We need to eat fats Eating fats may kill us
Nutrition is not simple, and there are many paradoxes where dietary practices can have both good and bad effects depending on the circumstances and situation. Fats are perhaps a major example of a nutritional paradox. For many years we have been inundated with information on the undesirable health problems due to fats in food. On the other hand we know that fats are an important and valuable part of the diet. Here I present some of the benefits and problems of fats in food so we can better understand the reasons why we want to eat fats and the reasons why it might cause problems.
Fat is an extremely common and widespread component in foods. Many unprocessed foods or food ingredients contain substantial quantities of fats. These include nuts, milk, eggs, fish and meats. In processed foods oils and fats are found in varying amounts from 1.2% in spaghetti to 82.5% in butter and mayonnaise. Much of the fat in foods maybe hidden fat and this applies especially to meat, sausage and cheese.
THE NATURE OF FATS
In chemical terms (all food is a mixture of chemicals), fats are a very diverse group of compounds which have a general common property of being insoluble in water and soluble in organic solvents such as alcohol or hydrocarbons. Fats are a combination of various fatty acids together with glycerol. Three molecules of fatty acid are combined with one molecule of glycerol to make a triglyceride or fat. Many different fatty acids occur in nature and about 40 of these are important in food. The occurrence of many different fatty acids in foods means that many different combinations of triglycerides also occur. Consequently many different types of fats occur in food.
Fatty acids are usually classified into saturated and unsaturated fatty acids. Saturated fatty acids generally make hard fats as found in foods of animal origin such as butter, lamb or beef. Unsaturated fatty acids occur largely in vegetable oils such a rapeseed oil, soyabean oil or olive oil. Unsaturated fatty acids can be converted into partially saturated forms by a process known as hydrogenation and this is the basis of the margarine industry where various liquid oils can be converted into solid butter-like fats.
BENEFITS OF FATS IN FOOD
Fats are extremely important components in foods, have several well-recognised benefits and cannot be replaced by other substances. They are a concentrated source of energy for the body and a source of essential fatty acids. Fats enhance the absorption of fat-soluble vitamins and are excellent carriers of food flavours.
The efficiency of fat as a foodstuff is very high because the fat contained in food is almost completely absorbed by the body and very little is excreted. Fat is an important energy source although for humans glucose from starch and sugar is a more efficient source than fat. Fat consumption also influences utilization of energy. Fatty acids consumed in fats can be deposited into body tissues and this replaces the need for the body tissues to convert dietary carbohydrate into fatty acids. Consequently a diet high in fat and starch with adequate protein will certainly increase body mass and this is all too apparent today where obesity has become a major health problem.
Many animals such as rats, mice and pigs have limited abilities to synthesize polyunsaturated fatty acids such as linoleic and arachidonic acids and these maybe considered as essential fatty acids. In animals fed on deficient diets various growth and skin problems arise. Humans are unlikely to suffer from a lack of essential fatty acids as they are so widespread in a range of food components.
However various fatty acids are important for growth and in building body tissues in humans as in animals. Fatty acids are an essential component of phospholipids for example, which in turn are important in maintaining good structure in the cells of the body. Fatty acids are very important in the brain and nerves and participate in many metabolic processes.
Other important positive aspects of unsaturated fatty acids are their fat-lowering effect in blood and their ability to reduce cholesterol level in the blood. This has a special significance for health issues because both an increased level of fat and cholesterol in the blood are considered to be risk factors for heart attacks as discussed below.
Fats are excellent carriers of flavours, and dishes prepared with fats are much tastier than foods without fats. The flavour of many meat-based foods largely resides in the fat component and a good example is the marbling of beef which is related to flavour quality. Fats also provide a smoothy, creamy consistency to many dishes, which translates into good mouth-feel and encourages consumption. Low-fat foods are frequently dry and lacking in flavour.
Fats are extensively used in food manufacturing and even the fact that that fats are not soluble in water has been exploited in food technology by generating emulsions. An emulsion is prepared by mixing two immiscible liquids, water and fat or oil. Milk, mayonnaise, butter and margarines are all examples of various types of emulsions.
The effect of fats on flavour and texture of foods and in generating emulsions is certainly the reason that fats and oils have been appreciated for a long time and explains why the consumption of fat is still very high today.
DIGESTION OF FAT
In Western Europe 60-100 g of fats is the average daily intake and this is mainly in the form of triglycerides which must be processed in the digestive tract to become available to the body. Fat in food passes through the stomach and digestion takes place mainly in the small intestine. Dietary fats are insoluble in water yet the contents in the digestive tract are a water-based mixture. Digestive enzymes are also water-soluble proteins, so fat digestion immediately poses some difficulties. Fortunately other components in the digestive tract such as bile fluids and phospholipids are powerful emulsifying agents and help bring the dietary fat into an emulsion where it can be broken down by the digestive enzymes. Free fatty acids and monoglycerides released after enzyme digestion are still not very water-soluble and they would be absorbed very poorly from the digestive tract in their free state .
More rapid complete absorption is brought about through the formation of very small highly stable units in the digestive tract called micelles. These maintain the products of fat digestion in a water-soluble form. These micelles carry fatty acids and monoglycerides to the wall of the digestive tract for absorption. After the digested fat is absorbed through the intestinal wall it is reconstituted into triglycerides. These are transported in the blood to the liver for metabolism and any unneeded fat is stored in fat deposits in the body tissues.
