Your kidneys are remarkably hardworking little organs. Every day, they filter your blood, remove waste, balance fluids and minerals, help regulate blood pressure, and even support red blood cell production. They do all of this quietly, usually without demanding much attention.[1]

Unfortunately, quiet organs are easy to ignore until they are no longer quiet.

Chronic kidney disease often develops gradually and without obvious symptoms. Diabetes and high blood pressure are among its most important risk factors, which means kidney health can’t (and shouldn’t) be separated from the wider conversation about metabolic health.[1] 

Increasingly, researchers are also asking whether the types of food dominating modern diets may be contributing, if not actually driving, the problem.

And ultra-processed food has, once again, entered the chat. 

First, what is ultra-processed food?

Almost all food undergoes some form of processing. Chopping vegetables, freezing meat, fermenting yoghurt and turning milk into cheese are all forms of processing. This does not make these foods unhealthy.

Ultra-processed foods are different. They are generally industrial formulations containing ingredients rarely used in an ordinary kitchen, such as modified starches, protein isolates, emulsifiers, artificial colours, flavour enhancers and various preservatives. They are designed to be convenient, intensely palatable and able to sit on a shelf for rather longer than seems natural.[2]

Common examples include sugary drinks, packaged snacks, instant noodles, confectionery, many ready meals and some reconstituted meat products. While these products may differ in their ingredients and nutritional claims, they share an important feature: they are industrial formulations made largely from refined ingredients and additives, with little intact whole food remaining. Attractive packaging, expensive marketing campaigns and impressive claims do not change that. And when these products form a large proportion of the diet, a consistent pattern of concern is emerging.

Another organ joins the conversation

Higher consumption of ultra-processed food has already been associated with obesity, type 2 diabetes, cardiovascular disease and premature death.[3] Kidney-specific research is more recent, but it is beginning to point in the same direction.

A growing body of observational research has linked greater ultra-processed-food consumption with declining kidney function and a higher risk of chronic kidney disease. Researchers have also examined people who already have the condition. In the US Chronic Renal Insufficiency Cohort study, greater consumption of ultra-processed food was associated with a higher risk of kidney disease progression and death, particularly during the earlier stages of the disease.[4]

This does not prove that ultra-processed food directly caused the decline. People who consume more of these products may differ in many other ways, including income, healthcare access, physical activity, smoking, and overall diet quality. Dietary intake is also notoriously difficult to measure accurately. Most people struggle to remember what they ate last Tuesday, never mind what proportion of it contained an emulsifier.

Nevertheless, the findings deserve attention because they are consistent with what we already know about metabolic and cardiovascular health… the two major systems with which kidney health is closely intertwined.[1]

It is about more than one nutrient

Ultra-processed foods are frequently high in added sugar, refined starches and poor-quality fats, while displacing nutrient-dense whole foods. Their salt content is often singled out too, but salt should not automatically be treated as the central problem. Its effects depend on the broader dietary and metabolic context, as well as an individual’s blood pressure, kidney function and salt sensitivity.

A dietary pattern that contributes to obesity, hypertension, insulin resistance and type 2 diabetes will inevitably have consequences for the kidneys. However, researchers suspect the relationship between ultra-processed food and kidney health may be more complicated than any single nutrient.

Some ultra-processed foods contain inorganic phosphate additives, which are more readily absorbed than the phosphorus naturally present in whole foods. Phosphorus is an essential mineral, but the kidneys help regulate its concentration in the blood. When kidney function is impaired, managing excess phosphorus can become more difficult.[5]

Importantly, phosphate additives may not be obvious to consumers because the total phosphorus content is not always clearly displayed on the label. Ingredients containing terms such as “phos” may indicate that a phosphate additive has been used.[5]

Other possible explanations include changes to the gut microbiome, inflammation, oxidative stress, and exposure to compounds introduced during manufacturing or through packaging. Foods engineered to be soft, convenient and difficult to stop eating may also encourage faster eating and greater energy intake before the body has had much opportunity to register that lunch has happened.[3]

The label on the front does not tell the whole story

Ultra-processed food does not always arrive wearing a neon sign announcing itself as junk food. Some products are marketed as “high protein”, “low fat”, “plant based”, “heart healthy” or “fortified with vitamins”. Those claims may be technically correct, but they do not necessarily tell us how the entire product was made or what else is in it.

A protein bar containing a long list of syrups, isolates, gums, sweeteners and flavourings may carry an impressive-looking health claim while bearing very little resemblance to any food found in nature. Adding a vitamin to a product does not automatically turn it into lunch.

This does not mean we need to become frightened of every packet, tin or frozen food. Packaging is not always the problem. Frozen vegetables, tinned fish, plain dairy products and minimally processed meats can all make nutritious eating more practical and affordable.

The more useful question is whether the product is still recognisably food, or whether food has become a minor ingredient in an industrial formulation.

What can we do?

The research does not give us grounds to promise that avoiding ultra-processed food will prevent kidney disease. It does, however, provide one more reason to build most meals around whole and minimally processed foods.

In practice, that means:

• Choosing water instead of sugary or artificially sweetened drinks.
• Using eggs, meat, fish or dairy products rather than relying on reconstituted “protein” products.
• Selecting vegetables in whatever practical form is available (fresh or frozen both count).
• Reading ingredient lists, not only the health claims on the front of the packet, and choosing those products with the shortest list (if any at all)
• Looking beyond calories and individual nutrients to consider what the product is actually made from.
• Cooking simple meals from recognisable ingredients whenever time and resources allow.
• Start reducing ultra-processed food from today rather than waiting for a perfectly organised kitchen and a free Sunday afternoon.

 

People with chronic kidney disease should seek individual advice from an appropriately qualified healthcare professional. Depending on kidney function, medication, blood pressure, and blood-test results, recommendations on protein, potassium, phosphorus, and fluid may differ. A generic internet “kidney diet”, however confidently presented, is not a replacement for personalised care.[1]

This Kidney Health Week, perhaps the most practical message is also the simplest: look after the organs you rarely think about by eating more food that does not require quite so much explanation.

Your kidneys may not be able to read an ingredient list, but they still have to deal with what is on it.

 

 

References

1. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4 Suppl):S117–S314. doi:10.1016/j.kint.2023.10.018.
2. Monteiro CA, Cannon G, Levy RB, Moubarac JC, Louzada MLC, Rauber F, et al. Ultra-processed foods: what they are and how to identify them. Public Health Nutr. 2019;22(5):936–41. doi:10.1017/S1368980018003762.
3. Lane MM, Gamage E, Du S, Ashtree DN, McGuinness AJ, Gauci S, et al. Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses. BMJ. 2024;384:e077310. doi:10.1136/bmj-2023-077310.
4. Sullivan VK, Appel LJ, Anderson CAM, Kim H, Unruh ML, Lash JP, et al. Ultra-processed foods and kidney disease progression, mortality, and cardiovascular disease risk in the CRIC Study. Am J Kidney Dis. 2023;82(2):202–12. doi:10.1053/j.ajkd.2023.01.452.
5. Benini O, D’Alessandro C, Gianfaldoni D, Cupisti A. Extra-phosphate load from food additives in commonly eaten foods: a real and insidious danger for renal patients. J Ren Nutr. 2011;21(4):303–8.