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The SACN latest report puts a stop to the saturated fat controversies

Added on
01 Aug 2018

The Scientific Advisory Committee on Nutrition (SACN) published its Saturated Fats and Health draft report in May after an extensive review of the data from high quality prospective cohort and randomised controlled trials.1 The consultation period closed on the 3rdJuly and the final report is due in the autumn. The overall findings strongly support current dietary advice to lower saturated fat intakes and the importance of which macronutrient replaces it. Additionally, the report highlights the limitations of much of the data responsible for the recent controversies.

The SACN latest report puts a stop to the saturated fat controversies

Introduction
There has been much debate in the medical and consumer press on the benefits of lowering saturated fats in the diet for improved health outcomes. Recent meta-analysis2 -4 have disputed recommendations from government,5 heart health organisations6,7 and the World Health Organisation (WHO)8 that the reduction in saturated fat intakes will yield heart health benefits. Since the current UK dietary recommendations to restrict saturated fats to no more than 10% of total energy intake were set back in 1994,9 it was time to review more up to date evidence. 
 
The SACN was tasked with reviewing the evidence for saturated fat’s impact on numerous health outcomes (heart health, cognition, diabetes, cancer etc.) as well as disease markers and risk factors. After reviewing all prospective cohort trials (PCT) and randomised controlled trials (RCT) published between 1991 and 2016, the SACN identify 47 systematic reviews, meta-analyses and pooled analyses which met with their eligibility criteria.

Significant limitations of the available data could be responsible for fuelling the saturated fat debate. 
In its thorough evaluation of the evidence, the SACN did highlight the significant limitations in the data that limits the possibility of drawing clear conclusions on many health associations with saturated fat. Interestingly, the handful of publications fuelling the saturated fat controversy are guilty of failing to take into considerations these significant limitations, which included:

  • Limited length of follow-up time of RCT and PCT assessing disease as an outcome hence unable to make conclusions with regard to the impact of saturated fat on cardiovascular disease (CVD) or coronary heart disease (CHD) mortality.
  • Lack of information on:
    • Statistical power.
    • Type of carbohydrate used to replace saturates e.g. sugars, refined carbohydrates or wholegrains.
    • Type of polyunsaturated fatty acids (PUFA) substituted for saturated fats – therefore unable to come to any clear conclusion around the impact of n-3 / n-6 PUFA specifically.
  • Confounding factors:
    • Use of trans fat, particularly in older studies e.g. the Sydney Heart Study used in 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.

The SACN’s key findings
Due to the limitations in the available data, the evidence was only strong enough to draw conclusions on the relationship between saturated fats and serum blood lipids and cardiovascular disease (CVD) and coronary heart disease (CHD) events.

Saturated fatty acid dietary manipulationReduction in CVD / CHD events?Reduces Total cholesterolReduces LDL cholesterolReduces total:HDL cholesterol ratioReduces triglycerides
Reducing dietary saturated fats YesYesYesNoYes
Replacing dietary saturated fats with polyunsaturated fatty acids (PUFA)YesYesYesYesNo
Replacing dietary saturated fats with monounsaturated fatty acids (MUFA)NoYesYesYesNo

Replacing dietary saturated fats with polyunsaturated fatty acids (PUFA)

  • Additionally, glycaemic control is improved.
  • As the majority of studies did not differentiate or specify the sub-class of PUFA (i.e. n-3 or n-6), no further recommendations could be made.

Replacing dietary saturated fats with carbohydrates

  • A key limitation of the available data was the lack of clarity on the type of carbohydrate (i.e. wholegrain vs refined carbohydrates) used as a replacement. This would explain the inconsistency in results between studies and the recent claims that reductions in saturated fats do not improve heart health outcomes. 
  • Replacing saturated fats with refined carbohydrates / sugars would not result in the same health outcomes as replacement with wholegrains.

Replacement of saturated fats with protein

  • The evidence is inconclusive.


The SACN Recommendations for the UK
The report advises that saturated fat recommendations should remain at ≤10% total energy intake, and that emphasis should be placed on replacing with PUFA or MUFA. Additionally, the SACN highlights that better quality studies are required if we are to gain any insight into the true impact of carbohydrate as a replacement for saturated fatty acid reductions and the association between saturated fatty acids and out health outcomes.

