A major report on dietary fats from the American Heart Association (2017)

This post is made up of two pieces from my “behind the headlines” section of this blog. They were posted in June 2017 in response to press coverage of a major American Heart Association report on the relationship between diet and heart disease risk. Some press coverage of this report focused on its conclusions that coconut oil had similar effects upon raising blood cholesterol and heart disease risk as highly saturated animal fats like beef. Other press coverage focused on its claim that changes in the composition of dietary fats could theoretically be as effective as statins in lowering blood cholesterol levels. I have re-posted them here because the messages within them have long term relevance.

Coconut oil “as unhealthy as beef fat and butter”

This headline appeared on the BBC news web-site on 16/6/17 and similar headlines appeared in other UK newspapers like The Sun and in the American national newspaper USA Today . These news reports relate to an authoritative review by an expert panel on “Dietary Fats and cardiovascular disease” released as “A Presidential Advisory” from the American Heart Association (AHA) . The report reviews the current case for reducing dietary saturated fat intake and whether it is better to replace it with carbohydrates or with unsaturated fats. The report covers more than 20 pages and yet, despite the media headlines, the section dealing with coconut oil covers less than half a page. I will therefore split this post into two and comment in this post on the specific findings in relation to coconut oil and in second post (now below) on the wider conclusions of the report using a headline from NBC News .

Sales of coconut oil and coconut containing food products have been increasing very rapidly in the UK and other countries and many coconut-based cosmetic products are also available. Coconut oil/milk is widely used as an alternative to milk, butter and cream in many recipes and in many prepared savoury products and desserts. It is widely used in a range of dairy-free alternatives to conventional foods. Coconut oil is known to be very high in saturated fats and saturated fats are known to raise the “bad cholesterol” (LDL) in blood. This, in turn, increases atherosclerosis and the risk of heart attacks, strokes and other cardiovascular diseases. A huge volume of experimental evidence stretching back over 6 decades shows that diets high in saturated fats lead to raised LDL-cholesterol levels but that diets with similar amounts of unsaturated fats, especially polyunsaturated fats from vegetable oils, result in lower LDL-cholesterol levels and reduced cardiovascular risk (see below). Table 1 shows the breakdown of the fatty acids in seven common food fats.

Table 1             The percentage of total fatty acids that are saturated, monounsaturated and polyunsaturated in seven food fats.

Fat                               Saturated %                monounsaturated %    polyunsaturated %

Sunflower oil                        14                                34                                53

Rapeseed oil                          7                                  60                                33

Lard                                        45                                44                                10

Palm oil                                  48                                44                                8

Butter                                      63                                33                                3

Coconut oil                             91                                7                                  2

Olive oil                                  15                                73                                 13

Milk and meat fat are high in saturates and low in polyunsaturates whilst most common vegetable oils like sunflower oil, corn oil, soy oil, safflower oil and peanut oil are low in saturates and high in polyunsaturates.  Olive oil and rapeseed oil are low in saturates but particularly high in monounsaturates rather than polyunsaturates. As can be seen from the table the two tropical oils, palm oil and coconut oil, have fatty acid profiles that are more like meat and milk than other vegetable oils and so high intakes might be expected to raise LDL-cholesterol levels and predispose to cardiovascular disease.  Thus promoting coconut oil as a “healthy alternative” to dairy fat seems to be difficult to reconcile with these figures although its supporters rightly point out that the saturated fatty acids in coconut oil are different to those seen in most other fats. Most of the saturated fatty acids in coconut oil have shorter chains (14 or less carbon atoms) whereas in most other fats and oils those with 16 or more carbon atoms predominate. It has been suggested that coconut oil fatty acids might raise the “good cholesterol” (HDL) in the blood although the AHA report suggests that this is not a significant beneficial effect. In the AHA review it is concluded that the common individual saturated fatty acids, including those in coconut oil, raise LDL-cholesterol and replacing them with unsaturated fatty acids lowers LDL-cholesterol. A meta-analysis (weighted amalgamation) of seven clinical trials comparing the effects of coconut oil upon LDL-cholesterol with other oils rich in monounsaturated or polyunsaturated fatty acids found that these trials unanimously reported that coconut oil raises the LDL-cholesterol. There is also no difference between coconut oil and other highly saturated oils (like butter and palm oil) in their raising effect upon LDL-cholesterol, hence the headline conclusion that coconut is as unhealthy as beef fat or butter.

My assessment is that coconut oil raises LDL-cholesterol just as one would expect from its fatty acid profile shown in table 1. There seems to be no rational case based upon blood cholesterol and heart disease risk for replacing saturated dairy and animal fats with saturated coconut oil or palm oil. Coconut oil is, however, a palatable and very useful alternative to dairy fat in many recipes and provides a good alternative for those who for a variety of cultural, ethical and allergy reasons want or need to avoid dairy products. Treat it like butter or cream, something to enjoy in moderation. If you want an ice cream, a tiramisu, a creamy curry sauce or “cheese”  without milk then products made from coconut enable good dairy-free versions to be made but they are not “healthier” unless you are intolerant to a component of milk. As will be seen below, the main health message from this AHA report is to replace as much of the saturated fat in your diet as you reasonably can with unsaturated vegetable oils, especially those high in polyunsaturated fatty acids.

Good fats as helpful as statins against heart disease, group says

This headline is from NBC News 16/06/17 and was prompted by an authoritative report on “Dietary Fats and Cardiovascular Disease” commissioned by the American Heart Association (AHA). Many media comments on this report have focused upon its conclusions about coconut oil and this was dealt in another post (now above).

