By Dr Joanna McMillan, PhD.
Governments and health authorities around the world give us the advice to cut down on foods that contain saturated fats and, instead, increase our intake from unsaturated fats. This advice is primarily about reducing the risk of cardiovascular disease (CVD), such as heart disease and stroke. But is it correct?
A major scientific journal published a meta-analysis (which is a study that pulls together results from available quality studies, to create a clearer picture of overall results) indicating there is actually no association between saturated fat intake and CVD. In response, questions have been raised about the impact of saturated fat on health.
To understand the full picture, it is helpful to revisit the history of how advice regarding saturated fat came about.
It started with the famous Seven Countries study led by Ancel Keys. He showed a clear linear relationship between saturated fat consumption and CVD. Although there have been criticisms of this study, there were many subsequent trials in animals and in humans that added to his claims against saturated fats.
Key to this was the emerging story on cholesterol. High levels of cholesterol in the blood and particular in LDL-cholesterol levels (the so-called ‘bad’ cholesterol) were being linked to CVD, while HDL-cholesterol (the ‘good’ cholesterol) was found to offer protective qualities. Numerous studies examined how different dietary fats affected cholesterol levels and the findings that saturated fats raised LDL and total cholesterol levels, led to the advice to cut down on consumption of these fats. It made sense to assume that reducing LDL would, in turn, reduce CVD risk.
But what do you consume instead of the saturated fat?
In the early days, the advice was to replace fattty foods with carbohydrate-rich foods. The food industry went into overdrive to bring us what we wanted – low fat foods. The problem was that these foods were largely made from processed grains and many had extra refined sugar; think: processed breakfast cereals, white rice, rice crackers, low fat snack bars, low fat ice-cream, white bread (I can remember eating a whole French baguette thinking ‘I can eat as much as I like because its low fat’; it was crazy!), and so on.
So at this point in time fat was the demon, so out it went. But in its place we ended up with an extremely high GI, highly processed carb-rich diet, which does – in fact – lower cholesterol levels; however, the trouble is it brings down 'good' HDL-cholesterol as well, while also pushing up triglycerides (another blood lipid that is also a risk factor for heart disease).
To compound matters, this diet creates glucose 'spikes' in the blood, in turn raising the demand on the body to produce insulin. Overall, it’s not a good metabolic picture, and certainly with no benefit for weight control.
Advice then moved towards recognising that while saturated fats tended to raise LDL, polyunsaturated fats (PUFA) lowered it, without also pulling down HDL. Through an influence on gene expression, PUFA actually turned down cholesterol synthesis in the liver, and so the blood pool of cholesterol falls. The advice therefore shifted to become ‘replace saturated fats with PUFA!’. As a result, sunflower and other plant oils became popular.
The concern from many researchers is that PUFA are easily oxidised while saturated fats are much more stable (for those interested in the chemistry, this is because there are no double bonds in a saturated fat molecule, while there are many found in PUFA; and it is the double bond where oxidation occurs.) In itself, LDL is not the problem, but when it is damaged by oxidation, it is this oxidised LDL that is taken up into the plagues that line the arteries (leading to a narrowing of the blood vessel that is called ‘atherosclerosis’).
So, if PUFA are incorporated into LDL, the question arises: does this increase the risk of oxidation? And could this be a problem in other cells around the body too?
This kind of thinking has fuelled the question of whether we should return to saturated fats. Interestingly, there is some belief that plant oils, particularly seed oils, are toxic to us. While I do agree that consuming seed oils is not in the best interest of our health, I do not believe they are toxic. Here's why:
A recently published meta-analysis of the gold standard randomly controlled trials (RCTs) by Harvard University researchers, has confirmed that replacing saturated fats with PUFA does, indeed, reduce CVD risk. This does not stick with the theory on PUFA promoting oxidation. Part of this may be because PUFA-rich foods also tend to be high in vitamin E and in plants, vitamin E protects the PUFA from oxidation and that's exactly the same role vitamin E has in our cells (i.e., protecting the fats in the cell membranes from oxidative damage). Additionally, it could also be an effect of reducing the saturated fats, without increasing the refined carbs.
