A Scientific Review of Clean Label Project’s Report on Heavy Metals in Dog Food

Recently, the Clean Label Project (CLP) released a report alleging concerning levels of heavy metals and other contaminants in commercially available pet foods. Given the potential impact such claims may have on pet owners, veterinarians, and the broader pet food industry, the methodology, transparency, and scientific validity of this report must be carefully examined.  

While consumer safety and contaminant monitoring are critically important components of responsible pet food production, conclusions that influence purchasing decisions should be grounded in rigorous, peer-reviewed science and free from conflicts of interest. The following evaluation assesses the CLP report’s stated mission, research design, data interpretation, and the broader context of established toxicological thresholds for domestic animals. 

The Clean Label Project 

As far back as 2017, the not-for-profit Clean Label Project has claimed its mission is to “educate the consumer so they can make informed choices on cleaner options every time they shop.” It is important to note there is no regulatory definition for what a “clean label” is. This means it is an arbitrary term that is open for interpretation.  

In 2017, CLP surveyed pet parents to assess a possible link between pet food and cancer in pets. Jaclyn Bowen, Former Executive Director of CLP, stated their intention was “to use this data to identify systematic relationships between brands of pet food and the incidence of cancer using both anecdotal reports from pet owners and our own analytical chemistry data on the presence of known or suspected carcinogens on pet food products.”  

Unfortunately, the described survey relied entirely on pet parents uploading their pet’s medical histories and the type of food they ate. There was no mention of how medical diagnoses, treatment of the medical condition, or the pet’s diet were verified. This type of research leaves too many unaccounted-for variables, making it nearly impossible to draw any reliable scientific conclusions. In other words, it would be completely useless as sound research for the stated purpose of trying to identify if certain pet foods were correlated to cancer in pets. 

Heavy Metal Contamination in Question 

CLP claims to have conducted over 11,000 tests on pet food for heavy metals (including lead, cadmium, arsenic, and mercury), as well as bisphenols, phthalates, acrylamide, pesticides, and glyphosate. It claims to have tested tested 50 dry dog foods, 11 air-dried/freeze-dried dog foods, and 18 fresh/frozen dog foods out of the “79 top-selling” dog foods but does not say what data was used to determine which brands to test. It states that sources such as Nielsen, SPINS, Amazon, and others were used to determine which foods to test.  

Interestingly, the CLP FAQ states that the CLP study is not peer-reviewed because “it can take years” to complete. It is universally accepted in the scientific community that all credible research should undergo peer review,as it is our only tool to evaluate whether the research and the conclusions drawn are valid or flawed. It is okay to share preliminary, well-vetted research findings; still, evaluations by other research scientists are critical to determine the validity of findings. Since this CLP study has not undergone peer review of the data, it is impossible to validate any conclusions made from it. 

It is also noted that, although CLP claims to be a non-profit, it completes all testing at “an independent third-party laboratory” named Ellipse Analytics, which promotes CLP on its website. While third-party testing can be valuable, public cross-promotion between an organization and its testing partner can create perceived conflicts of interest and should be clearly disclosed and managed. 

Additional context around CLP’s survey methodology also raises questions about potential conflicts of interest. CLP included links in its online pet cancer survey that asked pet parents to donate to its cause. Additionally,CLP included links directing survey takers to purchase pet food through Amazon affiliate links. When consumers used these links to purchase certain pet foods, even those classified as “low-rated,” CLP reportedly received a commission (approximately 4%) on those sales. This creates a situation in which the organization may financially benefit from consumer purchasing behavior influenced by its own rating system. 

Conflicts of Interest Continue 

CLP also operates a SKU-level certification program. On its website, it states the program “is funded by a mix of donations, grants, and certification fees from brands that display the CLP mark on products that have been independently tested and evaluated to meet our standards.” Currently, only one complete-and-balanced pet food brand seems to have this certification, and, interestingly enough, it is among CLP’s “Clean Sixteen” top pet food brands reported to have the lowest levels of contamination. 

Furthermore, the heavy metals study report compared three dog food categories overall, reporting heavy metals, phthalate, and acrylamide findings at the highest and average levels in each diet category. The study goes on to then conclude that the fresh/frozen diet category is superior because both the highest sample and average values of the dry and air dried/freeze dried categories depicted “exceedingly high amounts of arsenic, cadmium, mercury and lead… because there are few regulations for dog food related to contaminants.” 