Since the 1960s, it has been the generally accepted scientific and medical wisdom that dietary saturated fats from meat fat, milk fat and tropical oils like coconut and palm oil raise the “bad cholesterol” (LDL) in the blood. A raised LDL-cholesterol level leads to furring up of arteries (atherosclerosis) and this in turn increases the risk of cardiovascular diseases like heart attacks and strokes. Cardiovascular diseases are the biggest cause of death in affluent countries like the USA and account for over 17 million deaths per year globally. Official dietary guidelines in most western countries thus usually suggest strict limits on the intake of saturated fats. They also usually suggest limits on total fat intake (e.g. to reduce obesity risk) and this means that if total calorie intakes remain the same, that these fat calories are often replaced by carbohydrate calories; ideally from unrefined starchy products which are also rich in dietary fibre.

It is certainly possible to achieve substantial short-term reductions in saturated fat intakes and LDL-cholesterol levels by diet modification in motivated subjects when good dietary counselling and monitoring support is provided. This high level of support and monitoring would be likely, for example, in well-designed, short-term clinical trials of dietary interventions. It is much less effective if patients are simply told that their cholesterol is a bit high and they are just given a generic diet sheet.

Statins are a class of drugs that inhibit cholesterol synthesis in the body and they are very effective in reducing LDL-cholesterol levels and in clinical trials they reduce cardiovascular events and both cardiovascular and total mortality in subjects with raised LDL-cholesterol levels or who have already had a heart attack. They are the cheap, simple and effective option for lowering blood cholesterol levels, requiring little effort from either patient or practitioner. Up to 7 million people (in 2017) in the UK take statins regularly and recent changes in NICE guidelines might more than double the number eligible to be prescribed them. I written about statins in another post.

The AHA report was commissioned in response to some contradictory findings from recent meta-analyses (amalgamations) that seemed to question the traditional model i.e. saturated fats raise LDL-cholesterol and raised LDL causes increased furring up of arteries (atherosclerosis) and cardiovascular disease. This they say has created confusion amongst patients, physicians and the general public. Their report is intended to clarify the situation and reduce this confusion. In the UK there have been a number of media reports, based upon scientific publications, that have questioned this traditional wisdom e.g. reports that eating dairy products, even high fat dairy products does not increase risk of strokes or heart attacks and that saturated fats do not increase heart attack risk . The AHA report identifies several meta-analyses that produce apparently contradictory conclusions i.e. that replacing dietary saturated fats does or does not reduce cardiovascular disease events. In a meta-analysis there is a weighted amalgamation of studies with similar design, intervention strategies and outcome measures to essentially produce a single study of greater statistical power and thus to get a consensus finding from all of the studies. One reason why different meta-analyses addressing an apparently single question come up with different conclusions is because of differences in the criteria they use for selecting studies to include. The AHA report suggested that it was differences in what replaced the saturated fat that resulted in differences in outcomes from meta-analyses, clinical trials and observational studies. Those studies that replaced saturated fat with polyunsaturated fat led to bigger reductions in LDL- cholesterol and to reductions in cardiovascular disease whereas those that replaced the fat with “carbohydrate” did not produce significant reductions in cardiovascular disease. There was an indication that replacing saturated with monounsaturated fats was less effective than polyunsaturated fat. Much of the evidence upon which the conclusions of this report are based is from experimental studies (like clinical trials) rather than from less valid observational studies. I am particularly unimpressed by observational studies that look at the associations between crude estimates of intakes of particular foods and particular diseases. For example, the claimed lack of association between eating dairy products and cardiovascular diseases mentioned above especially as some of the authors have affiliations to or sponsorship from the dairy industry.

Essentially this AHA report, reinforces and refines some of the longstanding beliefs about diet, blood cholesterol and cardiovascular disease risk. This report is mainly focused upon cardiovascular disease which is understandable as it is produced by an organisation primarily concerned with the prevention and treatment of cardiovascular diseases. Some of the conclusions from this report:

  • All saturated fats, from both animal and vegetables sources, tend to raise LDL-cholesterol levels
  • In clinical trials, replacing saturated fats with unsaturated fats, especially polyunsaturated fats from vegetable oils, reduces both LDL-cholesterol and prevents cardiovascular disease
  • In observational studies, diets that are low in saturated fat and high in polyunsaturated and monounsaturated fat are associated with lower rates of cardiovascular disease and death from all causes
  • In both clinical trials and observational studies, when saturated fat is largely “replaced” by unspecified carbohydrate there is no reduction in cardiovascular disease or all-cause mortality
  • Their findings suggest the strategy for reducing cardiovascular disease should be to reduce saturated fat intakes and replace them mainly with polyunsaturated fats from vegetable oils.

Persuading 15 million UK adults to take statins may produce similar or only slightly bigger reductions in LDL-cholesterol, cardiovascular and all-cause mortality than those that could be produced if these suggested dietary changes were universally implemented. It may be seen as the cheap and easy (lazy?) strategy that requires little effort or commitment from either health practitioners or patients. Producing dietary changes amongst the least health conscious and most vulnerable section of the population will be a long and difficult process requiring considerable commitment and resources; this persuasion process has already been ongoing for decades. Dietary change may be the preferred option but mass use of statins may be the pragmatic, easy option likely to do the greatest good to the largest number in the short or medium term.

 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s