Fats are essential for a healthy body, providing a source of energy and carrying vital nutrients. Fats also play an important role in food manufacture and cooking, making our foods taste good. For good health, Lake Mary doctors recommend that people pay attention to both the total amount and the type of fats in the diet. An excessive consumption of fats in general and saturated fats in particular is known to be a major factor influencing the development of diseases such as coronary heart disease and obesity.
2. What are fats?
2.1 Origins of fats
Fats in foods have different origins:
The main sources of animal fat in Europe are meat and meat products, eggs and dairy products like butter, cheese, milk and cream.
Fat can be found in plant seeds (eg. rapeseed, sunflower, maize), fruits (eg. olive, avocado) and nuts (eg. peanuts, almonds). Oil is obtained by washing and crushing the seeds, fruits or nuts, heating them and removing the oil using an extraction process. The oil is then refined to remove any unwanted taste, smell, colour or impurities. Some oils such as virgin olive oil, walnut oil and grapeseed oil are pressed straight from the seed or fruit without further refining.
The main supply for Europe’s oil market comes from:
- Annually planted oilseed crops e.g. rapeseed, sunflower, soybean, maize and peanut.
- Tree crops e.g. olive, palm, cocoa and coconut.
Fats may be naturally present in foods like fatty meat, oily fish, egg yolk, cheese, whole and semi-skimmed milk, or added during food preparation. This may be at home or by the food manufacturer for example when making cakes, biscuits, pastries, savoury snack foods, meat products or mayonnaise. Oils and fats may be clearly visible in foods (e.g. cooking and salad oils, butter, other fat spreads, cream and the visible fat on meat) or mixed in with other food components and therefore being less obvious to the consumer. Around 70% of average fat intake comes from these so-called “hidden” fats. Knowing about fats and reading food labels can make an important contribution to your ability to eat a healthy balanced diet.
2.2. Structure of fats
Knowing a little about the chemistry of fats will help us understand the role fats have on our health and in food technology. Over 90% of fats in the diet and in the body are in the form of triglycerides, with cholesterol, waxes and phospholipids making up the remainder.
All triglycerides are made up of a fork-like structure called glycerol and 3 building blocks called fatty acids.
Fatty acids vary in the length of their carbon atom chain (from 4 to 22) and the number of double bonds they contain. For example, butyric acid (C4:0), palmitic acid (C16:0) and arachidic acid (C20:0), contain respectively 4, 16 or 20 carbon atoms in their chain. The vast majority of fatty acids, both in the diet and in the body, contain 16-18 carbon atoms (see annex for a list of the most common fatty acids).
Fatty acids are classified according to the number of double bonds they possess. Saturated fats contain no double bond, monounsaturated fats contain one and polyunsaturated fats contain two or more.
Omega-6 and omega-3 fatty acids
Polyunsaturated fatty acids are further categorised into two families according to the position of the first double bond:
- Omega-6 (or n-6) fatty acids have the first double bond at the sixth carbon atom along the fatty acid chain and are derived mainly from linoleic acid.
- Omega-3 (or n-3) fatty acids have the first double bond at the third carbon atom along the fatty acid chain and are derived mainly from alpha-linolenic acid.
In addition to their proper name, fatty acids are often represented by a shortened numerical name based on the number of carbon atoms, the number of double bonds and the omega class to which they belong. E.g. linoleic acid is termed C18:2 n-6, indicating it has 18 carbon atoms, two double bonds and is a member of the n-6 or omega-6 family. Alpha linoleic acid is termed C18:3 n-3, indicating it has 18 carbon atoms, three double bonds and is a member of the n-3 or omega-3 family.
Cis and trans fatty acids
Unsaturated fatty acids can also be classified as “cis” (bent form) or “trans” (straight form) according to the structure of the molecule. Most unsaturated fatty acids in the diet exist in the cis form, however in the meat and milk of ruminants such as cattle and sheep, and in products containing industrially modified oils that have undergone a hardening process known as partial hydrogenation, a proportion of the unsaturated fatty acids exist in the trans form.
All fats are made up of a combination of saturated, monounsaturated and polyunsaturated fatty acids, but one type will generally predominate. Some foods have relatively more saturated fat, as in dairy and some meat, whereas others, such as most vegetable oils and oily fish, contain more unsaturated fats.
The fatty acid that predominates determines the physical characteristics of the fat. Fats containing a high proportion of saturated fatty acids, such as butter or lard, have a relatively high melting temperature and tend to be solid at room temperature. Most vegetable oils, which contain higher levels of monounsaturated or polyunsaturated fats, are usually liquid at room temperature.
