Speaker: Kelly Picard PhD RD
This is a summary of a talk that I gave at the National Kidney Foundation Spring Clinical Meeting on April 11, 2025. Find the full list and summaries of the talks I attended here.
Objectives:
- Review different levels of food processing
- Discuss what is known about bioavailability
- Describe potassium and phosphorus additive use in the foody supply and how this impacts potassium and phosphorus content
- Discuss the accuracy of potassium and phosphorus content reporting in ultra-processed foods
What are the different levels of food processing?
One of the most common systems used to classify foods by level of food processing is the Nova System. Nova classifies foods into one of four categories:
- Unprocessed and minimally processed – such as fresh meat, fruits, vegetables and milk
- Processed culinary ingredients – such as sugars, oils, flour
- Processed foods – such as cheese and bread. These foods have been part of the human diet for a very long time and originally developed to help extend shelf life of group 1 and 2 foods.
- Ultraprocessed foods – such as chocolate bars, breakfast cereals and frozen ready to eat foods. These foods are newer in the human diet, they have often undergone industrial processing beyond what can be done in the a common home kitchen and include ingredients that we don’t typically find in a grocery stores, such as food additives.
Of particular importance to me when it comes to ultra-processed foods (UPF) are the additives that may impact mineral balance in the kidneys – potassium and phosphorus based additives.
How much processed foods do we eat?
A lot! Typically between 50-60% of intake is coming from UPF and one thing I was always found fascinating about this trend is that income isn’t protective. The people at the highest income levels consume the same amount as those at the lowest income levels. My own personal hypothesis for this is that UPFs are marketed at all levels. For example, boxed macaroni and cheese comes in:
- No name, generic versions
- Brand name versions
- Organic, high price point versions.
By the Nova system all of these options are UPF, but there is a product available at several price points.
How much processed foods do adults living with CKD eat?
The same as the general population. In a study that I did in my PhD, I calculated the % energy intake using the Nova Categories and found that 57% of energy intake came from processed foods among patients living with CKD.
What types of processed foods do we eat?
The primary category of processed foods were bread and bakery products. Followed by deli meats, processed meats and fish products.
How much of what we eat do we absorb?
This question has to do with the bioavailablity of nutrients from the foods that we eat. Not 100% of what we eat leaves the digestive tract and enters the blood stream. Some of what we eat will stay in the digestive tract and get excreted in the feces.
When it comes to hyperkalemia and hyperphosphatemia management, the potassium and phosphorus that we are concerned about will only come from the portion that leaves the digestive tract and enters the blood stream.
How is bioavailability studied?
For both potassium and phosphorus researchers use surrogate markers to calculate how much potassium and phosphorus is absorbed. The surrogate marker is the urine. Researchers can measure the amount of potassium or phosphorus in the urine and calculate the fraction that appears in the urine to determine the bioavailability.
What do we know about the bioavailability of potassium?
Truthfully, we have a lot to learn and there is very little understanding about individual foods. However, several studies have compared how consuming more fruits and vegetables impacts urinary potassium excretion. Most studies report that diets higher in fruits and vegetables have lower urine potassium recovery which suggests these foods have lower bioavailability. The bioavailability appears to be lower than diets high in animal foods, including meat and dairy products, and lower than the bioavailability of potassium from additives.
However, there was one study that compared potato products to potassium gluconate and in this study the researchers found that potatoes had higher bioavailability than potassium gluconate, which means that we need to be careful – as there are likely several factors at play.
What do we know about the bioavailability of phosphorus?
While it is generally reported that phosphorus bioavailability from plant foods is as low as 50-60%, animal foods 70-90% and additives 100%, it is important to note that not all studies have supported these numbers.
In a paper written by David St-Jules, him and his team reviewed the results of four previous studies. In all four studies the urinary phosphorus recovery was between 36-72%. Or said another way, based on the known amount of phosphorus that participants were eating, 36-72% could be found in the urine. This implies that the remaining 64-28% was not absorbed and was pooped out.
What factors could impact phosphorus bioavailability?
In plant foods, there is good recognition that the phosphorus is phytate bound which likely reduces the phosphorus absorption. However, I think one factor that may be overlooked when it comes to plant foods is how food processing impacts this. Evidence suggests that processed grains, for example those made into breakfast cereal, have lower phytates and therefore have higher phosphorus bioavailability.
There are other factors that are likely at play as well – which I highlighted in this slide above.
What do we know about different potassium additives and how they impact potassium content of foods?
