pH colour scale

Alkaline Diet explainer: what does the evidence say?

In Nutrition educationby RebeccaLeave a Comment

The Alkaline Diet was a big deal in 2016 and while interest has waned since then, some of the underlying concepts of the diet have lingered. What is the Alkaline Diet, and is there any science to support it?

What’s the premise of the Alkaline Diet?

This diet suggests that foods like meat, rice, pasta, alcohol, soft drink, sugar and coffee are ‘acidic’ and therefore make our bodies acidic. On the flip side, ‘alkaline foods’ like fruits, vegetables, nuts and apple cider vinegar make our bodies more alkaline, which is purportedly good for cell generation and disease prevention. This diet is particularly topical in relation to cancer prevention and treatment.

FYI: pH is a scale from 1 (very acidic) to 14 (very alkaline). pH 7 is neutral.

What’s true?

It’s great advice to eat more plant-based foods and less processed foods. Following this sort of dietary pattern is proven to be good for short- and long-term health and wellbeing.

What’s false?

The idea that this diet changes your body’s pH is simply false. That’s just not how physiology works.

Firstly, your stomach is an extremely acidic environment, and needs to be – chemical digestion (by acids, enzymes, and other compounds) works with mechanical digestion (chewing, churning) to break down food into smaller absorbable molecules. Acidity in the stomach is also a primary defence against illness, by creating an environment that kills many harmful pathogens. Whether your food is ‘acidic’ or ‘alkaline’, you stomach cares not a bit. It’ll all be churned up with gastric acid until it becomes what’s known as chyme, which has a pH of about 2. As chyme moves through the small and then large intestine, its pH is adjusted by other digestive secretions. A bit of apple cider vinegar won’t override our body’s incredibly efficient system of homeostasis (physiological equilibrium, or balance).

Secondly, our blood’s pH level is tightly controlled by many complex mechanisms, because a deviation outside of a very small window (7.35 to 7.45) can be life-threatening. If your blood is truly acidic (a condition known as metabolic acidosis), you’re probably experiencing some serious health concerns like kidney failure or uncontrolled type 1 diabetes. Likewise, alkaline blood (metabolic alkalosis) can be caused by kidney disease, excessive bleeding or prolonged vomiting.

The pH of the urine can change between being acidic and alkaline because the kidneys change the amount of acid excreted via urine to keep our blood’s pH tightly controlled. Urine’s pH fluctuates so that blood’s pH does not. Urine pH does not reflect the pH of your blood (or your cells).

Acids aren’t all bad – many are essential for health

When you hear ‘acid’ you might first think of harmful, corrosive stuff like hydrochloric acid or sulphuric acid. However acids come in many forms, and some are absolutely necessary for good health.

For instance, take ascorbic acid – aka Vitamin C. Without it, you’ll get scurvy. Ascorbic acid is an antioxidant, it’s essential for collagen development, and it helps us absorb iron which is essential for transporting oxygen via blood.

Our bodies need amino acids and fatty acids to stay alive, and we get them from food. Amino acids, which are the building blocks of proteins and are essential for cell growth and repair, are very important for all people, and especially those with cancer. Limiting ‘acidic’ protein-rich foods could have serious implications for people with cancer, who have higher protein requirements than normal and may risk malnutrition if they don’t consume enough.

What the evidence says

Practice-based Evidence in Nutrition (PEN), the global resource for nutrition practice, summarises the evidence as follows:

A conclusion [on the effectiveness of the Alkaline Diet] is either not possible or extremely limited because evidence is unavailable and/or of poor quality and/or is contradictory:

  • No evidence was found from randomized controlled trials or systematic reviews to support the assertions that an alkaline diet or changing the dietary acid load may prevent or cure chronic diseases such as obesity and cardiovascular disease.
  • There is no experimental evidence to validate theories about proposed mechanisms relating influence of dietary acid load on obesity, hypertension, or cardiovascular disease.
  • No evidence was found from randomized controlled trials or systematic reviews to support the assertions that an alkaline diet or changing the dietary acid load may prevent or cure type 2 diabetes.
  • There is no evidence to support that an alkaline diet may prevent or cure cancer.

Take home message

Generally speaking, the dietary pattern of the Alkaline Diet is healthful – eat more plant-based foods, less processed foods. Solid advice.

However, the alkaline=good / acid=bad mentality is another example of black and white thinking that just doesn’t mesh with real life (or real science). You can’t eat your way to an alkaline body pH and nor should you want to.

Good nutrition is about balance and variety. Drastically reducing intake of core food groups is unnecessary and is not good for our health.

References

Fenton T, Huang T. Systematic review of the association between dietary acid load, alkaline water and cancer. BMJ Open. 2016; 6(6): e010438. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4916623/

Kasprak A. Fact-check: Everyone Who Has Cancer Has a pH That Is Too Acidic. Snopes, 2016. Available from: https://www.snopes.com/fact-check/everyone-who-has-cancer-has-a-ph-that-is-too-acidic/

NHMRC. Nutrient Reference Values, Vitamin C. 2017. Available from: https://www.nrv.gov.au/nutrients/vitamin-c

Vancouver Cancer Centre. FAQ #2 Alkaline Diet. 2015. Available from: http://www.bccancer.bc.ca/nutrition-site/Documents/Health%20professional%20resources/FAQ_Alkaline_Diet.pdf