Brewers yeast, for the most part, is safe, but you do need to be careful.
Things to consider:
• Allergies. It seems a little ironic, especially given that it’s supplement to benefit skin and hair and to prevent fleas. However, some cats are allergic to it. Symptoms of allergies in a cat include flaking of the skin, red skin lesions, mutilated skin, licking, rubbing, chewing or scratching. Some cats may even develop small scabs or pull out tufts of their own fur.
Monitoring is important because a yeast allergy is caused by a yeast infection, and that can be localized or systemic. Therefore, left untreated, it can cause problems in pets prone to ear infections and other yeast-related illnesses.
• Digestive problems: Brewers yeast increases gas and fermentation in the stomach. Some report upset stomachs. If your cat has a tendency toward any gastrointestinal problem or sensitivity, you may want to avoid it.
• Blood sugars. On one hand, brewers yeast is a good source of chromium, which stabilizes blood sugar and improves glucose tolerance in cats. On the other, though, since it regulates metabolism, it can interfere with the insulin cycle, so it may not be a good choice for diabetic cats. The best defense is to speak with your vet.
• Palatability. This isn’t really a side effect, but should be mentioned because brewers yeast can be bitter, somewhat unpleasant tasting and have a strong odor (which is why some suspect that it’s a natural flea repellant. Be sure to find one that says “de-bittered” and maybe look for a brand that is flavored with something like peanut butter.
Be absolutely sure the brewers yeast natural and not made from beer or bread by-products, because the by-products can contain items harmful to your pet’s health, such as alcohol fermentation.