Fats in your diet

Written by: 
Dr Sarah Brewer

What different types of dietary fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. are there, why are they important and how should we regulate our intake? This page explains.

Fat is an important component of a healthy diet. In general, however, most people in Western societies consume excess amounts of fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body., which can lead to obesityExcess accumulation of fat in the body., abnormal cholesterol balance and an increased risk of cardiovascular disease.

The main questions are:

What types of dietary fat are there?

The two main types of fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. are saturated and unsaturated.

Unsaturated fats are subdivided into monounsaturated and polyunsaturated fats. Read more on saturated, monounsaturated and polyunsaturated fats.

Most dietary fats contain a blend of saturates, monounsaturates and polyunsaturates in varying proportions, although one type of fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. tends to dominate:1

In general, predominantly saturated fats are mainly from animal sources and are solid at room temperature, while monounsaturated and polyunsaturated fats derive mainly from plants and fish, and are liquid at room temperature, forming oils.

Fat source Saturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. Polyunsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. Monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body.
Olive oil 14% 8% 73%
Polyunsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. spread 16% 34% 15%
Butter 52% 3% 21%
Beef dripping 51% 2% 38%
Lard 40% 10% 43%
Suet 50% 2% 30%

Why do we need dietary fat?

A certain amount of fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. is important for health because it supplies:

  • A source of readily available energy
  • Essential fatty acids such as omega-6 and omega-3 fatty acids Essential fatty acids that may help protect against heart disease and dementia.- these are called essential because they cannot be synthesised from other dietary fats in the body and so must be taken in through what you eat
  • Building blocks for making cellThe basic unit of all living organisms. membranes
  • Building blocks for making hormones and hormoneA substance produced by a gland in one part of the body and carried by the blood to the organs or tissues where it has an effect.-like chemicals called prostaglandinsOne of a group of hormone-like substances that have a wide variety of actions, including the dilation of blood vessels and contraction of smooth muscle.
  • Molecules from which bile saltsSubstances present in the bile, which help to emulsify fats in the small intestine so that they can be more easily digested. are made
  • Fat-soluble vitamins A, D and E.

Find out more about omega-6 and omega-3 fatty acids.

What should I look for in controlling my dietary intake of fats?

Most people will benefit from limiting their intake of saturated fats, maintaining a good intake of monounsaturated fats and a balanced intake of polyunsaturated fats and taking care to avoid trans fats as much as possible.

Saturated fats

Saturated fats are mainly found in animal products such as milk, milk products including butter and cheese and red meat. Red meat is meat that is red when raw, such as beef or lamb.

There are several different types of saturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body.. Some of them are converted into cholesterol in the liverA large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats.. Find out more about cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy..

  • More than one-third of the total saturated fats in milk fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. or butter have no effect on bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. levels
  • Only saturated fats such as lauric acid, myristic acid and palmitic acid have a significant effect on bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. levels
  • Stearic acid, which is found in milk fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body., cocoa butter and meat fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body., has little cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy.-raising activity2 - this is because it is rapidly converted into a monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. in the body.3

The main reason to limit the amount of saturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. in your diet is because of its high calorific value, and because excess is readily deposited in fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. cells to contribute to obesityExcess accumulation of fat in the body..

Monounsaturated fats

Dietary sources of monounsaturated fats include olives, avocadoes, hazelnuts and macadamia nuts, along with olive oil and rapeseed oil.

Consuming more monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. in place of carbohydrate has beneficial effects on blood pressure and cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. balance and may help to reduce the risk of coronaryRelating to the arteries supplying the heart itself. arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. disease and stroke.4

Typical levels of monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. in various oils are:

Source % monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body.
Macadamia nut oil 78%
Hazelnut oil 78%
Olive oil 73%
Avocado oil 63%
Rapeseed oil 59%

Polyunsaturated fats

There are two main types of polyunsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. in the diet:

  • Omega-3 fatty acids - mainly derived from fish oils
  • Omega-6 fatty acids - mainly derived from vegetable oils.

Omega-3 fatty acids help to reduce inflammationThe body’s response to injury. and have a bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid.-thinning effect, while consuming excess omega-6 fatty acids promotes inflammationThe body’s response to injury. and increases bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. stickiness. Read more about omega-6 and omega-3 fatty acids.

