How long can a person survive without food?

—CARLOS SANTIAGO, DOMINICAN REPUBLIC

Alan D. Lieberson, an M.D., attorney and the author of Treatment of Pain and Suffering in the Terminally Ill and Advance Medical Directives, explains:

The duration of survival without food is greatly influenced by body weight, genetic variation, other health considerations and, most important, the presence or absence of dehydration.

Without liquids or food, people typically perish after 10 to 14 days. (Depending on whether the individual is dehydrated or overhydrated at the outset, the time may range from approximately one to three weeks.) This situation comes up frequently in two medical groups—the incompetent, terminally ill patients for whom artificial maintenance of life is no longer desired and the individuals who, though not necessarily terminally ill or incompetent, decide to refuse food and hydration to end their own lives.

In cases where healthy individuals are receiving adequate hydration but no food, reliable data on survival are hard to obtain. Mahatma Gandhi, the famous nonviolent petitioner for India's independence, survived 21 days of complete fasting while allowing himself only sips of water. A 1997 article in the British Medical Journal by Michael Peel, senior medical examiner at the Medical Foundation for the Care of Victims of Torture, cites well-documented studies reporting survivals of other hunger strikers for 28, 36, 38 and 40 days. But most such reports have been poorly substantiated.

Unlike total starvation, near-total starvation with continued hydration has happened frequently. Survival for many months to years is common in concentration camps and during famines. The body can moderate metabolism to conserve energy. The alteration of metabolism is not well understood, but it occurs at least in part because of changes in thyroid function. This ability may help explain the evolutionary persistence of genes causing diabetes, which in the past could have enabled survival during famine by fostering more economical use of energy.

Medical practitioners encounter cases of near-total starvation in patients suffering from, among other conditions, anorexia nervosa and end-stage malignancies, as well as in those adhering to “starvation” diets. Death may result from organ failure or heart attack when a person's weight corresponds to a body mass index (BMI) of approximately half of what is normal, or about 12 to 12.5. Normal BMI is 18.5 to 24.9, and many fashion models have a BMI of around 17.

How do scientists detect new elements that last only milliseconds?

—J. ADAMS, JESUP, GA.

Todd M. Hamilton, associate professor and chair of the department of chemistry at Adrian College, provides an answer:

Even elements that exist only briefly before decaying leave behind a calling card, in the form of an energy signature. The challenge for researchers is detecting that fleeting signal.

When a heavy element disintegrates, or decays, it gives off a unique radiation signature. Alpha-particle (essentially a helium nucleus) emission is the type most commonly used, because it gives off distinct energies.

Scientists make heavy elements by smashing together two elements that add up to the mass of the desired new element. One element, the projectile, is sped up in a cyclotron or other particle accelerator and shot at the second, the stationary target. Sometimes it takes millions of collisions and several weeks of bombardment to generate one atom of the new element.

In addition to using the unique energies of emitted alpha particles to identify new elements, heavy-element hunters turn to a cascade of alpha emissions to confirm their existence. Assembling all of this information is tricky business, but it can serve as convincing evidence that a new element was, in fact, created.

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