The alkaline diet promises that eating the right foods will make your body less acidic and protect you from everything from fatigue to bone loss. The diet itself, heavy on vegetables and fruit, is a healthy way to eat. The theory behind it is mostly wrong. Here is what pH is, what food can and cannot change, and what the alkaline diet gets right.
What is pH?
pH measures how acidic or alkaline (basic) a solution is, on a scale from 0 to 14:
- a pH of 7 is neutral
- below 7 is acidic, with 0 the most acidic
- above 7 is alkaline, with 14 the most alkaline
Different parts of the body have very different pH levels. Your stomach is strongly acidic, which helps digest food. Your blood is slightly alkaline, with a normal pH of about 7.35 to 7.45, and the body keeps it close to 7.40.
Can food change your body's pH?
Not your blood's. The body controls blood pH precisely, because even small changes can seriously affect organs. Your lungs adjust it minute by minute by breathing out carbon dioxide, your kidneys excrete excess acid or base over hours to days, and chemical buffers in the blood absorb the rest. Food does not override that system.
What food does change is the pH of your urine. As foods are metabolized they leave behind a small acid or base load, which the kidneys excrete. Researchers estimate this with a measure called potential renal acid load (PRAL), which predicts how a diet affects urine acidity. Changing your urine pH is a sign that your kidneys are doing their job, not that your body has become more alkaline.
"Acidosis," meaning blood that is too acidic, is real, but it is a sign of a serious underlying problem such as kidney, lung or metabolic disease, not something caused by eating bread or drinking coffee. It needs medical care, not a diet change.
Does an alkaline diet protect your bones?
A popular claim is that an "acidic" diet makes the body pull calcium from bones to neutralize acid, leading to osteoporosis. Careful research does not support it. A 2009 meta-analysis of calcium balance studies found no evidence that a higher dietary acid load causes bone mineral loss, and concluded that promoting the alkaline diet to prevent calcium loss is not justified. A 2011 systematic review likewise found no causal link between dietary acid load and osteoporosis and no evidence that an alkaline diet protects bone health. For what does help, see natural ways to support bone health.
Does an alkaline diet or alkaline water prevent cancer?
No good evidence says so. A 2016 systematic review found almost no research either supporting or disproving the idea, and concluded that promoting an alkaline diet or alkaline water to the public for cancer prevention or treatment is not justified.
What does the alkaline diet get right?
Quite a lot, as it happens, just not for the reasons it claims. The foods it encourages, vegetables, fruits, herbs, nuts and seeds, are the foods most of us need more of: only about one in ten US adults eats enough vegetables. The foods it limits, processed meat, sugary drinks, refined snacks and too much alcohol, are worth limiting anyway. A 2012 review of the alkaline diet concluded there may be some value in this way of eating for reducing chronic disease, while noting more research is needed.
Which foods are "alkaline-forming"?
The alkaline diet ranks foods by the acid or base load they leave after digestion, not by how acidic they taste. Based on PRAL estimates, in general:
- Base-forming: most vegetables and fruits, including citrus. Lemons taste acidic, but once metabolized they leave a base load.
- Close to neutral: fats and oils.
- Acid-forming: protein-rich foods such as meat, fish, eggs and cheese (hard cheeses especially), and many grain products. Many acid-forming foods, such as whole grains, are still nutritious.
Rather than sorting foods by pH, follow the simpler advice underneath it: build meals around plants, cook at home more, and drink plenty of water. If greens are hard to fit in, Easy Being Green adds more than 20 organic greens and superfoods to a glass of water or a smoothie. If you have kidney disease, talk to your doctor or dietitian before changing your diet, since you may have specific advice on potassium and acid load. For more on eating more plants, read what is in a greens supplement.
