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My pet isn’t losing weight – why?

Less food, but the scale won’t budge? Hidden calories or inaccurate measuring are usually behind it. Here’s how to find out.

The short answer

If a dog or cat doesn’t lose weight despite eating less, it’s usually hidden calories: treats, chews and table scraps count too (together at most 10% of daily calories), and cups are inaccurate – in a study, dog owners were off by anything from 48% too little to 152% too much. Dogs should lose about 1–2% per week, cats 0.5–2%. If weighing the food doesn’t help, plan the weight loss with your vet.

The most common reasons

  • Cups instead of a scale: in a study with 100 dog owners, measured portions ranged from 48% too little to 152% too much. Weigh the food.
  • Treats, chews and table scraps: they count too, together at most 10% of daily calories.
  • Several people feeding: agree on who feeds and what extras there are.
  • The amount wasn’t adjusted after weighing: without a new number, nothing changes.

How fast is normal?

Dogs should lose about 1–2% of their body weight per week (AAHA), cats 0.5–2% (Tufts). A 44 lb dog loses about 7–14 oz per week, a 13 lb cat about 1–4 oz.

Weigh every two weeks at the same time of day on the same scale. Small day-to-day swings are normal.

How to adjust the amount

Portiopet starts with the amount that maintains the target weight. If your pet doesn’t lose enough in two weeks, it gives 10% less, but never less than 0.8 × the resting energy for the target weight. The weight loss calculator shows the starting amount and the floor.

Cats must never go hungry

If an overweight cat fasts or loses weight too fast, it can develop a dangerous fatty liver (Merck Veterinary Manual, Cornell). That’s why you lower the amount only in small steps.

When to see your vet

  • Your pet doesn’t lose weight after several weeks despite weighed food and counted treats.
  • The amount is already at the floor.
  • The target weight is 20% or more below the current weight.
  • Your pet seems ill, suddenly eats less or drinks a lot more than usual.

Your vet can also check whether something else is going on.

Questions

Why isn’t my dog losing weight on less food?

Usually hidden calories: treats, chews, table scraps or inaccurate measuring with a cup. Weigh everything for two weeks and count the treats. If that doesn’t help, talk to your vet.

How much less food is OK?

Portiopet lowers the amount in 10% steps and never below 0.8 × the resting energy for the target weight. If it needs to be even less, plan it with your vet.

Can I let my cat go hungry so it loses weight?

No. Cats must never go hungry: losing weight too fast can cause a dangerous fatty liver. Cats should lose weight slowly, about 0.5–2% per week.

Sources

Last checked: October 2026