An elderly person can live approximately three weeks without food, according to Dina Spector for Business Insider. However, there are additional factors to consider when determining how long a person can survive without food. These factors include age, weight and hydration levels.
There is a bit of precedent established to determine how long an elderly person can live without food. For instance, Mahatma Gandhi, a renowned civil rights activist, lived for 21 days without food, according to Scientific American. Gandhi did, however, take occasional sips of water while he was undertaking this fasting period. Twenty-one days without food is not considered the longest period. Irish prisoners, as a sign of revolt against British military forces, survived a duration somewhere between 46 and 73 days without food consumption.
While a person needs food to survive, Canadian Virtual Hospice states that fluid intake is the more important basic need that is essential for survival. A person's body has the capability of adjusting its metabolism to account for a decrease in food intake. However, a lack of necessary fluids, specifically water, leads to abnormal kidney function. Other body organs suffer from the dehydration as well, resulting in immune system failure and eventually death.