Saturated fat = heart disease and death.

Is this true or a myth?

And should you worry about eating it?

I'll attempt to answer this whilst looking at what the evidence says.

Thread 🧵👇 https://t.co/hzafaUIw92

First, what IS saturated fat?

Fat comes in several forms.

There's saturated fat, unsaturated fat and polyunsaturated fat.

The difference lies in the number of double bonds in the fatty acid chain (I won't get too deep into the explanation of this here).

Unsaturated fats have one or more double bonds and fewer hydrogen atoms on their carbon chains.

Saturated fats lack these double bonds.

Saturated fats tend to be solid at room temperature, while unsaturated fats tend to be liquid.

Here's some sources of saturated fat:

- Fatty cuts of meat
- Products with meat in them
- Animal fats like butter, lard, tallow
- Coconuts and coconut oil
- Cheese
- Some oils, like palm oil
- Cream and ice cream
- A lot of snack and junk foods (varies by region)

Saturated fat has been believed to be bad for human health since the 1950s.

This was originally based on observational studies that showed a link between higher saturated fat consumption and higher rates of death from heart disease.

This led to the creation of the diet-heart hypothesis which states saturated fat raises levels of LDL (bad) cholesterol in the blood, which lodges in the arteries, causing heart disease.

This has never been scientifically proven but many official diet guidelines are based on it.

There are still lots of studies looking into this link, with many recent studies finding no association between saturated fat and heart disease.

The issue may be more nuanced than the diet-heart hypothesis makes it seem.

For example, this meta-analysis looked at 15 randomized controlled trials, totalling 59,000 participants in studies where saturated fat was reduced for at least 2 years.

The study found no reduction in deaths, heart attacks or strokes from reducing SF.
https://t.co/oELAr6cV44

However, it was found that replacing some saturated fat with polyunsaturated fat led to a 27% lower risk of cardiovascular events - but no significant findings for deaths, heart attacks or strokes.

This 2014 review looked at 76 studies, including 27 randomized controlled trials.

The conclusion was that current evidence doesn't support guidelines to reduce saturated fats and increase consumption of polyunsaturated fatty acids.
https://t.co/fD4nxbfMlr

Here's another meta-analysis, this time looking at 75 studies.

No link was found between consuming higher levels of saturated fat and heart disease, stroke, type 2 diabetes or dying from any cause.
https://t.co/wz8GsYYiir

This review looked at d 607 studies, analysing all of the data, and finding that saturated fats are not associated with all cause mortality, CVD, CHD, ischemic stroke, or type 2 diabetes.
https://t.co/2Ein5J510S

A limitation of these reviews is that they look at such a large amount of data from different studies, using different methods - so it's hard to draw overall conclusions.

Even so, no associations were found between higher saturated fat intake and cardiovascular diseases.

It has been argued that lowering saturated fat doesn't reduce CVD risk, but what those saturated fats are replaced with might

In some studies it's replaced with monounsaturated fat, in others it's replaced with polyunsaturated fat, and in others it's replaced with carbohydrates.

Saturated fat may be neither positive or negative for health, but other types of fats (for example, monounsaturated fats found in avocados and olives) may be a positive for health. 

Replacing some saturated fats with monounsaturated fats would therefore present a net benefit.

When studies claim a link between saturated fat intake and cardiovascular disease, you should question whether the levels of mono and poly unsaturated fats, carbohydrates, overall calories, etc. as well as  BMI and other risk factors are being controlled for.

It's also worth thinking about the different sources of saturated fat.

Saturated fat is present in lots of junk foods, whereas unsaturated fat is present in a lot of whole foods.

It seems logical that regular consumption of avocados and olives is going to be better for you than regular consumption of chips and ice cream (if the amount of fat is equated).

But is this because of the type of fat, or because of something else?

One thing that IS strongly linked to heart disease strongly, is obesity.

Whilst consumption of saturated fat hasn't been proven to cause build up of fatty material in arteries, there is strong evidence that being overweight and obese does.
https://t.co/f2sfMYFrTa

This is the case even if you have a healthy lifestyle with many health seeking behaviours and "healthy foods".

Being overweight increases your risk of heart attacks by up to 28%
https://t.co/keVOH05U9o

It's been found that overweight individuals tend to have a higher intake of saturated fat.

This study found that a higher intake of saturated fat (>15.5% of calories) was strongly linked with a BMI of over 25 (overweight).
https://t.co/dBFSN7XcYe

Correlation, however, is not causation.

Overweight and obesity is caused by consumption of more energy than you need over a prolonged period of time. As fat in all forms is the most calorific macronutrient, it explains why high intakes of SF tend to be correlated with obesity.

It would be interesting to see a randomized controlled study looking at saturated fat intake, over a long period, which splits participants by BMI.

If anyone knows of such a study, please mention it!

The number one thing you can do to decrease your risk of cardiovascular diseases is to achieve a healthy bodyweight.

You could do this by reducing ANY type of food from your intake whilst increasing your physical activity.

If you have a high intake of dietary fat, reducing this may be an effective way to lose weight - as fatty foods are more calorically dense than other macronutrients.

However, monounsaturated fats appear to have a health benefit, so it would be wise not to limit these too much.

It should be mentioned that fat is an ESSENTIAL part of a healthy diet.

Many vitamins are fat-soluble, meaning you need fat in your diet in order to absorb them.

Excessively limiting your fat intake could lead to nutrient deficiencies as you're unable to get these vitamins.

What do you think?

Are you convinced saturated fat is harmful?

Or has this thread made you reconsider?

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