Proteins

Let's analyze why the idea that proteins always "acidify the body" is an oversimplification and incorrect.

How proteins affect acid-base balance

Proteins are made up of amino acids — organic compounds, each with a unique structure and chemical properties.

From the perspective of their influence on the body's acid-base balance, amino acids are conditionally divided into three groups:

Acidifying amino acids. These are primarily sulfur- and phosphorus-containing amino acids, for example:

• Methionine, cysteine — during metabolism, they release sulfuric acid.
• Phosphoproteins — during breakdown, they release phosphoric acid.

These acids enter the bloodstream and temporarily shift the plasma pH towards the acidic side until the buffering systems (mainly bicarbonate) and kidneys neutralize and excrete them.

Alkalizing amino acids. Some amino acids contain side chains with nitrogenous and alkaline groups, for example: glutamine, arginine, lysine, alanine.

These compounds consume protons (H⁺) during metabolism or release ammonia, which binds with protons to form neutral or weakly alkaline compounds (such as urea or glutamate).

Thus, they contribute to alkalizing the internal environment of the body.

Neutral amino acids. Some amino acids have little direct effect on the acid-base balance but can participate in the synthesis of metabolites that indirectly influence the buffering systems.

Why complete protein is balanced nutrition

"Complete protein" provides the body with both acidifying and alkalizing amino acids, ultimately forming a natural metabolic balance.

How the body maintains blood pH

The body strictly regulates the plasma blood pH within the range of 7.35–7.45. The overall acid-base balance is controlled by:

• Blood buffering systems (bicarbonate buffer, protein buffer, phosphate)
• The kidneys, which excrete excess acids or bases
• The lungs, which regulate CO₂ levels (affecting carbonic acid levels)

Thus, no food can radically "acidify" the body if the organs are functioning normally.

Conclusion

The idea that "all proteins acidify the body" is a myth based on a superficial understanding of metabolism. In reality:

• Only a portion of amino acids have an acidifying effect.
• Alkalizing amino acids balance this influence.
• Complete proteins support homeostasis rather than disrupt it.

Therefore, with adequate, balanced protein nutrition, the body maintains a healthy acid-base balance naturally.

The Myth of Protein and "Acidic Urine"

Proteins do indeed produce acidic residues (mainly sulfuric and phosphoric acids) during metabolism, but this is a natural load to which the kidneys are adapted. With sufficient alkaline minerals (potassium, magnesium, sodium) and in the absence of insulin resistance, urine remains at a normal pH.

Moreover, a protein-rich diet usually increases fat intake, which does not activate aldosterone and does not cause sodium loss.

However, an excess of carbohydrates systematically acidifies urine:

Carbohydrates, insulin, and sodium. High carbohydrate intake stimulates insulin release. Insulin affects the kidneys: it reduces sodium excretion, promoting its reabsorption in the nephron tubules.

However, with prolonged and chronically high levels of insulin (for example, in insulin resistance), the kidneys' sensitivity to sodium is impaired. In this case, despite increased insulin, sodium is retained poorly, and the body begins to lose it in urine.

Sodium loss and activation of the renin-angiotensin-aldosterone system (RAAS). When the body loses sodium, it is perceived as a threat of dehydration and hypovolemia. In response, the RAAS is activated, and the adrenal glands release aldosterone—a hormone that stimulates the kidneys to enhance sodium reabsorption and excrete potassium and hydrogen ions (H⁺).

Aldosterone and urine acidification. Aldosterone activates proton pumps in the distal tubules of the kidneys, increasing the secretion of H⁺ ions into the urine. This makes the urine more acidic. Thus, increased aldosterone → increased H⁺ excretion → urine acidification. At the same time, there is a loss of potassium and a shift in the acid-base balance towards acidosis.

Additional contribution of glucose. At high levels of glucose in the blood and/or urine (glucosuria, characteristic of prediabetes or diabetes), glucose pulls along water and electrolytes (osmotic diuresis), which also leads to additional sodium loss, enhancing aldosterone activity.

Additionally, a high-carbohydrate diet reduces the level of citrates in the urine—these are the main natural buffers that protect against acidification. A low level of citrate is associated with the risk of stone formation and metabolic acidosis.

