20guidelines_04052018%20Public%20Consultation(1).pdf

Zhan S, Ho SC. Meta-analysis of the effects of soya protein containing isoflavones on the lipid profile. Am J Clin Nutr 2005;81:397-408.