Ultra-processed pet food: natural vs synthetic nutrients

In our last blog, we spoke about how, by definition, traditional kibbles and canned food are ultra-processed and that nutrients are lost during processing. What manufacturers do to ensure that the diets are complete and balanced is by supplementing with additional vitamins, minerals and sometimes, amino acids. Opponents of these diets state that the added nutrients are usually synthetic (meaning they are manufactured in a lab or in an industrial setting), and therefore undesirable. Instead, they say, feeding a varied diet with natural nutrients is better.

No doubt, getting all of the nutrients our body needs from food is clearly ideal … but in reality, how practical is it? And if in some circumstance it’s not, what are our options?  

I’m going to start by spending some time talking about human nutrition because I think it’s helpful to describe things in a way that is relatable. This was my diet the other day - which equalled about 1900 calories.

I tried hard, making sure I got a nice mix of vegetables, some leafy greens, fruits, whole grains, pulses, and lean meats. I’ve also had nuts and avocado, as well as some dairy products because I know it's difficult to get enough calcium.

The nutrients I got from eating these foods were naturally derived, as they came from the foods themselves. In an ideal world, we could all do this, eat whole foods, mostly plants, and get everything we need from them. But how did I do with my diet when compared to daily nutrient recommendations? Surprisingly average.

I took the Nutrient Reference Values for Australia and New Zealand which are a set of recommendations for daily nutrient intake and compared it to what I ate. These recommendations are similar to the USDA dietary guidelines for Americans. Out of the 29 essential nutrients, I ate too little of 5 of them - calcium, folate, iron, vitamin D, and iodine.

Vitamin D I might get a pass, just because I live in Sydney and get a fair share of sunlight on a daily basis. But if I lived in the UK, in winter, that would be another story. Another 7 essential nutrients I just skirted over, either nearly meeting the recommended amount, or I surpassed it by only a little bit. So, in total, 40% of my essential nutrients were dodgy or close to being dodgy. And remember, this was me trying!

There seems to be a misconception that humans eat a varied diet and if you eat one that is healthy, you’ll be fine nutritionally, but that’s not always the case. Nutrient deficiencies are common, even in first world countries. The World Health Organization found that iron, vitamin A and iodine are the most common nutrient deficiencies globally (1). I guess it's not too surprising that two of the three on the WHO’s list were on my list of deficient nutrients too! It’s hard to get this right.

A varied diet undoubtedly helps with this, as maybe the next day I’ll get enough calcium and iodine, but zinc might be low. For healthy people, and healthy pets, this is fine. But when there is disease, or other conditions where you need to be confident about what you’re eating (or what you’re feeding), that’s when it gets tricky.

Supplementing comes in as being an important nutritional support to fill in these gaps. This can be done with concentrated food ingredients or synthetic nutrients. Concentrated food ingredients providing natural nutrients are, again, the preferrable thing. As long as they actually contain the nutrients you’re needing. Kelp, for instance, is natural source of iodine, but how much iodine they contain depends on the species, location, season, and even which part of the plant is harvested (2). Beef and lamb livers are often used in pet diets because they are rich in minerals - but how much they contain too can vary depending on the age of the animal, location of the farm, and whether they are given supplemented feeds by farmers (3, 4). With synthetic nutrients, the amount is at least standardized so you know how much you’re giving.

The amount of iodine in kelp can vary from very little to potentially toxic doses.

What are the other positives and negatives of synthetic nutrients? I’ve heard of concerns regarding the isolation of synthetic nutrients and how they are not absorbed as well as natural sources. The evidence is mixed on this topic, with some nutrients more clear cut than others. For example, it is accepted that synthetic vitamin E (alpha-tocopherol) is only about 70% as bioavailable as natural vitamin E. Whereas vitamin C, the difference is not thought to be biologically significant. So, to take that argument into account, each nutrient should be considered, instead of brandishing a broad brush on all synthetic nutrients.

Another feature of synthetic nutrients is that they are high in potency because of their concentration. This is an important benefit because that means the volume you need to give can be much less than from the food form.

For instance, giving 200 grams of sunflower seeds would only equal a third of the amount of vitamin E in this capsule – even considering the differences in bioavailability, there is a significant difference in volume between these two!

There are concerns though that the higher potency of synthetic nutrients can cause a risk of toxicity. However, that could be true for natural sources of nutrients too, such as giving a toxic dose of vitamin A by giving too much liver. So, it’s not an exclusive concern for synthetic nutrients.

So, when are synthetic nutrients useful?

• Older animals where volume becomes an issue. They are eating less, so volume can be an issue, and they need to be eating nutrient dense foods.  

• Picky eaters or those on a restricted diet, such as pets with food sensitivities. They’re not able to vary their diets as often, if at all. It isn’t easy for everyone to source emu liver.  
  

Other times when dose is important.

• Vitamin B12 in pets with GI disease who have hypocobalaminaemia. You don’t want to be messing around with nutrient variations.
  

• Calcium in large breed puppies. These guys are at risk of developmental orthopaedic disease, so you want to be certain how much calcium they are getting. Bone can be given, but it needs to be finely ground as the size of the bone pieces can greatly affect digestion and absorption. It's not something you want to mess around with or just guesstimate.

As with so many things in life, there are nuances to these discussions. While obtaining all our nutrients through our food and not needing supplementation would be ideal, it is difficult to do all the time. This is okay for healthy humans and for healthy pets, if you can feed a varied, nutrient-dense diet, but it’s tricker for the young, the old and those with certain medical conditions. In those cases, synthetic nutrients can have an important role to play.

1. https://www.who.int/news-room/fact-sheets/detail/malnutrition

2. Teas, J., Pino, S., Critchley, A., & Braverman, L. E. (2004). Variability of iodine content in common commercially available edible seaweeds. Thyroid : Official Journal of the American Thyroid Association, 14(10), 836–841. https://doi.org/10.1089/thy.2004.14.836 

3. Puschner, B., Thurmond, M. C., & Choi, Y.-K. (2004). Influence of Age and Production Type on Liver Copper Concentrations in Calves. Journal of Veterinary Diagnostic Investigation, 16(5), 382–387. https://doi.org/10.1177/104063870401600503

4. Miranda, M., Cruz, J. M., López-Alonso, M., & Benedito, J. L. (2006). Variations in liver and blood copper concentrations in young beef cattle raised in north-west Spain: Associations with breed, sex, age and season. Animal Science, 82(2), 253–258. https://doi.org/10.1079/asc200522