According to research (Source), the body only needs 0.36g of protein per pound each day for maintenance. In 2009, the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine released an abstract supporting 0.5g to 0.8g of protein per pound each day as sufficient (Source).
You can take in a significant amount more than this and be fine, as excess protein is excreted, so long as you get enough fats and/or carbohydrates as well to balance your nutrition needs and solubilize your fat-soluble vitamins that your body requires, as well as calcium to replace that which the protein will leech from your system (Source). You must consume enough water to flush the excess. There's not any point in buying "extra" protein though if you already have plenty in your diet to start with. Those doing body-building will need to be on the high end of this scale.
Based on those research articles, at 250 pounds, the figures are as follows:
- 0.4g/lb = 100g/day (sedentary)
- 0.5g/lb = 125g/day
- 0.6g/lb = 150g/day (active)
- 0.7g/lb = 175g/day
- 0.8g/lb = 200g/day (body-building)
Regardless of the amount of calories in your diet, your "necessary" protein will fall into that range of amounts. Anything over that amount will be flushed from the body. If you eat more food, you won't need to also add more protein. The amounts listed above are sufficient. If you eat less food, you won't need to drop protein. Just stay within that range.
If you're cutting pounds, but not doing any serious weight training, you're going to fall somewhere between 0.4g and 0.6g of protein per pound. If you want to take more than that, as long as you're taking in enough fiber, you won't see much in digestive problems, taking in enough calcium will prevent bone density problems, and taking in enough water will prevent kidney problems.