Did you know that many healthy option foods are more likely to harm you than the so-called bad foods they replace? Andrew Hamilton explains how the latest research is turning our thinking on saturated fats upside down.

A professor of mine once told me: “An expert is someone who learns more and more about less and less, until they eventually end up knowing everything about nothing at all.” What he meant of course is that by focussing only on the fine detail in a very specific area of a topic, it’s very easy to miss the bigger picture and arrive at completely the wrong conclusions.

Nutrition is a case in point. Studying how a nutrient behaves in the lab is very different to understanding how it behaves in the human body, where the outcome is affected by a huge range of factors such as interactions with other nutrients, an individual’s lifestyle, environment and genetic makeup. Of course, this isn’t to criticise the scientists.

Scientific investigation is never simple, especially in an extremely complex area such as human nutrition. The best the researchers can do is to offer the most plausible theories using the currently available evidence, on the understanding that a theory might have to be adapted or thrown out completely if subsequent evidence suggests otherwise.

Dustbin of science

One theory that could be heading towards the dustbin of nutritional science on the above basis is the “saturated fat is bad” mantra that consumers have had thrust upon them by health professionals for well over 30 years. The reasoning behind this advice (now ingrained in the national consciousness) is that saturated fats act as killers in the body, raising blood cholesterol and causing heart disease.

Out with the butter, in with the marg!

On the basis of the possible link between raised blood cholesterol and an increased risk of coronary heart disease (CHD), consumers have been urged to remove foods high in saturated fat (see box 1) and instead replace them with unsaturated or low-fat alternatives. As a consequence, butter has become almost a rare sight on the supermarket shelves, replaced instead with a plethora of “butter substitutes”, claiming to be healthier courtesy of a reduced fat content, or higher unsaturated fat content, or “healthy heart additives” or various combinations of the above.

Likewise, full-fat yoghurts have virtually disappeared to be replaced with low-fat (but often sugar-laden) alternatives. Sales of red meat have declined, consumers are urged to cook and bake with unsaturated oils such as sunflower oil, while manufacturers have been busy replacing saturated fats with unsaturated in many of their products.

A big fat problem

Although this move away from saturated towards unsaturated fat seems logical, there’s a problem – namely there’s little evidence it’s improving our health. Indeed, many people may have been persuaded to make changes that may actually be harmful to their health!

The reason is because the advice given by health professionals was based on observations that saturated fats can raise levels of total blood cholesterol, theoretically increasing the risk of CHD. However, total blood cholesterol is only modestly associated with CHD. What seems to be more important than the total level of cholesterol in the blood is the number and size of low-density lipoprotein (LDL) particles that contain that cholesterol.

Also, saturated fat actually consists of a very large number of different and diverse compounds; we now understand that different saturated fats may have different effects on LDL, and on the wider risk of heart disease, based on the specific saturated fatty acids they contain. Importantly, people eat foods, not isolated fatty acids. So some foods rich in saturated fat may pose no risk for CHD or could even be protective. What’s more, recent evidence has emerged indicating that eating saturated fat over a long period of time is not linked to heart disease.

In a landmark study published just a few months ago, scientists looked at data on saturated fat consumption over many years and the subsequent incidence of heart disease by pooling together 12 previous studies in this area(1). Each of these studies was in itself very large (using between 90,000 and 340,000 subjects), which means that the overall results were based on more than a million people of all ages and backgrounds.

The results were damning; there was simply no association between saturated fat intake and the incidence of stroke, heart disease, death from heart disease, or indeed early death from any other causes such as cancer. That was the good news; the bad news was that consuming certain types of unsaturated fats called “trans fats” was strongly linked to an increased risk of heart disease and death from heart disease. And that’s worrying because trans fats tend to occur when foods containing unsaturated fats are processed – exactly the kinds of foods that the health professionals told us to eat more of instead of saturated fat.

More fat, less sugar

There’s also another downside to the “ditch saturated fat” health mantra because in a number of foods such as low-fat yoghurts, the manufacturers reduce the fat content but then add significant quantities of sugar to compensate for the thinner texture that inevitably occurs.

However, when saturated fats are replaced with refined carbohydrates such as sucrose (table sugar) or high fructose corn syrup, the end result is bad heart health. A newly published study reviewing all the evidence has concluded that such a replacement inevitably leads to unfavourable changes in LDL cholesterol and blood fats, which increase the risk of CHD, and that a diet high in added sugars can cause a 3-fold increased risk of death due to CHD(2).

The way forward

At this point, you may be feeling more than a little confused and wondering what this means for your weekly shopping trip? Well, let’s try and put these findings into context. These (and other) recent studies are not saying that we should be switching to a diet of steak and clotted cream. But what they do suggest is that switching from foods naturally rich in saturated fat to those where saturated fat is replaced with unsaturated fat is not supported by scientific evidence.

Indeed, it could actually be a bad move since processed products containing unsaturated fats are likely to contain higher levels of harmful trans fats. But let’s add a couple of caveats. Firstly, if you train seriously, a diet rich in natural, unprocessed carbohydrate is essential to help fuel your workouts. By reducing junk fat in your diet, you can increase the proportion of carbohydrate without the need to consume an excess of calories, which could dent performance by piling on the pounds. Secondly, some unsaturated fat (“essential” fats) is very important for health – especially omega-3 oils, which tend to be lacking in the typical British diet.

On the latest and best available evidence to date therefore, a sensible approach is not to assume that products labelled “low-fat”, “fat-free” or “low in saturated fat” are any healthier than their traditional counterparts. Instead, reduce your intake of processed and refined foods, which are more likely to contain harmful fats, ensure you consume some high-quality essential fats.

Watch out too for low-fat foods with added sugar – one of the biggest health cons in the book. Finally, if you enjoy butter on your toast, or the occasional slab of red meat, tuck in, enjoy and don’t feel guilty.

Practical tips

  • Reduce your intake of fast/processed/junk foods, which are high in fat and may contain significant levels of trans fats.
  • Don’t switch to low-fat products that contain added sugar.
  • Use butter for spreading, not margarines – even low-fat, polyunsaturated or cholesterol-lowering margarines.Forget “easy spread” butters too – they have hydrogenated vegetable oils added to make them “spreadable”.
  • Use only pure olive oil for cooking – not sunflower, corn oil or any other vegetable oil. While not a good source of essential fats, olive oil is relatively heat stable and doesn’t produce harmful compounds when heated.
  • Reduce your consumption of the following (even low-fat versions), which can all contain adulterated harmful fats when produced commercially: crisps, biscuits, cakes, pastries, crackers, confectionery, pies, frozen or prepared meals, mayonnaises, salad dressings, chips, processed meats, “cook in” sauces and curry pastes.
  • Avoid products containing “hydrogenated vegetable oil”. Check all labels – you’ll be surprised where they pop up.For baking or treats, use butter or cream.
  • To boost your intake of essential fats (especially omega-3s): use fresh seeds sprinkled on salads, especially hemp, pumpkin and sunflower; switch from white breads, cereals, rice and pasta to whole grain versions; eat fatty fish (mackerel, herring, sardines, salmon, trout pilchards etc) at least once a week.

References 1. BMJ 2015;351:h3978; 2. Prog Cardiovasc Dis. 2015 Nov 13. pii: S0033-0620(15)30025-6. doi: 10.1016/j.pcad.2015.11.006.