Despite increasing references to the benefits of eating saturated fats such as coconut oil in the mainstream media recently, the majority of the people I meet still remain firmly committed to the idea that polyunsaturated oils, or ‘vegetable’ oils are heart healthy and safe, and saturated fats such as lard and butter are ‘artery-clogging’ and bad for us. However, as with so many things in life, when you delve more deeply into the subject, it isn’t quite as simple as that and over the next couple of posts I’d like to challenge some of your ideas about fat and provide some pretty convincing, and still largely unknown (at least to the general public) scientific evidence to support it.
There is no doubt that some polyunsaturated oils can be very healthy (such as fish oil) while others, particularly those that have been hydrogenated to create trans-fats (which then behave like saturated fat and are found in all those oh-so-tempting baked goods available in every coffee shop and supermarket across the country) are definitely not healthy. And these are a world away from the naturally occurring kind of saturated fat we get from healthy, well raised grass fed animals, wild caught fish and plant sources such as palm and coconut oil.
Firstly, let’s clarify what we mean by the words saturated, mono- and polyunsaturated. These terms have become so familiar to us that we use them without really thinking what they mean, but could you explain to someone what the difference actually is between them? What is it about saturated fat that makes you believe it will ‘clog your arteries’? I suspect that most of us would struggle to answer these questions. If this is the case with you and you’d like to know more, I’ll deviate into the science for a while to hopefully shed some light.
A short deviation in to some chemistry
The way a fat is structured chemically determines its physiological action. Fats come in varying lengths (short, medium, long and very long chain) but all fatty acids (fats) consist of the elements carbon (C), hydrogen (H) and oxygen (O) arranged as a carbon chain skeleton with a carboxyl group (-COOH) at one end. Saturated fatty acids have no double bonds between the carbon atoms meaning that they have all the hydrogen that the carbon atoms can hold, hence they are ‘saturated’ with hydrogen (see illustration of butyric acid as an example). Monounsaturated fatty acids (MUFAs) have one double bond between the carbons, polyunsaturated fatty acids (PUFAs) have more than one. An example of an PUFA is linolenic acid, an omega 3 polyunsaturated fatty acid. It has 3 double bonds between the carbon atoms which means fewer connections to hydrogen, hence the term ‘unsaturated’. Fats are usually bonded three at a time to a glycerol molecule, known as a triglyceride.
Solid or liquid?
This chemical arrangement determines what a fat looks like at room temperature – saturated fats have a more rigid structure, meaning that it they are solid at room temperature (lard, tallow, butter, ghee and coconut, although being a tropical oil coconut is only solid in colder climates such as in the UK) whereas unsaturated fats are liquid at room temperature (olive, seed and nut oils). The chemical structure also determines how stable a particular fat or oil is, how quickly it will go rancid (oxidise) and what its ‘smoke point’ is, i.e. the temperature it can be heated to before it begins to break down. This has important health implications as not only does smoke contain toxins but the oil or fat will start to form harmful free radicals. Generally, the more saturated a fat is the safer it is to cook with. Polyunsaturates are highly reactive and quickly oxidise – these should never be heated or used for cooking. However, there isn’t a direct correlation between degrees of saturation and the smoke point, i.e. saturates do not necessarily have a higher smoke point – more on this in the next instalment.
So where do trans-fats fit in?
Well, in chemical terms, trans fat is a fat molecule that contains one or more double bonds in trans geometric configuration. A double bond may exhibit one of two possible configurations: trans or cis. In trans configuration, the carbon chain extends from opposite sides of the double bond, whereas, in cis configuration, the carbon chain extends from the same side of the double bond. The trans molecule is a straighter molecule. The cis molecule is bent.
Cis configurations are naturally occurring whereas trans fats are artificially created by catalytically hydrogenating them (reacting them with hydrogen gas and a metal catalyst such as platinum or nickel at high temperatures), to produce a partially saturated fat. This artificial fat provides a cheap ingredient for the food industry as it melts at the right temperature and lasts virtually forever on the supermarket shelf without refrigeration. (There is one naturally occurring trans fat called conjugated linoleic acid (CLA), found in meat and dairy from grass fed ruminants, which is very healthy and not to be confused with that produced in industrial food preparation). Our bodies have a hard time assimilating these trans fats (it seems that adding hydrogen makes the fat difficult to digest) and as the technology required to produce them has only been around for just over a century our bodies haven’t yet evolved to deal with the amounts many of us are now eating.
Naturally occurring CLA is between 2-5% trans fat, whereas processed food can contain anything up to 45% – no wonder our bodies struggle to deal with them. Many studies have shown that trans fats raise LDL cholesterol and reduce HDL, contributing to heart disease, so should definitely be avoided. Denmark has banned the use of trans fats in its processed food but despite a global campaign this is not yet the case in the UK.
Enough of the science – what does it all mean?
