The Alkaline Diet - Good or Bad for Bones?

Bone-Healthy Living / January 18, 2019
by Monica Straith, BS

It all started in the 1960s.

Studies on patients with chronic kidney disease drew a conclusion that has snowballed into a popular theory for protecting bone health in recent decades…

The food you eat can affect the pH level of your body. Specifically, that an alkaline diet protects your bones.

So is it true? Well, your diet does play a major role in your bone health. Eating foods that provide bone-building nutrients and avoiding overly-processed foods that cause low-grade inflammation which accelerates your bone loss is crucial.

But as far as the alkaline diet theory is concerned, there’s been a lot of debate since the 1960s. So I’ve reviewed the most recent research– on both sides – to put the alkaline diet in perspective for you.

What is The Alkaline Diet?

The alkaline diet– also known as the acid-alkaline or alkaline ash diet –revolves around the idea that each food you eat can have an affect on the pH level of your body.

See, when you break down the food that you eat, a residue or “ash” is left in your body as a by-product. This residue can be either acidic or alkaline depending on the balance of acid-forming and alkaline-forming components in that food.

* Note: When researchers discuss the pH level of a food, they’re referring to the effect it has on your body, not the actual pH level of that food. The pH level of a food isn’t always an indicator of whether it’s acid- or alkaline-forming. For example, tomatoes are naturally acidic but are alkaline-forming when they’re broken down by your body.

The net alkaline- or acid-forming property of a food is called Potential Renal Acid Load (PRAL). The term was coined in 1995 by a pair of scientists named Remer and Manz. Their PRAL model for estimating the pH impact of different foods is still used today. The table below shows the PRAL scores for 100 g portions of various foods. The higher the PRAL score (indicated by a positive number) the more acid-forming the food is. And the lower the PRAL score (indicated by a negative number) the more alkaline-forming the food is.

The alkaline diet hypothesis suggests that too much acidic ash makes your blood pH level too acidic. And this makes you vulnerable to disease and illness. Alkaline ash, however, is thought to affect your blood pH level favorably and provide many health benefits.

This theory also carries connotations for bone health too, but before we delve into that, it’s important to understand what pH level is, and why it’s important.

The Role of pH

To fully understand the alkaline diet and how it might affect your bones, we need a brief chemistry recap to see exactly what pH is.

A pH level measures how acidic or alkaline a substance is. The pH level runs from 0.0 to 14.0. A pH from 0.0 to 6.9 is acidic (with 0.0 being the most acidic.) A pH of 7.0 is neutral. And a pH from 7.1 to 14.0 is alkaline or basic (with 14.0 being the most alkaline.)
Note: The PRAL measure we covered earlier and the pH scale actually work a little differently. The PRAL measure uses negative numbers to indicate an alkaline-forming food, and positive numbers to indicate an acid-forming food. So, the alkaline-diet advocates eating lots of foods in the PRAL table above that have negative numbers. The pH level, however, works on a 0 to 14 scale which can confuse things.

Let’s take lean beef as an example. Lean beef has a PRAL score of 7.8. If you applied that number to the pH level above, you’d think that lean beef is slightly alkaline, right? But remember, the PRAL measure works differently. A negative PRAL score means that a food has an alkalizing effect on your body and a positive PRAL score means that a food has an acidic effect on your body. So lean beef’s 7.8 PRAL score would correlate to a number below 0 on the pH level because it has an acidic effect.

Now, to ensure every cellular process in your body is functioning properly, your pH level is regulated very tightly. The majority of your cells are slightly alkaline, but different parts of your body need to be kept at different pH levels. For example, your stomach is rather acidic– between 1.35 and 3.5 –to help you break down and digest the food you eat.

So what pH level should your blood be?

Your blood is naturally a little alkaline and hovers at a pH level between 7.36 – 7.44. If the pH level of your blood becomes too acidic and falls below a pH level of 7.35, it’s called acidosis and can be fatal. (We’ll cover acidosis in more detail in just a moment). According to the alkaline-diet theory, acidosis can cause bone loss too…

The Alkaline Diet and Osteoporosis

Now you know the basic alkaline diet theory and the role of pH levels in your body. So how does it all relate to bone health and osteoporosis?

Well, if you recall from the “What is the alkaline diet” section, the alkaline diet theory proposes that eating too many acid-forming foods leaves residual “acid ash” which makes your blood pH level too acidic (acidosis).

The alkaline diet theory goes on to explain that to maintain your blood’s natural, slightly alkaline pH level, your body draws alkaline minerals– like calcium –from your bones to act as a buffer. Obviously, if acid-forming foods did draw calcium from your bones, it would negatively impact your bone health and contribute to osteoporosis.

