Fat from a biochemical point of view
Fats, or more specifically lipids, are water-repellent (=hydrophobic) molecules. This means that they are difficult to mix with water. This can be observed by pouring some oil into a glass of water and stirring it; the oil quickly settles back to the surface of the water in large fat droplets. There are different types of lipids; fatty acids, phospholipids and steroids. The fatty acids are described in the next section.
Phospholipids are the main components of all cell membranes. The membrane of a cell consists of a double layer of phospholipids and thus forms an interface between the cell and its environment. It is therefore obvious that this layer must necessarily be intact for a living cell to exist. Steroids are a group of lipids that include cholesterol and numerous hormones derived from it2. The function of cholesterol and steroids will be discussed in a later section.
Different fatty acids - the importance of saturated and unsaturated
A fat molecule of a fatty acid consists of glycerol and fatty acids. Glycerol is a trivalent alcohol that should not be confused with ethanol in alcoholic drinks. A fatty acid is a long-chain carboxylic acid. This can be thought of as a skeleton of carbon atoms surrounded by hydrogen atoms and a carboxyl group (hydrogen, oxygen and carbon). The carboxyl group serves as a binding site to glycerol.
Basically, there are always three fatty acid molecules linked to a glycerol molecule, thus forming a triglyceride; the chemical word for this form of fat. Depending on whether double bonds of carbon atoms are present in the skeleton of the fat molecule, these are so-called unsaturated or saturated fatty acids. If a double bond is present, the skeleton bends, and because of this curvature, the fat molecules cannot form too close together at room temperature.
This results in a liquid oil which belongs to the unsaturated fatty acids. One example of this is olive oil. If there is not a single double bond, a saturated fatty acid is present. This is the case with butter, for example. Without the double bonds, the fat particles can accumulate close together, resulting in a solid fatty acid2. However, there is another form; polyunsaturated fatty acids, which still have at least two or more of the carbon double bonds. These include omega-6 and omega-3 fatty acids6. These will be described later in this article.
Artificially hardened fats and the problem of trans fats
So how is it possible that vegetable oils like sunflower oil can be hardened in a spreadable way if they were liquid due to their chemical structure? To do this, the unsaturated fatty acids must be converted into saturated ones in a hydrogenation process. This reduces the carbon double bonds.
The best-known example of this is margarine, but peanut butter or inexpensive frying fats are also included. The worrying thing is that free trans fats are produced as by-products of this operation. These are also found in lower quality fats such as frying fat2.
According to the current state of science, these trans fatty acids contribute massively to arteriosclerotic deposits, promote obesity and inflammation in the human organism. These factors are in turn directly related to an increased risk of heart attack and stroke4.
How can you avoid fats that are harmful to your health?
It is understandable that one should avoid this form of fats. Thus, obvious trans fats such as margarine, palm oil and co. as well as all fried foods should be removed from the daily diet. However, less obvious hardened fats that are found in industrially processed foods are particularly problematic. So, one should always take a closer look at the ingredients of products. If the term hydrogenated vegetable fat or palm oil is used, it can be assumed that trans fats are contained.
It should also be borne in mind that if more sensitive oils are heated too much, oxidation can occur, and trans fats are formed again because the natural chemical structure of the fats is destroyed. The heat resistance of the respective grease should therefore be considered.
Which greases are heat resistant?
First and foremost, the fatty acid composition should be considered: Saturated fatty acids are more heat-resistant than unsaturated ones, polyunsaturated ones are generally very sensitive to temperature. Another point is industrial fat processing; if the respective oil has been cold-pressed, it is less thermostable than refined oils.
High-quality cold-pressed oils are called native oils. Native means that they should retain their typical taste and colour, thus preserving valuable ingredients. The raw materials, such as olives, are put into an oil press and mechanically processed at low temperatures, so that the oil is filtered out at the end.
Refined oils, on the other hand, are pressed using heat and often undergo further chemical processing. This includes processing steps such as degumming, neutralisation and deodorisation. This extends the shelf life, for example, and neutralises odour and colour. At the same time, however, valuable micronutrients are also destroyed7. Refined oils and hardened fats are therefore very heat-stable but are less recommendable from a health point of view.
Pasture butter, ghee (clarified butter), cocoa butter or virgin coconut fat is well suited for frying and baking at high temperatures, as they belong to the saturated fatty acids and have additional health benefits. The former also contains butyric acid, which promotes the microbiome in the intestine, i.e. the intestinal bacteria that help to build up the intestinal mucosa. In this way, it supports intestinal health and helps maintain the barrier that prevents harmful substances from entering the bloodstream.
Cold-pressed olive oil containing unsaturated fatty acids can be heated up to 180⁰C, so it can be used to steam vegetables. Linseed oil, however, should not be heated at all, as it consists of polyunsaturated fatty acids that are sensitive to heat and oxidise immediately.
