Understanding how much phosphorus additives we eat is becoming an increasingly asked question. With current labeling laws, producers do not have to declare how much phosphorus they have added to their foods. And as changes in manufacturing mean changes in phosphorus content, there is growing awareness that food nutrient databases, such as the Canadian Nutrient File, aren’t keeping up.
So today I am looking at a study that has tried to figure out how much phosphorus additives adolescents are eating in Sweden.
What did they do?
The authors used data collected by the Swedish Food Agency from a national representative sample of kids from grades 5, 8 and 11. Based on what I read, the data collection is similar to the NHANES studies in America.
The Swedish Food Agency collected 2 * 24 hour recalls using a validated, country-specific tool and also spot urine samples.
The researchers in this study, used the data to Swedish Food Agency to focus in on phosphorus. Let’s get into a the nitty gritty details on this next!
How did they figure out how much phosphorus additives were in the food?
The specific phosphorus additives investigated in this study were:
- Phosphorus acid (E338)
- Sodium phosphates (E339)
- Calcium phosphates (E340)
- Magnesium phosphates (E343)
- Sodium/Potassium/Calcium/Magnesium DIphosphates (E450)
- Sodium/Potassium TRIphosphates (E451)
- Sodium/Potassium/Calcium POLYphosphates (E452)
The authors acknowledge that while there are other phosphate additives unfortunately there is insufficient information about them. This makes it impossible to study them.
Using EU regulations the authors divided foods into two groups. If P-additives weren’t allowed, it was considered an additive free food. All other foods were considered potential additive containers. And had their ingredients lists reviewed. For food items with more than 15 different products, they aimed to review 90% of the food items. If there were less than 15 products, all items were reviewed.
If more than 10 of the reviewed products contained additives, anytime someone responded that they ate that food item, it was considered an additive containing food. Consider here that this means an assumption is being made. It is possible that sometimes people were eating a food item that DIDN’T contain phosphorus additives.
Once a food was considered to contain an additive, they used industry data to figure out how much.
What statistics were performed?
Using the statistical methods section of the article, you can see that they main outcome there were looking at was how the urinary phosphorus test compared with their calculated phosphorus intake from diet recalls.
That’s a good question. Why? Because it helps us understand how urine phosphate measurements compare with diet recalls that have been adjusted for phosphorus additives. In other studies, if an attempt to figure out how much additives have been used isn’t done, then it is possible the urine phos doesn’t match because the diet recall method wasn’t accurate.
What did they find?
Question 1: How much phosphorus additives is in food?
- 16% of food items contained phosphorus additives
- Additives added an average of 479mg to every kg of food stuff
- Interpretation comment: Notice that kg unit. 479mg sounds like a lot, but many people are probably not consuming 1kg of the food item.
- The food items with the most phosphorus additives were:
- Processed Cheese at 10,535mg/kg
- Chewing Gum at 4986mg/kg (does it count if you don’t swallow it? I don’t know the answer to this question just my thoughts…)
- Milkshake with extra protein at 4000mg/kg
- Frozen seafood at 4000mg/kg (I think this has good applicability in the North American markets as most of our seafood is frozen using a phosphate-based brine)
Question 2: How much phosphorus additives were consumed and where did they come from?
- Mean intake ranged from 35mg per day in the youngest age group to 56mg per day in the oldest age group
- The main sources of phosphorus were:
- Cola drinks
- French Fries (that I found surprising, I don’t think of French Fries and phosphorus additives)
- White tortilla bread
- Sausages
- Juice
- Chewing gum
How did diet recalls compare with urinary phosphorus measures?
Easy answer, poorly. The authors reported a very low correlation between urinary phosphorus and dietary intake (0.12 and this result was significant).
What does it mean to have reached significance in this case? Simply that the chances that there was a there was a correlation but the data didn’t show it was low. Significance in this case doesn’t change anything about how strongly correlated it was.
The raw numbers are pretty staggeringly different. When intakes of P from diet records was >3000mg the urine phosphorus concentration was only 665mg/L. And furthermore, intakes of<3000mg P were not very different from the >3000mg group at 609mg/L.
Take Aways
Methods to determine the amount of phosphorus in foods are challenging and better resources are needed to help us understand how much phosphorus is in our food.
Urine phosphorus estimates from a random spot sample were poorly correlated with phosphorus estimated from food records. So make sure next time you read a study about phosphorus you check their methods and see how phosphorus was estimated.
The main sources of phosphorus were colas, french fries and sausages. French fries have not previously been on my radar but sure enough, according to McCain’s website they contain sodium phosphate too.