It also stated that results were compared to more than 3,000 in human food, beverage, and supplement samples, illustrating the elevated contaminant levels in dog food compared to human-consumable products. The problem with this statement is that the human consumable products in question were not disclosed. Comparing complete-and-balanced pet foods to unnamed human foods is an irrelevant comparison, because there’snothing to base a conclusion upon. 

Uncontrolled Variables Mean Untrustworthy Results 

A closer evaluation of CLP’s comparison of the three diet categories reveals several uncontrolled variables that limit the conclusions' validity. One of those is very large moisture differences in the diet categories, which can drastically change the values of tested analytes. It is well-accepted that all pet food must be compared on a dry matter basis (accounting for high moisture in some formats, such as fresh/frozen and canned food) for nutritional analyses to be comparable across formats. This is known as an uncontrolled variable in research, and when present in a research summary, it confounds the conclusions and makes them useless. 

This study also does not disclose where most of the “contaminants” in pet food actually come from. For instance, it is well known that some ocean fish higher on the food chain may contain higher levels of heavy metals than poultry. This is well known, so if we wanted to compare diets with different proteins, it would not be valid to compare an ocean fish-based diet to a poultry diet. This is another uncontrolled variable in the CLP study.Also, the fact that the three diet categories were not comprised of the same number of diets is another uncontrolled-for or confounding variable that questions the validity of the reported values. 

Further review of CLP’s website reveals a “Dog Food Contaminant Predictor.” CLP touts this self-described tool for consumers as being able to “predict” the “contaminants” in a pet food simply by a consumer typing a pet food ingredient list into the website. However, there is no credible way to predict the concentrations of heavy metals or other compounds from ingredient lists. Ingredients with the same name (i.e., wheat flour) may come from different ingredient suppliers, be grown and harvested in different parts of the world or different seasons of the year and may come from different varieties of the same ingredient name. All of these factors may affect levels of any elements, compounds, or nutrients in the ingredient.  

To promote the idea that typing an ingredient list for a pet food into an online tool can accurately provide this information is highly misleading to pet food consumers. The only way to truly predict any element or compound in a pet food is to analyze the raw ingredients used to make it and use that information, along with finished product analyses, to validate accurate values. This “contaminant predictor” has the potential to give misleading and unfounded information to pet food consumers about the diets they are feeding.  

‘Clean Sixteen’  

To test this theory, the ingredient declarations of the CLP’s proclaimed “Clean Sixteen” dog foods were typed into the Dog Food Contaminant Predictor tool. CLP describes these foods as “2026’s highest-rated dog foods for purity.” When using ingredient declarations for these 16 diets from the manufacturer’s websites, the Dog Food Contaminant Predictor ranks them for each “contaminant” with the following scores: elevated, moderate, low/trace, and clean. It is unknown how each score description term was determined, as CLP does not share that information. 

Plugging the ingredient declarations in for each of the “Clean Sixteen” diets gave the following results: 

• Acrylamide: elevated for all 16 diets 

• Arsenic: elevated for two diets; moderate for 11; low/trace for two; clean for one 

• Cadmium: elevated for three, moderate for 10, low/trace for three 

• Glyphosate: elevated for all 16 diets 

• Bisphenols: elevated for all 16 diets 

• Pesticides: elevated for all 16 diets 

• Mercury: elevated for three, moderate for 13 

• Lead: elevated for two, moderate for 12, low/trace for one, clean for one 

After performing this exercise, it is hard to understand how CLP could claim diets to be “clean” (which is still an arbitrary term) when very few of them scored on the “low/trace” or “clean” end of their unexplained rating system for the elements and chemicals measured. This suggests the “Dog Food Contaminant Predictor” is nothing more than an arbitrary system that could very easily mislead consumers into thinking a diet is unsafe.There is simply no visible or reviewed evidence to prove this tool is helpful, and this may actually be harmful to pet parents. 

Understanding Toxicology 

One of the worst conclusions observed in the review of this study centers on the heavy metal values reported and the CLP’s concern about their values in the dry and air-dried/freeze-dried categories. Analytical techniques can detect extremely small amounts of these compounds, and the fact that they are present does not necessarily mean they are at levels that cause health concerns. It is important to keep in mind that, to date, it is unknown what level would be considered normal or safe for these heavy metals in pet food.  

