The alkaline diet promises to optimise your health by changing your body's pH through food choices. "Acidic" foods supposedly cause disease, while "alkaline" foods promote health.
There's just one problem: your body's pH is tightly regulated by your lungs and kidneys, and what you eat cannot significantly change it. The entire premise is built on a misunderstanding of basic biology.
What Is the Alkaline Diet?
The alkaline diet classifies foods based on the pH of their "ash" - the residue left after burning food in a laboratory. Foods are categorised as:
"Alkaline" Foods (Encouraged)
- Fruits and vegetables
- Nuts (most types)
- Legumes
- Tofu and tempeh
"Acidic" Foods (Discouraged)
- Meat and fish
- Dairy products
- Eggs
- Grains
- Alcohol
The theory claims that eating too many "acidic" foods creates an acidic internal environment that promotes disease, while "alkaline" foods create a healthy alkaline state.
Why This Is Scientifically Impossible
Your Body Controls pH, Not Your Diet
Blood pH is maintained between 7.35 and 7.45 by your respiratory system (which expels CO2) and your kidneys (which excrete acid or base). This regulation is essential for survival - a blood pH below 7.0 or above 7.7 is life-threatening. Your body cannot allow food to change blood pH. If it did, eating a lemon would kill you.
Different Body Parts Have Different pHs
Your stomach is highly acidic (pH 1.5-3.5) to digest food and kill bacteria. Your small intestine is slightly alkaline (pH 7-8) for nutrient absorption. Your skin is slightly acidic (pH 4.5-5.5) for protection. These different environments exist simultaneously and are maintained regardless of what you eat.
Urine pH Changes, But That's Not Your Body
Alkaline diet proponents often measure urine pH to "prove" the diet works. But urine pH simply reflects what your kidneys are excreting to maintain blood pH - it tells you nothing about your internal environment. If anything, acidic urine shows your kidneys are doing their job.
The Claims Debunked
Claim: "Acidic foods cause cancer"
This is a dangerous misrepresentation. Cancer cells do produce acid as a metabolic byproduct (the Warburg effect), but this is a consequence of cancer, not a cause. Eating "alkaline" foods does not prevent or treat cancer. The American Institute for Cancer Research has explicitly debunked this claim.
Claim: "Acidic foods leach calcium from bones"
The theory suggests that your body pulls calcium from bones to neutralise dietary acid, causing osteoporosis. Multiple systematic reviews have found no evidence for this. Protein and dairy - supposedly "acidic" foods - are actually associated with better bone health, not worse.
Claim: "Alkaline water is healthier"
Alkaline water (pH 8-9) is neutralised by stomach acid within minutes. There's no credible evidence it provides any health benefit beyond normal hydration. It's expensive water.
Why People Think It Works
Despite being scientifically baseless, some people report feeling better on an alkaline diet. Here's why:
- More fruits and vegetables - The diet emphasises produce, which most people don't eat enough of. Benefits come from the nutrients, not the pH.
- Less processed food - Many processed foods are classified as "acidic," so followers reduce junk food intake.
- Placebo effect - Believing you're doing something healthy creates genuine perceived improvements.
- Increased attention to diet - Any structured eating plan increases food awareness.
The Irony
The alkaline diet accidentally promotes healthy eating (more vegetables, less processed food) through completely wrong reasoning. You'd get the same benefits by simply eating more vegetables - without the pseudoscience about pH.
What to Do Instead
If you're attracted to the alkaline diet's emphasis on plant foods, great - just drop the pH mythology:
- Eat plenty of vegetables and fruits - Not because of pH, but because of vitamins, minerals, fibre, and phytonutrients
- Don't fear protein - Meat, fish, eggs, and dairy are nutritious and don't "acidify" your body
- Limit processed foods - For actual nutritional reasons, not pH reasons
- Ignore pH test strips - Urine pH tells you nothing useful about your health
The Bottom Line
The alkaline diet is based on a fundamental misunderstanding of how your body works. Your pH is controlled by your lungs and kidneys, not your diet. The foods classified as "alkaline" are mostly healthy for other reasons - but the pH theory is simply wrong. Eat your vegetables because they're nutritious, not because they change your pH (they don't).
References
- Fenton, T.R. & Huang, T. (2016). Systematic review of the association between dietary acid load, alkaline water and cancer. BMJ Open, 6(6), e010438. doi:10.1136/bmjopen-2015-010438
- Fenton, T.R., et al. (2011). Causal assessment of dietary acid load and bone disease. Nutrition Journal, 10, 41. doi:10.1186/1475-2891-10-41
- Schwalfenberg, G.K. (2012). The Alkaline Diet: Is There Evidence That an Alkaline pH Diet Benefits Health? Journal of Environmental and Public Health, 2012, 727630. doi:10.1155/2012/727630
- American Institute for Cancer Research. (2020). No, Alkaline Diets Do Not Prevent Cancer. aicr.org
