Yeast: nutritional or brewer’s?

Nutritional yeast (alongside brewer’s yeast) is sometimes touted as a natural flea repellent for dogs. This is due to its high content of B vitamins, particularly thiamine (B1). The theory behind this claim is that when dogs consume nutritional yeast, particularly in larger quantities, their bodies excrete thiamine through their skin, giving off an odour that fleas don’t like.

First, although both may be derived from the same species (Saccharomyces cerevisiae), brewer’s yeast and nutritional yeast are not the same.

Brewer’s yeast

Brewer’s yeast is a by-product of the beer brewing process. The yeast is harvested and dried after fermentation (and sometimes pasteurised) before being sold as a commercial product. Many of the nutrients I retained after the brewing process: brewer’s yeast is known for being rich in B-complex vitamins, particularly B1 (thiamine), B2 (riboflavin) and B6 (pyridoxine). It also contains various minerals such as iron, potassium, phosphorus, manganese and zinc. Brewer’s yeast is used as an ingredient in commercial dog food and in commercial supplements, where it is marketed in particular on the basis of its B vitamins and antioxidants. Itis generally the sterilised brewer’s yeast, i.e. the inactive yeast, that is used as an ingredient in pet food. Brewer’s yeast (make sure you buy yeast that is of high quality and produced specifically for dogs) is said to be good for skin and coat and to help with skin irritations and dry skin.

Nutritional yeast

Nutritional yeast, on the other hand, is grown specifically for nutritional purposes. Nutritional yeast is also a source of fibre, iron, potassium, thiamine, riboflavin, folate and pyridoxine. Often fortified with additional nutrients, this product is marketed as a source of protein for vegans and vegetarians. In our experience nutritional yeast is a very successful palatability ingredient, perhaps because of its mild cheesy flavour.

As one of the dry staples in the Well Dog Pantry, yeast is used quite frequently in treats.

Yeast and fleas

Returning to the claims about yeast as a repellant, it’s probably best to approach such claims with caution – and understand the limitations and potential risks:

  1. Although there is anecdotal evidence, there is limited scientific evidence to directly support the claim that nutritional yeast effectively repels fleas. Most of the anecdotal evidence comes from pet owners who have observed varying degrees of success. Scientific studies specifically testing nutritional yeast as a flea repellent in dogs are scarce. I was only able to find one dating from 1983 which did not support the claim (see below).
  2. The effectiveness of nutritional yeast as a flea repellent may vary depending on factors such as the individual dog’s metabolism, the amount of yeast consumed (probably far too much), and the specific environment in which the dog lives.
  3. Everything in moderation. While nutritional yeast is generally safe for dogs in moderate quantities (and they love it in treats), too much can lead to digestive upset or other health issues.
  4. Nutritional yeast, even if it has some repellent effect, is unlikely to provide comprehensive flea control on its own.

In one study[1] (the only study I was able to find), dogs were given 14 g of active and inactive brewer’s yeast a day. In three groups – one control, one receiving inactive and the other receiving activities for a five-week period – there was no difference in three counts for the first four weeks (although in the fifth week a difference was seen, not between the ‘control’ dogs, but between the active and inactive yeast recipients).

For me, in the unlikely event that the small amounts of yeast I feed my dog do repel fleas, all well and good. As they say in Dutch: “Baat het niet, dan schaadt het niet“. In other words it won’t hurt to try! But personally, I’ll stick to using yeast for the purpose for which it is intended: to provide nutrition. I certainly won’t be relying on yeast as a strategy for flea prevention.

 

References:

[1] Baker NF, Farver TB. Failure of brewer’s yeast as a repellent to fleas on dogs. J Am Vet Med Assoc. 1983 Jul 15;183(2):212-4. PMID: 6885593.

 

Important Considerations:

  • Some dogs have used allergies or are prone to yeast infections. In some cases, yeast can lead to ‘wind events’.
  • Always consult your veterinarian before making any significant dietary changes, particularly where there are pre-existing health conditions or dietary restrictions.
  • Brewer’s yeast contains protein: be careful if feeding to dogs with a protein-restricted diet and as usual – if in doubt – check with your vet.
  • As some commercial foods contain yeast as an ingredient, check the label to see whether it’s in your dog’s food before giving more. Excessive intake of any foods can have adverse effects.
  • Ensure (where possible) that you use high-quality, organic products specifically formulated for pets (or better still, human grade ingredients) to avoid any potential adverse effects.
  • Introduce new foods gradually to avoid adverse effects such as gastrointestinal upset or diarrhoea.
  • I provide nutritional information purely as a helpful guide. Nutritional information on ingredients is obtained from the US Department of Agriculture’s FoodData Central site (https://fdc.nal.usda.gov/index.html) and any nutritional information provided in recipes is based on an online calculator: calories and other information will vary based on brands, ingredients and other factors.
  • Check nutrient levels and recommendations for your dog’s weight, age and activity. For example this nutritional guideline produced by FEDIAF.