Conclusion

It is not protein per se that acidifies urine, but an excess of carbohydrates through hormonal and electrolyte mechanisms.

Protein foods can only slightly shift pH if consumed in the context of a mineral- and water-deficient diet. In contrast, carbohydrates—especially refined ones—systematically and deeply acidify urine, causing a cascade of reactions through insulin, aldosterone, sodium loss, and electrolyte disturbances.

This is indeed an important physiological observation that debunks the common myth about the harm of protein due to ammonia formation.

When a person limits protein intake, believing that this will reduce the burden on the liver and kidneys (due to ammonia as a byproduct), they overlook the main fact: the body still needs protein. Proteins — are the building blocks for enzymes, hormones, immune cells, muscles, and organs. In the case of protein deficiency, the body begins to break down its own proteins — primarily from muscles, and in severe cases, from internal organs.

What is ammonia and where does it come from

When amino acids (the main components of protein) are broken down, an amino group (–NH₂) is formed, which is converted into ammonia (NH₃) in the body. This toxic compound is quickly neutralized in the liver, where it is converted into urea and excreted through the kidneys with urine — this is the normal and safe pathway.

What happens on a low-protein diet

Against the backdrop of protein deficiency:

• Catabolism of muscle tissue is activated — muscle protein is broken down to meet the minimum needs of the body.
• At the same time, ammonia is produced directly in the tissues, where there are no specialized enzymes or cells to quickly neutralize it. It accumulates locally, which can cause cytotoxicity, disrupt cell function, and lead to inflammation.
• Subsequently, amino acids and protein remnants enter the bloodstream and reach the liver, where the second stage occurs — ammonia formation in the intestines (especially in the large intestine) under the influence of putrefactive bacteria.
• In the intestines, some ammonia is reabsorbed into the bloodstream, creating additional stress on the liver, which is already working in a compensatory mode.

Why more ammonia is produced, not less

In practice, it turns out that on a full diet, ammonia is produced once — during food digestion, and is immediately utilized. And on a protein deficiency:

• First — in the tissues (where it is harmful),
• Then — in the intestines (where some of it will still enter the bloodstream).

Thus, more ammonia is produced even than with normal protein consumption, and it circulates longer, causing more toxic stress to the body.

Conclusion

The fear of ammonia with protein consumption — has no physiological basis if there are no serious liver function disorders. On the contrary, protein deficiency increases ammonia load and makes it less controllable.

The acid-base balance of the body is determined not by the source of protein (plant or animal), but by the amino acid composition and how these amino acids are metabolized in the body.

How proteins affect the acid-base balance

Proteins are made up of amino acids, each of which can produce either acidic or alkaline products during metabolism.

Amino acids that acidify the body. Some amino acids produce strong acids, such as sulfuric, phosphoric, and hydrochloric acid, when broken down. Examples:

• Methionine, cysteine (contain sulfur) → produce sulfuric acid (H₂SO₄)
• Phosphorus-containing amino acids (e.g., phosphoserine) → produce phosphoric acid (H₃PO₄)

These products acidify the internal environment of the body (in particular, they increase the acidity of urine), as the body has to neutralize or excrete these acids through the kidneys, lungs, and blood buffer systems.

Amino acids that alkalize the body. Other amino acids produce alkaline ionic forms (e.g., bicarbonate, ammonia) as a result of metabolism:

• Glutamine, asparagine, histidine, etc. → provide ammonia groups (NH₃), which can be used to form ammonium (NH₄⁺), and also stimulate the production of bicarbonate (HCO₃⁻), which alkalizes the blood.

Why it doesn't matter whether the protein is plant or animal

Each protein — whether plant or animal — is a mixture of amino acids. It is impossible to say that all protein from plant sources alkalizes, while that from animal sources acidifies. It all depends on the balance of amino acids in a specific product:

• Animal proteins (meat, fish, eggs) contain all essential amino acids and often more sulfur-containing ones, which can lead to a greater acidic response.
• Plant proteins (legumes, nuts, grains) also contain acidic amino acids — especially in grains. For example, wheat produces a significant amount of acidic residues during metabolism.

