As veterinary nutritionists, we often get asked, “how often should I feed my dog?”. In the past, we’ve not had much more sound advice other than to answer, “do what works best for your dog”. However, research is slowly bringing into light a new, and perhaps more interesting way to ask the same question: “how long should I fast my dog?”
Intermittent fasting (IF) is not a new concept for humans. Its origins are rooted in cultural and religious practices that stem from ancient times. More recently though, IF has become somewhat trendy, mainly as forms of weight-loss programs; you may have heard of some of them: the 16:8 (where you eat within an 8-hour window) or the 5:2 (where you limit your meals during two days a week). No matter the different names, the primary idea of IF is to modify the timings of meals to extend the fasting period. It's a pretty big topic, so what we won’t cover in this article is how the food you eat between fasting periods affects your metabolism. Stay tuned for that, including a more in-depth discussion about ketogenic diets! For today, we’ll stick to talking about the general, overarching concept of intermittent fasting.
The use of IF for weight loss is the most commonly described, and there is good evidence in humans and rodent models of its effect on reducing fasting blood glucose and insulin levels, decreasing markers of inflammation and improving cardiac and cognitive function following injury (1). In dogs, IF is significantly less explored compared to human. However, it’s perhaps an even more interesting idea in this species, compared with humans. Although we must be careful not to weigh too heavily on ancestry, as after all, dogs are not wolves and have undergone thousands of years of domestication (2–4); it is interesting to ponder how different the feeding routines of a typical dog can be from wolves. The feeding behaviour of wolves entails the periodic killing and feasting on large prey, which is followed by a period of fasting. In Yellowstone National Park, packs of grey wolves have been reported to kill and consume an elk every 2 – 3 days (5). In contrast, the domesticated dog is commonly fed on average twice daily. So it’s worthwhile considering whether the domestic dog would benefit from a more ancestral type of feeding regimen.
How much evidence do we have that extending the fasting period is healthier for dogs? The short answer is very little. There are a few studies that have examined the effects of food restriction on disease development, lifespan, and performance in dogs (6–8). However, it’s hard to decouple the effects of intermittent fasting from caloric restriction. They can go hand-in-hand, where you end up eating less calories when you’re undergoing an IF program, so it’s hard to know which one had the positive effect.
Even in my own study where we tried to keep body weight the same in the dogs, there was some weight loss. We found that feeding a higher fat diet was needed to reduce the amount of weight lost (9). We were also concerned that prolonged fasting could lead to a suppression of immune system, but we did not find that in the dogs that were fasted up to 48 hours.
Finally, in 2022, a publication from the Dog Aging Project team indicated that dogs who were reportedly fed once-a-day by their owners were less likely to have gastrointestinal, oral, orthopaedic, kidney, urinary and other health conditions compared to dogs fed more frequently (10). While super interesting as this study had a big data set, it doesn’t show definitively that there is a health benefit to fasting; the researchers couldn’t distinguish whether the dogs who ate less frequently were also eating less calories. Or whether dogs with illness actually needed more frequent feeding.
With all of that in mind, we are still in the early phase of understanding if intermittent fasting could improve the health of dogs. For cats, we’re even farther behind in the research! So where does that leave us today, then? For the average, healthy dog, if you are interested in IF, you can try to slowly transition down to feeding once-a-day. Evidence suggests that this can reduce overall caloric intake and promote a healthy weight.
However, it’s important to remember that IF is not suitable for all dogs, such as in any situation where there is a struggle to maintain weight or muscle mass due to disease (or in senior animals). It’s also been reported that thirst cues are reduced in humans when they eat less meals (11,12). So, in cases where maintaining hydration is important, such as with chronic kidney disease, IF is not a suitable feeding regime. Some dogs also can develop bilious vomiting if left with an empty stomach for too long. Finally, we do not recommend IF for puppies as they have a higher metabolism and are growing, and so need a steady intake of food.
Still so much to explore and research in the area of intermittent fasting in dogs (and cats) - we’ll keep you updated as the science evolves!
1. Lee JH, et al. Intermittent fasting: Physiological implications (2020) https://journals.physiology.org/doi/full/10.1152/physiol.00030.2019
2. Vila C, et al. Phylogenetic relationships of the domestic dog (1999) https://academic.oup.com/jhered/article/90/1/71/2187103
3. Perri A. A wolf in dog’s clothing (2016) https://www.sciencedirect.com/science/article/abs/pii/S0305440316000406
4. Axelsson E, et al. The genomic signature of dog domestication (2013) https://www.nature.com/articles/nature11837
5. Stahler DR, et al. Foraging and Feeding Ecology of the Gray Wolf (2006) https://www.sciencedirect.com/science/article/pii/S0022316622083481?via%3Dihub
6. Kealy RD, et al. Five-year longitudinal study of dogs. (1997) https://europepmc.org/article/med/9018356
7. Lawler DF, et al. Diet restriction and ageing in the dog (2008) https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/diet-restriction-and-ageing-in-the-dog-major-observations-over-two-decades/3DDCC1DDF5A7D85518684AA687FBA63E
8. Hill RC, et al. Effect of mild restriction Greyhounds (2005) https://avmajournals.avma.org/view/journals/ajvr/66/6/ajvr.2005.66.1065.xml
9. Leung YB, et al. Metabolic and immunological effects of intermittent fasting (2020) https://www.frontiersin.org/articles/10.3389/fvets.2019.00480/full?amp/
10. Bray EE, et al. Once-daily feeding (2022) https://link.springer.com/article/10.1007/s11357-022-00575-7
11. McKiernan F, et al. Relationships between human thirst (2008) https://www.sciencedirect.com/science/article/abs/pii/S0031938408001042
12. de Castro JM. A microregulatory analysis of spontaneous fluid intake (1988) https://www.sciencedirect.com/science/article/abs/pii/0031938488903678