According to Dr Vincent Renaud, acid-base balance rests on the management of protons and bases. Blood pH stays within a very narrow range (approximately 7.32 to 7.42) thanks to several buffer systems and the combined action of the lungs, the kidneys, the blood and, in case of overload, reserve tissues such as the mesenchyme. When the acid load exceeds the body’s capacity to adapt, the terrain shifts towards latent metabolic acidosis, associated with numerous functional disorders and diseases of civilisation.
The organs that maintain pH
The kidneys excrete strong acids and reabsorb bicarbonate; their capacity declines with age. The lungs mainly clear weak acids through CO2/water exchange, which is why breathing exercises and cardiac coherence are valuable. The gut also plays a part in the balance. The skin excretes protons through sweating (dry or cracked skin can point towards latent acidosis). When the buffers and elimination pathways become saturated, the body draws on bone and then muscle, which contributes to demineralisation, osteoporosis and sarcopenia.
Which signs point to an imbalance
The clinical picture is often functional and wide-ranging: reduced energy, fatigue on exertion, feeling the cold, slow recovery, dry or cracked skin, brittle nails, sensitive gums, difficult digestion and reflux, cramps and spasms, joint and tendon pain, heightened sensitivity to pain, and increased susceptibility to infections. These signs should prompt you to look for latent tissue acidosis.
Where the acid load comes from
It has two sources: diet and metabolism. Animal protein mainly supplies strong acids (uric, phosphoric, sulphuric), partly neutralised by the liver and then eliminated via the kidneys or sweat; once saturated, they accumulate in tissues, particularly the mesenchyme. Fruit and vegetables mainly supply weak acids (citric, oxalic, pyruvic), a portion of which the lungs clear quickly. Stress, intense physical activity (lactic acid), and an acid-forming diet low in minerals also add to the load.
Why urinary pH is not enough
Urinary pH varies with meals, renal elimination, sweating and other excretion pathways, and it does not reflect the full picture of buffering mechanisms, particularly ammonia. A more useful marker is the acidity excreted in 24-hour urine (the sum of excreted protons minus bases). The mesenchyme, rich in mucopolysaccharides, acts as a metabolic sponge: it stores the excess acid, which promotes pain, stiffness, inflammation and poor recovery.
Acid-forming and alkalising: do not confuse the two
The goal is to aim for roughly one third acid-forming foods and two thirds alkalising foods. Acid-forming foods are mainly animal protein, dairy products, sugar and refined starchy foods; alkalising foods are fruit, vegetables, nuts and seeds, pulses, spices and herbs. Be careful: an acidic food is not necessarily acid-forming. Lemon or tomato can, after digestion, contribute to a rather alkalising load. Gastric pH matters a great deal too: persistently low gastric acidity (for example under long-term PPI use) disrupts digestion, the microbiota and the conversion of organic acids into alkalising forms.
How to rebalance the acid load
- Rebalance the plate: more vegetables, fruit and plant foods, less refined and starchy food; pair every portion of protein with vegetables or fruit (as a rough guide, about 250 g of vegetables for 150 g of meat).
- Choose the right mineral forms: potassium, calcium, magnesium and zinc, preferably as citrates, which alkalise more effectively than bicarbonates.
- Support vitamin D and vitamin K2: they help the bones use calcium rather than letting it deposit in the kidneys or tendons.
- Hydration: waters rich in bicarbonate and low in sodium support the terrain; take care with high-sodium waters.
- Movement and sweating: physical activity, sauna and steam baths help eliminate protons.
- Inflammatory and oxidative terrain: omega-3 and vitamins D, K and E follow the same logic.
Profiles to watch and useful assessments
Particular attention is needed for people prone to urinary stones or gout, athletes, low consumers of fruit and vegetables, and older, stressed or PPI-treated patients. In athletes, mineral and electrolyte balance is key to limiting cramps, myalgia, stress fractures and recovery problems. On the biology side, the 24-hour urinary ionogram, the urinary sodium to potassium ratio (which should not exceed 1) and calciuria are more useful than urinary pH alone. In malnourished older people, glutamine can support buffering via ammonia, but only within an overall strategy, to avoid muscle wasting.
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