Acid-Base Balance Explained: What Your Diet Changes

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Why pH is so tightly regulated

Almost every process in the body depends on pH. Enzymes only work within a narrow range, how well oxygen binds to hemoglobin varies with pH, and nerves and muscles react sensitively to deviations. That is why the body keeps blood between pH 7.35 and 7.45, which is slightly alkaline. Values below that range are called acidosis, values above it alkalosis. Both are serious medical conditions that diet alone does not cause.

Other parts of the body can differ a lot. The stomach is strongly acidic at pH 1 to 2, the small intestine is slightly alkaline, and urine ranges from about 4.5 to 8 depending on your diet.

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The three control systems

1. Buffers in the blood (seconds). The most important one is the bicarbonate buffer system. When acid enters the blood, it combines with bicarbonate to form carbonic acid, which breaks down into water and carbon dioxide. Proteins such as hemoglobin and phosphate also act as buffers. Buffers absorb fluctuations, but they do not remove the acid.

2. The lungs (minutes). The carbon dioxide from the buffer system is exhaled. When acid in the blood rises, you automatically breathe a little deeper and faster. This lets the body get rid of volatile acid in large amounts: several hundred liters of carbon dioxide every day.

3. The kidneys (hours to days). Only the kidneys can excrete non-volatile acids, such as sulfuric acid from protein and phosphoric acid. They release acid into the urine as ammonium and phosphate and, in the process, make new bicarbonate that refills the buffers. An adult on a Western diet excretes about 50 to 100 mmol of acid this way every day.

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What diet has to do with it

Your diet determines how much non-volatile acid builds up each day, and so how much work your kidneys have to do. Protein and phosphorus raise it. Potassium and magnesium from vegetables and fruit lower it, because they come with organic acids such as citrate, which the body metabolizes into alkaline bicarbonate. The PRAL calculates exactly this balance for a single food.

In all three cases, blood pH stays the same. What changes is your urine and the work your kidneys and bones do. With a persistently high acid load, the body draws small amounts of alkaline minerals from bone and excretes more calcium. Studies do not consistently show whether this harms bone density in the long run. The link is clearer for kidney stones and for how kidney disease progresses.

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Being “too acidic”: what it means and what it doesn’t

“Being too acidic” is used for two very different things:

• Metabolic acidosis is a lab finding: bicarbonate in the blood is too low, and in severe cases blood pH drops. Causes include kidney disease, uncontrolled diabetes and poisoning. This needs medical treatment.
• Latent acidosis describes a persistently high acid load with normal blood pH, which shows up as acidic urine. There is no scientific evidence that it causes complaints such as fatigue or joint pain. What is proven is that a diet rich in alkaline foods raises urine pH and eases the load on the kidneys.

You can read more about symptoms and the research in the article Being too acidic: symptoms and what’s behind it.

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What helps in practice

1. Add vegetables to every serving of protein. 200 g of vegetables or potatoes balance out a serving of meat or fish.
2. Potassium before sugar. Fruit, vegetables, potatoes and legumes are the main source of bases.
3. Go easy on cheese and sausage. Per 100 g, they have the highest acid values of everyday foods.
4. Drink enough. More urine means more acid excreted without extra strain.
5. Balance instead of bans. What counts is the total for the day, not a single food.