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Good Fats & Bad Fats

About the author: James Collier BSc (Hons), Registered Nutritionist. James has over 25 years of experience working in nutrition and dietetics, including 7 years as a Clinical Dietitian in the NHS. Covering an array of clinical areas, he worked with people with a wide range of ailments and food intolerances. He also has an Honors Degree in Nutrition with Dietetics: Read more about James here.

Fats have had bad press over the past few decades since being linked as a possible contributor to heart disease back in the 1960s. ‘Fat’ is a word that brings up negative thoughts and it’s often associated with poor nutrition.  Also, some people believe eating fat means getting fat, which is not the case. The bad image fats have is not warranted.

Attitudes to fat need to change and the poor information the media gives is overly simplistic. During the 1990s, we were led to believe that saturated fats were bad and polyunsaturated fats were good. The real picture is very different. This article aims to unravel the issues that have been made unnecessarily over-complicated.

Fats are essential: we need fat for a number of healthy body functions. Without fat, we die. Indeed, some fatty acids are essential due to the fact that humans lack an enzyme involved in their metabolism or insufficient amounts of that fatty acid can be synthesized in the body for it to function effectively for good health.

Fats are triglycerides (TGs), made up of three fatty acids with a glycerol backbone. Each type of fatty acid differs by the number and position of double bonds in their structure and it’s the type of fatty acid present in the TG that denotes the type of fat.

What are the main types of fats?

There are six main groups of fats:

  1. Saturated fats
  2. Monounsaturated fats
  3. Omega-3 polyunsaturated fats
  4. Omega-6 polyunsaturated fats
  5. Trans fats
  6. MCTs

Saturated Fats
Saturated fatty acids (SFAs) have no double bonds in their structure. They are most commonly found in foods of animal origin such as meat and dairy produce, but also in some plant fats. SFAs have been given a bad reputation in the past due to the fact that observational studies have linked their intake to increased risk of cardiovascular disease (CVD) by increasing blood cholesterol levels. However, more recent information may indicate that this isn’t the case (discussed below).

Monounsaturated Fats
Monounsaturated fatty acids (MUFAs) have one double bond in their structure; they are also known as omega-9 fats.  These are found in high amounts in olive, rapeseed and flaxseed (linseed) oils. Consuming more of these fats as a proportion of our total fat intake may help to reduce our blood LDL or 'bad' cholesterol level, whilst keeping HDL or 'good' cholesterol levels high. This reduces the risk of CVD.

Polyunsaturated Fats
Polyunsaturated fatty acids (PUFAs) have more than one double bond in their structure and there are two types: omega-6 and omega-3 PUFAs. As a general rule, increasing levels of PUFAs in our diet has been shown to help reduce total blood cholesterol. However, this also means the good HDLs may be reduced. Omega-6s are found in a wide range of nut and seed oils as well as other foods of plant origin. Due to their cheap cost of production, many heavily processed junk foods are also high in omega-6s (we’ll come back to this point later).

Omega-3s are found in high amounts in flaxseeds (linseeds) and oily fish. The benefits of a good intake of omega-3s are improved cardiovascular health, reduction in some cancers, improvement in brain function, and possibly enhanced athletic performance.

People who consume oily fish, for example salmon, mackerel, sardines, pilchards and trout, have a diet high in the omega-3s EPA and DHA, but vegetarians will need to ensure they have a good intake of omega-3s from other sources and flaxseeds are an ideal choice. Read our
Guide to EPA and DHA for more information. Flaxseed oil is also a great source of MUFAs.

Trans Fats
Fatty acids can also differ in structure at the point of the double bond, making them trans which in turn changes the appearance and behavior of the molecule. Trans fats are formed from the hydrogenation of fats and are used in confectionery, margarines and some heavily processed foods. Trans fats are bad and we should limit their consumption.

All the above are long chain triglycerides (LCTs); there’s another group known as medium chain triglycerides (MCTs). Although a lot rarer in nature, they are present in a few popular fats, most notably coconut oil. MCTs are absorbed and metabolized differently to LCTs and are treated like a more energy-dense carbohydrate source than a fat. MCTs are in fact a type of saturated fat so on food labels are listed as saturates.

Which fats are essential?

There are two completely essential fatty acids (EFAs), essential because we need to include them in our diet in order to survive. These are linoleic acid (LA), an omega-6, and alpha-linolenic acid (ALA), an omega-3. In addition, there are four conditionally EFAs, in that if we don't consume enough LA and ALA, then they become essential. These are the omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and the omega-6s arachidonic acid (AA) and gamma-linolenic acid (GLA).

