I think it is safe to say that we all consider white bread and wheat bread to be of poor nutritional value, hence the need for bread companies to add nutrients to make their product "fortified." Which is funny dince most of those added nutrient are not even accessible to the body because they are either: fake (manufactured) or the anti-nutrients in the grains do not allow it to be used.
Regardless McCollum and Downey found that the simple addition of GELATIN to a diet of white wheat bread improved nutrition so much to impact growth rates.
It is clear that gelatin both adds to the digestive abilities, allowing the rats to access more nutrients and it provides essential protein that allow the rats to overcome the poor quality of the diet. Does this mean eat crap and eat gelatin and you will be fine! Of course not! It simply is an illustration how real food, harnessed from real bone broth can be of tremendous benefit to both your digestion and nutritional profile.