Why "limited ingredient diet" has become almost meaningless

by Ben, co-founder

Walk down the dog food aisle in any pet shop and you'll see the same three words on bag after bag: limited ingredient diet. LID, for short. The implication is obvious. Fewer ingredients, less chance your dog reacts to something. Safer. Simpler. Better.

There's a problem with that promise. It isn't one.

There's no legal definition of "limited ingredient diet" in the UK, the EU, or the US. None of the regulatory bodies that govern pet food labelling - FEDIAF here, AAFCO across the Atlantic - have a standard for what the term means or doesn't mean. A brand can put it on a bag with 5 ingredients or 35. Both are legal. Both happen.

The next time you're looking at a "limited ingredient" bag, do the simplest possible test: turn it over and count.

Most "LID" foods aren't limited at all

Pick up most so-called LID kibbles and you'll find 20 to 40 ingredients on the back panel. A protein source, a carbohydrate source, then a long tail of fats, fibres, vitamins, minerals, preservatives, palatability enhancers, and what the industry calls "functional ingredients" - chicory root, yeast cell wall, herbs, supplements.

The marketing framing is that the protein and carb are limited. One protein, one carb. Everything else is "support". The trouble is that the other 30-odd ingredients can also trigger reactions in a sensitive dog. Yeast, peas, beet pulp, alfalfa, brewer's yeast, flaxseed - none of them are inert. Plenty of dogs react to them.

If the goal of an LID is to reduce the number of things your dog is exposed to, calling something "limited" because two of those things are labelled and the other thirty aren't isn't limiting much.

Then there's what's in the bag that isn't on the label

This is where it goes from misleading to actually documented.

In 2011, Raditic and colleagues tested four commercial dry dog foods marketed for use in dietary elimination trials. ELISA testing - which detects specific proteins - found that three of the four contained proteins not listed on the label. One of them, marketed as containing only venison, contained detectable levels of beef, chicken, and soy. (Raditic, Remillard & Tater, Journal of Animal Physiology and Animal Nutrition, 2011.)

That was a small sample. But the pattern keeps repeating in larger ones.

In 2014, Willis-Mahn and colleagues tested 12 dry dog foods marketed for elimination trials and found soy in 4 that didn't declare it on the label. (Journal of the American Animal Hospital Association.)

In 2018, Ricci and colleagues at the University of Padua used PCR to test 12 dry dog foods - some over-the-counter, some prescription, some marketed as hypoallergenic. Ten of them contained DNA from animal species that weren't on the label. (Veterinary Research Communications.)

These weren't all consumer "LID" brands. Some were prescription veterinary diets sold for dogs already diagnosed with food allergies. If those can't keep cross-contamination out, the bag with the leaf graphic and the "single protein" claim on a supermarket shelf certainly isn't more rigorous.

Why this happens

Most dog food in the UK is contract-manufactured. A handful of factories produce kibble for dozens of brands. The same extruder that runs a chicken-and-rice formula in the morning runs a venison-and-sweet-potato formula in the afternoon. Between runs there's a flush, but a flush isn't a sterilisation. Trace residue makes it through.

For most dogs this doesn't matter. They don't notice. For a dog with a genuine adverse food reaction, even trace amounts can trigger a response. Which is the whole point of the diet in the first place.

This is why veterinary dermatologists running elimination trials usually recommend either a hydrolysed protein diet - where the proteins are broken into fragments too small for the immune system to recognise - or a home-cooked novel protein diet where you control the inputs. Off-the-shelf "limited ingredient" food, even from premium brands, can't be relied on for that purpose.

What "novel protein" actually means

Novel protein means a protein your dog hasn't been exposed to before. The clinical use of the term comes from the elimination diet. If your dog has spent its whole life eating chicken and beef, you pick a protein it hasn't met (venison, kangaroo, rabbit) and feed only that for 8-12 weeks. If symptoms resolve, you've narrowed the cause.

That definition is functional. It depends on the individual dog's history. Venison is novel for a dog that's only eaten chicken. It isn't novel for a dog that's been eating venison-based food for two years.

The pet food industry has taken the term and used it to describe the protein, not the dog. A bag labelled "novel protein" tells you the protein is uncommon in the category. It tells you nothing about whether it's novel for your dog. After a few months of "novel protein" food, the protein isn't novel anymore.

What we'd actually want on the label

If "limited ingredient" meant something useful, it would mean:

• A standardised maximum ingredient count - say, 10 or fewer
• Verified single-source protein, with cross-contamination testing
• No legally permitted use of the term on foods where the manufacturing line isn't dedicated

Nothing close to that exists. FEDIAF's guidance covers "complete and balanced" and nutritional adequacy but doesn't touch the LID claim. Until that changes, the term tells you almost nothing about what's in the bag.

What to do instead

If you're trying to figure out whether your dog reacts to food, don't rely on the LID label as a shortcut. The label is marketing. The actual diagnostic step is an elimination diet, properly run, with food that's either home-prepared (so you know the inputs) or hydrolysed (so the protein structure can't trigger a reaction).

If you're just trying to feed a sensitive dog something simpler, look past the front of the bag:

• Count the ingredients. If there are 30, "limited" is a stretch.
• Look at whether the brand publishes a manufacturing statement on cross-contamination. Most don't.
• Check whether the protein source is single-species (not "meat and animal derivatives" or "poultry meal").
• Be sceptical of any "free-from" claim on a bag made in a multi-protein factory.

Limited ingredient diets aren't useless. Some of them are genuinely cleaner than the alternative. But the words on the front of the bag aren't doing the work. The work is in the ingredient list, the manufacturing process, and what the brand will and won't tell you about both.

Sources

• Raditic DM, Remillard RL, Tater KC. "ELISA testing for common food antigens in four dry dog foods used in dietary elimination trials." Journal of Animal Physiology and Animal Nutrition, 2011.
• Willis-Mahn C, Remillard R, Tater K. "ELISA testing for soy antigens in dry dog foods used in dietary elimination trials." Journal of the American Animal Hospital Association, 2014.
• Ricci R, Granato A, Vascellari M, et al. "Identification of undeclared sources of animal origin in canine dry foods used in dietary elimination trials." Veterinary Research Communications, 2018.
• Olivry T, Mueller RS. "Critically appraised topic on adverse food reactions of companion animals (5): discrepancies between ingredients and labelling in commercial pet foods." BMC Veterinary Research, 2018.
• FEDIAF Code of Good Labelling Practice for Pet Food, European Pet Food Industry Federation.