When is it necessary?
Any diet characterized by a reduced protein intake is defined as hypoproteic. The adoption of such a diet is justified in the presence of hepatic or renal dysfunction. These organs are in fact directly involved in protein metabolism.
Proteins, Liver and Kidneys
The liver intervenes in the removal of the amino group of amino acids, through the incorporation of the ammonium ion NH4 + (highly toxic) in a non-toxic waste molecule called urea (for further information: amino acid metabolism and urea cycle). This by-product of the amino acid metabolism is then eliminated in the urine thanks to the excretory action of the kidneys.
If the latter do not work properly, or too much urea is produced due to excessive protein intake with the diet, there is an increase in the concentration of nitrogenous substances in the blood (called hyperazotemia or, in the most serious cases, uremia). Renal failure, a pathological condition characterized by loss of kidney function, is a common cause of hyperazotemia.
In the presence of a malfunctioning liver (hepatic insufficiency) the ammonium ion is no longer converted into urea and there is an accumulation of ammonia in the blood (hyperammonemia). Viral hepatitis or liver cirrhosis is a common cause of hyperammonemia.
In all the conditions listed so far, or in the presence of disorders of the metabolism of amino acids due to specific enzyme deficiencies (hyperthyrosinemia, phenylketonuria, histidinemia, urea cycle disorders or organic acidosis), a hypoprotein diet is useful to reduce work to liver and kidney load, thus preventing the appearance of particularly serious systemic disorders. The scrupulous adherence to this particular diet plan slows down the evolution of the disease and must therefore be undertaken as early as possible.
How many proteins in healthy subjects?
In a normal balanced diet, proteins must neither be abolished nor reduced.
If dietary restrictions are necessary, it is good to favor vegetable and legume proteins, while among animal ones, milk, fish and low-fat cheese proteins are preferred.
It should also be remembered that a reduced protein intake depresses the immune response, causes growth defects in the child and is accompanied by a worsening of the general state of health (see malnutrition), particularly during growth, pregnancy and lactation.
How many proteins in the Hypoprotein Diet?
The hypoproteic diet is based on the reduced consumption of protein-rich foods, whether they are of animal origin (fish, meat, eggs, dairy products) or vegetable (legumes, but also cereals such as bread, pasta, rice, biscuits, etc.).
All this with the aim of reducing the protein content from the normal 10-14% to a 4-8% depending on the condition; in other words, we pass from the ordinary daily intake of 0.9-1.1 g of protein per kg of body weight to a 0.5-0.8 g / kg.
The reduction in protein content can be of varying degrees depending on the type and severity of the disease.
Aproteic foods
When it is remarkable, special dietary foods with a low protein content (aproteic bread, aproteic paste, aproteic biscuits, etc.) must be used to ensure the energy and carbohydrate intake. In these food products the protein content is around one gram per 100 grams, a quantity about 10 times lower than their traditional counterparts. The caloric intake is instead similar, since the hypoprotein diet must be particularly careful to satisfy the energy needs of the body (if this were not the case, the body would consume its own proteins for energy purposes, aggravating a condition already complicated by the reduced intake nitrogen).
Supplements
For the same reason, the more strict the protein limitation is, the greater the quality of the few proteins introduced with food must be; sometimes it is necessary to supplement with preparations based on essential amino acids.
Finally, there are dietary products with a reduced content of particular amino acids, such as phenylalanine, suitable for patients with specific disorders of amino acid metabolism, such as phenylketonurics.
