At a glance:
- The alkaline diet classifies foods by their effects on pH, but blood pH stays within a narrow range of 7.35–7.45 regardless of what you eat.
- The diet includes plenty of fruit, vegetables and legumes, aligning with many general recommendations for healthy eating.
- Scientific evidence for the diet’s specific pH-based mechanisms is weak, although the food choices themselves may support overall health.
- Following the diet too restrictively can lead to calcium and vitamin B12 deficiencies.
The alkaline diet is an approach to eating that classifies foods as acidic or alkaline based on their presumed effects on acidity in the body. Although the alkaline diet has become widely popular, scientists disagree about its physiological basis and specific health effects. In this article, we examine what the science actually says.
How does the alkaline diet work, and what is its physiological basis?
The alkaline diet is based on the concept of potential renal acid load (PRAL): after digesting food, the body excretes either acid or base equivalents (Remer & Manz, 1995). Most fruit, vegetables, legumes and nuts are considered alkaline-forming, while meat, fish, eggs, grains and some dairy products are considered acid-forming.
Blood pH in the human body is tightly regulated within a range of 7.35–7.45, and deviations from this range require urgent medical intervention (Schwalfenberg, 2012). The kidneys and lungs continually maintain this balance, preventing food from significantly disrupting it. In healthy people, food instead changes urine pH — a measurable effect that does not directly reflect blood acidity or health status.
For a more detailed overview of pH balance and its relationship with nutrition, read pH and healthy eating.
What health effects of the alkaline diet have studies found?
Supporters of the alkaline diet claim that it supports bone health, reduces the risk of chronic diseases and helps regulate body weight. The scientific literature, however, presents a mixed picture.
Bone health. The acid load hypothesis proposes that the body uses calcium from bones to neutralize blood pH. In a systematic review, Fenton et al. (2011) found no strong association between dietary acid load and fractures or reduced bone density. Bonjour (2013) emphasized that the kidneys, rather than the bones, play the main role in this compensatory mechanism, and that the acid load hypothesis overlooks the kidneys’ essential role in maintaining homeostasis.
Body weight and overall health. The alkaline diet resembles the Mediterranean diet in its composition: plenty of dietary fiber, vegetables and legumes, with few processed foods. WHO recommends eating at least 400 g of fruit and vegetables per day, which aligns with the principles of the alkaline diet (WHO healthy eating). These food choices help you feel full and naturally manage your calorie intake, but this benefit comes from the overall quality of the diet, rather than a pH-based mechanism.
You can learn about the general principles of healthy eating in Healthy eating.
Is the alkaline diet suitable for athletes?
The alkaline diet poses no inherent barriers for physically active people, but it requires careful planning to ensure adequate protein and calorie intake. During intense training, lactate is produced and acidity increases in the muscles, which the body regulates automatically — the diet’s pH profile does not replace this buffering process.
Nutrition also has broader effects on hormone levels, including testosterone — read more in Nutrition and testosterone. Getting the right macronutrients is critical for post-workout recovery, a topic covered in depth in Post-workout nutrition – II.
What are the main risks of the alkaline diet?
A moderate approach to the alkaline diet is safe for most adults. Risks arise when the diet becomes too restrictive.
- Calcium deficiency: Eliminating dairy products entirely without alternatives (legumes, leafy green vegetables, fortified plant-based drinks) can lead to calcium deficiency. EFSA recommends a daily calcium intake of 1000 mg for adults (EFSA, 2015).
- Vitamin B12: Restricting animal products increases the risk of B12 deficiency, especially when maintained over the long term.
- Adequate protein intake: Cutting back on meat and some grains requires careful planning of protein sources to meet an athlete’s daily needs.
Overall, the alkaline diet can fit well within a healthy eating pattern, provided it does not become extreme and supplies all essential nutrients.
References
- Remer T, Manz F (1995). Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc. 95(7):791–7. PMID: 7797810
- Schwalfenberg GK (2012). The alkaline diet: is there evidence that an alkaline pH diet benefits health? J Environ Public Health. 2012:727630. PMID: 22013455
- Fenton TR, Tough SC, Lyon AW, Eliasziw M, Hanley DA (2011). Causal assessment of dietary acid load and bone disease: a systematic review & meta-analysis applying Hill’s epidemiologic criteria for causality. Nutr J. 10:41. PMID: 21529374
- Bonjour JP (2013). Nutritional disturbance in acid-base balance and osteoporosis: a hypothesis that disregards the essential homeostatic role of the kidney. Br J Nutr. 110(7):1168–77. PMID: 23551968
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2015). Scientific Opinion on Dietary Reference Values for calcium. EFSA Journal. 13(5):4101. DOI: 10.2903/j.efsa.2015.4101
Frequently asked questions
Does the alkaline diet change blood pH?
No. In healthy people, the kidneys and lungs regulate blood pH within a narrow range of 7.35–7.45, regardless of what you eat. Urine pH does change, but this does not reflect blood acidity or health status.
Which foods should you prioritize on the alkaline diet?
Prioritize fruit, vegetables, legumes, nuts and seeds. Limiting red meat, processed foods, alcohol and refined sugar is recommended.
Does the alkaline diet help you lose weight?
There is no direct evidence for a pH-based mechanism, but a diet rich in dietary fiber helps you feel full and may naturally help you manage your calorie intake.
Is the alkaline diet suitable for athletes?
Generally, yes, but you need to ensure adequate protein and calorie intake. Intense training requires a nutritionally balanced diet that meets your recovery needs.
What are the main nutrient deficiency risks on the alkaline diet?
An overly restrictive approach can lead to inadequate intakes of calcium (especially if you avoid dairy products), vitamin B12 and protein. A varied diet significantly reduces these risks.
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