The research is split on whether a BMI of 26–27 is healthy for a 5-foot-1 person, but underfueling during marathon training does seem to raise injury risk.

On weight loss during marathon training, other research only offers a hint: a study of male runners found that those who ate too little for their exercise had weaker bones, which could make injuries more likely, but it did not directly test whether losing weight during training causes injuries. The underfueling claim has more backing: one study found that teaching runners to eat enough may lower some bone injuries, though the effect was not strong, and another found that a risk score including not eating enough predicted more bone injuries in male distance runners, though it did not isolate underfueling by itself. The BMI question is where things get messy. Some other research suggests a BMI of 26–27 is not harmful in specific groups—older adults over 80 had lower death risk if overweight, and heart failure patients at that BMI did not have higher death risk—but those studies were not about 5-foot-1 people or all health outcomes. On the other side, a direct study found that people in the overweight range had more health problems and higher death risk than normal-weight people, so the evidence genuinely conflicts. For the calorie-deficit danger at 5-foot-1, the research we found did not look at short people specifically; one study of calorie restriction in general found it mostly safe but noted some bone density loss and more anemia checks, so that claim is not directly tested.