What are dietary fats - and how much do we need daily?

There was a time when standard advice over fat in our diets was pretty simple: cut it out. However, as time as gone on, we've come to realise that while it is advisable that we cut back on some fats, others can be very good for us.

What is fat?

Fat itself comes from building blocks called fatty acids, and is a rich source of energy for us. It is classified into a number of groups, included saturated, monounsaturated and polyunsaturated, with each group reflecting a different chemical structure of the fat molecule.

Regardless of which type of fat a food is made up of, all fats contain the same amount of calories per gram, which means that eating too much of any fat can lead to a person gaining weight. If this happens consistently over time, it can give rise to excess weight gain and all the health conditions that come with it, such as type 2 diabetes risk, cardiovascular disease and certain cancers.

How much fat do we need on a daily basis?

The Department of Health's guidelines suggest that fat shouldn't exceed 35% of our total daily intake of food, with no more than 11% coming from saturated fat. While most of us in the UK are close to the 35% guideline, many of us eat too much saturated fat which can increase our blood cholesterol level.

Adult males are advised not to consume more than 95 g of fat in total a day, with no more than 30 g of saturated fat, while women are advised not to eat more than 70 g, with no more than 20 g of saturated fat. However, people who are overweight or obese should be looking to reduce these levels, which will help promote weight loss.

To give you an idea, here are some examples of how much fat is contained in some common foods and drinks;

• One standard sausage: around 8 g

• One digestive biscuit: around 3 g

• A glass of whole milk (half pint): 14 g

• One Mars® bar: around 10 g

• One pack of crisps: 10 g

Cutting back on unhealthy fat s

Increased cholesterol from eating too much saturated fat raises our risk of heart disease and stroke. However, if you replace the saturated fat with an unsaturated alternative, blood cholesterol levels should start to normalise and your cardiovascular risk will reduce.

There has been some recent media coverage over the past couple of years questioning whether or not saturated fats increase your cardiovascular risk.

It's important to understand that this observation was based on flawed analysis of published research studies which failed to take into account that when people reduce their saturated fat intake they tend to increase their intake of sugars and refined carbohydrates instead (which itself will increase risk).

As a result, it appeared that reducing saturated fat intake had no effect on reducing cardiovascular risk.

The message remains the same - there is a direct relationship between saturated fat intake and your risk of having a heart attack or stroke.

Foods which are a large source of saturated fat

Common foods with a particularly high proportion of saturated fats include full-fat dairy products, processed foods and fatty cuts of meat. Many will tend to be solid at room temperature, such as butter and lard, but some oils such as palm and coconut oil are also high sources of saturated fat.

Saturated fats are typically found in high amounts in animal and dairy products, especially:

• Full-fat dairy products such as milk and cheeses (especially hard cheeses)

• Cream and ice cream

• Fatty cuts of meat

• High-fat meat products such as sausages, burgers, salami and meat pies

• Butter and lard

• Cakes and pastries

• Biscuits and chocolate.

What about trans fats?

Trans fats, also known as trans fatty acids or hydrogenated fats, are oils which have been artificially hardened in order to lengthen the shelf-life and increase flavour stability of foods - they are also used to create margarines.

Much like saturated fats, trans fats can significantly affect your cholesterol profile by raising your levels of both unhealthy LDL cholesterol and triglycerides. On top of that, they can also lower your level of healthy HDL cholesterol, increasing your cardiovascular risk even further.

In fact trans fats are so harmful that many manufacturers in the United Kingdom have significantly reduced levels in their products in response to pressure from Government and public health agencies. Our intake here in the UK therefore is now relatively low.

Unfortunately, food manufacturers are under no obligation to declare trans fat levels on food labelling so it's still worth being aware of foods that can contain relatively high levels, including:

• Margarine and lard

• Biscuits

• Crackers

• Doughnuts

• Chips

• Crisps

• Cakes

• Pie crusts

• Frozen pizzas

• Sausage rolls.

You should minimise your intake of trans fats as far as possible. If you're checking the label and trans fats aren't displayed then check out the ingredients and look for 'partially hydrogenated fats or oils'.

Making healthier fat choices

While foods tend to contain a mixture of saturated and unsaturated fatty acids, unsaturated options are a far healthier choice.

Unsaturated fats are normally liquid at room temperature and can be found in vegetable oils, avocados, nuts and seeds. A particular type of polyunsaturated fats - omega-3 fatty acids - are particularly healthy - great sources include oily fish such as salmon, tuna, trout, herring, mackerel and pilchards.

Sunflower seeds, flaxseeds, flaxseed oil, soybean oil and walnuts are also good sources but neither these nor fish oil supplements appear to be processed in the body as beneficially as omega-3 fats from oily fish.

Replacing unhealthy saturated fats as much as possible with with healthy monounsaturated and polyunsaturated fats as part of your daily diet will help to boost your cardiovascular health.

You should also consume at least two portions of fish a week, of which at least one should be the oily variety, in order to ensure you're benefiting from healthy levels of omega-3 fats.

A word of caution for pregnant women

Increasing fish oil consumption beyond two servings of oily fish per week or relying on fish oil supplementation is not appropriate during pregnancy due to the potential effects on the unborn baby of heavy metal levels in fish and high vitamin A levels found in some fish oil supplements.