SACN dietary fat recommendations vs current UK adult intakes


Recommendations as
% total dietary intake1
(from 5 years upwards)
Current UK adult intakes
g per day & % total energy10,11
(19-64 years)
Total fats≤ 35%33.2% total energy
Saturated fats≤10%11.9% total energy
Cis MUFANo specific recommendations25.1g per day – 12% total energy
Cis PUFA6%5.8%
Cis n-3 PUFA- Long chain n-3 PUFA (EPA/DHA) – 0.45g per day (~0.2%)
- α-linolenic acid ≥0.2%
- Total n-3 PUFA @ 2g per day – 1% total energy.
- Long chain n-3 PUFA @ 0.2g per day.
Cis n-6 PUFAOverall, no further increase but linoleic acid should be ≥1%Total n-6 PUFA @ 10g per day – 4.8% total energy.
Trans fat≤2%0.5%

Outside the remit of the SACN report: Are all saturated fats created equal?

A. The impact of individual saturated fatty acids on serum lipids and CVD outcomes.
Although not reviewed by the SACN, this was investigated at length by a 2016 WHO publication12 and re-iterated in the recent 2018 WHO draft guidance on saturated and trans fatty acid intake for adults and children.8 The review identified three saturated fatty acids as most cholesterol-raising, whilst others such as stearic acid (C18) had no impact.

Saturated fatty acids proven to increase serum LDL-cholesterol levels in order of increasing magnitude:12 -14 

  1. Palmitic acid (C16): palm oil, cocoa butter, meat fat and dairy products.
  2. Myristic acid (C14): coconut oil, butter and palm kernel oil.
  3. Lauric acid (C12): coconut oil (45% of total fat content) and palm kernel oil. Despite the current consumer health trend, coconut oil is by far the biggest contributor of the most cholesterol-raising saturated fatty acid.

Fat within the food matrix is often a combination of many fatty acids, and interestingly, the foods rich in the cholesterol-raising raising saturated fatty acids are also the key sources of total saturated fat in the UK diet.

Food sources of total saturated fat in the UK diet for adults aged 19-64 years.11 

  • 24% from meat and meat products: rich source of palmitic acid.
  • 21% cereal and cereal products:
    • Predominantly biscuits, cakes, buns, pastries and pizza. Many of these foods will contain palm or palm kernel oil (rich in palmitic and myristic acid) as well as animal fats rich in palmitic acid.
  • 21% from milk and milk products: providing palmitic and myristic acid.
  • 9% from fat spreads: mainly driven by butter consumption, a source of myristic acid.
  • 6% from vegetable dishes and fried potatoes: palm oil is often used in their production.

B. The impact of the food matrix.15 

The food matrix within which the saturated fatty acids are contained could influence the overall impact on health outcomes and could help explain some of the inconsistencies within study results. As an example, dairy constituents such as conjugated linoleic acid, calcium, magnesium, potassium and whey protein are proposed to have cardio-protective effects.
Putting the recommendations into context of the UK’s dietary habits and the obesity epidemic.
It is clear, that reductions in saturated fat is necessary to help reduce current levels of hypercholesterolaemia which is a key modifiable risk factor for CVD and CHD; one of the major causes of ill health and death in the UK.16 Additionally the evidence is clear that the macronutrient replacing saturated fats plays a key role with PUFA providing the biggest benefit followed by MUFA.1 


Should the government encourage the population to replace the calories saved from the saturated fat reductions with more fat calories – be it from PUFA or MUFA?

  • The national diet and nutrition survey clearly indicates that PUFA and MUFA intakes are more than adequate and exceed recommendations.1,10,11 
    • However, the balance of long-chain vs short chain n-3 PUFA intakes needs to be addressed.
  • The obesity epidemic is not abating.17 
  • The population needs to reduce their calorie intake rather than maintain it as highlighted by the latest Public Health England Calorie Reduction programme.18 
  • Fat is the most concentrated form of energy. 

