Final answer:
Rukmani and Nathan have to share a single portion of food because of economic constraints which limit their food affordability, not due to cultural traditions or deliberate food proscriptions like fasting or dieting.
Step-by-step explanation:
Rukmani and Nathan have to share a single portion of food because they can't afford more. In many parts of the world, including South Asia, cultural traditions might dictate certain food distribution patterns within families, such as women eating after men or consuming less desirable foods like meats and fish. However, this does not appear to be the reason in Rukmani and Nathan's case. Instead, their sharing is likely due to economic constraints that limit their ability to purchase enough food. This situation can lead to 'hidden hunger,' where individuals may consume enough calories but lack essential nutrients and vitamins.
Moreover, when someone moves to a different region or country, they could experience temporary digestive upsets due to changes in diet and the body's initial unfamiliarity with new foods, which can disrupt the digestive system. Over time, the body can typically adapt to the new dietary patterns.