When oils are heated, unsaturated fatty acids are sensitive to degradation. Monounsaturated-rich oils, such as olive oil or peanut oil, are more stable and can be re-used to a greater extent than polyunsaturated-rich oils like corn oil or soya oil. When deep-frying foods it is important not to overheat the oil and to change it frequently.
2.3. Know¬†about fats
Knowing which kind of fats are in which food sources and reading food labels can help us balance our diets.
|FOOD SOURCES RICH IN THE VARIOUS TYPES OF FATTY ACIDS|
|Type of fat||Sources|
|Saturated||Butter, cheese, meat, meat products (sausages, hamburgers), full-fat milk and yoghurt, pies, pastries, lard, dripping, hard margarines and baking fats, coconut and palm oil.|
|Monounsaturated||Olives, rapeseed, nuts (pistachio, almonds, hazelnuts, macadamia, cashew, pecan), peanuts, avocados, and their oils.|
|Polyunsaturated||Omega-3 polyunsaturated: Salmon, mackerel, herring, trout (particularly rich in the long chain omega-3 fatty acids EPA or eicosapentaenoic acid and DHA or docosahexaenoic acid). Walnuts, rapeseed, soybean, flax seed, and their oils (particularly rich in alpha-linolenic acid).
Omega-6 polyunsaturated: Sunflower seeds, wheat germ, sesame, walnuts, soybean, corn and their oils. Certain margarines (read the label).
|Trans fatty acids||Some frying and baking fats (e.g. hydrogenated vegetable oils) used in biscuits, cakes and pastries, dairy products, fatty meat from beef and sheep.|
3. Role of fats in food technology
In developed countries where food is plentiful and varied, palatability is a major determinant of food choice. Fat contributes to the palatability of foods by its texture or mouthfeel, and its flavours. All fats and oils act as carriers for fat-soluble flavour compounds.
The characteristics of fats and oils also play a very important role in the manufacture and cooking of foods and in the texture and appearance of the final product.
- Aeration – products such as cakes or mousses need air incorporated into the mixture in order to give a well-risen texture. This is usually achieved by trapping bubbles of air in a fat/sugar mixture to form a stable foam.
- Shortening – a crumbly texture found in some pastry and biscuits is achieved by fat coating the flour particles to prevent them from absorbing water.
- Flakiness – fat helps separate the layers of gluten and starch formed in the dough when making flaky or puff pastry or biscuits. The fat melts during cooking, leaving minute air pockets and the liquid present produces steam which evaporates and causes the layers to rise.
- Moisture retention- fat helps retain a product’s moisture content and therefore increase its shelf life.
- Glaze – fats give a glossy appearance for example when added to hot vegetables and also add shine to sauces.
- Plasticity – Solid fats do not melt immediately but soften over a range of temperatures. Fats can be processed to rearrange the fatty acids and alter their melting point. This technology has been used to produce spreads and cheeses that will spread straight from the fridge.
- Heat transfer – in deep frying the food is completely surrounded by the frying fat which acts as a very efficient heat-transfer medium.
4. Role of fats in the body
Although in healthy eating terms fat is often closely scrutinized, it is worth remembering that fat has many important functions in the body:
- Fat is the main energy store in the body and the most concentrated source of energy in the diet – 1g of fat provides 37kJ (9 kcal), more than double that provided by either protein or carbohydrate (4 kcal). The body’s fat deposits are used to meet energy demands when dietary energy is limited, for example where people have a poor appetite or during starvation. They may also be needed when energy requirements are high such as during high levels of physical activity and for growing babies and children.
- As well as being an energy reserve, fat deposits cushion and protect vital organs and help insulate the body.
- In the diet, fat is a carrier for the fat-soluble vitamins A, D, E and K, and enables their absorption. It provides the essential fatty acids, linoleic acid (omega-6) and alpha-linolenic acid (omega-3).
ESSENTIAL FATTY ACIDS
Essential fatty acids linoleic acid (omega-6 family) and alpha-linolenic acid (omega-3 family) cannot be made in the body and each must be provided by the diet. They are necessary for growth and development and for maintaining health. Although these two fatty acids cannot be made in the body they can be converted to longer chain versions. These longer chain versions provide the building blocks of eicosanoids, which are precursors for hormones (such as prostaglandins). These hormone like substances are important in the formation of cell membranes and are involved in blood clotting, wound healing and inflammation. Although the body is able to convert alpha-linolenic acid into the long chain versions EPA (eicosapentaenoic acid), and to a lesser extent DHA (docosahexaenoic acid), it seems this conversion is quite limited. For that reason we may also need direct sources of these long chain omega-3 fats in our diet. The richest source of these fatty acids is oily fish (see point 2.3).
