Fats

Functions

Dietary fats play many important roles - aiding in the absorption of fat-soluble vitamins A, D, E and K; providing a supply of essential fatty acids; providing the most concentrated source of energy for the body; and improving the flavour and texture of foods. Three main types of fatty acids occur naturally, these are saturated, monounsaturated and polyunsaturated (see below for typical food sources of these different fatty acids).

The degree of hardness of a fat and its melting point tend to increase with the length of the fatty acids it contains and their degree of saturation. Thus, fats that are solid at room temperature are generally speaking more 'saturated' than fats which are liquid at room temperature. A good example is a hard block of lard, which contains around 40-50% saturated fats and is solid at room temperature; versus canola oil which contains around 7% saturated fats, a larger amount of polyunsaturated fats and even more monounsaturated fats, canola oil is liquid at room temperature. 

A balanced diet requires sources of saturated, monounsaturated and polyunsaturated fats. Each type of fatty acid has important roles to play in our body. For example, the long-chain omega-3 fatty acids are needed for structural roles in cell membranes, particularly for our nervous system and vision. 

Role in Disease Prevention

Dietary Fat and Heart Disease

LDL and total serum cholesterol levels increase with an increased intake of saturated fats, resulting in an increased risk of coronary heart disease. Trans fatty acids produce a similar change in cholesterol profiles, however in addition to increasing 'bad' LDL cholesterol levels trans-fatty acids also decrease 'good' HDL cholesterol levels. Again resulting in an increased risk of coronary heart disease.

On the other hand, polyunsaturated fats have a number of positive effects on cardiovascular disease risk. High intakes of omega-6 polyunsaturated fats are associated with positive changes in cholesterol levels that produce a reduced risk of coronary heart disease. And research suggests that omega-3 fatty acids have both anti-inflammatory and cardiovascular benefits. The World Health Organisation (WHO) considers the evidence for the role of long-chain omega-3 fats in reducing cardiovascular disease risk to be "convincing".    

Food Sources

Dietary fats are found in both plant and animal derived foods. Saturated fatty acids are found in dairy products such as milk, butter, cheese and cream as well as coconut and and palm oils. Rich sources of monounsaturated fats are olive, canola and peanut oils. Two different types of polyunsaturated fats predominate in our diet. The omega-6 polyunsaturated fats are found in seed oils such as sunflower, safflower and corn oils.

Humans are unable to produce omega-3 fats and thus we need them in our diet - they are 'essential' fatty acids. Alpha-linolenic acid (ALA) is the parent fatty acid of the omega-3 fatty acids. Dietary sources of ALA include legumes, canola oils and margarines, linseed oils, walnuts and certain other nuts, and some leafy green vegetables. If we are supplied with a dietary source of ALA our bodies can, to a very limited degree, convert the ALA into other important forms of omega-3 fatty acids that we need, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, this conversion is very limited and therefore we are best to rely on dietary sources of EPA and DHA, as well as docosapentaenoic acid (DPA). These fatty acids (EPA, DHA, DPA) are referred to as the long-chain omega-3 fats as they have longer fatty acid chains. Rich dietary sources of long-chain omega-3 fats are oily fish such as mackerel, herring, sardines, salmon, tuna and to a lesser degree other seafood. 

Typical Contributions from Food

Food	Saturated Fat (g)	Monounsaturated Fat (g)	Polyunsaturated Fat (g)
Beef, sirloin steak, grilled (100g)	3.1	3.0	0.3
Beef, mince, lean, stewed (100g)	2.4	2.3	0.2
Chicken, breast flesh, grilled (100g)	1.2	1.9	0.4
Pork, leg steak, lean, grilled (100g)	1.2	1.2	0.3
Milk, trim, (1 cup)	0.7	0.3	Trace amounts
Milk, standard (1 cup)	5.4	2.2	0.3
Cream, (1 tbsp)	3.7	1.5	0.2
Cheese, Edam (20g)	3.4	1.2	0.1
Cheese, blue vein (20g)	4.0	1.3	0.14
Coconut oil (1 tbsp)	11.8	0.9	0.2
Olive oil (1 tbsp)	2.3	9.1	1.6
Sunflower oil (1 tbsp)	1.6	3.0	8.7
Salmon, red, canned (100g)	0.9	1.8	1.6
Tuna, canned in brine (100g)	0.8	0.6	1.2

Source: The Concise New Zealand Food Composition Tables 5th Edition.

Adequate Intake (AI) Levels

Neither an RDI or AI level has been set for total fat intake as it is the types of fats that are consumed, rather than the total amount that is more important in meeting essential needs for physiological and health outcomes. Following are the adequate intake (AI) levels for intake of long-chain omega-3 fats, namely DHA, EPA and DPA

Total Long Chain omega-3 Fat (DHA,  EPA & DPA) AIs – New Zealand and Australia

Life Stage	Age	Males (mg/day)	Females (mg/day)
Children	1-3 yr	40	40
	4-8 yr	55	55
	9-13 yr	70	70
	14-18 yr	125	85
Adults	19+ yr	160	90
Pregnancy	14-18 yr	-	110
	19+ yr	-	115
Breastfeeding	14-18 yr	-	140
	19+ yr	-	145

Acceptable Macronutrient Distribution Ranges to Reduce Chronic Disease Risk

The New Zealand and Australian governments recommend that between 20% and 35% of the energy in our diet comes from fats.

For a moderately active young man (height 1.8m) a daily energy intake of 12,000kJ would be normal. Hence, between 2,400 and 4,200kJ of energy should ideally come from fats for this man. This equates to around 65-115g of fat each day for a man. For a  moderately active young woman (1.6m tall) energy requirements are typically lower at around 8700kJ/day. At this energy intake level, fat contribution would ideally be between 45-82g.

Deficiency

Research suggests that a diet containing less than 20% energy from fat may be lacking in energy to maintain body weight and also may be lacking in micronutrients as dietary fat is a carrier of many fat-soluble vitamins and the essential fatty acids. Hence, a diet overly low in fat may be characterised by not only weight loss but also a number of micronutrient deficiencies.

One particular deficiency state of note is that of the omega fatty acids. A deficiency of omega-3 and omega-6 fats is characterised by dry, rough, scaly skin and dermatitis, amongst other things.

Toxicity

An intake of at least 20% dietary energy from fat is necessary in the opinion of the New Zealand and Australian health authorities in order to provide all the associated micronutrients found with fat in foods. Additionally, irrespective of the trend to limit carbohydrate intake and allow increased intake of protein and dietary fats it would be prudent to limit fat intake to providing a maximum of 35% of dietary energy (see above for calculation).  

References

Garrow JS, James WPT & Ralph A. (2000). Human Nutrition and Dietetics (10th Ed). London: Churchill Livingstone.

Ministry of Health. (2006). Nutrient reference values for Australia and New Zealand. Canberra: Commonwealth of Australia.

Last Updated: 22 October 2008

The material provided by Thinking Nutrition Ltd on this website is for information purposes only. It is not a substitute for appropriate health advice from a qualified medical practitioner.