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  • Writer's pictureDr Meredith Wall

In depth: Ingredients vs. nutrients in pet food + some Michael Pollan

Updated: Dec 20, 2023

To begin, here is a link to read Michael Pollan's essay titled 'Unhappy Meals', which was published in the New York Times magazine in 2007. It's quite a long article, but definitely well-written and very interesting.

It provides the perfect platform from which to discuss the ingredients vs. nutrient debate that comes up so often in the world of pet food, so please do give it a read.

I know we are all very busy though, so if you can't squeeze it in - here's a brief summary of the key points. Pollan begins with his now-famous statement; 'Eat food. Not too much. Mostly plants.'

This is apparently 'the short answer to the supposedly incredibly complicated and confusing question of what we humans should eat in order to be maximally healthy.' From this starting point, he gives us an overview of (some of) the history of nutritional science, and the gradual movement away from eating simple whole foods, described as 'coarse, old-fashioned and decidedly unscientific things', towards a focus on the nutrients within those foods.

Pollan terms this 'the rise of nutritionism', which he describes as an ideology:

In the case of nutritionism, the widely shared but unexamined assumption is that the key to understanding food is indeed the nutrient. From this basic premise flow several others. Since nutrients, as compared with foods, are invisible and therefore slightly mysterious, it falls to the scientists (and to the journalists through whom the scientists speak) to explain the hidden reality of foods to us. To enter a world in which you dine on unseen nutrients, you need lots of expert help.

One of the problems with this, according to Pollan, is that 'any qualitative distinctions between processed foods and whole foods disappear when your focus is on quantifying the nutrients they contain (or, more precisely, the known nutrients).' Another key problem is that a focus on nutrients (rather than foods) has, unfortunately, led us astray in the past. A 1977 document prepared by a Senate Select Committee on Nutrition, titled "Dietary Goals for the United States", advised Americans to minimise consumption of saturated fat (which they did). As we all know, obesity and chronic disease increased following this recommendation, as did consumption of sugar and trans fats.

Kellogg's rice krispies with false health claim on box
This antioxidant, nutrient and immunity health claim cost Kellogg's $5 million as part of a class action in the U.S. District Court Central District. of California

Not content with taking aim at policy makers and food manufacturers, Pollan then turns his attention to nutritionists themselves - pointing out that nutritional research is often deeply flawed, because it focuses on one nutrient at a time. He quotes Marion Nestle, a nutritionist from New York University: 'The problem with nutrient-by-nutrient nutrition science is that it takes the nutrient out of the context of food, the food out of the context of diet and the diet out of the context of lifestyle.' Whilst this is often the only way nutritionists can study individual variables, it overlooks the complexity of the food itself, the complexity of the human consuming it, and also the interactions between different foods consumed together.

Spinach and orange salad
Vitamin C from citrus fruits like orange or lemon can enhance absorption of non-heme iron in leafy greens like spinach.

The essay goes on to make further points about the problems inherent in nutritional research. Pollan then makes this statement, which is an important one to consider:

No one likes to admit that his or her best efforts at understanding and solving a problem have actually made the problem worse, but that’s exactly what has happened in the case of nutritionism. Scientists operating with the best of intentions, using the best tools at their disposal, have taught us to look at food in a way that has diminished our pleasure in eating it while doing little or nothing to improve our health. Perhaps what we need now is a broader, less reductive view of what food is, one that is at once more ecological and cultural.

In the interests of succinctness, I won't discuss more of the essay, except to say that it finishes with nine practical 'guidelines' for healthy eating, which I personally think are pretty sound. Again, it's a piece of writing that's well worth reading - but how does it relate to pet food? And why would I (a nutritionist) be so interested in it? After all, Pollan spends about 75% of the article putting the boot into nutritional science and everything it has supposedly 'accomplished'.

First of all, do I agree with Pollan's arguments? In the context of human nutrition, by and large - yes. I think he makes a lot of valid points. Arguing for a return to diversification instead of the industrial simplification of food and agriculture, for a return to culture and cooking, for the appreciation of flavour and the pleasure of eating, and for the benefits of gardening and growing - it's all brilliant stuff, without a doubt.

Like anything though, it's not that simple, and I do think Pollan comes down too hard on the field of nutritional science. To state that it has done little or nothing to improve our health is perhaps a little harsh, because it ignores some of the ground-breaking research that has been done. The work of Lucy Hills in the 1930s and subsequent researchers in the 1960s revealed the important role folic acid has in preventing neural tube defects. In 1938, Richard Kuhn was awarded the Nobel Prize in Chemistry for his work on carotenoids and vitamins, specifically vitamin B2 and B6. In 1943, Edward Adelbert Doisy and Henrik Dam were awarded the Nobel Prize in Physiology or Medicine for their discovery of vitamin K and its chemical structure. Contributions like this should be considered with respect; they are great achievements.