Essential and 'conditionally' essential fatty acids, their classification and principal dietary sources

Fatty acid

Type of PUFA

Rich dietary source

Linoleic acid (LA)


Corn, safflower, sunflower, soybean, peanut oils

α-linolenic acid (ALA)


Flaxseed, soy, rapeseed oils

Arachidonic acid (AA)


Small amounts in animal fats

γ-linolenic acid (GLA)


Corn, safflower, sunflower, soy oils

Eicosapentaenoic acid (EPA)


Oily fish

Docosahexaenoic acid (DHA)


Oily fish

Fats and Oxidation

To help understand which fats are good and which are bad, we need to first look at oxidation. Oxidation is a naturally occurring process where any molecule reacts with oxygen and forms free radicals; this is where the molecule becomes potentially damaging to tissues. Free radical formation through oxidation is involved in the process of some diseases including CVD and some cancers, as well as ageing. Although free radical formation is natural and inevitable, we can help minimize their formation and slow the damage they do.  Antioxidants are substances which help stop oxidation and these include vitamins C and E, selenium, types of vitamin A and phytonutrients like carotenoids and flavonoids. Eating a diet rich in these substances will go a long way to help slow down oxidation processes.

Cardiovascular disease (CVD) is the term that covers heart disease, stroke and peripheral vascular disease. The process of CVD is where fatty deposits build up on artery walls, making them narrower until a blood clot gets stuck and cuts off the blood supply to that area. Cholesterol in the blood is harmless enough until it oxidizes, which makes it ‘sticky’, and attaches to the artery walls forming a plaque by a process known as atherosclerosis.

Diets high in saturated fats have been shown to be linked to a high blood cholesterol level, in particular ‘bad’ LDL cholesterol.  High blood cholesterol and LDL levels have been linked to CVD risk. This is because there’s more cholesterol floating around the blood; higher blood cholesterol levels means there’s an increased chance of some of it oxidizing and forming a plaque. This is how the theory came about where diets high in saturated fats were linked to heart disease. However, there is one very important point here: saturated fats cannot be oxidized while unsaturated fats can.

We can help to prevent oxidation of fats in the blood by consuming a diet rich in antioxidants. One problem is the modern Western diet is high in overly processed junk food (note: not all processed foods are bad: read our article here) that are not only high in saturated fats, but also contain large amounts of cheap vegetable oils. Some of these vegetable oils have been hydrogenated and are high in trans fats that are atherosclerotic, i.e. plaque forming, as mentioned above. These vegetable oils are also high in omega-6s; not the good omega-6s found naturally and in nuts and seeds, but processed omega-6s which have been damaged by oxidation. By consuming these you are consuming oxidized fats with a high risk of their fate being plaque formation.

How much of each type of fat should I consume?

The healthy eating guidelines suggest around 30-31% of total energy intake should be from fats.  From this around 10% should be from saturated fats.  Although saturated fats aren’t as bad as we’ve been lead to believe, do bear in mind that diets too high in saturates have been associated with high cholesterol levels and also that none of the saturated fatty acids are essential, so we don't need them per se. They are, however, excellent sources of energy and should not be shunned.

The optimal ratio of omega-6:omega-3 is thought to be around 1-2:1.  However, Western diets have been shown to be somewhere as high as 6-20:1.  Areas where the ratio is high, CVD rates are also high, and in regions where the ratio is nearer to 1-2:1 the incidence of CVD are significantly lower.  An omega-6:omega-3 ratio of 1-2:1 is suggested with total polyunsaturates being 10-12% of total energy.

Monounsaturates should make up the remainder of the 30% of total energy.

Do I need to supplement with EFAs?

It’s quite rare for people to be consuming insufficient omega-6s, but not uncommon for low intakes of omega-3s. If you are not consuming oily fish or flaxseeds, then supplementing with flaxseed oil or a specifically formulated oil blend might be an idea. Be careful with oils though, as they are very prone to oxidation: they must be stored in cool, dark conditions. If they taste bad, they’re rancid (rancid is the term for an oxidized fat).

Cod liver oil supplements have been available for decades but offer little benefit in respect of fatty acid supplementation, as the doses of EFA are low. If you prefer to take a capsule fish oil supplement, check that it’s a reputable brand first, as some cheaper low quality contain low amounts of EPA and DHA and haven't been treated properly in the manufacturing process; they may even be rancid. Marine algae supplements are also available and these provide EPA and DHA; again, check the quality first.

ALA supplements are also available, but don’t overdo these. Exceptionally high intakes of supplementary ALA have been linked to a higher incidence of prostate cancer in men.

Fats in Huel

Huel provides 30% of total energy from fat and all the fats in Huel are from natural ingredients: ground flaxseeds, sunflower lecithin, MCTs from coconut, and even from the oats.  Huel has been formulated to provide the optimum amounts of all the fats: it has an ideal ratio of omega-3s:omega-6s providing optimal amounts of ALA for conversion to EPA and DHA, as well as ample LA. There’s a high proportion of monounsaturated fat; and 8% of the total energy comes from saturated fats, a large amount of which are MCTs providing an efficient source of energy.

Key Points:


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