Thus, both can either acidify or alkalize — it all depends on the specific amino acid profile and combination of products.

The role of complete protein

Complete protein — is a protein that contains all essential amino acids in the necessary proportions. Such proteins are better absorbed, put less strain on the kidneys and liver, and allow the body to:

• Effectively use amino acids for the synthesis of tissues, enzymes, and hormones (rather than for energy purposes)
• Reduce the formation of excess acids or toxins, as there are no excess amino acids to be broken down

Thus, high-quality protein (e.g., egg, collagen, whey protein, a blend of plant proteins with a complete amino acid profile) better maintains the acid-base balance because it does not overload with individual acidic metabolic products.

The proton pump — is a protein on the surface of parietal cells in the stomach that "pumps" hydrogen ions (H⁺) into the lumen of the stomach in exchange for potassium ions (K⁺). This is the main mechanism of acid production — that is, it is thanks to it that gastric juice becomes acidic (pH can be 1–2).

How is this related to blood alkalinity?

During active acid secretion in the stomach, equivalent amounts of bicarbonates (HCO₃⁻) are simultaneously released into the blood — this is called "alkaline tide". That is:

The more acid is produced in the stomach, the more alkali enters the blood.

This is physiologically conditioned:

When H⁺ is formed in parietal cells from water and CO₂ (with the help of the enzyme carbonic anhydrase), HCO₃⁻ is also formed simultaneously. H⁺ ions are released into the stomach, while bicarbonates are released into the blood. Thus:

• The stomach — becomes acidic (high acidity);
• The blood — becomes alkaline (temporarily).

What does this give to the body?

1. Alkalinization of the blood during the active digestive phase helps to compensate for the acidity that can potentially occur due to metabolic products.
2. The bicarbonate system — is one of the main buffers in the blood, and the additional influx of HCO₃⁻ strengthens its ability to maintain a pH around 7.35–7.45.
3. This is also an important component of detoxification and overall homeostasis: with sufficient alkalinity, the blood better binds and removes metabolites, especially acidic ones.

Protein food — the main stimulator of gastric juice secretion

When proteins or amino acids enter the stomach, a powerful chain of stimuli is triggered to activate the proton pump. This is related to several mechanisms:

Amino acids → Gastrin. Proteins, especially aromatic amino acids (phenylalanine, tyrosine, tryptophan), stimulate the production of gastrin — a hormone of the stomach. Gastrin activates parietal cells, stimulating the proton pump: H⁺/K⁺-ATPase begins to actively release hydrogen ions into the lumen of the stomach. As a result — gastric acid sharply increases.

Neural (vagal) stimulation. At the sight, smell, and especially chewing of protein food, the vagus nerve (n. vagus) is activated. It enhances the release of acetylcholine, which directly stimulates parietal cells. Protein food enhances this effect more than carbohydrates or fats.

Proteins require an acidic environment. To break down proteins, an active enzyme pepsin is needed, and it only works in an acidic environment (optimal at pH 1.5–2). The body knows: if there are many proteins, more acid is needed to digest them. This creates a positive feedback loop: the more protein → the more acid → the more actively the proton pump works.

Protein — not just a building material, but also a key participant in maintaining acid-base homeostasis. The exocrine secretion of the gastrointestinal tract (GIT) heavily depends on the composition of food, particularly on the amount of protein.

With low-protein nutrition, there are pronounced shifts in the composition and volume of digestive juices, which ultimately also affect the acid-base balance and the internal state of the body, including the acidification of the blood.

Reduction of gastric juice secretion (HCl)

Protein — the main stimulator of hydrochloric acid (HCl) secretion in the stomach. Its presence activates gastrin, which triggers the activity of parietal cells in the stomach.

With low-protein nutrition, gastrin production decreases → HCl secretion falls → gastric juice becomes less acidic. In response, the body tries to compensate for this secretion deficit by increasing HCl release, taking bicarbonate (HCO₃⁻) from the blood (through exchange in the stomach cells). This is the alkaline "debt," which acidifies the blood.

