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.
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
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.
Potential Renal Acid Load of Common Foods
|Coffee (5-minute infusion)||-1.4|
|Cocoa (made with semi-skimmed milk)||-0.4|
|Indian Tea (infusion)||-0/3|
|Mineral Water (Volvic – natural)||0.1|
|Mineral Water (Apollinaris – sparkling)||-1.8|
|Fats and Oils|
|Sunflower Seed Oil||0.0|
|Fruits and Nuts|
|Apples (variety of 15)||-2.2|
|Meat and Fish|
|Trout (browned, steamed)||10.8|
|Grains and Legumes|
|Rolled Oats, Oat Flakes||10.7|
|White flour, whole meal||8.2|
|Lentils, green and brown||3.5|
|Milk, Dairy Products, and Eggs|
|Chicken eggs, whole||8.2|
|Cheddar. Reduced fat||26.4|
|Vanilla ice cream||0.6|
|Yogurt, whole milk, plain||1.2|
|Sugars and Sweets|
Table Source: Remer and Manz. (July 1995). Potential renal acid load of foods and its influence on urine pH. Journal of American Dietetic Association, (95) 7.
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.
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.) You can see the pH level in the graphic below:
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.
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.
So Is The Alkaline Diet Beneficial For Bone Health?
At the time of writing, there just isn’t any solid, well-designed research that supports the notion that the alkaline diet is beneficial for bone health.
A lot of the studies that have been conducted into the alkaline diet theory are observational studies. Now, these observational studies (study 1, study 2, study 3) have produced mixed results. But observational studies don’t provide us with definites. An observation merely indicates that there could be a potential relationship. It doesn’t prove a cause.
Let’s put that into context. A study on the observational study method itself took 52 findings gleaned from observational studies and attempted to replicate them in randomized clinical trials (a superior study design.) Not one of the 52 findings stood up in a randomized clinical trial!
So let’s apply this to the case of the alkaline diet and bone health. Some observational studies may find a link between eating an alkaline diet and healthy bones. But this finding could just be a coincidental factor a group of participants share. What an observational study doesn’t take into account is other coincidental factors the participants may share. For example, the participants may all eat an alkaline diet and have healthy bones. But they may all also exercise five days a week and take supplements, which could be the real reason they have healthy bones.
An analysis of the few randomized human trials carried out to investigate the alkaline diet and bone health didn’t share the mixed results of the observational studies. Here are the conclusions it came to:
- There is a linear relationship between net acid excretion and urine calcium levels.
- There is no relationship between net acid excretion with either body calcium levels or bone metabolism.
What these conclusions mean is that yes, the more acidic your diet, the more calcium you’ll tend to excrete via your urine. But, and it’s a big but, this urinary calcium level has nothing to do with the amount of calcium in your body and bones.
So, at least until further quality research is conducted to prove otherwise, there is very little in the way of concrete evidence to support the alkaline diet for improving bone health. In fact, the available research actually suggests the alkaline diet could be less than ideal for bone health.
You see, on one hand, the alkaline diet promotes more fruit and vegetable consumption. Eating more fruits and veggies is never a bad thing! But on the other hand, the alkaline diet theory advocates eating less protein because it’s acid-forming. The problem with excluding or limiting protein is that it plays a vital part in your bone health. It’s
P.s. If you’d like to read more about the importance of protein and bone health check out our “Everything You Need to Know About Protein and Bone Health” post.
Besides a lack of protein, nutrition experts believe the alkaline diet lacks other key minerals like calcium. In a U.S. News review, dietary experts noted the complexity of sticking to the alkaline diet and the lack of scientific evidence to back it up. The overall “score” for the alkaline diet was 2.5 out of 5. Granted, this is only one review, but the opinion of dietetics and nutrition experts is valuable. We’re talking about diet after all!
The alkaline diet is a tricky subject.
There are those that sing its praises and those that bemoan it. But at the end of the day, there just isn’t any concrete evidence to confirm the alkaline diet is beneficial for bone health.
If you recall, the studies in the 1960s that formed the basis for the alkaline diet were on participants with chronic kidney disease. Since then, there has been nothing to suggest the– often questioned– conclusions drawn from those studies can be applied to healthy individuals.
Having said that, there are no studies to suggest the alkaline diet is outright bad for your bone health. Although the lack of protein could become an issue.
I hope this review has helped clear the murky waters of the alkaline diet a little and will help you make an informed decision for your bone health. And if you have any comments or thoughts I’d love to hear them in the comments section below!