Nutrition and behaviour: is food causing your pup to behave differently?

Dogs are more like us than you might think. What we eat affects us in profound ways, and the same happens to them.

Think about the last time you ate an entire share bag of Haribo on your own. How did you feel after? Probably a bit sluggish, sick, and too full. And maybe a whole lot of regret. 

Now think about the last time you ate something that was packed with nutrients. It probably left you satisfied, energised, and not too full. Your brain might have been on top form too. 

Now think about dog food. A lot of the time, we have no idea what’s in it. Companies hide behind phrases like “animal derivatives” and “EC approved additives”. The truth is, no one really knows what’s in it. You probably have a better chance of winning the EuroMillions than accurately guessing what’s in that tin of dog food on the shelf in Tesco. 

Are those tins the doggy equivalent of a nutrient-dense meal that leaves them feeling energised? Or are they the share bag of Haribos? We’ll never know, but I’d hazard a guess it’s the latter. That’s because low-quality ingredients and fillers are cheaper.

The point I’m trying to make is that diets have such profound effects on everything from behaviour to physical health. And if your dog has been behaving a bit unusually recently, it could be down to their diet. Nutrition and behaviour are linked in ways you might not even realise.

From aggression to hyperactivity, their behaviour could change in multiple ways. Let’s look at what that could be.


When your sweet, cuddly fur baby suddenly starts snapping, it can be distressing. You wonder if something happened that you don’t know about, if they’re scared, if you did something wrong – the mind spirals. 

But fear isn’t always the cause. Carbohydrates are cheaper than high-quality protein sources and so many dog food brands have a high percentage of carbs in their food. But when a dog gets too many of them and not enough protein, it can cause aggressive behaviour. 

When they have too many carbs, too much fat, or are overfed, the chances of lipopolysaccharides causing damage increases. Lipopolysaccharides (LPS) are bacterial toxins that live in the gut. And while it’s normal for these toxins to be housed here, when LPS get into the blood, it causes health issues. 

LPS destroy the brain cells that create dopamine and serotonin – the chemicals that make us feel calm, content, and happy. This is what can make some dogs aggressive. So to limit the amount of LPS circulating in your dog’s system, it’s essential not to overfeed them or feed them too many carbs or fats.

Calcium deficiency can also lead to signs of aggression. This is common in small breed female dogs with large litters as their bodies are producing more milk. 

If they have low levels of calcium, they may show other symptoms like muscle twitching, weakness, lethargy and loss of appetite. Low calcium levels are treatable, but bear in mind that they can also be dangerous. If you think your dog is low on calcium, talk to your vet.

But muscle twitches can be a symptom of allergies too. Only when it’s an allergy, it typically occurs at night. 

One case study tells the story of a lovely, friendly young pup who experienced bouts of aggression. He’d walk around growling and biting his own legs. The behaviourist noticed his legs spasmed a lot in his sleep. And after realising it could all be the sign of an allergy, they changed his food, and the results were almost immediate – he was no longer a grumpy boy. 

Both the leg biting and muscle spasms were symptoms. And the pup seemed mostly angry at himself. He bit his own legs, not other peoples and mostly just stropped to himself. If your pup’s been behaving similarly, it could be an allergy. 

Or your doggo might just be territorial. One study found as many as 20% of all dogs are territorial over their food. And while being protective isn’t really about nutrition, it’s a common issue. So I think I should be let off for this one.

Dogs still have their instinct at play, and some still hold on to the idea that they must protect their food. They think everyone’s trying to pinch it. So they growl, snap, even bite to keep it for themselves. 

In the wild, you have no idea what might be lurking around the corner ready to pounce on your latest catch. Even a member of your own pack could be plotting to steal your food. And some dogs have held onto this instinct stronger than others. Territorial behaviour over food is more likely to be noticed in breeds like Springer Spaniels and German Shepherds.

Dogs can also get territorial over their food when they don’t get enough to eat. Think about the time you were starving and out with a friend. You ordered food, and they didn’t because they weren’t hungry. As soon as they see you eating, they try to pinch a chip. And you’re gobsmacked. You might even swat their hand away and give them a death stare. Why? You’re starving, it’s your food and… it’s yours

A doggo that isn’t getting enough to eat might feel the same. Their growl is their version of a death stare and a bite is their version of a slap to the hand. This doesn’t make their behaviour acceptable, of course. But simply filling their bowl a bit higher should stop this behaviour if this is the cause. 


Remember all the fuss around the blue Smartie? Nestle stopped creating it among fears that synthetic colourings have bizarre, undesired side effects. And while we don’t actually know if that’s the case with the blue Smartie, we know that hundreds of colours, additives, and flavours were banned for their nasty side effects.

Here’s one particular example: Red 40.

Red 40 is banned in the UK because it’s linked to allergies, migraines, hyperactivity, and ADHD – especially in children. It may even be carcinogenic (cancer-causing). 

