Are there are any resources for realistic portion sizing? It stands to reason that two people who are very different sizes will have different nutritional needs. Calculating macros isn’t something that seems sustainable. If both people are trying to shift their weight, should the deficit be calculated as a percentage of total caloric need individually or a flat number of calories ?
The general rule of thumb is that to lose weight, one should consume 200-300 calories under their maintenance calories; some studies say up to 500 below is sustainable and effective . The tricky part is sorting out what your maintenance calories should be, and requires An honest assessment of your caloric needs and activity level.
A calorie/macro counter like MyFitnessPal, while not absolute, can help you ballpark your needs and keep an eye on your intake.