Despite the popularity of this myth, the fact is that adding brewer’s yeast or nutritional yeast to the diet does nothing to detract fleas. I’ve often been pointed to websites and books that make this claim and some people insist that they can prove it’s true. Their “proof” is that their dog never had fleas while ingesting this yeast, or better yet, that the dog had fleas during the one month the yeast had not been fed. Belief systems are difficult to change, and I admit that this myth is one that needles me often. By the same logic presented as “proof” above, I can point to my Zoey who never ingested brewer’s yeast and never had fleas, therefore I could claim that not eating it kept fleas away. Obviously, it’s ridiculous at best!
Consider my Ming, who lived to be sixteen years old, ate a combination of kibble and (healthy) human foods, and finally a prescription diet. He never consumed yeast, yet never had fleas despite being walked along the boardwalk (a beach area in Toronto that is known for heavy flea populations) almost daily. But these are only personal stories. The facts should hold more weight, so let’s look at them:
Both brewer’s and nutritional yeast provide some B vitamins. It’s been said that fleas don’t like the taste of B vitamins, especially thiamin. If this is true, dogs would have to excrete thiamin through their skin in order to keep fleas away. This would happen via sweat, and so, through sweat glands. Unlike people who have many sweat glands, dogs have very few and most are located in the footpad. So, unless a flea happened to land between the dog’s toes, it won’t be deterred.
If you feed brewer’s or nutritional yeast as part of the diet and continue to believe it’s a magic bullet against fleas, you’re probably not doing any harm. But, keep in mind that yeast ranks highly on the list of allergens for dogs. So, while Rover may not be scratching due to fleas, he may nevertheless scratch due to an allergic reaction. You had better check it out because Rover wouldn’t be the first dog who ate brewer’s or nutritional yeast and had fleas.
You might ask yourself why I mention fleas now as we get into the colder months of the year. It happens that a client of mine is dealing with a flea infestation at the moment. This is despite the fact that she’s in a cold part of the U.S. Her dog has both flea bites and tapeworms (fleas often transmit these worms), and her home must be treated in order to get rid of the fleas. The dog is nine years old, eating a raw diet with brewer’s yeast added daily. Enough said.