These are the little-known acidic foods you need to cut back on for your health

We’ve long known that a highly acidic diet can undermine your health, but the foods you should avoid might not be as obvious as you think

While oranges and lemons are commonly associated with being acidic foods, dietitians say our bodies determine if a food is acidic by how it is metabolised and broken down during digestion. Picture: iStock

In 2020, nutrition researchers at Trinity College Dublin conducted an investigation into the typical Irish diet. They concluded that the average person gets most of their dairy calories from a mix of cereals, red meat, dairy, and miscellaneous ultra-processed convenience foods. Legumes, non-starchy vegetables like leafy greens or broccoli, and fruit, comprise less than 5% of those calories.

This heavily-skewed balance towards protein, carbohydrates, and processed meals represents what nutrition experts call a high dietary acid load.

While this is a relatively new term within the nutrition lexicon, studies have suggested that consuming a highly acidic diet over time is linked to a whole raft of chronic diseases, from type-two diabetes to hypertension, liver disease, cardiovascular disease, cancer, anxiety, depression, and even neurodegenerative diseases such as Parkinson’s.

This might initially seem confusing. After all, the kinds of foods we commonly associate with acids are lemons, limes, vinegar, and grapefruit. Yet, dietitians say whether your body deems a particular food acidic or not has nothing to do with its taste or pH levels, but with how it is metabolised and broken down during digestion.

In fact, the most acidic foods in a typical Irish diet are forms of animal protein — meat, fish, seafood, and dairy — along with ultra-processed foods and any food with a large amount of added salt.

“A diet rich in animal proteins and processed foods increases dietary acid load and causes a more acidic urine pH,” says Beverley Beynon-Cobb, specialist dietitian and research fellow at University Hospitals Coventry & Warwickshire.

“It does this because protein, especially animal protein, is made from building blocks called amino acids, and they break down into acids — hydrogen ions, phosphoric acid, uric acid, and sulphate.”

Likewise, added salt — or sodium chloride to use its chemical name — is broken down into chloride ions, which are acids.

Many common ultra-processed foods, from ready meals to processed meats, canned soups, and even some forms of packaged bread, not only contain a surprising amount of salt but also a common additive called phosphoric acid — a preservative and flavour enhancer. However, as the name suggests, phosphoric acid is acidic.

Kidneys at capacity

I spent many months researching the connection between a consistently high dietary acid load and different aspects of the ageing process while writing my new book The Age Code — to be published in April — a deep dive into the relationship between what we eat and how quickly we age, and how all of us can age better through making some key lifestyle changes.

In particular, my discussions with a variety of scientists worldwide revealed that an acidic diet can have a deeply damaging impact on the kidneys, the organs that are crucial for removing toxins as well as serving as the body’s main acid regulators.

“An acidic diet places a huge demand on the kidneys because when you’re consuming a lot of dietary acids, you’re basically maxing out their capacity,” says Hana Kahleova, a nutrition scientist at the Physicians Committee for Responsible Medicine, a non-profit research institute in Washington DC.

“The kidneys need to filter out so many other chemicals and toxins, and if you overwork them, that leaves less room for their other functions.”

This does not mean that animal foods are bad. On the contrary, the protein and vitamins in meat and dairy are critical for our health — while fish is a key source of healthy fats, such as omega-3.

However, we also need a sufficient amount of fruits and vegetables, and often much more than we think. This is because these foods contain minerals like potassium, which are then metabolised into bicarbonate, an alkaline substance which the kidneys can use to neutralise the acids in our diet.

Yet, given that the average Irish person gets only 5% of their calories from fruits, vegetables, and legumes — rather than the recommended 50% — it’s likely that many people have a high dietary acid load.

The average Irish person gets only 5% of their calories from fruits, vegetables, and legumes — rather than the recommended 50% Picture: iStock

Dangers of high acid load

One easy way to assess whether your diet is worryingly acidic is to use a simple chart known as the potential renal acid load table, recommended by researchers such as Beynon-Cobb and other experts on dietary acid load.

This reveals that some of the most acidic foods include sweets like marshmallows or gummy bears — made from gelatin, an animal-based protein — as well as mussels, prawns, eggs, and Parmesan cheese. Dried herbs and leafy greens like spinach and kale are on the alkaline side of the PRAL table as they serve as key sources of minerals.

Researchers are beginning to understand why population datasets show that a high dietary acid load is harmful over time. Kahleova says that, as well as stressing the kidneys, it can also affect bone health, making us more prone to bone thinning and fractures as we age. This is because the kidneys start to take calcium from the bones to generate the bicarbonate they need to neutralise acids.

“If you’re consistently eating a highly acidic diet for many years, eventually the kidneys will be out of options, and need to turn to the bones and get some of the calcium out, so that it can buffer the dietary acids,” she says.

While the kidneys closely regulate the pH levels of our blood, through neutralising acids with minerals from our diet, or as a last resort, from our bones, some researchers believe that a consistently high dietary acid load can lead to a progressive accumulation of acids in and around the body’s cells.

Studies have suggested that this can drive inflammation, cell damage and potentially even change the shape and structure of key proteins so that rather than performing useful functions, they act as toxins.

However, some scientists believe more evidence is needed to show that a high-acid diet directly increases disease risk before it is included in mainstream nutrition guidelines.

“The possible links between dietary acid load and many chronic conditions are being explored, but the underlying mechanisms that possibly mediate these relationships are still poorly understood,” says Annemarie Bennett, associate professor in dietetics at Trinity College Dublin.

The possible links between dietary acid load and many chronic conditions are being explored, but the underlying mechanisms that possibly mediate these relationships are still poorly understood

The ‘low acid’ diet

Over the years, research funding for dietary acid load has been affected by a discredited fad known as the alkaline diet, which was accompanied by claims not backed by scientific evidence.

“Claims that an alkaline diet prevents cancer, osteoporosis, or heart disease are unsupported,” says Beynon-Cobb. “There is, however, observational evidence that a high acid diet can contribute to the development of these diseases.”

While the alkaline diet concept might be best added to the dustbin of nutrition history, Beynon-Cobb simply recommends trying to eat a ‘low-acid’ diet, which can be achieved through consuming 25% protein, 25% carbohydrates and 50% fruits and vegetables — ensuring you are meeting your protein requirements but getting enough minerals in your diet to balance out the acid.

This balance roughly matches recommendations for a Mediterranean diet — mainly fruits, vegetables, whole grains, beans, fish, and olive oil, while limiting red meat and processed foods — which has been shown to be one of the healthiest in the world.

If you want to know whether your meals are adding excess acid to your body, one simple way of checking is to buy some pH strips and dip them into your urine after a meal.

We’re still learning more, but there’s every chance that taking steps to minimise dietary acid load, especially as you get older, could go a long way to maintaining your health.

• ‘The Age Code’ by David Cox is available for pre-order on all online bookstores
• “If you’re eating a highly acidic diet for many years, eventually the kidneys will be out of options, and need to turn into the bones and get some of the calcium out