Another problem with Pollan's essay is that the arguments he makes are valid, but he makes these arguments from a position of privilege and education - and as a reader, I also agree with them from the same position of privilege and education. To tell someone to eat mostly plants is good advice, but it assumes that this person has enough knowledge about food and nutrition not to give themselves a severe vitamin B12 or iron deficiency by eating a poor-quality vegan diet. When I read this essay, I'm considering it as someone who has bookcases full of cookbooks and nutrition textbooks. I read nutrition-related research, I garden, I learn about soil health and farming, and I travel and enjoy the food of many different countries and cultures. If only everyone could be so lucky.

So when we consider pet food, and the ingredients vs. nutrients question, this also applies. Not everyone has the background knowledge to feed their pets a healthy, balanced diet by selecting appropriate whole foods. In fact, this sometimes goes very wrong. We routinely see cases where the pet's owner is going to a huge amount of trouble to feed their pet 'the best and healthiest ingredients'. Here's an example of what one owner was feeding their 5 month old Rottweiler puppy for dinner every night:

One cup lightly cooked pumpkin, grated raw carrot/celery/cabbage/broccoli, one small skinless chicken breast, 30 grams of blueberries, two spoonfuls of goat's milk yoghurt, a teaspoon of maca powder, a teaspoon of turmeric, and a tablespoon of coconut oil.

And this is what that puppy's front legs look like:

This is not the actual pup in question, but it shows what rickets looks like in a growing dog.

In this case, the pup has developed a skeletal deformity called rickets, due to severe vitamin D and calcium deficiency. It was also very underweight, had multiple rib fractures, skin disease, and some concerning neurological signs. Euthanasia was the end result for this pup - entirely preventable, if a complete and balanced diet had been fed.

Sadly, this has become more common as pet owners reject the concept of nutritional requirements and focus solely on feeding desirable ingredients or 'superfoods'. When you google 'ingredients vs. nutrients in pet food', you come across veterinary nutritionist Dr Lisa Freeman's blog post, titled 'Stop reading your pet food ingredient list!' I suspect it's cases like the one above that prompted Freeman to write the post - for which she received some fairly unpleasant criticism online. Freeman correctly points out that reading the ingredients list on a bag of pet food tells you almost nothing about whether that food is well-formulated and nutritionally complete - and this is a really important point to remember, if even you don't agree with some of her other comments.

So I hope what you can see from the example above is that ignoring what we know about canine or feline nutrition can be harmful. There's no reason to do this - why dismiss decades of nutritional research that has made some really important advances? We certainly don't know everything, but we do know some minimum requirements for essential vitamins and minerals, and we do know some safe upper limits for these nutrients too. However, we can see that Dr Freeman's position is in opposition to the recommendations given by Michael Pollan in his article. One school of thought is telling us to prioritise nutrients, the other, ingredients. Confusing indeed.

Combine this with the current pushback against processed foods for humans, and it becomes even more confusing. Should we avoid any pet foods that are processed, even though they are complete and balanced? Aren't almost all diets for pets processed, for example, kibble, or air-dried diets, or canned diets? Are processed pet foods the same as processed human foods?

Are these ultra-processed pop tarts the same as a bag of kibble for a dog? The kibble is perhaps a bit more akin to processed foods developed by NASA for consumption by astronauts. Attention must be given to meeting the astronaut's nutritional requirements, while ensuring that the food is appropriate for space travel - lightweight, easily prepared and palatable. Ultra-processed foods for humans are not generally formulated to provide complete nutrition - whereas most pet foods are. Therefore, the argument that processed foods for humans = bad, so processed foods for pets also = bad, isn't very sound.

In his essay, Pollan makes this comment on processed human foods: 'Processing foods depletes them of many nutrients, a few of which are then added back in through “fortification”: folic acid in refined flour, vitamins and minerals in breakfast cereal. But food scientists can add back only the nutrients food scientists recognize as important. What are they overlooking?' This gets to the heart of why we might argue for the importance of ingredients in both human food and pet food. I think perhaps what it is more relevant than what food scientists are overlooking, is what they don't know yet. In my opinion, this is the most powerful reason to focus on the ingredients (and how they are prepared) - as well as the nutrients - when considering any diet.

As Pollan pointed out, unfortunately nutritional science is difficult and extremely complex. Even though great work has been done on vitamins and minerals, on amino acids and fatty acids - there's undoubtedly more to learn. The humble broccoli contains a range of vitamins and minerals, but it also contains different types of fibre, and a huge number of phenolic compounds such as flavonoids and hydroxycinnamic acids. We know little to nothing of what these compounds actually do, how they interact, or how they affect the gut microflora. We don't know a lot about how cooking and processing affects all these compounds, or whether any or all of them are important for optimal health.