Omega-3 and Omega-6 fatty acids
As already mentioned above, these are polyunsaturated fatty acids, which are therefore sensitive to heat and should therefore not be processed under the influence of heat. Omega-3 and omega-6 fatty acids are essential, so they must be supplied with food. They consist of a chain of at least 18 carbon atoms. The first double bond is located at the 3rd or 6th atom of the skeleton, from which their names were derived14.
Omega-3 can be found in tuna, salmon, sardines, linseed oil, hemp oil, chia seeds and walnuts, among others. Omega-6s are mainly found in virgin olive oil, sunflower oil, safflower oil, grape seed oil and avocado.
Both fatty acids are of great health importance, but their relation in daily intake must be considered. An optimal ratio would be 5:1, so it is beneficial to consume five times as much omega-6 as omega-3 fatty acids.
The problem with today's diet is that it does not take this into account. In the USA, for example, the current ratio is 10:1, in Germany 8:1. This is probably since most of the population eats the wrong food and consumes many industrially processed foods. These are mainly fortified with cheap vegetable fats, consisting of omega-6 fatty acids. This imbalance is a risk factor for vasoconstriction, increased platelet aggregation and cardiac arrhythmia.
It is therefore advisable to consciously pay attention to a balanced ratio and to avoid industrially processed food15.
The reason for this is the inflammation-promoting effect of omega-6 fatty acids. Omega-3 fatty acids on the other hand inhibit inflammation. Omega-3 fatty acids also have a positive effect on mood and memory. For example, fish oil has already been successfully used in the treatment of dementia and AHDS8.
The digestive system
The digestion of nutrients begins in the mouth, where our teeth break down the food and enzymes become active, which already partially break down more complex carbohydrates. Fats, on the other hand, first pass through the mouth, oesophagus and stomach without being broken down into their smallest particles.
The low PH value in the stomach and its digestive enzymes such as pepsin do not affect the fatty acids. Nevertheless, the gastric peristalsis - the contraction of the ring muscles in the stomach - already emulsifies 15% of the fats. Proteins and carbohydrates, however, are largely broken down up to this stage1. Between the stomach and the small intestine is the pylorus, a sphincter muscle that regulates the passage of food from the stomach to the intestine. The food pulp is released in small quantities into the small intestine3.
The fats, which are now in the small intestine, are emulsified by bile acids, which are produced by the liver. Emulsification means that the fats, which are insoluble in water, are dispersed into smaller droplets. This process increases their surface area so that they can be optimally attacked by the lipases.
These are enzymes that break down free fatty acids - in other words, they break them down so that they can be absorbed by the intestinal mucosa and released into the blood. This produces the various lipids mentioned above: triglycerides from vegetable oils, cholesterol from eggs, meat, etc. and fatty acids1. They are then transported via the blood to the respective target organ or tissue.
Health & fat?
The intestinal mucosa consists of a lipid layer which is nourished by probiotic intestinal bacteria. Thus, on the one hand, these microorganisms must receive enough fibre to stay alive. On the other hand, enough good fats in the diet are necessary to ensure that the raw materials for the intestinal cell wall are available8.
Fat-soluble vitamins & health risks of a fat-free diet
Vitamins A, D, E and K can only be ingested with the help of fats in the diet. When the fats emulsify, they bind to the small fat globules and can thus be absorbed into the bloodstream and transported to the liver, for example.
For example, if carrots containing vitamin A are consumed completely without fat, the vitamin cannot be absorbed and is excreted again5. If a low-fat diet does without dietary fats, as was recommended until recently, based on the mistaken belief that they are associated with increased body fat, a vitamin deficiency is provoked.
Why carbohydrates should be cut out instead of fats in a radical diet
In principle, radical diets should be viewed critically anyway. A diet that becomes routine and consists of foods that are as natural and unprocessed as possible and have no intolerance potential such as cow's milk, cereals and the like is much more sustainable than a short-term extreme diet.
However, if you want to do without a macronutrient for a while, then carbohydrates should be the choice. They are not essential and can be produced by the human organism from fats or amino acids if too little of them is taken in with food.
According to this, in a low carb diet, stored fats are transported from the cells to the liver where they are converted into sugars. However, various fatty acids are essential, so they cannot be produced from other substances present in the body1. In addition, there is the factor mentioned in the last section with vitamins that can only be absorbed with fat.
Steroids and cholesterol
The term steroid is quickly associated with doping and the bodybuilder scene. However, it is in fact a chemical group of substances belonging to lipids and of great importance for the human organism. Steroids are composed of a carbon skeleton, but in the form of four rings. Functional groups of substances are attached to the rings, which specify their characteristics.