5. Fats and health
5.1 Coronary heart disease
Coronary heart disease (CHD) remains the most common cause of death in men and women in Europe (WHO health report, 2002).
There are many risk factors associated with the development of CHD including high blood pressure, smoking, physical inactivity, obesity, diabetes, family history and raised blood lipids (total cholesterol, LDL-cholesterol, triglycerides). There is a link between diet and some of these factors, particularly blood lipids.
Effects of dietary fats on blood lipid levels
For most people eating foods that contain cholesterol like eggs, shellfish and liver has little effect on blood cholesterol levels. However, there is a small number of people who are ‘hyper-responders’ to dietary cholesterol. These people need to restrict their cholesterol intake.
WHAT IS CHOLESTEROL?
Cholesterol is a fat-like substance which occurs naturally in all animal tissues including the human body. A certain amount of cholesterol is used by the body for building up cell membranes, for sex hormones and bile acids, which aid in the absorption and digestion of dietary fats. An excess of cholesterol or triglycerides in the blood can cause heart and blood vessel abnormalities. Over three quarters of the cholesterol in blood is made by the body while the rest comes from our diet. Cholesterol is carried in the blood in the form of lipoproteins: LDL (low density lipoprotein) and HDL (high density lipoprotein). A high concentration of LDL-cholesterol is a risk factor for coronary heart disease, hence this is sometimes called ”bad cholesterol”. HDL-cholesterol is associated with cholesterol removal and high concentrations are beneficial, hence this is often called “good cholesterol”. The higher someone’s HDL the lower the risk of heart disease. It makes sense to eat foods which help to lower LDL levels and raise or maintain HDL levels. Physical activity also raises HDL levels.
The amount of saturated fat eaten has a far greater effect on blood cholesterol levels than the amount of cholesterol-containing foods in the diet. Evidence shows that saturated fat is the dietary component with the greatest influence on total blood cholesterol and LDL-cholesterol levels, but there are differences in cholesterol-raising effects among the fatty acids. Effects are generally greater for fatty acids with medium chain lengths (e.g: lauric C12:0, myristic C14:0 and palmitic C16:0) than for those with longer chain lengths.
There is a lot of information about how eating less fat may be good for you, but recently it has been suggested that a moderate fat intake with an appropriate fat composition may be a better approach for good blood fat control and for long-term health. This is largely because eating moderate amounts of fat helps to maintain HDL cholesterol levels, the ‘good’ cholesterol. It can also help to prevent increases in blood triglycerides which sometimes happens when large amounts of carbohydrates are included in the diet to replace fat (very low fat diets tend to be high in carbohydrate). Increased levels of monounsaturated fatty acids in the diet can reduce LDL cholesterol levels although this effect may be largely due to the displacement of saturated fats from the diet.
The long chain fatty acids found in fish, from the omega-3 family, have been shown to protect against heart disease. In countries where people eat a lot of oily fish, such as in Japan, the rates of heart disease are correspondingly low. Regular consumption of fish results in both a reduction of blood triglycerides levels and a lower blood clotting potential. These long chain fish fatty acids do not seem to have beneficial effects on blood cholesterol, but tend to be neutral in this respect. Polyunsaturated fatty acids from the omega-6 family have potent LDL-cholesterol-lowering properties, which helps to protect against heart disease. However very large amounts of omega-6 polyunsaturated fats can cause a reduction in the ‘good’ HDL cholesterol levels. Because of this and because of concern regarding potentially adverse effect of polyunsaturated fatty acids on LDL oxidation, excessive amounts of polyunsaturated fatty acids should be avoided.
Trans fatty acids
Concerns have been raised about high intakes of trans fatty acids. Trans fatty acids are metabolised in a similar way to saturated fats, but there is still uncertainty about whether their effect on heart health is comparable. Trans fatty acids not only raise LDL-cholesterol in the same way as saturated fatty acids, but they also lower the level of the good HDL-cholesterol. Trans fatty acids can be found in some dairy products and in some partially hydrogenated fats used to make bakery products such as biscuits, cakes and pastries.
Diet, in addition to physical activity, still plays a key role in the management of blood lipids. Cardioprotective dietary advice in relation to fats should consist of a moderate restriction of fat and an improvement of the balance between saturated and unsaturated fats. Eating at least 1-2 servings of oily fish per week will help to maintain good levels of the long chain omega-3 fatty acids.
