High-Fat Diet: Principles, Applications, Effects, and Nutritional Assessment

A high-fat diet, often synonymous with a ketogenic diet, is an eating plan where the majority of energy intake (approximately 70-80%) comes from fats. Contrary to general healthy eating recommendations, where carbohydrates constitute over half of daily calories, in a high-fat diet, they make up only a small percentage of the daily menu.

A notable example of a high-fat diet is the Kwaśniewski diet, which recommends a fat intake of 3-3.5 g per kilogram of body weight. Another highly popular variant today is the ketogenic diet. This dietary approach aims to induce a state of ketosis in the body, where it primarily uses fats instead of carbohydrates for energy. This process leads to the production of ketone bodies, which serve as fuel for the brain and other organs.

While shifting the metabolism to fat burning can lead to rapid weight loss, it also presents specific challenges and potential risks that require careful consideration and professional guidance.

The basic premise of any high-fat diet is the dominance of fatty acids over other dietary components. For instance, Jan Kwaśniewski's proposal recommended specific nutrient proportions: per 1 kg of ideal body weight, one should consume 1 g of protein, 3-3.5 g of fat, and 0.8 g of carbohydrates. For a person weighing 70 kg, this translates to approximately 70 g of protein, 245 g of fat, and 56 g of carbohydrates daily.

It's crucial to note that, according to the American Institute of Medicine, 100 g of carbohydrates per day is the minimum necessary for proper brain energy supply – almost double what Kwaśniewski recommends. In his view, strict adherence to these ratios is paramount, requiring precise weighing and analysis of ingredients for every meal.

The diet's foundation, according to these guidelines, should consist of fatty meats, cream, butter, eggs, lard, yellow cheese, and processed meats. Carbohydrate-rich foods such as groats, flour products, bread, legumes, and most vegetables should be severely restricted, with vegetables limited to 300 g per day. Sugar is strictly forbidden.

A drastic reduction in carbohydrates leads to an increased production of ketone bodies, which can be unfavorable and even dangerous for the body in the long run. The Kwaśniewski diet, similar to the Atkins and South Beach diets, has been categorized as high-fat ketogenic diets, against which the Polish Society of Nutritional Sciences officially warns.

These diets are not recommended for most people, especially those aiming for weight reduction (although they are promoted for this purpose by their creators). An exception applies to individuals suffering from neurodegenerative diseases, such as epilepsy. In these conditions, a diet stimulating the production of ketone bodies can improve prognosis and reduce symptoms. The exact mechanism leading to such beneficial effects is not fully understood, but studies indicate a direct anticonvulsant action of ketone bodies. Furthermore, high glucose levels can trigger seizures, and in this case, glucose intake is limited to a minimum.

Despite the positive results, this diet is not free from side effects and should only be implemented under strict medical supervision.

The high-fat ketogenic diet significantly impacts the metabolism of fats, carbohydrates, and proteins, often with adverse effects. While it is indeed associated with weight loss, the other consequences are frequently undesirable. A low intake of carbohydrates causes a decrease in blood glucose levels (the primary energy substrate) and depletes glycogen stores in the liver and muscles (glucose reserves), forcing the body to switch to alternative energy sources.

Consequently, amino acids derived from protein breakdown are utilized for glucose synthesis. This leads to a substantial loss of muscle mass, and in the long term, also affects proteins of other substances, potentially causing a reduction in the concentration of certain hormones or neurotransmitters in the nervous system. The weight loss observed during this type of diet thus results not only from fat burning but also from a decrease in muscle mass and water loss (glycogen, whose reserves are depleted, binds water, which is then excreted).

Furthermore, there is a risk of reduced levels of certain neurotransmitters, which is associated with various complications such as mood and behavioral changes. Through the oxidation of fatty acids, the body produces ketone bodies – compounds that the body uses as an energy fuel when an adequate supply of glucose is not ensured. This state helps us during periods of starvation, but in the long run, it leads to what is known as ketoacidosis. Symptoms include nausea, fatigue, headaches, weakness, and increased urination.

Moreover, fat digestion leads to an increased production of cholecystokinin by the intestinal mucosa, which, among other functions, stimulates the pancreas. Besides its role in food digestion, cholecystokinin also stimulates the satiety center in the brain, thereby suppressing appetite. This mechanism partly explains the high-fat diet's influence on appetite suppression. This could be considered one of the positive aspects of this type of nutrition, similar to the reduction of blood glucose levels in people with diabetes. Nevertheless, a similar effect can be achieved by following a balanced diet with reduced simple sugars and high fiber content, in accordance with the recommendations of the Institute of Food and Nutrition.

A diet primarily based on fats, especially saturated fats from animal sources, does not have a beneficial effect on the body if prolonged. Even when applied for a few weeks or less, it causes changes in a range of metabolic processes. Due to insufficient carbohydrate intake, the body must switch to other energy sources, namely amino acids and fatty acids.

If this process is extended, there is a loss of proteins, especially muscle proteins, as well as the production of ketone bodies, which are not physiologically a primary energy compound. This leads to dehydration and weakness of the body. Additionally, both deficiencies and excesses of certain minerals and vitamins occur. With a high intake of animal products, offal, eggs, and butter, excessive consumption of retinol or iron can occur, while other vitamins and elements such as magnesium, vitamins C, D, E, and folic acid are not supplied in sufficient quantities.

This diet is definitely contraindicated for healthy individuals. Any potential benefit of weight loss can be achieved in other, more rational ways. Similar to democracy, the food pyramid is not a perfect creation, but it represents the best recommendations developed to date. A balanced diet, rich in whole grains, fruits, vegetables, and lean proteins, remains the safest and most effective path to long-term health and weight management.