 
Based on the above, it may be more prudent for public health messages to focus advice on reductions in saturated fatty acid intakes per se rather than actively encouraging a replacement of the calories with PUFA or MUFA. To address the re-balance of long-chain n-3 PUFA, strategies should be put in place to help the nation achieve the Eatwell guide recommendation of one oil-rich fish serving per week.5 
 
Conclusion
The SACN thorough review of the evidence (predominantly RCT), has confirmed the need to lower saturated fatty acid intake for improved serum lipid profiles and CVD and CHD events. Additionally, it provides insight into the cause of much of the controversies surrounding saturated fat, namely the limitations and confounding factors within the current data which have been overlooked by those disputing national and global recommendations. Although the evidence clearly indicates that replacement of saturated fat with PUFA and MUFA is the ideal, in the current environment of over-consumption and obesity, a public health message focus on lowering saturated fats per se may be more impactful.

References

1. SACN. Saturated fats and health: draft SACN report [Internet]. 2018 [cited 7/13/2018]. Available from: https://www.gov.uk/government/consultations/saturated-fats-and-health-draft-sacn-report
 
2. Ramsden C, Zamora D, Leelarthaepin B et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ.. 2013;346:10.
 
3. 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(6):398-406.
 
4. Harcombe Z, Baker J, Cooper S et al. Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis. Open Heart.. 2015;2(1):10.
 
5. PHE. The Eatwell Guide [Internet]. 2016 [cited 7/13/2018]. Available from: https://www.gov.uk/government/publications/the-eatwell-guide
 
6. HEART UK. Low Cholesterol Diets & High Cholesterol Foods - food that increase choleserol [Internet]. 2017 [cited 7/19/2018]. Available from: https://heartuk.org.uk/cholesterol-and-diet/low-cholesterol-diets-and-foods
 
7. The British Heart Foundation. Fats explained - types of fat [Internet]. 2018 [cited 7/19/2018]. Available from: https://www.bhf.org.uk/informationsupport/support/healthy-living/healthy-eating/fats-explained
 
8. 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
 
9. Committee on Medical Aspects of Food Policy. Nutritional Aspects of Cardiovascular Disease. 46 ed. London: HMSO; 1994.
 
10. PHE. Saturated fats and health: draft SACN report - Supporting documents: Annexes [Internet]. 2018 [cited 7/19/2018]. Available from: https://www.gov.uk/government/consultations/saturated-fats-and-health-draft-sacn-report
 
11. FSA, PHE. The National Diet and Nutrition Survey: results from years 7 and 8 (combined): rolling programme for 2014 to 2015 and 2015 to 2016 [Internet]. 2018 [cited 7/13/2018]. Available from: https://www.gov.uk/government/statistics/ndns-results-from-years-7-and-8-combined
 
12. Mensink R. Effects of saturated fatty acids on serum lipids and lipoproteins: a systematic review and regression analysis. Geneva: World Health Organization; 2016.
 
13. Forestfield Software Ltd.. Diet Plan7. McCance & Widdowson 7th summary edition of the composition of foods plus the revised composition of food integrated data set (CoFids). Patent Diet Plan7. 2018.
 
14. USDA. USDA Food Composition Databases [Internet]. 2018 [cited 7/19/2018]. Available from: https://ndb.nal.usda.gov/ndb/search/list?home=true
 
15. Siri-Tarino P, Chiu S, Bergeron N et al. Saturated Fats Versus Polyunsaturated Fats Versus Carbohydrates for Cardiovascular Disease Prevention and Treatment. Annu Rev Nutr.. 2015;35:517-43.
 
16. BHF. Heart statistics - cardiovascular disease in the UK [Internet]. 2018 [cited 4/18/2018]. Available from: https://www.bhf.org.uk/what-we-do/our-research/heart-statistics
 
17. NHS Digital. National statistics: statistics on obesity, physical activity and diet, England 2017 [Internet]. 2017 [cited 7/16/2018]. Available from: https://www.gov.uk/government/statistics/statistics-on-obesity-physical-activity-and-diet-england-2017
 
18. PHE. Calorie reduction: the scope and ambition for action [Internet]. 2018 [cited 7/19/2018]. Available from: https://www.gov.uk/government/publications/calorie-reduction-the-scope-and-ambition-for-action