Fats

The fat in butter, spreads, oil and lard is called ‘visible’ fat. We might be less aware of the ‘invisible’ fat within food such as cakes and pastry. Fat contributes to flavour and contains the fat-soluble vitamins A, D, E and K. It is calorie dense, and therefore very ‘fattening’. In the UK, people obtain most of their fat from meat, cereals, cereal products, which include biscuits and pastries, milk and milk products (Bates et al., 2014). The body can break down the fats we eat into fatty acids and glycerol and, like protein, it can remake the types of fat that the body needs.

Box 8.1 Cholesterol

Blood cholesterol

Once inside the body, all types of fat are called lipids. Lipids include very small

fat molecules called triglycerides and cholesterol.

  • • Cholesterol is an essential component of every cell membrane. We need it for synthesising bile acids, some hormones and vitamin D
  • • Cholesterol is mostly made in the liver and carried in the blood (blood cholesterol) by proteins, at which point we call them lipoproteins
  • • Low-density lipoproteins (LDL) deliver cholesterol to tissues
  • • High-density lipoproteins (HDL) transfer cholesterol to the liver
  • • Both LDL and HDL contribute to measures of total blood cholesterol, and high total cholesterol is strongly associated with cardiovascular disease
  • • LDLs become part of the plaque that clogs up arteries
  • • HDLs are seen as ‘protective’ because we know that, in populations, low average levels of HDL in the blood are associated with greater cardiovascular disease
  • • LDLs can be increased or decreased by the diet
  • • HDLs can potentially be enhanced by physical activity, but research is unclear
  • • The ‘total blood cholesterol to HDL cholesterol ratio’ is often used to assess the risk of cardiovascular disease
  • • Blood ‘cholesterol-raising’ foods include those that are high in saturated fats such as processed meats
  • • Blood ‘cholesterol-lowering’ foods include fruit, vegetables and oats

Dietary cholesterol

We eat cholesterol in the diet.

  • • Foods which have a high cholesterol content are those of animal origin
  • • If we eat a lot or a little dietary cholesterol, the liver will compensate and make less or more accordingly
  • • Eating dietary cholesterol has very little effect on people’s blood cholesterol unless they have certain health conditions
  • • The general population do not need to restrict foods containing dietary cholesterol

Types of fat in the diet include saturated, unsaturated, trans and essential.

Saturated fats

Saturated fats are usually solid at room temperature, such as butter and lard. Most saturated fats in the British diet come from meat, cereals/cereal products, milk and milk products (Bates et al., 2014). They raise harmful LDL blood cholesterol which contributes to atherosclerosis and cardiovascular disease. Reducing saturated fats reduces cardiovascular disease and coronary heart disease events, and they improve the ‘total cholesterol: HDL cholesterol ratio’ (SACN, 2019).

Saturated fat, not dietary cholesterol, is strongly associated with raising blood cholesterol.

Palm oil and coconut oils contain high quantities of saturated fat. The demand for palm oil by the food industry has led to mass de-forestation which is associated with global warming.

Unsaturated fats

Unsaturated fats are usually liquid at room temperature. Monounsaturated and polyunsaturated fats are found in vegetable oils, fish and fish oils, and some fat spreads, nuts, seeds and avocados. Reducing saturated fats and replacing them with monounsaturated and/or polyunsaturated fats lowers harmful LDL cholesterol, but polyunsaturated fats are better for controlling blood sugar as well (SACN, 2019).

People in the UK are eating about the right amount of total fat but too much saturated fat which needs to be replaced with unsaturated fats.

Trans fats

Most trans fats are formed when the food industry adds hydrogen to an oil to make it a hard spread like margarine. In turning the liquid unsaturated fats into solid saturated fats, some fats are malformed into trans fats. Trans fats raise LDL cholesterol. They are also associated with a wide range of health concerns beyond cardiovascular disease, such as breast cancer, pregnancy-related risks, disorders of the nervous system and diabetes (Dhaka et al., 2011). No more than 2% of calories should come from trans fats and, largely due to changes in food processing, the average UK diet contains much less than this (Roberts et al., 2018).

Essential fats

Essential fats are those which the body cannot make from other fats. We must have these in the diet to be healthy. Omega 6 fats are unsaturated, eaten widely, and found in seeds, most vegetable oils, poultry, eggs and nuts. Omega 3 fats are unsaturated and found in oily fish.

Both omega 6 and omega 3 fats compete for the same enzymes to make them work, and so too much omega 6 prevents the benefits of omega 3. The UK diet is high in

Table 8.2 Types of fats

Percentage saturated fat

Percentage monounsaturated fat

Percentage polyunsaturated fat

Almond oil

9

73

18

Sunflower oil

11

20

69

Corn oil

13

29

57

Olive oil (refined)

14

75

11

Olive oil (extra virgin)

14

75

11

Olive oil (light)

15

42

44

Sesame oil (light)

15

42

44

Margarine (soft)

20

47

33

Goose fat

35

52

13

Lard

41

47

12

Ghee

65

25

5

Butter

68

28

4

Margarine (hard)

80

14

6

omega 6 and low in omega 3, and this imbalance is associated with cardiovascular disease, cancer, inflammatory and autoimmune diseases and impacts on brain development (Simopoulos, 2010; Zivkovic et al., 2011). The diet can be rebalanced by eating more oily fish such as mackerel, kippers, salmon, sardines and trout.

Heated fats

Heating fats to high temperatures, and re-heating them, encourages the development of unhealthy trans fats and saturated fats, as well as volatile aldehydes which are toxic (Harinageswara et al., 2010; Bhardwaj et al., 2016). Saturated animal fats such as goose fat, lard and butter are more chemically stable, and recommended for deep fat, extensive frying and baking.

People in the UK need to eat more oily fish.

 
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