High-protein diets: guidelines, meal plan, and outcomes

Given the wide range of dietary recommendations available for a high-protein diet, it is difficult to specify a single, universal definition of this type of diet, as recommended by the Institute of Food and Nutrition. Some sources consider high-protein diets to be those where the percentage of energy derived from protein exceeds 25% or where the protein content per kilogram of lean body mass is greater than 1.6 g. However, according to the Institute's recommendations, the recommended amount of protein consumed daily by an adult is approximately 0.9 g/kg of body weight.

Considering the daily energy requirement of an average, healthy person, the percentage of energy derived from protein in a well-balanced diet should be within the range of 10–15%. For active individuals or athletes, due to increased bodily needs, these values can rise to as much as 1.6–2 g/kg of body weight per day. From a purely clinical perspective, high-protein diets are considered those that provide the body with 100 g or more of protein daily. A higher intake of this macronutrient is used in nutritional therapy for many disease entities, including malnutrition, body wasting, extensive burns, fevers, or neoplastic diseases.

All the mentioned recommendations, despite many quantitative differences, share a common denominator: the purpose of applying such a measure. This purpose includes providing the body with an adequate pool of amino acids essential for the process of thermogenesis, the building and rebuilding of cells, the creation of immune bodies, enzymes, or hormones that condition its homeostasis.

The composition of a high-protein meal plan should always be preceded by an appropriate nutritional and medical interview. This interview allows us to assess the patient's health, possible indications, or even contraindications for the planned nutritional intervention. The reason is trivial: the meal plan for a high-protein diet will look completely different for healthy, training individuals whose sole goal is to reduce body fat, maintain, or build muscle tissue, compared to malnourished or severely ill individuals (e.g., after surgical intervention resulting from extensive burns), where a precisely planned nutritional strategy is required.

In the case of sick individuals, e.g., those treated for burns, nutritional intervention begins when the circulatory system is stabilized and edema has subsided. This most often occurs on the third day after the burn. Parenteral and/or enteral nutrition via a probe is recommended for severe burns. The parenteral nutrition solution should contain all nutrients, including an increased protein intake, reaching even 2.5–4 g/kg of the patient's body weight. With appropriately conducted nutritional therapy, the burn wound should then close within the next 6 weeks.

For completely healthy individuals or those struggling with obesity, the situation is quite different. The meal plan is characterized by significantly fewer restrictions, and protein intake ranges from 1.6–3 g/kg of body weight. Meals should be as varied as possible, rich in complete proteins (containing a full pool of amino acids), sources of which can be found in meat, fish, dairy, nuts, legumes, tofu, or eggs. Popular preparations among athletes, enriching the daily protein pool, also include whey protein supplements in the form of concentrates (WPC), isolates (WPI), or hydrolysates (WPH). To maximize the process of muscle protein synthesis, a single protein intake of 20–25 g per meal is assumed, where the content of the amino acid leucine should be at least 2 g. Due to the higher proportion of protein in the diet, the proportion of other macronutrients (fats or carbohydrates) decreases, although if the goal is fat loss, from a physiological point of view, it does not matter which of the remaining macronutrients is reduced.

Commonly practiced dietary schemes are:

• Protein at 30% of total energy, Fat at 20% of total energy, Carbohydrates – constituting 50% of total energy.
• Protein at 40% of total energy, Fat at 20% of total energy, Carbohydrates – constituting the remaining 40% of total energy.
• Protein at 40% of total energy, Fat at 40% of total energy, Carbohydrates – the remaining 20% of total energy.

Scientific studies almost unequivocally confirm that dietary protein can have a beneficial effect on weight loss. Several mechanisms are responsible for this. First and foremost, it has been proven that protein influences an increase in satiety by increasing the secretion of satiety hormones (GIP – glucose-dependent insulinotropic peptide and GLP-1 – glucagon-like peptide-1) while simultaneously decreasing the synthesis of ghrelin (referred to as the hunger hormone). In other words, individuals following a high-protein diet enjoyed a longer feeling of satiety with a simultaneously reduced daily energy intake.

Scientists also noted that individuals whose dietary plans included a higher daily protein pool had a correspondingly higher resting metabolic rate than individuals whose diet was defined as normo-protein (daily protein intake averaged 0.9–1 g/kg of body weight). Despite the undeniable benefits of a high-protein diet in the context of fat loss, it should be noted that long-term, excessive intake of this macronutrient can also carry certain risks, especially concerning kidney function. For this reason, high-protein diets should not be used by individuals with diagnosed kidney dysfunction or ongoing renal replacement therapy. Any dietary changes, especially regarding protein intake, should then be consulted with the treating physician or dietitian.

It is also an undeniable fact that products that are a rich source of complete protein often also contain a significant amount of saturated fatty acids and cholesterol, which should be limited in the diet of individuals with excessive body weight or diagnosed ischemic heart disease. Saturated fatty acids are associated with a higher risk of developing atherosclerosis due to their pro-thrombotic and pro-inflammatory effects. It is then recommended to increase the proportion of high-protein plant-based products such as legumes, soy products (tofu), and nuts, or preparations in the form of dietary supplements.

While high-protein diets can offer many benefits, especially for athletes and those looking to lose weight, they are not suitable for everyone. Long-term excessive protein intake can carry certain health risks. The primary concern relates to kidney function. The kidneys are responsible for filtering waste products from protein metabolism. A very high protein intake can strain the kidneys, especially in individuals with pre-existing kidney conditions or a predisposition to them. Therefore, individuals with kidney dysfunction or those undergoing renal replacement therapy should only consider high-protein diets under strict medical supervision and in consultation with a dietitian.

Another potential risk is the increased consumption of saturated fatty acids and cholesterol, often associated with high-protein animal products. This can elevate the risk of cardiovascular diseases, particularly in individuals who are overweight, obese, or have diagnosed coronary heart disease. It is crucial to choose lean protein sources and moderate the consumption of red meat and processed meat products. Instead, plant-based proteins such as legumes, tofu, nuts, and seeds, as well as lean poultry and fish, should be preferred.

Furthermore, an unbalanced high-protein diet that lacks sufficient fiber, vitamins, and minerals can lead to digestive issues like constipation. Adequate intake of fruits, vegetables, and whole grains is therefore essential to support gut health and ensure comprehensive nutrient supply. It is always advisable to consult a doctor or dietitian before starting a high-protein diet to assess individual needs and potential risks.

A high-protein diet can be an effective tool for weight loss, muscle building, and improving satiety. Its benefits are supported by numerous scientific studies highlighting its positive impact on metabolism and body composition. Increased protein intake contributes to a higher resting metabolic rate and reduced feelings of hunger, which facilitates adherence to the diet and leads to better long-term results.

However, it is crucial to consider the potential risks associated with long-term excessive protein intake. Particularly, individuals with kidney problems or cardiovascular diseases should exercise caution and undertake such a diet only under medical supervision. The selection of high-quality protein sources, both animal and plant-based, is essential to ensure balanced nutrient intake and minimize the consumption of saturated fats and cholesterol.

In conclusion, a high-protein diet, when applied correctly and considering individual health conditions and needs, can be very beneficial. Consultation with a dietitian or doctor is always recommended to create a tailored plan that promotes health and safely achieves desired goals. A balanced intake of all macro and micronutrients remains the key to a healthy and sustainable diet.