If a diet calls for 9 ounces of protein daily, how many grams would that be?
Nine ounces equals 255 grams, but if a diet calls for nine ounces of protein, the first thing I would recommend is checking out just exactly what the author meant by the word 'protein'. Technically, proteins are organic molecules made up of amino acids, which are the basic building blocks for life. Your body uses amino acids to build or repair tissue. They are also necessary for almost every chemical reaction in the human body.
According to the USDA, by this definition of protein, you need about 0.75 grams per kilogram (2.24 pounds) of weight. An average person weighing 155 pounds would need 155 / 2.24 X 0.8 = 52 grams of protein per day, or 1.8 ounces. Pregnant or lactating women need more protein, as do people engaged in strenuous physical activity. Protein requirements also change with age. By the technical meaning of protein, 255 grams would be almost 5 times the amount needed by an average healthy person.
The other way in which the word 'protein' is used it to mean foods, such as meats, that are the primary source of protein in western omnivore diets. This is what is meant, for instance, when someone refers to a meal as having a protein, a vegetable and a starch. The protein content of foods varies widely. For example, cod has around 22% protein by weight, while turkey breast meat has about 32% protein by weight.
In order to simplify dietary guidelines, recommendations are frequently made in terms of the amount of protein rich foods to eat, since most people don't track specific nutrients, if they watch anything at all. Unfortunately, in the process the word 'protein' has now become ambiguous. Are they talking about protein rich foods, or the actual protein amount itself?
If a diet says to consume 9 ounces of protein rich foods such a meat and fish, at say 20% protein by weight on average, that means you would get about 1.8 ounces of real protein, or very close to the recommended amount.