PROBLEMS OF FATS IN FOODS
There are two basic problems caused by fats in foods. One is the deterioration of food quality brought about by oxidation of fat in foods and the development of rancidity. The second problem is the interaction between dietary fat and health and disease. This is one of the most active areas of biochemical, nutritional and medical research today. Nevertheless the role of dietary fat in health and disease remains one of considerable controversy.
Fat Oxidation and Rancidity
Rancidity is a familiar indication of the deterioration of fats and oils. In dairy products rancidity is usually the result of breakdown of the triglycerides by micro-organisms to release short-chain fatty acids which have unpleasant odours and flavours. In other fats and oils, and the fatty parts of meat and fish, rancidity is the result of the oxidation of the unsaturated fatty acids.
Fats and oils exposed to the atmosphere and heating over a long period also undergo polymerisation reactions. This is particularly important in frying oils. Polymerised oils are very poorly digested and so lose a lot of nutritional value. There is no hard evidence that polymerised oils are toxic and fried foods have a long history of safe use. Any health concerns over fried foods relate more to the quantity of fat consumed in the food rather than to concerns about polymerisation.
Fat oxidation is undoubtedly one of the major causes of food spoilage. It is of great economic concern to the food industry because it leads to the development in fat-containing foods of various flavours and off-odours generally called rancid. In addition oxidation can decrease the nutritional quality of food and certain oxidation products are potentially toxic. On the other hand, under certain conditions a limited degree of fat oxidation is sometimes desirable as in aged cheeses and some fried foods. It is probably not a good idea to deliberately consume large quantities of rancid fats. However this is not very likely as humans generally reject rancid foods.
There has been an enormous amount of scientific research directed towards controlling oxidation in fats. Development of rancidity in fats can be retarded by careful processing procedures such as avoiding high temperatures and excluding air. This is not always possible and some fatty foods such as biscuits and pastry are particularly susceptible to rancidity as their structure necessarily exposes the maximum surface of the fat to the atmosphere.
One of the major successes of food research has been to develop products known as antioxidants which can massively extend the shelf life of fats. Antioxidants are compounds added in very small quantities to fats (usually in mg/k) and can significantly delay the onset of oxidation and the development of rancidity. Literally hundreds of compounds both natural and synthetic have antioxidant properties. However only a limited number of antioxidant compounds are used in foods as they are considered as food additives and their use is regulated in most countries.
Antioxidants are not a panacea and have to be used with care as they do not abolish rancidity but significantly delay its appearance. Furthermore antioxidants cannot reverse rancidity so it is pointless treating rancid foods with an antioxidant in the hope of recovering the original quality. In terms of fat oxidation and development of rancidity, prevention is not only better than cure it is the only cure.
Fats and Disease
The consumption of high levels of fats, particularly those containing saturated fatty acids will cause elevated levels of fatty acids in the blood and this is a risk factor for the development of various heart diseases as is high levels of cholesterol in the blood.
Many hidden fats in red meats for example are rich in saturated fatty acids and contain cholesterol together with the triglycerides. This is certainly one reason for the move away from the consumption of red meats in recent years. Vegetable oils on the other hand have a large component of unsaturated fatty acids and are considered cholesterol-free as they normally contain only very small amounts of cholesterol.
The disease, artherosclerosis is caused by metabolized forms of cholesterol commonly described as "bad cholesterol" in LDL (low-density lipoprotein). Another form of cholesterol, HDL (high-density lipoprotein) is considered "good cholesterol". HDL is responsible for transporting surplus cholesterol to the liver. A high level of LDL is directly related to heart disorders.
Increasing the ratio of polyunsaturated to saturated fatty acids in the diet has a beneficial effect in lowering blood cholesterol. A strong positive lowering influence of monounsaturated fatty acids, chiefly oleic acid, on cholesterol level has also been found. Oils rich in oleic acid such as rapeseed oil and olive oil are suitable for a cholesterol-reducing diet as well as those with a high polyunsaturated fatty acid content such as sunflower oil.
The interaction of fats, health and disease is further complicated since it appears that fatty acids found in fish oils have quite beneficial effects in protecting against heart disease and possibly against various joint problems such as a some forms of arthritis. These are known as Omega-3 fatty acids and many dietary recommendations today include regular consumption of oily fish to increase the intake of these particular fatty acids.
BALANCING THE PARADOX
The recognition that high consumption of starch, fat and protein leads to increased body mass has led to the development of an entire diet industry with various dietary combinations being proposed to control body weight and improve health. In addition many Government Departments have published guides to healthy eating and weight control.
Reduction of fat intake is obviously one solution. This has led to general recommendations in both the USA and the EU that people should not obtain more than 30% of their total calories as fat. Moreover they should limit the intake of saturated fatty acids to less than 10% of the calorie intake
Increased consumption of unsaturated fatty acids in oils of vegetable origin and from fish seems to have desirable benefits and has the advantage that foods with attractive flavours can still be consumed.
Reduction of starch intake is another possibility as this will force the body to use more fat as an energy source and less will be available to be deposited in the body.
Probably the best advice for the majority of the population however is simply to eat a well-balanced diet that includes ample amounts of all essential nutrients, fresh fruits and vegetables and regular exercise.
Dr. Adams has also written a book: NUTRICINES, Food Components in Health and Nutrition. You may order your book through www.nup.com or visit his website .