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Good fats, bad fats: What’s behind them?


Whether in our food, blood, or body tissue, fat has a rather bad reputation – even though it is actually vital. In food, it is part of the macronutrients such as protein and carbohydrates, supplying our bodies with energy and has a saturating effect. In our blood and metabolism, it is the basic substance of many hormones, a carrier of many vitamins, and a provider of energy. As tissue, it is involved in the development of body structures such as cell membranes and nerves, protects joints and organs and keeps us warm.

When we talk about fat as a nutrient, it is by far the most complex and most varied macronutrient. Although the effects of carbohydrates and proteins are far easier to asses, fat is the one that we make generalizations about most often. But fat, with all its subtypes and variants, must be regarded in a highly differentiated way – both with respect to the relationship between its types as well as with respect to other macro- and micronutrients. In the following paragraphs, we will first present the most basic facts about fat before going into more details elsewhere.

How are fats structured?

With carbon as a basis, fats are organic nutrients. Depending on how many carbon atoms a fat or fatty acid contains, it is referred to as a short-, medium-, or long-chain fatty acid. Regardless of their chemical nature, naturally occurring fats supply 37 kilojoules per gram (9.3 kilocalories per gram) of energy.

In a nutritional sense, especially when it comes to digestion, the chain length of a fat plays a role, whereby with increasing chain length – similarly with carbohydrates – its decomposition is slower and more time-consuming.

More important for our daily diet, however, is the nature of the bonds, which link the carbon atoms forming a chain. Based on this nature, a fatty acid is classified as a saturated, mono-unsaturated or polyunsaturated fatty acid. In addition, there are also the so-called trans-fatty acids, which are unsaturated fatty acids, but accorded a special place.

Typically, the carbon atoms are linked via a single bond. If one of these links is a so-called double bond, it is a mono-unsaturated fatty acid. Two or more double bonds make the chain a polyunsaturated fatty acid. The number in names such as “Omega-3 fatty acid” does not stand for the number of double bonds, but for the position of the first double bond looked at from a particular end of the chain (in this case the Omega end).

What kind of fat do we need?

Saturated fatty acids, as for example in butter or fatty meats, are not essential. This means that the body itself – through metabolic pathways – can synthesize them from other substances. Unsaturated fatty acids with all their subtypes, however, are essential and must be absorbed through food. Whether saturated or unsaturated, both types of fatty acids occur in animal as well as vegetable products, but the presence of unsaturated fatty acids in plant products is significantly higher. However, the extraction of vegetable, as opposed to animal fats, is a little more complicated and more expensive.

We often speak of healthy unsaturated fatty acids and emphasize their importance, while saturated fatty acids – even though these latter ones are vital too – are described as harmful. Their bad reputation stems from a surplus of saturated fatty acids in our modern food supply. A disproportionately high intake of saturated fatty acids is linked to many diseases in modern society such as obesity, elevated blood lipid levels and hardening of the arteries, while an imbalance in favor of the unsaturated fatty acids promotes and may cause inflammation in the body, as these tend to react with free radicals. As a result, the consumption ratio of saturated fatty acids to mono- to polyunsaturated fatty acids is of primary importance.

But which one is the bad fat?

The so-called trans-fatty acids or (partially) hydrogenated fats are the only kind of fat that is not vital and may even be harmful. By heating – especially in industrial manufacturing processes – the spatial structure of an unsaturated fat is altered so that it is more stable and the product more durable. Positions of the double bonds also change in the process. For this reason, we find large amounts of trans-fatty acids in ready-made products, fast and fried food, baked goods and in sausage products. The body cannot – or at least not efficiently – metabolize this artificially changed structure in a useful way, because the spatial structure resembles a saturated fat even though it is a polyunsaturated fatty acid (albeit with changed positions of these double bonds).

Trans-fatty acids are therefore directly linked to inflammation in the body and an increase in deposits of LDL cholesterol in the blood and thus constitute a threat to the heart and vessels. They are also suspected to cause or promote diseases such as high blood pressure and diabetes.

At this point, it is worth mentioning that trans-fatty acids occur in smaller quantities in natural animal products (e.g. milk), resulting from bacterial metabolic processes – particularly in the digestive tract of ruminants – as well as in small quantities when some edible oils are heated to high temperatures (e.g. roasting).

Fat is not just fat!

An excess of saturated and trans-fatty acids in our diet has given the dietary fats in their entirety a bad reputation. When it comes to fats, the primary target should therefore not be to minimize the amount, but to select the right ones and to establish the proper ratio. First and foremost, it is the quality of the fat that matters. This does not mean that the quantity of fats is unimportant. As with all nutrients, it is a question of finding the right balance. Nevertheless, the quality – the type of fat – makes the difference here. You will soon learn about which ratio is ideal for your body, what individual differences there are, and other exciting topics about fat.