Why your 3 kg cat feels each berry more
When comparing two cats eating identical amounts, body weight determines how their systems process the sugar. Your 3 kg cat has less metabolic capacity to handle even small sugar loads compared to an 8 kg cat. Think of it like two cars — a compact versus an SUV — both getting the same fuel dose, but the smaller one will feel the impact more noticeably.
While neither cat is likely to face toxicity from a few blackcurrants, your lighter pet may show earlier digestive sensitivity. The first signs usually appear within 6-12 hours: slightly looser stool or a temporary dip in food interest. Keep fresh water available to help dilute the sugar concentration in her system.
What the 8 kg cat handles differently
Your friend's larger cat distributes the same berry quantity across more body mass, so each kilogram of tissue gets less sugar exposure. This doesn't mean zero reaction — any cat can have individual sensitivity — but the odds of noticeable effects drop as weight increases. An 8 kg cat might process those berries with no outward signs at all.
Still, observe both cats for the next day. The bigger one could theoretically have delayed stool changes if his system isn't used to fruit sugars. Neither case requires panic, but the smaller cat merits closer watching due to her proportional intake.
When size isn't the only factor
Age and baseline health matter alongside weight. A senior 3 kg cat with existing digestive quirks might react more strongly than a young, robust one. Similarly, an 8 kg cat with weight management issues could show subtler signs like increased thirst after repeated small sugar exposures.
For your specific situation today, the key difference is proportionality. You're not dealing with a toxic threat, but rather a digestive load that hits your petite cat harder. If she's otherwise healthy and this was a one-off, she'll likely self-regulate with minimal fuss.
Next time: safer ways to share fruit
If you want to occasionally offer treats, consider smearing a tiny bit of blackcurrant pulp (not whole berries) on a lick mat for your 3 kg cat. This controls portion size while still letting her enjoy the novelty. For the 8 kg cat, whole berries aren't a major risk, but removing stems and cutting them in half prevents gulping.
Remember that cats lack sweet taste receptors, so they're not drawn to fruits like dogs are. The interest is usually texture or curiosity. For both cats, watching waistlines matters more than acute reactions when dealing with non-toxic fruits in very small amounts.
The full verdict, portion guidance and serving notes are collected on the Blackcurrant food facts page.