It’s important to remember that fats are also used to form cell membranes – called the ‘lipid by-layer’. Interestingly, saturated fats are very rigid and linear (i.e., they are packed closely together), while PUFA have 'kinks' in the molecule where the double bonds are, which makes them much more fluid (envisage oil – a PUFA – compared to butter, which is a saturated fat). In the cell membrane these differences are crucial because the more saturated fats there are, the less fluid the cell structure is. In addition, saturated fats also activate a series of enzymes that have been implicated in obesity and insulin sensitivity. So the message here is simply, that fat consumption can impact on the body beyond just affecting one’s cholesterol levels.
It really all comes down to quality. The bottom line is, until relatively recently we did not have the ability to extract and refine the oil component of a seed. And although we now can, consider the technology required to do that. Olive oil is a good example: it's been a part of the human diet in some parts of the world for thousands of years for one reason – you gently squeeze the fruit and the oil comes out. That is, literally, all that happens in the production of extra virgin olive oil today. In contrast, seed oils require high pressure, high heat and/or chemicals to separate the oil. Furthermore, most supermarket oils are highly refined (including the cheaper olive oils). Quite simply, they have become processed foods. For optimum health your best decision, therefore, is to stick to extra virgin olive oil – it really is all you need in your pantry.
It’s important to understand that we typically don't eat nutrients such as saturated fat in isolation; instead, we eat food and meals and create dietary patterns that see us consume saturate fat. And it is these types of patterns that are most strongly linked to the development of CVD. We also need to realise that consuming saturated fat from a piece of cheese is different to consuming it from a meat pie or a meat-lover’s pizza. Similarly, eating a steak is not the same as eating a processed hot dog.
Interestingly, recent evidence has shown that full fat milk and cheese do not actually raise cholesterol but may even be beneficial, or at least neutral in their impact, with regards to CVD. On the other hand butter, however, does raise cholesterol levels, due to the combination of the saturated fats with the protein and calcium in the milk and cheese. This means it does affect the body differently to when the fat is extracted and eaten on it’s own.
We also know that not all saturated fats affect blood cholesterol levels in the same way. This is because there are several different types of saturated fats with varying chain lengths. Lauric acid, for example, is one with a shorter chain length and may, in fact, improve the cholesterol profile of the blood. This fat is abundant in dairy and is a key fatty acid in coconut oil – another fat often found on the 'avoid' list of most health authorities. Lumping these foods in a broad category called ‘saturated fat’ is most likely causing confusion surrounding fats and their influence on health. That said, there is very little substantiation for the health claims made about coconut oil. Communities with coconut as their staple fat do not have lower rates of heart disease and obesity, and coconut oil does not have any magical superfood qualities. It may be unfair to classify it with other high saturated fat foods, but I urge caution and would not recommend it for daily use.
So, what conclusions can we draw?
The strongest evidence is for embracing healthier dietary patterns, with the Mediterranean diet coming out as a shining example. This diet is characterised by a high intake of vegetables, olive oil, nuts, legumes, wholegrains, moderate alcohol with meals (that means a glass or two of red wine though, not getting sloshed every night!), fish and seafood, and moderate consumption of meat and dairy. For optimum health of your vascular system this is an ideal way of eating. Taking a fish oil supplement is also advised, just to ensure a sufficient intake of omega-3 fats, which have been shown to provide protective qualities.
Our ancestral diets did not contain high levels of saturated fats and I don't believe we should be doing so today; but, this doesn't mean you should avoid them completely. Instead, focus on foods rather than nutrients; this means cutting down on pastries, biscuits, cakes, processed meats and crisps/chips (regardless of the fat they are fried in). These not only contain saturated fats but the harmful trans fats, preservatives, salt and sugar.
On the other hand, do enjoy grass-fed and wild meats (which tend to be lower in saturated fat and are sources of omega-3 fats), a little cheese and other dairy foods (just be mindful of the kJ contained in your portions, as full fat dairy is more energy dense). And include other natural nutrient-rich fats including extra virgin olive oil, avocado, nuts and seeds.
The bottom line is, stick to natural and wholesome foods and you’ll be 80 per cent there to achieving your best possible diet and, ultimately, optimum health.
Article by Dr Joanna McMillan, PhD.
This article is associated with the article of the same name, which appeared in Issue 1 of OH! Magazine.