# data[].attributes.body
First they belived that most the nitrogen from rats came from the protien they ate.

# data[].attributes.body
The question that the scientist asked was how much of the protein eaten is excreted, and how much becomes protein in the body? This led to them doing this experiment.

# data[].attributes.body
The first step of the rat experiment is that they mixed the amino acids with isotopes with regular amino acids. They fed 4 rats with 23mg of the product and waited to see the results.

# data[].attributes.body
After the rats were fed, scientists collected the feces and urine excreted and analyzed them. The new proteins that were fed were made of isotopes, which were heavier than the old proteins.

# data[].attributes.body
On day three they killed the animals and investigated their blood and a variety of organs for the isotopes.

# data[].attributes.headline
results of experiments what did they learn 

# data[].attributes.subject
results of experiments what did they learn 

# data[].attributes.body
the results were 57%of the nitrogen isotope that the rats eat was found in proteins in the rats bodies therefore the amino acids the rats eat are the reactants of a chemical reaction that produces proteins that are used in the body

# data[].attributes.body
the term "built up" means the gradual accumulation or increase of a substance, energy, or condition over time.