Polyunsaturated fatty acids such as the omega-6 linoleic acid are involved in the processing of cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. and can lower cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. levels when consumed in small amounts. This effect is lost when excess is consumed.2

Polyunsaturated fatty acids have a molecular structure that makes them susceptible to chemical changes known as oxidation.5 This leads to the formation of toxic substances called lipidOne of a group of compounds that are an important energy source. peroxides that are associated with atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow..

You encourage oxidation and the formation of toxic lipidOne of a group of compounds that are an important energy source. peroxides if you:

  • Eat excessive amounts of polyunsaturated fatty acids
  • Overheat oils containing polyunsaturated fatty acids so that the oils smoke while cooking
  • Re-use cooking oils
  • Have too few antioxidants in your diet - antioxidants are found especially in fresh fruit and vegetables.

Trans fatty acids

When making cooking fats and spreads such as margarine, polyunsaturated oils undergo a chemical process called hydrogenation to solidify them. In this process some trans fatty acids are produced.

Trans fats are harmful to health:

  • They increase 'bad' LDL-cholesterolSubstance that carries cholesterol around the bloodstream, a form of so-called 'bad cholesterol'. and lower 'good' HDL cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. - LDL-cholesterolSubstance that carries cholesterol around the bloodstream, a form of so-called 'bad cholesterol'. is said to be 'bad' because it seeps into arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. walls to contribute to plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth. formation, while HDL-cholesterolA substance that mainly exists to carry cholesterol from the circulation to the liver; commonly referred to as 'good cholesterol'. is 'good' because it mops up LDL-cholesterolSubstance that carries cholesterol around the bloodstream, a form of so-called 'bad cholesterol'. and transports it back to the liverA large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats. for processing, thereby lowering the risk of atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow. and heart disease
  • They increase inflammationThe body’s response to injury.
  • They may interfere with the way the hormoneA substance produced by a gland in one part of the body and carried by the blood to the organs or tissues where it has an effect. insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. pushes glucoseA simple sugar that is an important source of energy in the body. into muscleTissue made up of cells that can contract to bring about movement. and fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. cells, so that bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. glucoseA simple sugar that is an important source of energy in the body. levels increase and an individual gains weight.6

Read more on the difference between 'bad' LDL-cholesterolSubstance that carries cholesterol around the bloodstream, a form of so-called 'bad cholesterol'. and 'good' HDL-cholesterolA substance that mainly exists to carry cholesterol from the circulation to the liver; commonly referred to as 'good cholesterol'. in Cholesterol.

Trans fats have also been linked with the development of certain cancers, including those of the breast and prostate glandAn organ with the ability to make and secrete certain fluids.. As a result, margarines and low fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. spreads are now being reformulated to reduce their trans-fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. content.

Tip: Check labels, and select foods with the lowest content of trans fats - sometimes labelled as hydrogenated or partially hydrogenated fats.

How can I achieve a healthier balance of dietary fats?

To obtain a healthier balance of dietary fats, most people would benefit from eating:

  • Less fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. overall
  • More monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. - for example, olive, rapeseed and nut oils
  • More omega-3 fatty acids, especially those found in oily fish
  • Fewer omega-6 fatty acids - they are mainly found in processed vegetable oils
  • Fewer processed foods - these are a source of both omega-6 fats and trans fats
  • More fresh fruit and vegetables for antioxidants that protect polyunsaturated fatty acids from oxidation.
References: 
  1. Food Standards Agency. McCance & Widdowson's The Composition of Foods: Summary Edition. Royal Society of Chemistry, Cambridge, 2002.
  2. Hayes KC. 'Dietary fatty acids, cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. and the lipoproteinOne of a group of compounds that consist of a protein combined with a lipid, and help to transport lipids in the blood and lymphatic system. profile.' Brit J Nutr. 2000; 84: 397-399
  3. Grundy SM, Denke MA. 'Dietary influences on serum lipids and lipoproteins.' J Lipid Res. 1990; 31(7): 1149-72
  4. Appel LJ, Sacks FM, Carey FJ et al. 'Effects of protein, monounsaturated fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. and carbohydrate intake on blood pressure and serum lipids: results of the OmniHeart randomised trial.' JAMA. 2005; 294(19): 2455-64
  5. Jessup W, Kritharides L, Stocker R. 'Lipid oxidation in atherogenesis: an overview.' Biochemical Society Transactions. 2004; 32,part 1.
  6. Mozaffarian D, Aro A, Willett WC. 'Health effects of trans-fatty acids: experimental and observational evidence.' Eur J Clin Nutr. 2009; 63 Suppl 2: S5-21