On the surface, having heavy metals detected in pet food sounds scary to pet food consumers; but one has to remember that heavy metals are naturally present in the soil, oceans, and even the atmosphere, all of which constitute where our food is grown and harvested. This means heavy metals are unavoidable to some degree and will be detectable in most human and pet foods. While surveillance of environmental contaminants is important, interpretation of such findings must occur within established toxicological frameworks.  

In clinical toxicology, dose, bioavailability, duration of exposure, and species-specific tolerance are central to risk assessment. The CLP report claims arsenic was almost 12-times higher in dry food than in fresh/frozen, yet the highest value listed for arsenic in the dry pet food category is 442.3 parts per billion (ppb). Mineral Tolerance of Animals, published by the National Research Council (NRC), states that the accepted level of arsenic(Maximum Tolerable Level or MTL) in domestic animal diets is 30,000 ppb. This means that the highest reported arsenic level among all the dry pet foods tested is still more than 65-times below the NRC's recommended maximum tolerable level (MTL) for arsenic in domestic animal feed. 

Similarly, reported cadmium concentrations (~154 ppb) are substantially below the 10,000 ppb level at which adverse effects have been documented in dogs; reported mercury levels (~35 ppb) fall far below the 1,000 ppbtolerance for inorganic mercury; and the highest reported lead value (~985 ppb) remains well under the NRC’s MTL of 10,000 ppb. Based on currently established NRC MTLs, values reported by CLP do not even approach concentrations associated with adverse effects in dogs. Ongoing contaminant monitoring and regulatory oversight remain important, but conclusions regarding safety should be anchored to validated toxicologicalthresholds rather than analytical detectability alone.  

Additionally, CLP analyzed for phthalate di(2-ethylhexyl)phthalate (DEHP), which is a chemical used to make plastic. The US Food and Drug Administration (FDA) recently evaluated the safety of phthalates used in plastic materials that come into contact with food. At this time, the FDA does not have a safe upper limit for phthalates in human or pet food, but is encouraging packaging and food manufacturers to use alternative plastic materials in packaging that comes into direct contact with food. This study cited the highest tested DEHP value at 570 ppb in the dry food category, and classifies this level as concerning without providing any basis for what an acceptable level of DEHP would be. Sound research should be performed to better understand the health implications of DEHP, but this study does not provide that. 

Finally, CLP analyzed for acrylamides. Acrylamides form during the cooking process, resulting from reactions between amino acids in protein- and starch-containing ingredients, such as those found in pet food. The CLP study stated the dry food category had the highest tested level at 570 ppb. The FDA does not have limits on acrylamide levels in pet food. However, research that is available suggests that pet foods with up to 7,000 ppb of acrylamide are acceptable. Still, more research is needed to understand what, if any, level is detrimental in pet or even human food.  But again, this study does not provide that. 

Don’t Take This Study at Face Value 

In summary, the report detected trace environmental minerals at levels far below established safety limits. There is no credible evidence that these foods pose a health risk, and the CLP report lacks almost all scientific rigor. It is impossible to tell whether the shared data is valuable because of the too-numerous-to-count research flaws, incomplete data reporting, lack of identification of the human foods tested, and the staggering amountof confounding variables. 

This research offers little-to-no value in its claim to help inform pet food consumers. What it does is draw a link between CLP, Ellipse Analytics, and a certification program that pet food companies can pay for to have their products listed if they meet non-regulatory, CLP-defined “clean” criteria. This may be viewed as a direct conflict of interest between the “research”, how it is communicated, the conclusions drawn from it and business goals of all entities involved . 

It is always good for nutrition research to continue in the pet industry, and this includes sound research in evaluating compounds and elements to better determine safe maximum levels. What isn’t good is promoting non-transparent data disguised as research in a way that can mislead pet parents into switching from perfectly safe, wholesome products they may currently be feeding their pets.  It is important when performing research to work with experienced experts like those at BSM Partners that understand how to conduct, interpret and write about research in a credible manner that follows accepted scientific rigor principles. 

Follow us on LinkedIn for the latest updates on all things happening here at BSM Partners.

About the Author

Dr. Bradley Quest, DVM, is the Principal Veterinarian at BSM Partners. Dr. Quest is a leading innovator in the pet dental health products, having several decades of experience formulating in this category. He has practiced clinical veterinary medicine, developed and tested hundreds of pet food and health products, performs extensive animal health research, and helps navigate pet food ingredient approval for clients.