The easy answer, is not a lot. Potassium content in the 2018 Branded Foods Product Database was not frequently reported. However, we are starting to see signals in the data that not all potassium additives may be associated with significant increases in potassium content.
Which potassium additives do we think might add or a little or a lot?
| Additive | Potassium mg/ 100g | Mean difference | Sig | Potassium mg/Serving | Mean difference | Sig |
| No Additives | 278 ± 306 | 0 | n/a | 169 ± 156 | 0 | n/a |
| i. Potassium Sorbate | 172 ± 7 | -106 | <0.01 | 173 ± 130 | 4 | 1.00 |
| ii. Acesulfame Potassium | 163 ± 31 | -115 | 0.01 | 129 ± 127 | -40 | 0.03 |
| iii. Potassium Phosphate | 452 ± 43 | 174 | <0.01 | 140 ± 124 | -29 | <0.01 |
| iv. Potassium Chloride | 1210 ± 302 | 932 | 0.08 | 349 ± 254 | 180 | <0.01 |
| v. Potassium Citrate | 254 ± 33 | -24 | 1.00 | 231 ± 214 | 62 | 0.01 |
| vi. Potassium Lactate | 570 ± 39 | 292 | <0.01 | 298 ± 111 | 129 | <0.01 |
This table summarizes the most frequently found additives in the 2018 Branded Foods Product Database that reported a potassium content. It shows that per serving, potassium chloride, potassium citrate and potassium lactate were all associated with a higher potassium content. Per 100g potassium phosphates were associated with a higher in potassium content. While potassium sorbate and acesulfame potassium did not appear to be associated with significant increases in potassium content.
Why do we need to care about this?
If we are going to tell patients to adjust their food intake to lower potassium levels, we want to ensure we are telling them information that is correct. We want to avoid telling people to eat foods that they can safely eat.
The caveat to this is that we need more information about the potassium content of food to really know how additives are impacting content, but early evidence suggests there are differences.
What do we know about how phosphorus additives impact phosphorus content?
Phosphorus reporting in the branded foods product database is very low, which means that we can’t make firm conclusions. However, based on the information that is currently available for phosphorus salts that are partnered with sodium, calcium, iron and potassium (e.g. sodium phosphate, calcium phosphate etc), as the co-mineral increases so too does the phosphorus content.
This of course makes sense, but it also means that sometimes we can figure out how much phosphorus will be added to a food if we know how much of the co-nutrient has been added.
I have talked this in a previous blog post here – about how much phosphorus is added to rice Krispies which contain iron phosphate.
What about other phosphorus additives?
Lecithin is the most common phosphorus additive, so understanding how it might be impacting phosphorus content of foods is becoming increasingly important. Unfortunately few studies have been done on this, however, if I did a deep dive into lecithin specifically, in my previous post here.
The other two common phosphorus additives are disodium inosinate and disodium guanylate. These phosphorus additives are 7.9% and 7.6% by weight phosphorus. There is no information available about how much the addition of these additives could impact phosphorus content. However, given that they are relatively low phosphorus content by weight, there is hope that their impact is minimal.
What do we know about the accuracy of potassium and phosphorus reporting on food labels and in nutrient databases?
As potassium becomes a mandatory nutrient to report, it is likely that some of (and our patients) have started to come across products that report containing 0mg of potassium, when there is no possible way, based on the ingredient list, that this is true.
And it is not surprising that when we look at large databases, such as the Branded Food Product databases, it is likely that there is mis-reporting of both potassium and phosphorus.
This makes it really difficult to understand studies that are using nutrient databases to estimate potassium and phosphorus intake, as it is possible that the estimates of the minerals are incorrect. It also makes it hard for clinicians and patients to correctly identify foods that may or may not be compliant with diet recommendations.
Studies comparing lab analyzed amounts for potassium and phosphorus in foods have reported that foods that contain these additives tend to contain higher amounts of these minerals than what is reported in nutrient databases.
Though one part of this, is that labelling legislation uses a one-sided limit for potassium and phosphorus reporting, which may mean that mineral content is under-reporting by a significant amount though will still be compliant with labeling laws.
Key Take Aways
- Processed foods can be significant sources of highly bioavailable potassium and phosphorus
- Some additives appear to change mineral content more than others and as clinicians we may need to take a personalized approach when discussing food adjustments with our patients
- Labels and nutrient databases may under-report potassium and phosphorus, which can make interpreting research findings more challenging, as well as make it difficult for both clinicians and patients to choose foods compliant with different diet recommendations.
