Healthy fats and Cholesterol

There is a great deal of misunderstanding regarding which type, and how much fat we should eat. On this page we will deal with the primary misconceptions about fat, namely:

1)   Saturated fat does not cause heart disease and should be part of a healthy diet. 

2)   Over consumption of Omega 6 rich vegetable fats contribute to the current epidemics of heart disease, cancer and obesity.

3) Cholesterol is essential for health, and consumption of cholesterol has little impact on the amount of cholesterol circulating in the blood.

4) Trans fats remain in our food, especially in polyunsaturated vegetable oils.

Learn about Lipids and fatty acids including saturated, unsaturated and monounsaturated fatty acids here.

Saturated fat as part of a healthy diet:

Saturated fat should be part of a healthy diet, and should replace some calories obtained from carbohydrate particularly refined carbohydrates like sugar and flour. It is worth clearing a misconception up here, consumption of fat alone does not make us fat, what makes us fat is the consumption of excess calories. In modern Western diets, carbohydrates are the biggest contributors to excess calorie consumption, and therefore obesity, and the associated increased risk of cancer, heart disease and diabetes (see the graph below).

Comparison of fat consumption and obesity
Can fat consumption really be to blame for the obesity epidemic?

As seen in the graph above, the proportion of calories obtained from fat and saturated fat in the United States diet has fallen. It is important to realise that this is a percentage of total calories consumed and the total calories consumed in America has risen over the period described in the graph, such that the actual amount of fat consumed has not decreased but the calories obtained from other food groups, specifically carbohydrate has increased which has driven down the proportion of fat in the diet. That said the alarming increase in obesity over the same period would suggest that something other than fat consumption is driving this epidemic, and the most likely cause is the increase in carbohydrate consumption and the consumption of omega 6 fats.

Omega-3 and omega-6 essential fatty acids

Linoleate is by far the most commonly found PUFA in the vegetable, seed and nut oils which have now largely replaced the animal fats traditionally used in cooking. This dietary change has resulted in a massive imbalance in the ratio of omega-3 to omega-6 fatty acids in the diet.

Omega-3 and omega-6 fats are essential to health, and are vital for normal growth and development, but excessive consumption of omega-6 fats can have damaging side effects through stimulating the process of inflammation. Both the total amount and the even ratio between these fats are important, as they compete for conversion in the body to powerful hormone-like substances called prostaglandins that govern nearly every biological function.

There are ‘friendly’ prostaglandins that enhance health, made from omega-3 oils, and proinflammatory prostaglandins that can be bad for the health, made from omega-6 oils to stimulate the immune system in response to pathogens. Excessive consumption of omega-6 fats leads to the over-production of arachidonic acid, the immediate precursor of the proinflammatory prostaglandins. In addition, omega-6 fats predominate in grains fed to livestock, leading to higher omega-6:omega-3 ratios in the fat of grain-fed cattle and chickens when compared to the ratios found in those fed solely on grass.

Omega-3 oils were initially discovered by Drs Burr and Burr in the 1930s, during a study of the Inuit, who consumed high levels of fish oil, which is rich in omega-3 fatty acids. The results of their studies indicated an extremely low incidence of heart disease and cancer amongst the traditional Inuit. Since then, numerous studies have suggested that omega-3 oil is good for our health. The higher fish intakes of the Japanese population relative to those of North America and many parts of Europe have been associated with their considerably lower rates of acute blocking of arteries, and other forms of heart disease, despite there being only moderately lower blood cholesterol levels in the Japanese population [1, 2]. Indeed, studies have suggested that diets that are rich in omega-3 fatty acids are inversely correlated with CHD disease in men [1].

Omega-6 fat is essential in small amounts for a healthy immune system, but becomes toxic at high levels. It is adipogenic (stimulates fat synthesis) in abdominal fat ,which is a known risk factor for cardiovascular disease. It is proinflammatory  and may stimulate tumour growth.

The dangers of over-consumption of omega-6 fat cannot be overstated and together with high fructose corn syrup make up the two greatest dietary threats to human health this century.

An healthy dietary ratio of omega-6 to omega-3 fat would be 1:1, but many nutritionists suggest the ratio of 3:1 which is more easily attained without to much dietary modification. Currently the dietary ratios stand at around 30:1 in the USA and 10:1 in the UK, and these figures are probably underestimates. Adjusting these ratios can be brought about in two ways, reduce Omega 6 consumption or raise Omega 3 consumption.

