8th June 2016

For years, we’ve been told that saturated fat is bad for the heart. The dogma was that this particular type of fat raises levels of cholesterol, promotes atherosclerosis and causes heart disease. But a new report and rash of media headlines (‘Eat Fat to get thin’) has claimed that saturated fat doesn’t cause heart disease and that dietary guidelines are deeply flawed. So, should we start adding butter and bacon back to our diets?

Not so fast! While a recent review suggested saturated fat may not be as harmful to heart health as once thought, it didn’t quite give the full picture in terms of what people were replacing saturated fat with.  In studies where saturated fat was replaced with refined carbohydrate, heart disease risk didn’t go down. But if it was replaced with unsaturated fat, then there was a reduction in risk.

One of the strongest pieces of evidence linking saturated fats and heart disease comes from a Cochrane review of 15 clinical trials, which changed the diets of almost 60,000 people for at least 2 years. It concluded that if you cut saturated fat and replace it unsaturated fat then you’ll cut your risk of a heart attack.

One of the problems is that people have been replacing fat with highly processed refined carbohydrates – a recipe for disaster.  Since the 1980s, manufacturers, keen to capitalise on the low-fat trend, churned out mountains of reduced fat biscuits, cookies, snack bars, crisps, cakes and desserts – which we happily ate. But these foods usually contain more sugar and refined carbohydrate than the original versions, and for not much calorie saving.

According to a 2011 review published in the American Journal of Clinical Nutrition replacing saturated fat with highly refined carbohydrates results in a higher risk of heart disease, but replacing it with unsaturated fat lowers the risk. Another meta-analysis of 8 trials concluded that replacing 5% of energy from saturated fat with unsaturated fat reduced heart disease risk by 10%.

There may also be benefits in replacing some of your saturated fat with wholegrains. An analysis by Harvard Medical School researchers, involving more than 120,000 people concluded that replacing 5% of energy intake from saturated fats with the equivalent from polyunsaturated fats, monounsaturated fas, or carbohydrates from whole grains was associated with a 25%, 15%, and 9% lower risk of heart disease, respectively

But, the dietary guidelines never advised cutting saturated fat and replacing it with reduced fat cookies, so it would be wrong to blame rising obesity, type 2 diabetes and cardiovascular disease rates on them. Instead, they should have made it clear that we should replace saturated fat with unsaturated fat from foods such as olive oil, avocado, oily fish, nuts and seeds. 

It’s also important to realise that not all saturated fatty acids behave the same in the body. They don’t all raise cholesterol. For example, stearic acid and palmitic acid (found in meat and dairy fat) have been shown to raise cholesterol and heart disease risk while pentadecanoic and margaric acids (found in dairy) are associated with a lower risk. Surprisingly, milk – regardless of fat level – is associated with a reduced risk of heart disease, stroke and type 2 diabetes. This is not just down to its ‘good’ saturated fats but also the fact that it contains protein, calcium and other nutrients that may modulate the effect of saturated fat.

It’s not possible to say what are the real culprits when it comes to obesity, type 2 diabetes and cardiovascular disease. There are numerous factors that can contribute, including your genetic make-up (having 2 copies of the risk variant of the FTO gene, for example), appetite-regulating hormones and the composition of your gut bacteria (the microbiome). Eating too many calories is ultimately a major issue but we should stop blaming individual nutrients and foods and, instead, look at people’s diets in the broader context of their lifestyle. Most experts agree that traditional Mediterranean diet is probably the way to go.

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