Should I Fast my Cat or Dog?

Here at My Pet Nutritionist, we see a lot of confusion with regards to fasting your pets. The topic can cause quite the scuffle on social media, with largely varying opinions on the matter – so this blog article aims to help you, the readers, understand more about fasting, and when it is, and is not appropriate, or beneficial to do so. This post covers both cats and dogs, which both have very different needs, so we will split the blog into two sections; one for our feline friends, and one for our canine companions.

What is Fasting?

Fasting is quite a hot topic in both the pet, and human worlds! Fasting simply is, as it suggests – not feeding for a fairly lengthy period of time. The two types are:
  • Intermittent fasting: feeding once per day, or twice per day, but no more than 6 hours apart, giving 16-23 hours between feeds
  • Complete fasting: giving no food at all for a day or more.

We will discuss length of fasting time for each species through this blog post.

Should I Fast my Cat?

The answer to this question isn’t a simple one – yes, and no. Cats should never be completely fasted, but can be fed one large meal per day in an intermittent fasting style.

Cats are generally very susceptible to toxicity. Intake of dietary nutrients is extremely important for detoxification in cats, so regular and frequent feeding is essential.
Cats should never go more than 24 hours without food!
If the body is unable to suitable detoxify through nutrition, the risk of acute fatty liver increases.

Lets take a deeper look at the science behind the importance of detox in cats.

Cats are deficient in enzymes involved in later stages of detoxification. One notable example of this is glutathione peroxidase. Glutathione peroxidase is a catalytic enzyme, which reduces hydrogen peroxide to water, which detoxifies the body and limits the harmful effects of hydrogen peroxide.

Findings Here

A process involved in the later stages of detoxification, known as sulfation, is dependent on sufficient consumption of the amino acid, taurine. Unlike dogs and us humans, cats are unable to synthesise taurine from cysteine in their diet, so cats require direct taurine sources to ensure sulfation can occur. Ensuring a taurine rich diet for cats, helps to improve hepatic detoxification (liver detox).

Findings Here

Finally, cats are not able to synthesize arginine. Arginine is an essential part of detoxification via urea, and if lacking it in the diet, this can lead to acute encephalopathy.

Findings Here
Findings Here

Should I Fast my Dog?

Fasting dogs, in most cases, is ok… and can actually be very beneficial. Unlike cats, dogs don’t necessarily need to feed every day, as they produce enough of the enzymes and amino acids required for detoxification. In the wild, species in the Canidae family would only eat maximum one larger meal per day. There are some situations where dogs should not be fasted – we will take a look at these next!

When Not to Fast

While fasting may have some health benefits, it certainly isn’t for all dogs. In the following situations, dogs should not be fasted:
  • If the dog has hunger pukes if not fed twice per day
  • Dogs with acid reflux
  • Puppies
  • Dogs on medications which require food to be consumed before or after
  • Underweight dogs, needing to gain weight
  • Diabetic dogs
  • Bitches in welp

How Long to Fast For

The length of time you can fast your dog for, very much depends on the individual. Generally speaking, dogs can safely go up to five days without eating, however hydration is important during this time.

Most dog owners who fast their dogs, tend to do one or two full fasting days per week, others cut down to just one large meal every day, much like the fasting process for cats, discussed above. When a fast day is included in your dog’s schedule, it’s important to increase their daily portion of food for the rest of the days each week, to allow for the day with no food – so the fast day(s) allowed portion is split between the rest of the dog’s meals that week.

We tend to recommend only fasting for one day at a time, and we would always recommend consulting with a professional before beginning your fasting journey, if you’re not a seasoned faster!

Benefits of Fasting

Once you have established whether you could possibly fast your pet, and for how long, we can look at the benefits this new feeding regime could have.


Research shows that fasting can greatly improve longevity. Studies are mostly carried out on mice. Results show that mice who were fasted for complete days, and allowed to eat as much as they wished on days they’re given food, lived far longer than those fed a set amount every day.

Not only were length of lives analysed, but the brain function was also studied. The part of the brain which is affected by Alzheimer’s disease in humans, the Hippocampus, was tested – those who were fasted regularly had less brain damage than those who ate daily, showing enhanced cognitive ability in aging individuals when fasting occurred.

Findings Here
Findings Here

Stronger Immune Function and Infection Fighting Ability

The immune system contains many different specialized cells, which each have their own function, and work together to create an immune response, and fight infection.

The first cells we will discuss are Macrophages. Macrophages destroy bacterial cells, viruses, and foreign bodies by engulfing them. Another important role they play, is the engulfing and subsequent destruction of dead cells within the body. Fasting is known to increase macrophage activity, making fighting illness quicker.

The next immune cells we will talk about are Neutrophils. These are a type of white blood cell – the most commonly found! Their role in the immune system is to engulf bacteria and other microorganisms. Neutrophils destroy the initial invading bacteria when bacterial infections first occur. Fasting increases Neutrophil activity, which is important for reducing infection in the body, and healing faster.

The third immune cells, another type of white blood cell, are Monocytes. These work similarly to Neutrophils, but the engulf and remove larger particles, and aim for chronic infections, as well as enter inflamed tissues. Monocyte activity is increased through fasting.

Findings Here
Findings Here

Physical Trauma Recovery

As with many health concept tests, rats have been used in various studies, to trial the speed and efficacy of recovery in individuals who are fasted either completely, or intermittently. Groups of rats with Thoracic Contusion Spinal Cord injuries were split into two groups – a control group who are fed as normal, and a trial group who are fasted intermittently.

In individuals who were fasted, recovery was faster, mobility was regained more efficiently, and surgical site lesions were smaller.

It’s thought that the science behind this response, is that fasting reduces the amount of regeneration-blocking cells from reaching the site of injury, allowing for quicker recovery.

Findings Here

Weight Loss and Detoxification

We have grouped weight loss and detoxification, which may seem an odd pairing, but hear us out!

In dogs, intermittent fasting can aid detoxification, particularly after exercise. Glucose and ketones are both used for energy in dogs, and humans. When the body lacks glucose, ketones are used during exercise, and your dog will begin to exercise in ketosis. Ketones are stored in fat cells. Toxins are also stored in the fat cells when they are unable to be excreted through urine and faeces. When fasted, there is a lack of glucose in the system, so ketones are used, which causes more rapid fat burn – as the fat burns, the toxins in the fat cells are also removed, which ultimately detoxes the body.

This type of detox is also important in cancer patients, who require a ketogenic diet, which you can read more on here.

Findings Here


Inflammation can be related to the endocrine system – the system of hormones in the body. The hormone in question here, is Insulin. During a fast, insulin levels circulating in the body, drop; this is why it’s important not to fast a dog with diabetes.

Insulin is a pro-inflammatory hormone, so a reduction in circulating insulin has an anti-inflammatory effect which is essential for health and longevity as it also results in a reduction in stress on the body.

Findings Here

If you feel your pet may suit being fasted, why not give it a try? If you are still unsure if fasting could work for your pets, please don’t hesitate to contact us using the chat function on our website, or booking in with one of our team!

Team MPN x

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