Increasing oily fish consumption is not a realistic option. It would decimate fish stocks and overload the human system with oxygen sensitive fat. The total intake of polyunsaturated fat must be reduced and this means drastically limiting the intake of vegetable oils and processed food-a tall order.

Cholesterol is essential for health and very low blood levels (less than 3mmol) are associated with  age-onset dementia, haemorrhagic stroke and several other neurological problems such as Alzheimer’s and Parkinson’s Disease.. What constitutes a healthy level of cholesterol is highly disputed, and may well vary from individual to individual. Modern research refutes the dogma that cholesterol and dietary fat are the main causes of heart disease. It is now understood that inflammation of the arteries, stress, dietary sugar, refined carbohydrate and omega-6 fats are the major factors. Efforts to reduce these, whilst increasing physical activity, would be far more beneficial than lowering blood cholesterol by drug therapy.


Contrary to conventional wisdom, consuming cholesterol does not increase the amount of cholesterol in the blood.

Scare mongering about consumption of eggs, butter and animal fat being unhealthy, arises from 1970s US food guidelines based on flawed research. In fact consumption of carbohydrate raises blood cholesterol by stimulating insulin secretion. Insulin increases the production of LDL-cholesterol and triglyceride in the liver. The liver controls the level of cholesterol in our blood by responding precisely to dietary cholesterol and circulating insulin levels. It provides 100% of the daily requirement in vegans who consume a cholesterol-free diet.

Learn how statins are dangerous here.

Are Trans-fats still hidden in our food?

Yes, the processing of vegetable oils for cooking involves a process of scrub hydrogenation to prevent the oil going rancid during storage. This process is ubiquitous in the production of vegetable oils and is another reason, along with the high levels of omega 6 fat, why most vegetable oils should be avoided in a healthy diet.

What’s the problem with Trans-fats:

ITFs are unique in that they affect our blood lipids (fats) in almost every possible way that is harmful to our health.

A study performed in 1994 showed that almost three quarters of the fat found clogging arteries is trans fat rather than cholesterol and comes from artificially hydrogenated ITF containing vegetable oils and cooking oils, not animal fats [99].


In the USA obesity remained at a steady 13% of the population throughout the 1960’s until high fructose corn syrup began to replace sugar as a sweetening agent. The obesity rate began to rise more steeply and has now more than doubled with associated rises in the incidence of type 2 diabetes and heart disease

Government responses in Europe and the USA appear to support the food industry lobby which vociferously refutes the excellent science supporting these claims. Already the European Food Standards Agency (EFSA) has recommended unrealistic dietary guidelines for omega-3 fats with no attempt to address the dangers of omega-6 fat over-consumption. More recently , as Dr Lustig reports, the EFSA have also ignored recent findings on the toxicity of excessive fructose intake, to sanction its use as a sugar replacement in processed foods and drinks.

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  1. I read that Olive oil should not be used for cooking because heat makes it susceptible to oxidative damage. What I don’t read is anything written by a cook.
    I wouldn’t use olive oil for high temperature frying; that’s anything in a frying pan or wok.
    I do use olive oil for sautéing/sweating onions, garlic, celery which form the basis of many meals I cook (Mirepoix / Sofrito / Refogado).
    What is the critical temperature at which olive oil becomes damaged?
    I do feel that statements like “do not cook with olive oil” are ready made, sensationalist straplines which offer the cook little practical advice.

    1. The vegetable cooking oils that line our supermarket shelves are extremely susceptible to oxidative breakdown when heated, with the polyunsaturated oils being the most unstable. Even olive oil which is monounsaturated and much more stable will nevertheless break down when heated to smoking point. Better to use for sauteing or sweating vegs as you suggest for mediterranean type dishes. However, as an enthusiastic amateur cook I have found that the more heat stable coconut oil can replace olive oil in wok cooking and stir-frying without any loss of flavour or quality. The cheaper non-virgin olive oils sold for cooking add little to the flavour of a dish and the wide variety of delicious extra virgin oils should be reserved for salad dressings , sauces and dips.

  2. This evening, whilst cooking my Sofrito, I used my food thermometer on a couple of occasions during the cooking: 90 degrees C.
    Is Olive oil damaged at this temperature?
    Thank you, Andrew

    1. Some oxidative damage will occur at 90C, but it is the higher smoking point temperature at which serious breakdown occurs .
      The actual smoking temp will depend on the chemical composition of the oil.

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Site authors: Professor Rodney Bilton, Dr Larry Booth, and Joseph Bilton M.Sc B.Sc