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1970s dietary advice – a big fat mistake?
Many service users are of the generation that vividly recollect the cholesterol advice in the 1970s and 1980s – and remember being advised to cut down on cream, butter, cheese, even eggs. This was an era of the more traditional ‘meat and 2 veg’ cooking, an era when smoking was far more socially acceptable and when there was a belief that dietary cholesterol itself raised blood cholesterol levels. Now we firmly recognise that healthy eating is a broader subject than cholesterol alone.
Saturated fat, rather than dietary cholesterol, has more impact on blood cholesterol
However, over the past 50 years, research has allowed our scientific understanding of the role of fat in our diet on heart disease risk to increase considerably. We know for example, that for most people, the amount of saturated fat they eat has much more of an impact on their blood cholesterol levels than eating foods that contain cholesterol, like eggs, We also know there is no one single cause for high cholesterol.
Different factors can contribute to high cholesterol such as:
- eating a diet that is high in saturated fat
- being overweight/obese
- lack of physical activity
- high alcohol intake
- kidney or liver disease
The inherited condition, familial hypercholesterolemia, can also cause exceptionally high cholesterol.
Perhaps it is somewhat of a surprise then to see the media flurry this week suggesting that established advice to reduce saturated fat in the diet is not supported by science. Such headlines were based on a paper, published in the journal Open Heart which suggested that dietary guidelines published in 1977 and 1983 in the UK and US, recommending a reduction in saturated fat, were not backed by sufficient evidence. The authors carried out a meta analysis and systematic review of six small randomised controlled trials (RCTs) available at the time and concluded that this evidence showed that reducing dietary fat intake to the level set within the guidelines would not significantly reduce death from heart disease.
Is this type of retrospective approach helpful?
On the basis of the few RCTs at the time, the study has an interesting point but it is wrong on other counts. Firstly, even the authors acknowledge the limitations of the data used – the trials were small, all in male adults, mostly with a history of heart disease, varied dietary and lifestyle factors, and short follow up periods. It didn’t include non-fatal heart disease events which are key health outcomes in this area.
Importantly, it ignores the totality of evidence available at the time. Dietary guidelines are rarely solely based on RCT evidence alone but look at the consistency of a number of lines or types of evidence. Research by this point had already generated a useful knowledge of risk factors for smoking, elevated blood pressure and elevated cholesterol – the latter which particularly reflects the cholesterol raising effect of diets high in saturated fats.
Indeed, evidence for the impact of saturated fat on raising cholesterol is available from a number of evidence sources which illustrate that reducing saturated fat has a benefit in reducing LDL (bad) cholesterol, and there is separate evidence that high LDL cholesterol leads to heart disease. Since the early 1980s there have been other large positive RCTs that support these findings and further population evidence which is suggestive of an association between dietary saturated fat and coronary mortality trends.
Public health guidelines may not belong in the same arena as drug trials looking at benefit vs side effects. In the 1970s, Western countries were facing an epidemic of coronary heart disease – and had perhaps to make a choice between following what the evidence suggested or doing nothing, and it suggested that reducing saturated fat would lower blood cholesterol. In absence of clear evidence it seems reasonable that scientists produce best advice with the totality of evidence available.
Marked reduction in heart disease and intake of saturated fat over last 40 years
Countries that have introduced guidelines for the reduction of saturated fat, with partial replacement with unsaturated fatty acids, have seen a fall in mortality from heart disease. UK statistics show a significant decline in coronary heart disease mortality over the same time period as reductions in smoking and saturated fat consumption. From 1981 to 2009 mortality from coronary heart disease decreased from around 178 000 to 82 500, more than 5o per cent, and saturated fat intake decreased from around 48g to 32g per day over the same period.
The true relationship between diet and our health is not simple. Unlike drug trials, studies on diet and disease are difficult to conduct, and dietary guidance in the UK is based on consensus of the total evidence available. Some of the difficulty in demonstrating a link between saturated fat and heart disease can lie in the multiple risk factors that may impact on heart disease, such as smoking hypertension, diabetes, obesity, family history, physical activity, so cholesterol is one factor amongst many others. What we now know to be very important is what people replace the saturated fat in their diet with – replacement with unsaturated fats (polyunsaturated or monounsaturated fat) or complex carbohydrates should be recommended.
Replace saturated fat with some unsaturated fats not sugar
And the advice for reducing fat in the diet did not, as is sometimes mistakenly suggested, advise that fat should be replaced with sugar or refined carbohydrates. It advised selecting lean meat and fish, choosing reduced fat dairy, and using unsaturated vegetable oils, such as olive, rapeseed and sunflower, instead of the harder fats, higher in saturated fat. In addition reducing total fat has an advantage of also reducing calories.
The relevant question now surely is whether all the evidence up to 2015 supports the dietary guidelines today. Should we be concerned that current advice is pinned on flawed recommendations from 40 years ago? No, after all research has moved on. We now try and look more closely at the relationship between whole dietary patterns rather than vilify single nutrients. As well as the fats we eat we need to pay attention to our diet as a whole and the balance of foods with it, and it is this is the approach that should be taken in designing menus. Diets that reflect healthy eating guidelines will include wholegrains, fruit and veg, unsaturated fats and moderate intakes of meat, oily fish and dairy.
Fat advice for frail or malnourished elderly may differ
For the general population, including our residents in care homes, the advice would remain to keep saturated fat intake low and to partially replace these with unsaturated fats where possible. However, for frail elderly service users that have poor food intake and are of poor nutritional status, such as a low body mass index, it is often important that calorie/protein content is maximised and this can involve use of whole milk products including yogurt and cheese as part of the diet to support weight maintenance. For health professionals and carers working in the area of elderly malnutrition, the fear that some users have that such foods are ‘unhealthy’ can make introducing these foods to increase energy density challenging, yet it is important to educate malnourished older people and their carers as to the importance of including these foods to support their weight.
At the end, we keep looking at advice and evidence that are behind the guidelines. Maybe it is better to keep looking forward rather than back.