Are all dog foods created the same?
Tl;dr - No. Different foods are created to suit different needs.
This difference applies to commercial foods too. Some foods are extremely calorie dense, others seem to be higher in carbohydrates than anything else. I often see people asking what commercially available food is "best", and I enjoy seeing the whole list of responses saying one food or the other is the best. However, the truth is, the best food is the one that suits the individual dog's needs best.
One of my favourite analogy is about how feeding our dogs is like buying a dress.
We can certainly head to the boutique or clothing shop to find ourselves the dress. However, even within the same brand, sizes may differ depending on the the way the clothes was cut. And the most beautiful dress doesn't always make us look our best because we have unique body shapes. If we want the clothes to fit like they were made just for us, well, we will have to get them altered by the tailor, or have them made from scratch using our personal measurements and using the materials, colours that will suit our body shape, skin tone etc best.
The same with our dogs' diets. We can make sure they get all they need by serving them a premade food that is complete and balanced. However, nothing can beat a diet that is tailored and custom built for each individual dog's life stage, activity levels and unique needs.
Here’s an example using my own two dogs.
The black one, Cara, is one, and because they are small breeds, she has been more than 80% of her adult weight at 8 months old and is fully grown by 12 months. If I wanted to, I can feed her an adult recipe, although I’ll be keeping her on a puppy formulation for a little longer till she’s about 15 months old. Her day is all "play like crazy, fall over and sleep like a log, wake up" and repeat cycle. Not fat tolerant, a little bit more of a slightly fattier treat and it'll be "poopaggadon" until the fat is processed out of her system!
The grey one, Oreo, is 9 years old. Her metabolism is relatively high, but she has a history of clostridium infection. She sleeps quite a bit more than her younger sister but enjoys a good game of chase around the house a few times a day. She tolerates a higher fat diet, but requires a lot more fibre to keep the clostridium count in check.
Weight wise, they are almost exactly the same, Oreo is 700g heavier than young Cara.
Yet when it comes to their diet, even though they eat exactly the same ingredients, the amounts of each individual ingredient is absolutely different. High fibre diets (like what Oreo needs) has lowered vitamins and minerals because the fibre can inhibit nutrient absorption. So I have to formulate Oreo's recipe so that she doesn’t miss out on her nutrients just because the fibre level is higher. Cara has a high energy need because she’s young and burns through the energy more quickly, but she actually tolerates very little fat. Although she is 700g lighter than Oreo, she eats about 20% more in terms of calories in order to maintain her weight and good body condition.
If I were to feed both of them premade foods, they will not be able to eat the same foods at all in order to meet their nutrient needs. This is also something that few people realise - if a dog is on a premade food, and the dog isn’t maintaining weight well (put on too much weight when fed according to the label recommendations or lose weight and needs to eat way more than recommended amount), the food is the wrong one for the dog and a different food should be selected. So even when it comes to commercially available foods, it’s not one size fits all still!
Hope this explains it! =)