Fats; they’re bad, they’re good, they’re saturated, mono-unsaturated, poly-unsaturated, trans, cis, hydrogenated… the so called “advice” and media around this macronutrient is endless. Confused?! Don’t be, here I give you the low down on what all those labels mean, which ones to avoid, which ones are good for you, and how you should store and use them in your kitchen.

Are fats bad?

No! Well, not all of them. In fact, fats are essential for a variety of functions in the body. They are components of cell membranes (and are particularly important in the brain), they are needed for cell to cell communication, for protection of vital organs and are also used for storage and production of energy[1].

Of course, too much fat, just like too much of any kind of food, will lead to weight gain. Excess fat is stored easily in the body, but remember, excess protein and carbohydrates can also be turned into triglycerides (the storage form of fat). One thing to keep in mind though, is that gram for gram, fat is more calorie dense at 9 calories per gram, compared to 4 for carbohydrates and protein. Alcohol by the way is 7 calories per gram, so if you want to lose weight, that’s an important area to consider![2]

So, you need some fat, but not too much. How do you know which ones to consume and which to avoid?

The science

To help you understand which fats are good and bad, and what happens to them in the body, I want to explain a little bit of chemistry – don’t worry, I’ll keep it simple! Fats are made up of chains of two elements, hydrogen and carbon (plus an acid on the end, but we won’t go into that here). In saturated fats(find for example in butter, coconut oil, fat on meats and in egg yolks), there are single bonds between each atom. This makes them fairly stable and is why they are solid at room temperature. They are best for cooking, because they are more able to withstand high temperatures without being damaged. In unsaturated fats, there are some double bonds, which make the chain ‘kinked’. This is essentially what makes these fats liquid at room temperature. It also makes them more prone to damage, so they go bad (rancid) more easily, which can set off a chain reaction of damage in your body by acting as free radicals. Being unsaturated doesn’t make fats bad per se, but you need to be aware of their properties when you think about using added fats (i.e. oils etc) in cooking. Many of the problems with fats, is in how they have been treated. E.g. oil that has been heated to a high temperature for frying can cause problems in the body because it has been destabilised and can produce high levels of malondialdehyde which is a potential mutagen[3].

Back to the terms you may hear, or see on packaging;monounsaturatedfats only have one double bond, while polyunsaturated fatshave at least two. Cis and trans refer to the formation of these bonds. Cis are the ones found in nature, while trans are unnatural and can cause more harm in the body so these are the ones you really want to avoid! Trans fats can be created when fats are hydrogenated, so again, these are fats to stay away from.

Saturated fat and heart disease

So far, it sounds like saturated fats are the good guys, but you are probably all aware that it is saturated fat that we are generally told to limit (The UK guidelines recommend limiting to a maximum of 11% of your energy intake daily)[4]. This is because significant amounts of research have shown correlations between high saturated fat diets and higher rates of death from heart disease[5]. This is because saturated fat appears to raise LDL cholesterol (this is considered the “bad” cholesterol). However, some recent research questions this link, suggesting the correlation between saturated fat intake and heart disease is not actually significant[6]. The jury is still out on this one but there is certainly a lot of research which suggests limiting saturated fat is a good idea.

Essential Fatty Acids – the good guys!

You have probably heard of omega 3 and omega 6 fats, or the essential fatty acids (EFAs). These are polyunsaturated fats which the body needs, but is unable to make. The average western diet gets plenty of omega 6 fats, as these are abundant in most plant and vegetable oils including sunflower oil which is widely used in processed foods, as well as meat and dairy. Many people however, are short of omega 3s which are found in oily fish, and in flaxseeds (linseeds), hemp seed and walnut oil.

The ratio of omega 3 to 6 oils is important for the body, and ideally this should be close to 1:1 (guidance is maximum 1 omega 3 to 4 omega 6. The average Western diet is actually closer to 1:12, so far too high in omega 6 relative to omega 3.[7]To limit omega 6, avoid lots of fried and processed food, and to increase omega 3, have 2 to 3 portions of oily fish a week if you eat fish (think SMASH: salmon, mackerel, anchovies, sardines and herring), or add a spoonful of flax or hempseed to smoothies or porridge each morning. You need to grind both first though, as the body is unable to break down and use the whole seed.

Omega 3 fats are generally anti-inflammatory and anti-clotting, which is why fish oil capsules are often recommended for inflammatory conditions.

Using and storing fats in the kitchen

When it comes to cooking, especially at high temperatures, saturated fats (eg butter, ghee and coconut oil) are best, as are least likely to be damaged by the heat. If you want to use something like olive oil, add after cooking, or do so at low temperature. For example, when stir frying, add a little water to the pan first (don’t add water to hot fat or it may spit and burn you). The water will prevent the oil from getting too hot and causing damage. You want to avoid ever letting oil get so hot that it smokes.

Oxygen (in the air), light and heat all turn oils rancid (this makes them taste bad, but also causes damage in our body), so always store fats/oils at a cool temperature and away from light[1]. Good quality oil should be sold in a dark coloured bottle (to keep light out). You’ll often find this is the case with olive oil, but sadly, it is rarely so with coconut oil, so make sure you keep it in a cool dark cupboard. If your kitchen is warm, you are better keeping oils in the fridge. More unstable oils, like flaxseed should always be refrigerated, and are actually best kept in the freezer as they have such a low melting point.

The same goes for oil supplements, e.g. fish oil capsules; keep these in the fridge too. If you are being really pedantic, raw nuts and seeds are also best kept in the fridge, but as long as you aren’t keeping them for very long periods, a cool dark cupboard is generally fine!

Good dietary forms of fat

Remember that you do need fat in the diet! Fats are best obtained through whole foods where possible, rather than added as oils and healthy options include:

  • Nuts and seeds
  • Avocado
  • Olives
  • Oily fish

Healthier oils:

  • Olive oil: buy “cold pressed” oils which have not been potentially damaged by exposure to heat in the processing. Do not use olive oil at high temperatures.
  • Avocado oil: do not use for cooking
  • Flaxseed oil: for omega 3, but it is highly unstable so should always be kept in the fridge or freezer and NEVER heated
  • Butter, ghee or coconut oil for cooking (but keep the amounts to a minimum as all contain saturated fat)
  • And remember to store all oils somewhere cool and dark

And the ones to avoid:

  • Any trans or hydrogenated fats (it should say on the label if foods include these). They are most likely to be found in fried and processed foods and margarine/“spreads”



[1]  Haas, E. (2006) Staying Healthy with Nutrition. USA: Crown Publishing Group

[2]Astrup, A. and Tremblay, A. (2009) “Energy Metabolism” in Gibney, M. et al Introduction to Human Nutition, 2ndEdition

[3]National Cancer Institute (2018) NCI Term Browser: Malondialdehyde https://ncit.nci.nih.gov/ncitbrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&ns=NCI_Thesaurus&code=C94711

[4]British Nutrition Foundation (2017) Nutrition Requirements www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/nutrient-requirements.html

[5]Hooper, L. et al (2015) “Reduction in saturated fat intake for cardiovascular disease”.The Cochrane Database of Systematic Reviews10(6)CD011737 Available at www.ncbi.nlm.nih.gov/pubmed/26068959

[6]Souza et al (2015) “Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies,” BMJ, 351, p.h3978 www.ncbi.nlm.nih.gov/pubmed/26268692

[7]Simopoulos, A. (2006) “Evolutionary aspects of diet, the omega-6/omega-3 ratio

and genetic variation: nutritional implications for chronic diseases”. Biomedicine and Pharmacotherapy60; 502-507 www.nutrasource.ca/files/omega_3_chronic_nov2006.pdf