Additives and chemicals have serious effects on humans and dogs alike. And when dog food companies can hide behind “EC permitted additives”, we have no idea what those are, what the side effects are, and if they could be carcinogenic. 

That list of “EC permitted additives” contains over 4,000 entries. Any one of those could be in your dog’s food, causing hyperactivity amongst other problems. Since they use this phrase, you’ll never know what’s exactly causing your pooch to act a certain way, making it difficult to avoid. 

Switching to more natural food that contains no additives or chemicals could help reduce hyperactivity in your dog. 

Allergies can also cause hyperactivity. The best way to test this is to switch their food. A hypoallergenic food could be just what they need to calm them down and, of course, soothe their allergies. But always consult your vet before making drastic changes to your pet’s lifestyle.

Switching food can help for other reasons too. A diet that’s too high in sugar, salt, or fat can make a pup hyper or unfocused. But if you’re planning on switching their food, remember to transition them slowly or you may worsen their symptoms. 

While too much of something can make them hyper, so can underfeeding. It’s confusing, I know. But when insulin is low, their bodies produce less dopamine and serotonin. As a response, they produce higher amounts of adrenaline to raise their blood sugar levels and that high adrenaline can cause agitation and reactiveness. 

Another potential cause of hyperactivity is magnesium deficiency. Keep an eye out for other behaviours such as improperly triggered reflexes, pain, difficulty walking, weakness or trembling, and other abnormal behaviours. 

As always, if you’re worried about your pup, speak to the vet. 


I’ve grouped lethargy and depression together as often the symptoms are quite similar. Your pup’s tired and doesn’t want to do anything they normally would. It could be something like separation anxiety, but as with all the rest, it could be a certain deficiency.

Calcium, magnesium, and iron deficiencies can all cause depressive or lethargic behaviour in your pup. We’ve already covered calcium and magnesium deficiency, so let’s focus on iron deficiency symptoms.

The big one here is black, tarry poo. It’s the most obvious as a professional pooper scooper. But also keep an eye out for weakness, rapid breathing, and anorexia. If you ever see warning signs like these, get to the vet.

Your pup may also be feeling lethargic from excessive eating. We’ve all been here before: ever had to roll back after an all-you-can-eat buffet? You pile food up on your plate and go back and forth until you regret coming to the buffet at all. We probably won’t go that wild again for some time. We’ve learnt our lesson.

The difference is, doggos still have a survival instinct that makes them do the exact same thing, only they don’t learn from it. Their instincts tell them they never know when they’ll eat again, so they cram everything they can into their mouths. You might just think they’re hungry, but some dogs will do it every time. Even when they’re stuffed, they’ll try to fit more in. 

And you remember what happens when you get back from the buffet. You fling yourself on the sofa or even get in bed for a quick eight-hour nap. Dogs are the same. They’ve eaten so much and now they need to work to digest it all. It’s exhausting.

Eating a lot of junk food and high-sugar foods can have similar effects. Most junk food is deficient in amino acids, and these play an essential role in preventing depression and regulating mood. If your dog’s been pinching a few too many kebabs and slices of pizza and not eating enough of their own food, him feeling depressed as a result is definitely possible. 

Bad or unusual behaviour

Does your pup keep begging or stealing food from around the house? Then they may not be eating enough. Being hangry isn’t unique to humans. Not getting enough to eat can easily make a pup act up. They could be intentionally acting up to get your attention to let you know they’re peckish.

And other strange behaviours can be linked to diet too. That can include running away, being cheeky, ignoring commands, and more. This could be due to low-quality grains, chemicals, additives, and animal derivatives. If your pup feels good, they’ll behave well. But there’s a chance these ingredients are making them feel anything but good.

And changing food too quickly can cause these changes too so it can feel hopeless. But if you transition your dog properly onto a nutritious, high-quality food, this should solve the problem.

If your dog keeps chewing his paws, that could be a sign of an allergy. Dogs love a good chew. It helps alleviate boredom, anxiety and, in pups, helps with teething pain. But if they suddenly start attacking themselves, that’s something to look into. Skin problems are among the most common symptoms of food allergies.

It can be scary when your pup starts behaving differently, but the answer could lie in their diet. You can’t ignore the link between nutrition and behaviour. I hope I’ve helped shed some light on what might be causing your fur baby to behave differently. And if you think your pup has a problem such as a deficiency or an allergy, it’s always best to have a chat with the vet.

Looking to eliminate nasty chemicals and additives from your pup’s food? Swagwags is a strictly “no nasties” kibble designed to keep your pooch happy and healthy. Happy pup, happy pawrent. Check out our mouth-watering range now.

If you’re ever concerned about potential allergies, take one of our sensitivity tests. It’s non-invasive and takes 5 minutes to do – a small price for perfect pup health!