When parietal cells produce HCl, an equivalent amount of HCO₃⁻ (alkali) enters the blood — this temporarily alkalizes the blood after meals (the so-called alkaline "surge"). But with chronic reduction in HCl stimulation, this mechanism is disrupted:

• either the stomach compensatorily withdraws HCO₃⁻ from the blood to still produce acid,
• or with reduced HCl secretion, protein breakdown is disrupted, leading to secondary protein starvation and increasingly severe acidosis.

Weakening of pancreatic secretion (pancreas)

Proteins stimulate the production of secretin and cholecystokinin (CCK), which activate the release of pancreatic juice — containing bicarbonates and enzymes. With insufficient protein, the secretion of these hormones decreases → the production of alkaline pancreatic juice, which should neutralize stomach acid, worsens.

This leads to insufficient alkalization of chyme in the duodenum and gradual acidification of the mucosa, and subsequently the internal environment of the body.

Decrease in bile secretion

Proteins stimulate the release of bile through CCK. Bile contains alkaline salts and participates in the emulsification of fats, as well as in the buffer neutralization of acids. Low-protein nutrition → less CCK → bile secretion worsens → less alkalization in the intestines.

What this leads to:

The GIT disrupts the acid-base gradient, particularly at the transition from the stomach → duodenum. There is a compensatory increase in the absorption of hydrogen ions (H⁺) and a decrease in the excretion of acids with feces. Gradually, this affects the systemic blood pH, especially with weak buffer systems — as seen in individuals with low protein supply.

Let's break down step by step why adequate amounts of protein and ATP are critical for preventing acidosis (blood acidification), and why the alkalizing effect of fruits and vegetables is a myth when viewed from a biochemical perspective.

Acid-Base Balance and the Role of Protein

The pH of blood in the body is strictly regulated within the range of 7.35–7.45. Disruption of this balance can be dangerous and indicates pathological processes.

Protein is not just an "acidic" product. It contains both acid-forming amino acids and alkalizing ones. With sufficient protein intake, the body finds it easier to maintain its buffering system—especially with the involvement of protein amino acids in the synthesis of glutamine, which neutralizes excess protons (H⁺) in the kidneys.

With insufficient protein, the synthesis of enzymes, albumins, and buffering systems (especially the phosphate and ammonium buffers) is disrupted, reducing the body's ability to maintain pH within normal limits.

ATP as the Key to Maintaining Alkalinity

ATP is not just energy; it is the currency for ion pumps, in particular:

• Na⁺/K⁺-ATPase: maintains membrane potential and pumps protons out of the cell.
• H⁺-ATPase in the kidneys and mitochondria: participates in the removal of excess hydrogen ions (acidifying agents) and the reabsorption of bicarbonates (the alkaline component of blood).

If there is a lack of ATP:

• The kidneys cannot effectively excrete H⁺, which quickly leads to metabolic acidosis.
• The blood's buffering systems become depleted, especially the bicarbonate buffer.

ATP is primarily synthesized from fats and B vitamins:

• Fats, especially saturated ones, provide the highest yield of ATP per unit mass (1 g of fat → up to 9 kcal).
• During β-oxidation of fatty acids, acetyl-CoA is formed, which enters the Krebs cycle and produces the majority of ATP in the mitochondria.
• B vitamins (B1, B2, B3, B5, B7) are coenzymes in the metabolism of fats, proteins, and carbohydrates (e.g., NAD⁺, FAD, coenzyme A, TPP); without them, energy metabolism literally comes to a halt.

Why Lemon, Fruits, and Vegetables Do Not Alkalize the Blood

Indeed, many vegetables and fruits leave an alkaline ash residue during metabolism (mainly due to potassium, magnesium, calcium), but:

• This does not directly affect blood pH, but only reduces the burden on the kidneys for acid excretion.
• Urine pH may become more alkaline, but blood will remain at the same level provided that buffers and kidney function are maintained.

Vegetables and fruits, even despite their high content of organic acids (citric, oxalic), do not alkalize the blood and do not directly participate in the creation of ATP or buffers. They may play a supportive role, but are not decisive in combating acidosis.