French fries

Friend or foe?

Our relationship with fat? It’s complicated

Whether fat is good or bad – and there is much debate to be had on the issue – there’s no denying that we need some fat in our diets. The essential fatty acids alpha-linolenic acid (omega-3) and linoleic acid (omega-6), for example, have important roles to play in regulating our immune responses.

Cis and trans configurations of the carbon bonds in fatty acids

In unsaturated fats, the ‘cis’ configuration (shown in pink, above) is usual. In trans fats (shown in purple), some bonds are flipped.


Big Picture: Fat (2015)

Our bodies can’t make essential fatty acids, so we must get them from foods such as rapeseed and walnut. From these, we’re capable of making other types of omega-3 fatty acids, but because we don’t do so very efficiently, it’s easier to get them from oily fish like mackerel. Omega-3 and omega-6 fatty acids have more than one double bond in their carbon backbone and so are known as polyunsaturated (‘poly’, from the Greek for ‘many’).

The problem with low-fat diets is that in the long term, we need to get our calories somewhere else and that somewhere else is usually carbohydrate. Some scientists are now arguing that guidelines on fat need to be changed. There is evidence to suggest that rising levels of heart disease, diabetes and obesity may have more to do with people eating too much sugar than too much fat.

A certain way of processing vegetable oils produces what are known as trans fats, or partially hydrogenated oils. Trans fats are desirable to manufacturers because they extend the shelf life of cooking oils and baked and fried goods. However, eating trans fats is linked to heart disease and diabetes, and these fats are universally considered bad for your health. It’s worth noting that trans fats occur naturally in some dairy products.

Lead image:

Daniel Go/Flickr CC BY NC


Downloadable resources

About this resource

This resource was first published in ‘Fat’ in December 2015.

Cell biology, Health, infection and disease
Education levels:
16–19, Continuing professional development