The alkaline diet
The acid-alkaline diet or alkaline ash diet is increasing in popularity. Is there evidence to support the controversial claims made about its health benefits? Dr Linia Patel provides an evidence-based investigation of this trending way of eating.
What is the alkaline diet?
The concept of alkaline and acidic foods developed during the mid-1800s as the dietary ash hypothesis. It proposed that foods, once metabolised, leave an acid or alkaline ‘ash’ in the body. According to the proponents of the alkaline diet, the metabolic waste from the metabolism of these foods can directly affect the acidity and alkalinity of the body. Choosing more alkaline foods in theory should alkalise your body and prevent diseases like osteoporosis and even cancer1.
Certain food groups are considered acidic, alkaline or neutral:
- Acidic: meat, poultry, fish, dairy, eggs, grains and alcohol
- Neutral: natural fats and starchy food
- Alkaline: fruits, nuts, legumes and vegetables
Regular pH levels in your body
Put simply, pH is a measurement of how acidic or alkaline something is. The acid-alkaline diet suggests that people monitor the pH of their urine to ensure that it is alkaline (over 7) and not acidic (below 7). However, a key thing to note is that pH varies greatly within your body. While some parts are acidic, others are alkaline – there is no set level. Your stomach, whose job is to digest food, is loaded with hydrochloric acid making it highly acidic (pH 2-3.5). Human blood, however, is always slightly alkaline (pH 7.36-7.44). When your blood pH falls out of the normal range, it can be fatal if left untreated. For this reason, your body has many effective ways to closely regulate its pH balance. This is known as acid-base homeostasis. Excreting acids in your urine is one of the main ways your body regulates its blood pH. If you eat a large steak, your urine will be more acidic several hours later as your body removes the metabolic waste from your system. Therefore, measuring urine pH is a poor indicator of overall body pH and general health as it can be influenced by many factors, including diet1,2,3.
What does the science say?
Followers of the alkaline diet claim that eating a diet rich in alkaline-forming foods has unique health benefits, while a diet high in acid-production foods disrupts the blood’s normal pH level. As such, the theory of the diet is that an acidic diet triggers the loss of essential minerals such as calcium as the body attempts to restore equilibrium. The imbalance is said to increase susceptibility to illnesses like arthritis, osteoporosis, kidney disease and even cancer4.
The first thing to note is that there is no evidence to suggest that food doesn’t influence blood pH. Your body tightly regulates blood pH levels and in healthy people diet doesn’t significantly affect blood pH, but it can change urine pH. The diet was originally developed to help prevent kidney stones and urine infections, as the pH of your urine changes depending on what you eat1,2,3.
Most alkaline-diet followers believe that to maintain a constant blood pH your body takes alkaline minerals, such as calcium, from your bones to buffer the acids from acid-forming foods you can eat. Interestingly, the research linking dietary acid to bone density and fracture is mixed. While many observational studies have found no association, others have detected a link. However, clinical trials (which are much more accurate) have concluded that acid-forming diets have no impact on calcium levels in your body. In fact, eating sufficient protein activated a hormone (IGF-1) which stimulates the repair of muscle and bone. It’s obviously very important to eat lots of fruit and vegetables and they provide vitamin C, which is key to supporting collagen. Loss of collagen is linked to poor bone health4,5.
There is an argument that cancer only grows in acidic environments and can be treated or even cured with an alkaline diet. However, comprehensive reviews looking into this have concluded that there is no direct link. While tumours grow faster in acidic environments, tumours create this acidity themselves. It is not the acidic environment that creates cancer cells, but cancer cells that create the acidic environment. In fact, cancer cells can also grow in alkaline environments6.
In summary, the evidence to date does not support any of the claims made to support the premise of the diet.
The bottom line
The alkaline diet encourages a high intake of vegetables and fruit, plant-based protein and less junk, which is a good thing. However, any eating plan that shuns complete food groups isn’t cool. Food is not able to influence blood pH. Keeping it balanced is the way forward, hands down.
- Bonjour J et al (2013), Nutritional disturbance in acid-base balance and osteoporosis: a hypothesis that disregards the essential homeostatic role of the kidney, Osteoporosis Int., 110 (7): 1,168-77.
- Raghunand N et al (2001), PH and chemotherapy, Novartis Found Symp., 240: 199-211, 265-8.
- Santo N (1997), Effect of an acute oral protein load on renal acidification in healthy humans and in patients with chronic renal failure, J Am Soc Nephrol., 8(5): 784-92.
- Heaney et al (2018), Amount and type of protein influences bone health, Am J Clin Nutrition, 10: 1,093.
- Jonge E et al (2017), Dietary acid load, trabecular bone integrity and mineral density in an ageing population: the Rotterdam study, J Am Soc Nephrol., 28(8): 2,357-65.
- Moellering R et al (2008), Acid treatment of melanoma cells selects for invasive phenotypes, J Am Soc Nephrol., 25 (4): 411-25.
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Dr Linia Patel has a BSc degree in biochemistry and physiology and has recently achieved a PhD in public health. Linia is a leading dietitian and sports nutritionist. Her passion is translating nutritional science into easy-to-digest and practical advice.