Alkaline foods, on the other hand, are thought to favor calcium levels and prevent bone loss.

The alkaline diet theory is often referred to as the “acid-ash hypothesis of osteoporosis.” And because the Western diet contains a lot of acid-forming foods, this theory suggests it will cause you to lose bone mineral density.

But not so fast…

Your Kidneys Play a Role in Regulating Your pH Levels

What the alkaline theory doesn’t tend to take into account is the role the kidneys play in regulating pH levels.

A typical, healthy adult produces a net 1 mmol/kg of acid per day. But your body is very sophisticated and has a process to deal with the excess acid and maintain the acid-base balance. This process is called acid-base homeostasis. The two main players in acid-base homeostasis are the lungs and the kidneys.

Your lungs bring oxygen into your body and exhale carbon dioxide. Your body creates carbon dioxide as a waste product during the metabolism of oxygen and nutrients. Now, carbon dioxide is mildly acidic, so it’s important to remove it from your body to maintain a healthy pH level.

Your kidneys are the other half of the acid-base balance team. Think of your kidneys as a filter. They help remove anything your body doesn’t need, and that includes excess acid or alkaline residue. What’s more, during the process of excreting excess acid, your kidneys produce bicarbonate  (chemical formula HCO3). Bicarbonate is slightly alkaline and acts as a “buffer” to any remaining excess acid to further help maintain the necessary pH level.

When does acidosis come into play?

In “The Role of pH” section, I mentioned that if the pH level of your blood falls outside the optimal range and becomes too acidic, it’s called metabolic acidosis. But if your body has a process in place to overcome excess levels of acidity, when does acidosis become an issue?

Here’s the thing; the acid-base balance duo of your lungs and kidneys can deal with moderate levels of excess. But extreme cases can overwhelm the acid-base balance process and lead to acidosis.

The key thing to note here though, is that research suggests your diet is generally not capable of causing such extreme changes in pH level.

It seems advanced conditions like starvation, and ketoacidosis (a complication of diabetes) or alcohol intake are the typical cause of metabolic acidosis.

What’s more, if the alkaline-diet theory proposes that too many acid-forming foods can cause acidosis so we should eat an alkaline-based diet, wouldn’t the opposite be true too? See, if your pH level becomes too alkaline and increases above 7.45, it’s called alkalosis. And alkalosis can be just as fatal as acidosis.

But once again, the research doesn’t support the theory that your diet can cause this condition. Kidney disease and prolonged periods of vomiting are the more common causes.

Food Affects Your Urine, Not Your Blood

Given that foods can be acid-forming or alkaline-forming, the part of the alkaline-diet theory that talks about foods leaving behind an acidic or alkaline residue seems to be accurate to a certain extent. But given that your kidneys – and your lungs – work together to deal with pH imbalances it seems unlikely that your body draws calcium from your bones to buffer excess dietary acid.

So taking the kidneys into account, the food you eat can change your pH levels. But research shows that it’s your urine pH levels that food can affect, not your blood pH levels.

What’s more, research suggests that urine pH levels are not generally a good indicator of general health, or your body’s overall pH level. Why? Because it’s merely a short-term, temporary change in reaction to a recent meal.

Here’s an example: when you eat a lamb chop– which is an acid-forming animal protein – your kidneys work to remove the excess acid residue the protein leaves behind in your urine. So your urine pH level will be more acidic for a few hours following your meal, but your blood pH levels won’t change.

In fact, a review of the alkaline diet hypothesis published in the “British Journal of Nutrition” concluded that the most recent studies have shown “no relationship between nutritionally induced variations of urinary acid excretion and calcium balance, bone metabolism and the risk of osteoporotic fractures. Variations in human diets across a plausible range of intakes have been shown to have no effect on blood pH.” In other words, a whole variety of human diets show no impact on blood pH at all.

A final thing to consider about diet and urine pH levels is the bioavailability of the nutrients in food. A study published in the “Journal of the American Dietetic Association” calculated the acid load of common foods. (The same study that produced the PRAL estimates for foods that we referred to in the “What is The Alkaline Diet” section.)

Before the PRAL model was produced, different calculation models were used to estimate the net acid-forming or alkaline-forming properties of certain foods. These calculation models tended to support the alkaline-diet theory. But the PRAL researchers found that previous models were flawed because they didn’t take the bioavailability of nutrients into account. That means that foods might not leave such high levels of acid or alkaline residue because your body would absorb and use them instead.