A few weeks ago, I wrote a blog all about the importance of getting enough calcium in the diet, in particular the importance of calcium for healthy bones.
Last week I received an email from Mick, who expressed his concerns about how dairy foods that are rich in calcium, are also highly acidic and could result in increased loss of calcium from the bones and cause weak and brittle bones. If these effects are true, this would have catastrophic effects on conditions such as osteoporosis - a condition characterised by increased bone loss.
So where did this theory come from? Let’s take a journey back in time to the 1960’s where studies on patients with chronic kidney disease suggested that the foods we eat can affect the acid/alkaline levels in your body (aka pH levels) and have negative effects on bone health! (1, 2)
This topic has been debated for over 60 years, however, does this theory actually hold up? In this blog you’ll learn all about the acid-alkaline diet, why your body needs acid/alkaline balance, how acid/alkaline foods affect the body, and whether acidic foods can actually cause weak bones!
What is the alkaline diet?
The alkaline diet (aka acid-alkaline diet) is based on a theory that foods can alter acid and alkaline levels inside of your body, otherwise known as your pH value. When you eat foods, an “ash” residue remains, this metabolic waste can be either alkaline, neutral or acidic.
The theory is that if you eat more acidic foods your blood will become more acidic, while if you eat more alkaline foods your blood will become more alkaline.
What is pH balance?
Your body’s pH balance (aka acid-base balance) is the level of acids and bases (think of bases as alkaline) in your blood. Maintaining a healthy pH balance is essential for your survival and your body helps to naturally maintain this function. While the pH scale goes from 0 -14, human blood is always slightly alkaline, with a pH of 7.36–7.44.
Your lungs and kidneys play an important role in regulating your pH balance and when your lungs or kidneys are dysfunctional this can cause your blood’s pH level to become imbalanced and lead to medical conditions such as acidosis (too acidic) and alkalosis (too alkaline)(3).
What foods and acidic and what foods are alkaline?
There are common nutrients that leave acidic ash that include protein, phosphate and sulphur, while calcium, magnesium and potassium leave an alkaline ash.
- Acidic: meat, poultry, fish, dairy, eggs, grains, alcohol
- Neutral: natural fats, starches, and sugars
- Alkaline: fruits, nuts, legumes, and vegetables
pH values in the body
Advocates for the alkaline diet suggest that people monitor the pH of their urine to make sure they are alkaline. Sounds legit right?
However, different parts of the body vary in pH levels. For example, your stomach needs a highly acidic environment to break down food and it does this by producing hydrochloric acid that has a very low pH (highly acidic).
Can acidic foods cause weak bones?
There is a condition called osteoporosis that I discussed here, where bones can start to deteriorate that can result in increased risk of fractures. Osteoporosis is more common as we age, particularly in postmenopausal women where there is a loss of the hormone oestrogen that helps to make and rebuild bones (7).
Alkaline-diet advocates hypothesise that in order for your body to maintain a healthy blood pH, your body takes alkalising minerals (eg. calcium) from your bones to ‘buffer’ the acidic foods from the diet and this results in less calcium to build and maintain healthy bones leading to increased risk of osteoporosis and bone fractures.
While this is an interesting theory, this theory ignores the important role that your kidneys and lungs play in regulating pH levels – what’s called acid-base homeostasis (Homeostasis is where your body self-regulates things in the body to keep things healthy!).
After inhaling and using oxygen your lungs help to regulate your pH balance by exhaling carbon dioxide (C02) as a waste product. Carbon dioxide is mildly acidic, so your lungs remove it from your body to maintain a healthy pH balance.
Your kidneys also play an essential role in maintaining a healthy pH balance by filtering and removing anything your body doesn’t need, including excess acid and alkaline residue. Furthermore, your kidneys balance your pH levels by producing bicarbonate, that acts as a “buffer” to neutralize any remaining excess acid. (8)
So as long as your kidneys and lungs are functioning normally, there would be no reason for your body to take calcium from the bones to keep a healthy pH balance!
What does the science say about alkaline diets and bone health?
It seems very unlikely that acidic foods have an effect on bone health. In fact, an article published in the British Journal of Nutrition concluded that “Several recent human studies have shown that there is no relationship between nutritionally induced variations of urinary acid excretion and Ca balance, bone metabolism and the risk of osteoporotic fractures”. Basically, suggesting that acidic foods in the diet do not pose a risk to bone health.
While also stating that “long-term studies of alkalinising diets have shown no effect on the age-related change in bone fragility.” - meaning that alkalising diets have not shown any benefits for bone health. The acid-ash hypothesis also missed another important factor for bone loss, that being collagen, an important protein for bone tissue (9,10, 11).
What’s important to consider here is that the studies linking acid in the diet to bone health are mixed. Multiple observational studies have found no association, others have found a strong association. The problem is that observational studies can’t identify causation. For example, is it the acid/alkaline forming foods in the diet? Other nutrients in the diet? or other external factors altogether (eg. exercise, smoker/non-smokers, sleep etc)? (12, 13, 14, 15, 16).
That’s why clinical trials are a much better indicator for understanding causation. Multiple clinical trials have concluded that highly acidic diets have no impact on blood calcium levels, bone loss and increased risk of osteoporosis (17, 18, 19).
In fact, high protein diets may help to improve bone health by increasing calcium retention and activating the IGF-1 hormone, that help to stimulate the repair of muscle and bone. Meaning that high-protein diets that are considered to be acidic are associated with healthier bones (20, 21).
So why do people still believe that alkaline diets are better for bone health?
While acid forming foods are not able to affect the pH levels of the blood due to our fantastic kidneys and lungs, there is some evidence that acid-forming foods can influence our urine pH levels after a meal. However, studies suggest that urine pH levels are a poor indicator of your body’s pH levels. The reason why is that urine pH levels are only a temporary and short-term reading of your body’s pH levels (22, 23, 24).
So, what's the bottom line?
While the evidence is mixed, there just isn’t enough strong evidence to suggest that acidic foods can cause bone loss and increase the risk of osteoporosis. In fact, protein that is highly acidic may even be beneficial for your bones.
There are many other benefits to consuming an alkaline diet as it is typically rich in fresh fruits, vegetables, nuts, seeds and wholegrains that are rich in fibre, vitamins and minerals that are important for health.
In saying that, there is no evidence to suggest acidic foods are particularly harmful for bones, especially when consumed in a balanced diet. Generally, alkaline diets could be beneficial for your health, however the evidence suggests that these effects are due to nutrients and may have nothing to do with your pH levels!
If you have any questions or need support with your health, feel free to email our head nutritionist Ben at firstname.lastname@example.org
This article does not constitute medical advice and does not take into consideration your personal circumstances. Please see your medical professional before implementing the above.