All about dietary fats

What are they

Fats or lipids are the nutrients characterized by the greatest energy power: their digestion releases about 9 Kcal per gram against about 4 Kcal of carbohydrates and proteins.

But the role of lipids is not only to store and supply energy to the body. In both plants and animals, fats also have a structural function.

In fact, they represent one of the main components of cell membranes (in this case it is mainly phospholipids, sphingolipids and cholesterol) and of the scaffolding supporting or protecting different tissues and organs (for example, in the deeper layers of the skin or at the level of the sheaths that line the nerves).

Lipids and cholesterol are also precursors of many hormones and other substances characterized by an important activity of regulating countless biological functions.

When we talk about “animal fats” we refer essentially to cholesterol and triglycerides (compounds formed by the union of three molecules of fatty acids to one of glycerol).

Triglycerides tend to be solid at room temperature: this depends on the fact that the fatty acids that compose them are mostly saturated or monounsaturated, i.e. consisting of molecules with only one or no “double bond” between the carbon atoms of the main chain.

On the contrary, vegetable fats contain mainly unsaturated fatty acids and tend to be liquid at room temperature (oils).

Particularly interesting and useful fatty acids for the human body are the polyunsaturated ones of the omega-3 series, so defined for the particular position that the “double bonds” assume within the molecule.

These are essential fatty acids, that is, that our body is not able to synthesize and that, therefore, must be taken with food, which have shown in numerous clinical studies to help reduce cardiovascular risk, optimize development and functionality of the nervous system, as well as normalize the activity of the immune system.

Food sources

Among the foods of animal origin, the richest in lipids are dairy products (in particular butter, creams, the fattest cheeses – even if fresh – and all seasoned ones), as well as lard, lard, bacon, fatty meats and sausages (with the exception of bresaola and raw ham deprived of visible fat).

Fish are generally low in lipids, except those from cold seas such as herring, tuna, salmon, mackerel and sardines, which are the main natural source of valuable omega-3s.

Crustaceans, although essentially triglyceride free and low in calories, contain considerable amounts of cholesterol.

Vegetable fats are consumed mainly in the form of oils and margarines (which are oils made solid by chemical removal of the usual “double bond” in the chain of fatty acids) resulting from the pressing of fruits (for example, olives) or oilseeds (as in the case of soy, sunflower, flax, sesame, corn etc.).

Another category of plant foods rich in valuable fatty acids (in particular, for the functionality of the nervous system) is dried fruit, namely walnuts, almonds, hazelnuts, pistachios and so on.

The table lists some of the foods with the highest fat content:

Absorption

Although there are enzymes capable of attacking fats and starting their demolition already in the mouth and stomach, the true digestion of lipids takes place in the small intestine (duodenum) thanks to the combined action of bile salts and specific enzymes produced by pacreas, phospholipases.

The fatty acids, phospholipids and cholesterol thus released form balls known as “micelles”, which are absorbed by the cells of the intestinal wall, reworked and transformed into “chychromes”.

In this new form, triglycerides, cholesterol and phospholipids can enter the circulatory stream and reach the liver, where they will be further processed and directed towards different metabolic pathways in relation to the body’s needs.

Excess fatty acids that are not used immediately for energy, are incorporated into adipose tissue cells (adipocytes) for reserve purposes.

Recommended doses

A diet too rich in fatty foods should be avoided because it promotes weight gain which, in addition to the aesthetic impact, has important repercussions on health: it increases the risk of cardiovascular diseases, metabolic and hormonal alterations, as well as some types of cancer.

On the other hand, a minimum amount of lipids must always be present in the diet (even low-calorie) to allow the body to develop and function properly.

According to the Healthy Eating Guidelines, the ideal dose of total fat (saturated and unsaturated) to be taken each day corresponds to 25-30% of total calories, equal to about 0.8-1.2 g per kg of body weight. Saturated fats, however, should not exceed 7-10%.

For cholesterol the maximum daily threshold that should not be exceeded is 300 mg.

Precautions

When it is necessary to reduce the intake of lipids and cholesterol, it is not enough to simply eliminate visible fat from foods or avoid those known to be fatty.

It is always necessary to refer to the nutritional tables of industrial products and to the food composition tables (available on the website of the National Research Institute for Food and Nutrition) for fresh or unprocessed foods.

Often, in fact, even seemingly harmless foods such as breadsticks, crackers, dry biscuits, muesli, soups, risottos and other ready-to-eat or frozen dishes contain considerable amounts of fat.

Another warning concerns “ligth” products, the consumption of which can be counterproductive for two reasons.

The first is that, often, the percentage of lipids less boasted compared to the standard product is not really significant from the point of view of the amount of fat consumed per average dose of product.

The second is that the idea of consuming a non-fat and low-calorie product (which, moreover, is not always true) induces you to eat more, ending up exceeding.