Cholesterol is a steroid found in the cell walls among the phospholipids described in the first section. Its structure ensures the mobility of the cell membrane and prevents its solidification when temperatures are low. This would clarify an important function of this substance.
It also plays a role in hormone metabolism: cholesterol serves as the starting substance for various hormones such as oestrogen, testosterone, cortisol, calciferol (vitamin D) or progesterone. For this reason, this group is also known as steroid hormones. Cholesterol is the basis in hormone production. This is another reason why a completely fat-free diet is not advisable - especially for sports goals such as muscle building - because testosterone, for example, plays a central role here2.
Cholesterol-containing foods that also have health benefits include butter, ghee, eggs and calf's liver10.
HDL and LDL cholesterol
Cholesterol has a bad reputation because it can promote the clogging of blood vessels. However, we need to differentiate here and first gain an understanding of the function in the blood vessels: On the one hand, LDL cholesterol, the short form for low-density lipoprotein, circulates in the human organism.
Strictly speaking, it consists of only 50% cholesterol lipids, the remaining components being proteins and phospholipids. Its role is to transport cholesterol stored in the liver to the tissues11. Its antagonist, HDL cholesterol (high density protein), brings the cholesterol from the tissue back to the liver. The proteins thus act as a train that carries the cholesterol from A to B. Depending on whether the proteins have a high or low density, the lipid is transported to or into the tissue12.
So, it is obvious that the two must be in balance with each other. On the one hand, the tissue needs to be supplied with cholesterol, and on the other hand an excess lead to fat deposits in the tissue, which ultimately counts as a risk factor for the development of arteriosclerosis13. A strongly elevated LDL and a too low HDL value can therefore be considered a cause for concern, but a slightly elevated HDL value is not.
Not so long ago, doctors warned against the consumption of saturated fatty acids and eggs containing cholesterol, under the mistaken belief that this would raise cholesterol levels so massively that it would calcify blood vessels. However, current evidence clearly shows that this is not the case2.
Why milk fat is not an optimal nutrient for the human organism
Cow's milk is a potential allergen, not only the lactose it contains is important, but also other substances, including milk fat. In principle, a large proportion of it would not be absorbed by the human intestine, as the elements cannot be broken down into the small globules with a larger surface area to attack.
Commercial milk, however, is homogenised; in this process, the fat molecules are already broken down so that their surface allows absorption in the intestine. This is praised by producers as an advantage, but in fact it is a disadvantage: especially with conventional milk from intensive livestock farming, an increased pollution load is found above all in the milk fat content. Toxins, drugs such as antibiotics and hormones accumulate in the lipid molecules.
These would be excreted in the case of non-homogenised milk, but this industrial process allows them to be absorbed by the intestine with the small fat globules, which means that they enter the bloodstream and ultimately the tissues. There they promote inflammatory processes and additional storage of fat in the cells9.
Fat and energy density vs. how it is metabolized / fat as energy supplier
The high calorie content of dietary fats has so far not received much attention in this article, as all the above-mentioned relationships are more relevant. In fact, one gram of fat contains 9.3 calories, proteins and carbohydrates only 4.1 calories per gram. This means that the energy density of dietary fats is more than twice that of the other two macronutrients2.
On the one hand, however, it should be borne in mind that the amount of high-fat foods consumed is generally smaller, as they are more filling. On the other hand, the timing, the combination, the bioavailability of the respective fat and the associated biochemical processes in the body must be considered. (Especially the perfect breakfast should consist of at least one good source of fat).
As described in detail, not every calorie is metabolized in the same way, our organism functions in a much more complex way. Nevertheless, it is pointed out that overweight and health problems can of course also occur if too many energy-rich foods are consumed - be it fats, proteins or carbohydrates. As Paracelsus already said in the 15th century: "The dose makes the poison".
Literature & Sources:
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2 Campbell, Neil A. and Reece,Jane B.(2015): Biology. Munich: Pearson. 8th updated edition. S. 103-107.
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8 Axe-Gadermann, Dr. Prof. Michaela (2015): Slim with intestines - With the right intestinal flora to achieve the desired weight. Munich: Südwest Verlag.
9 Krieger, Dr. Elena (2015): The milk lie: Milk does it - but unfortunately not. Munich: CBX publishing house.
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13 Paolo Zanoni et al. (2016): Rare variant in scavenger receptor BI raises HDL cholesterol and increases risk of coronary heart disease. Science 11 Mar 2016: Vol. 351, Issue 6278, pp. 1166-1171 DOI: 10.1126/science.aad3517
14 Alimenta (2008): Omega-3 fatty acids in detail.
15 Singer, Priv.-Doz. Dr. med. Peter (2010): Practical aspects of the intake of omega-3 fatty acids. Stuttgart: Hippokrates Verlag in MVS Medizinverlage.