In the production of petfoods—no different than human foods—there are a number of compounds that make their way into the food that aren’t a part of the formula/recipe or stated on the ingredient listing. This is nothing underhanded or disingenuous, merely a function of the process, package and regulations. These compounds are often called “processing aids” because they make production of the food more effective. They appear in minute incidental quantities and do not impart any value to the food
Examples include things like carriers, flow aids and release agents. Other compounds in food may come from agents used in food contact surfaces such as detergents and biocides used in sanitation, gases used to flush oxygen from packages or barrier films impregnated with antioxidants to improve shelf-life.
In some cases, compounds used to produce the packaging itself can end up in the food. One such packaging compound that periodically lands in the newspapers’ health section headlines is bisphenol A (BPA). While most of these incidental compounds are quite safe, for BPA there is evidence that it may leach from the plastic packaging material into the food or drink and then impact health if exposure levels are excessive. The primary area of concern has surrounded bottles used for infant formula and soft drinks. Is there any cause for concern in petfoods?
Bisphenol A was first produced in 1891 from condensation of acetone (thus the “A”) with two phenol equivalents. Structurally, it looks a bit like a dumbbell with the two phenolic ends linked by an acetone handle. The “business end” of the molecule is the two phenolic groups.
On a global scale, BPA is produced in significant quantities, exceeding 60 million pounds annually. It has been used commercially since 1957, primarily in the production of polycarbonate plastics, epoxy resins, dental fillings, dental devices, sealants and carbonless copy paper. It is a precursor to one of the leading brominated flame retardants (tetrabromobispheonol A).
BPA functions as a “plasticizer” added to make plastics more resilient and pliable. The primary application is in clear plastic polycarbonate bottles used for infant formulas and soft drinks. In this capacity, it allows for the rigid polycarbonate to possess a certain degree of flexibility so that it doesn’t crack or break with the shifts and strains of everyday use and fluctuations in hot and cold temperatures. For petfood, the issue is its use in the epoxy resin that lines the inside of cans of wet petfood.
Due to its structural similarity to steroid hormones and research results with a wide variety of organisms, BPA has become known as an endocrine disrupting compound (often abbreviated as an EDC). This is due to its interaction with the endocrine system and interference with normal physiology of living organisms. It is thought to compete with steroid hormone receptors and transport proteins, alter endocrine feedback mechanisms and alter gene transcription and gene expression in cells. BPA is most disruptive during fetal development and continues to exert its impact through early post-natal maturation.
In experimental animals, BPA has been associated with prostate cancer, mammary gland cancer, urethral obstruction, decreased sperm count, early female puberty, oocyte chromosomal abnormalities, lack of sexual differentiation in the brain, increased body weight, insulin resistance, learning impairments and hyperactivity among many other conditions (Talsness et al., 2009). However, it must be kept in mind that most of this work has been conducted in laboratory rats, mice and amphibians at elevated dosages.
Based on this research, BPA is currently considered safe for humans at dosages of less than 50 ug per kg per day. No safe upper limit has been established for dogs or cats. The only evidence in pets comes from a 1984 Environmental Protection Agency study in Beagles which reported that feeding 9,000 mg/kg BPA for 90 days resulted in increased liver weight but had no effects at lesser amounts.
While these data would suggest BPA is safe for dogs and cats at levels much higher than humans, there are still concerns that it can leach out of the plastic resin in the can into wet petfood and over a lifetime of feeding have ill effects. Thermal processing temperature, makeup of the product contents, repeated container uses and pH swings are known to increase the amount of BPA that leaches from plastics.
In food contact surfaces, such as the resin in canned foods, the heating for retort sterilization can lead to measurable levels of BPA in the product contents. For example, Kang and Kondo (2002) reported that across a variety of wet petfoods, the BPA level ranged from 11 to 206 ng/g (parts per billion). How does that translate? At the extreme end of BPA content fed to the most vulnerable pet (3.5 kg lactating cat with 4 kittens), that would equate to consumption of 28.43 ug per kg per day—an amount about half that considered to be safe for humans.
At present, BPA is being evaluated by the Food and Drug Administration and other regulatory agencies around the world. It is allowed by most countries in plastics used in food contact surfaces, but FDA has recently provided recommendations to reduce the use of BPA plastics in infant bottles and food cups pending final rulings. FDA is working to assimilate evidence to determine what a safe level might be and actively supporting and funding research to develop alternatives to BPA.
While alternatives to BPA resins are becoming available, the cost and limited data on their efficacy are significant hurdles to widespread use. So, finding a universal alternative may be a long time in coming. Until then, the prevailing evidence would suggest that BPA levels in wet petfoods are within the boundary of what is considered safe.
Read more columns by Dr. Aldrich.
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