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Updated: Sep 4, 2021

As gut health is becoming a more common topic of late, so is the discussion around alkaline diets. The diet is based on the notion that what we eat affects the pH value of the body. Let’s dive a bit deeper behind the role of alkaline diets on the gut and whether this could be true.

Firstly, what do we mean by the term acidic and alkaline?

Without turning this into a chemistry lesson, put simply the pH value of food allows us to determine whether it is an acid (pH <7), an alkaline (pH >7), or neutral (pH 7).

Foods are typically categorised by their potential renal acid loads (PRALs), so fruits, vegetables, fruit juices, potatoes, and alkaline-rich and low phosphorus beverages (red and white wine and mineral soda water for example) have a negative acid load. Whereas grains, meats, dairy, fish, and alkaline-poor and low phosphorus beverages (pale beers and cocoa for instance) have relatively high acid loads (1).

What is key to understand before we delve into gut health, however, is that the pH of food before we digest it does not mean that this it will be the actual pH in the body. For instance, not all acidic foods behave the same when ingested and can be alkalizing when digested.

Also, the pH of your blood or the cells cannot be changed by the food we eat as it is primarily controlled by the kidneys.

So, what is best for gut health?

Well, the pH within the gut varies along its course; from neutral in the saliva (6.5-7.5) to an acidic pH of 4.0-6.5 in the upper aspect of the stomach. The lower portion of the stomach becomes extremely acidic (pH 1.5 – 4.0) whilst the small intestine then suddenly changes to alkaline (pH 7.0 – 8.5). The pH of the colon can, however vary dramatically between pH 4.0 – 7.0 and is dependent on the pH of the stomach and small intestine, gut flora acid production and influenced by certain supplements.

We know that the pH of the body and gut are very different, but that the optimal pH in the gut should be 4.5-5. The gut flora maintains this by producing sufficient amounts of lactic acid, but when the flora becomes compromised the lactic acid levels reduce and the pH becomes more alkaline, promoting dysbiosis (an imbalance in the gut microbiome favouring the growth of harmful bacteria and Candida) which is known to cause a number of health issues (2).

What can you do to have the best gut chemistry?

As the gut has trillions of micro-organisms and the pH varies along the course of the gut, we also have to appreciate that everyone is different, and will therefore have different tolerance levels and needs to eliminate particular trigger foods (fatty foods, caffeine, chocolate, spicy foods, carbonated beverages for example) to reduce gastroesophageal reflux disease (GERD) commonly associated with gut issues.

Though the alkaline diet is healthy by actively encouraging an increased intake of fruits, vegetables, and plant foods as well as restricting processed foods, there is very little evidence to categorically support the overall positive effect of alkalinisation on the body and that it has any impact on pH levels (1).

My advice?

Keep to a varied and rich diet that is whole and unprocessed as possible to ensure you are supporting gut health (as these are fibre, prebiotic, and micronutrient rich) without the unachievable desire to drive towards body alkalinisation.

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