However, research has demonstrated some interesting examples of the benefits of consuming whole foods. A 2016 meta-analysis by He et al. found that higher consumption of whole oats and oat bran, but not oat or barley beta-glucan extracts, was associated with lower HbA1c, fasting glucose and fasting insulin in type 2 diabetic, hyperlipidaemic and overweight subjects. Another 2019 study by Kristek at al. found something similar; that 'oat bran, but not its isolated bioactive beta-glucans or polyphenols, has a bifidogenic effect in an in vitro fermentation model of the gut microbiota'. These studies appear to hint at the possible benefits of whole foods and of particular nutrients or compounds having a synergistic effect. However, if you are looking for one study that proves that eating whole foods is better than eating a processed diet, you won't find it - we only have the puzzle pieces to consider, at the moment.

Perhaps this research does indicate, though, that we shouldn't assume that we know everything there is to know about a broccoli or an oat, from a nutritional perspective? I would rather listen to the guidance of Socrates ('wisest is he who knows he does not know') and hedge my bets. Like everything in the world of nutrition, the middle road is the one I'm taking here, because I do think there is evidence to suggest that we have more to learn about both human and pet nutrition.

Similar to Pollan's essay, I'm going to include two points of a more practical nature to finish:

1) What to do if you are worried about the nutrients in your pet's diet:

  • Ensure that the diet is formulated to meet AAFCO minimum requirements or FEDIAF guidelines. Check on the packaging for this claim, and/or the company's website. If it's not there, ask the company. AAFCO and FEDIAF guidelines are not perfect and they do lack completeness, but they are the best we have.

  • Make sure you are feeding your pet a diet appropriate for their life stage (growth/reproduction or adult maintenance).

  • If you are worried about specific nutrients in the diet (for example, fat, phosphorus, protein, sodium, calcium etc), feed a prescription diet, if you can. Relying on information from guaranteed analyses for supermarket and pet store diets can be unreliable and confusing.

2) What to do if you are worried about the ingredients in your pet's diet:

  • Consider feeding a well-formulated homemade diet - if you go with this option, you can select preferred ingredients for your pet and also ensure that the diet meets essential nutrient requirements. Veterinary nutritionists in the USA (UC Davis, Tufts etc) can offer this service, or we can help too. Don't feed a poorly formulated diet (commercial or homemade) based solely on the inclusion of 'healthy ingredients' or 'superfoods', or you may cause considerable harm to your pet.

  • There are a huge number of different types of commercial diets available, with very different ingredient profiles. Do some browsing and find options you are happy with - then make sure the diet/s also have an AAFCO or FEDIAF claim. You don't have to feed kibble - you can tried a canned diet, a freeze-dried diet, or a fresh-cooked diet.

  • If you feed treats or toppers, make them nutritious additions to the diet. Some good options are non-starchy steamed or raw vegetables, boneless oily fish or other seafood, or lean grass-fed meats like kangaroo or venison. Don't feed more than 10% of daily calories as treats, and remember that keeping your pet lean is very important.

  • If your pet needs a prescription diet and you are worried about the ingredients, please don't let this deter you from at least trying the diet for your pet. This is a common problem we encounter. Some pet owners would actually prefer to accept that their pet's lifespan is likely to be shorter, than feed a commercial prescription diet - because they think the ingredients are too off-putting. This is sad, because there is good evidence to support the use of many of these diets, and whilst the ingredients may not sound appealing, they are carefully selected to ensure that key nutritional goals are met. Consider a diet used successfully for many critically ill human patients, and its ingredient list:

Water, maltodextrin, vegetable oils (sunflower oil, rapeseed oil, MCT oil (coconut oil, palm kernel oil)), whey protein (from cow’s milk) cow’s milk protein caseinate, dietary fibres (inulin, oligofructose, arabic gum, soy polysaccharides, cellulose, resistant starch), pea protein, soy protein, fish oil, potassium citrate, emulsifier (soy lecithin), magnesium hydrogen phosphate, calcium carbonate, potassium hydroxide, carotenoids (b-carotene, lutein, lycopene), sodium chloride, choline chloride, potassium chloride, sodium L-ascorbate, di potassium hydrogen phosphate, ferrous lactate, zinc sulphate, nicotinamide, retinyl acetate, DL-a tocopheryl acetate, copper gluconate, manganese sulphate, sodium selenite, calcium D-pantothenate, cholecalciferol, chromium chloride, D-biotin, thiamin hydrochloride, pteroylmonoglutamic acid, pyridoxine hydrochloride, riboflavin, potassium iodide, sodium fluoride, sodium molybdate, phytomenadione, cyanocobalamin.

These ingredients aren't naturally appealing either, are they? Yet the use of these diets prolongs lifespan, speeds up recovery, improves wound healing and maintains gastrointestinal health, and there is a lot of evidence to support their use. Remember these diets are a form of medical treatment, just like prescribing medication.

So, let's not ignore what we know about the nutrient requirements of dogs and cats - even though it's limited, it's the best we have and it's still extremely helpful. But let's also remember the potential benefits of eating whole foods; of focusing on the ingredients as well as the nutrients. This surely gives us the best chance to feed our pets as well as we possibly can.

Any questions or feedback always welcome:

Read the full paper by Kristek at al. here:

Read the full paper by He et al. here:

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