So, now we understand what makes a fat saturated or not. What does this actually mean for our health? What does fat do in our bodies? Do we need it at all? Judging by the reaction I get from most people when the word ‘fat’ is mentioned, you would think that science had proved definitively that it’s the cause of all the world’s ills, from obesity and heart disease to high interest rates and bad reality TV. OK, I jest but you get the point. However, surprisingly enough, the science behind our fat-phobic society was always very shaky and is now plainly out of date. Known as the ‘diet-heart hypothesis’, the story of how one very ambitious man (Ancel Keys), some very dubious science (he only published the results that fitted his hypothesis), and a government in America in the 1970s determined to be seen to be ‘doing something’ about rising rates of heart disease, conspired to condemn saturated animal fat as the devil incarnate before all the facts were available is detailed in Gary Taubes’ fascinating book, The Diet Delusion, which I recommend everyone reads, so I won’t repeat here. Suffice to say, Keys’ theory won the day and the ‘diet-heart hypothesis’ has been declared ‘fact’ for over 40 years.
Dare to question
Many dissenting voices at the time (and since) have been ignored despite a mounting number of large-scale studies that have increasingly questioned the validity of these beliefs (the Framingham Heart Study, the Multiple Risk Factor Intervention Trial (MRFIT) and Lyon Diet-Heart Trial). These trials have found that, for most people, there does not appear to be a link between eating saturated fat, significantly raised blood cholesterol levels or an increased risk of heart attack or stroke. In fact, the director of the Framingham study is quoted as saying, “In Framingham, Mass., the more saturated fat one ate, the more cholesterol one ate, the more calories one ate, the lower the person’s serum cholesterol… we found that the people who ate the most cholesterol, ate the most saturated fat, ate the most calories, weighed the least and were the most physically active.” The MRFIT trial showed a marginal reduction in total coronary heart disease in those who reduced their saturated fat intake, cholesterol and the amount they smoked but overall mortality from all causes was higher (cancer, stroke, suicide and violent death). I could go on recounting results of other studies but this blogpost is long enough already!
These studies involved thousands of people, and in the case of Framingham, have been ongoing for decades. Despite this the public remain generally misinformed, continuing to eat heavily processed ‘low fat’, fat free or low/no cholesterol foods, while stocking up on healthy whole grains as promoted by most governments around the world. Interestingly, the American College of Cardiology and the American Heart Association have recently reviewed the basis on which doctors should recommend the use of statin drugs following an evaluation of all the available published evidence. They have now abandoned the old target levels for LDL cholesterol, and recommend an approach based only on level of risk. In fact, new research is suggesting that it is the overconsumption of grains that has a much more dramatic effect on LDL, as the carbohydrate is converted to a kind of fat (palmitic acid) that is being linked to atherosclerosis. (Much more on grain/carbohydrate consumption in a future post!). Could the perpetuation of the fat/cholesterol/heart disease myth be something to do with vested interests by any chance? Many industries benefit from the status quo – grain producers, refined food processors, pharmaceutical manufacturers and the diet and exercise industries to name but a few.
Anyway, I digress. Let’s get back to the question of what fat does and whether we need fat at all. Here’s a short list of bodily processes that require fat:
- the manufacture of every cell membrane
- regulation of the immune system
- inter-cellular communication
- hormone synthesis (i.e. oestrogen and testosterone)
- provides energy for the body
- lung function
- nervous system/cognitive function, mood regulation (over half the fat in the brain is saturated)
- suppression of inflammation
- assimilation of fat soluble vitamins A, D, E & K
- provides a sense of satiety
- promotes healthy skin and prevents wrinkles
- improves vision
- cushions our organs in the body
As you can see, the answer is yes, yes, yes and yes again! Our bodies need fat for so many things I find it hard to believe that we’ve been afraid of it for so long. Basically we can’t survive without fat (or cholesterol) and perhaps our fear of it isn’t doing our health any good. Just look at the people around you in your High Street on a Saturday morning – how healthy do they look? How many people look slim, fit, bright eyed and active? However, it’s not quite as simple as saying ‘just eat more fat’ – it’s all about which ones and the balance between them and that’s where the paleo template can be so useful. Anthropological evidence and information gathered from scattered populations around the world who still eat their traditional diets can help us to identify the best kinds of fat to eat and in what proportions.
So, in the next part in this series I’ll be delving more deeply into what we can learn from our ancestors and the few remaining hunter-gatherer societies, with particular regard to the mysteries of polyunsaturated oils to see which ones really are good for us and which ones to avoid – the answers might just surprise you!
Interested in knowing more? The following resources give a wealth of information to add context and content to this huge topic:
The Daily Lipid Blog – Chris Masterjohn
Wholehealthsource.blogspot.com – Stephan Guyenet
Marks Daily Apple – Mark Sisson
http://www.framinghamheartstudy.org/ (Framingham Heart Study)
http://www.ncbi.nlm.nih.gov/pubmed/9049571 (the Lyon Diet Heart Study)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2830458 (the effect of animal and trans fatty acids on HDL and LDL cholesterol levels in humans – a quantitative review)
http://www.ncbi.nlm.nih.gov/pubmed/16611951 (trans fatty acids and cardiovascular disease)
http://www.bmj.com/content/347/bmj.f6340 (saturated fat is not the major issue)
http://jaha.ahajournals.org/content/1/5/e003640.full (MRFIT Revisited: A new perspective)