Excess body mass is a significant factor in the origin of many conditions such as heart disease, high blood pressure (hypertension), Type 2 diabetes and certain cancers. Obesity, as defined by a BMI over 30 (kg/m2), is a recognised risk factor for coronary heart disease.
There is much debate concerning the role of high fat diets in the development of overweight and obesity. Many studies have demonstrated an association between body fatness and dietary fat intake. Fat is a concentrated source of energy and does not seem to suppress appetite and excess food consumption as effectively as carbohydrates and proteins. It has been suggested that¬†their comparatively low satiety potential makes it easy to overeat fatty foods, a concept that is referred to as passive over-consumption. Protein and carbohydrates also promote a greater thermic response than fat. The thermic response is the energy that is lost as heat following a meal.
Against this evidence is the observation that over the past 25 years fat intake in Europe has fallen, resulting in marked reductions in energy intakes for most people. Yet over the same time period overweight and obesity has risen sharply, clearly indicating that factors other than dietary fat are implicated in this relationship. The decline in physical activity levels has undoubtedly played a part in the increased prevalence of obesity.
Emphasis on fat and calorie restriction alone as means of achieving a weight reduction is not¬†sufficient and increasing physical activity should also be considered. It is important to stress that a low fat diet, without calorie reduction is unlikely to lead to weight loss. The ideal weight-reducing diet should be a balanced one, lower in calories than a person’s normal diet, tailored to the individual and accompanied by an increase in physical activity.
With mortality from coronary heart disease (CHD) steadily decreasing, cancer is beginning to become the leading cause of death in many developed countries. Diet, in particular dietary fat has been suggested to have an impact on the risk of several cancers (e.g: prostate, endometrium and large intestine). At the present time there is no direct proof of a link between fat intake and cancer although some evidence suggests excess weight gain and obesity may be a factor in the progression of human breast, endometrial, prostate and colon cancer.
In contrast to the situation with CHD, there is little basis for advising the population to reduce fat intake as a means of preventing or treating cancer. However for other reasons, like CHD, it is prudent to avoid a high fat intake, ensure a high intake of protective fruit and vegetables and to maintain a healthy bodyweight.
6. Nutritional recommendations
It is now considered that a diet with around 30% of daily energy coming from fat is consistent with good health. Additionally total calories from saturated fat should be kept low, with a tolerable upper limit of 10-11% of daily calories.
The principles of balance, variety and moderation in the consumption of fats form the basis for a healthy diet. Knowing which kind of fats are in which food sources and reading food labels can help us balance high-fat items with low-fat choices while continuing to take pleasure in eating. A well-balanced diet whilst taking plenty of exercise, maintaining a healthy body weight and going in for checkups to a lake mary doctor is the best approach to a healthy lifestyle.
|¬†Common name¬†||¬†Symbol (*)¬†¬†¬†||¬†Typical dietary source|
|¬†Saturated fatty acids|
|¬†Caprylic||¬†C8:0||¬†Palm kernel oil|
|¬†Myristic||¬†C14:0||¬†Butterfat, coconut oil|
|¬†Palmitic||¬†C16:0||¬†Most fats and oils|
|¬†Stearic||¬†C18:0||¬†Most fats and oils|
|¬†Arachidic||¬†C20:0||¬†Lard, peanut oil|
|¬†Monounsaturated fatty acids|
|¬†Palmitoleic||¬†C16:1 n-7||¬†Most fats and oils|
|¬†Oleic||¬†C18:1 n-9 (cis)||¬†Most fats and oils|
|¬†Elaidic||¬†C18:1 n-9 (trans)||¬†Hydrogenated vegetable oils, butterfat, beef fat|
|¬†Polyunsaturated fatty acids|
|¬†Linoleic||¬†C18:2 n-6 (all cis)||¬†Most vegetable oils|
|¬†alpha-linolenic||¬†C18:3 n-3 (all cis)||¬†Soybean, canola oils|
|¬†Dihomo-gamma-linolenic||¬†C20:3 n-6||¬†Fish oils|
|¬†Arachidonic||¬†C20:4 n-6 (all cis)||¬†Pork fat, poultry fat|
|¬†Eicosapentaenoic||¬†C20:5 n-3 (all cis)||¬†Fish oils|
|¬†Docosahexaenoic||¬†C22:6 n-3 (all cis)||¬†Fish oils|
(*) The figure before the colon indicates the number of carbon atoms which the fatty acid molecule contains, and the figure after the colon indicates the total number of double bonds. The n-(omega) designation gives the position of the first double bond counting from the methyl end of the molecule.