Finding ways to extend the human lifespan by observing certain diet and lifestyle regimens has been a centuries-old quest. Indeed, our average life expectancy has dramatically increased over time, at least in the wealthier parts of the world, due to improvements in hygiene, health care, and food supply. Yet science has still not been able to provide definite answers to what we can do to live longer.

Studies on longevity in connection with diet and lifestyle have been undertaken as early as the 16th century, most notably by one Luigi Cornaro, a Venetian who was known for his hard partying until his health failed him before he reached 50. In his autobiographical book, “Discourses on a Sober and Temperate Life,” which is still in print today, he claims that a radical change from unrestricted indulgence to Spartan simplicity not only restored his health but also added many more years to his life. He died at 98 – an exceptionally old age at his time.

A more systematic approach to studying the effects of diet on longevity was taken in the 1930s when scientists noticed that lab mice put on a calorie-restricted diet lived up to 40 percent longer than their abundantly fed counterparts. But still nobody knew the exact causes of the dramatic lifespan increases, let alone whether the findings were applicable to humans.

Two relatively recent studies tested independently from each other the impact of calorie restriction on health and mortality in rhesus monkeys. Both came up with opposite results.

In 2009, a study report issued by researchers from the University of Wisconsin claimed that a calorie-restricted diet regimen did actually favor longevity in the monkeys. But three years later, scientists at the National Institute of Aging laboratory in Baltimore who conducted similar studies found no evidence that providing their monkeys with less food made any difference in terms of lifespan, as they documented in their own report.

A subsequent dispute between the two research teams over their differing study results continues today.

Regardless of what animal tests are (or are not) able to show, it remains unclear how the outcomes can be made useful for humans.

To understand the effects of calorie restriction, one has to be careful to distinguish between undernutrition, in which all the essential nutrients the body needs to function properly and stay healthy are provided – albeit by using fewer calories, and malnutrition, where at least some nutrients are missing, potentially resulting in harmful deficiencies over time. The latter is certainly not recommended and is not likely to have any health benefits, including for longevity.

In the light of what we know about the health effects of diet to date, we can say with reasonable certainty that moderate calorie restriction in support of weight control is healthy and in any case preferable to excessive weight gain, one of the largest health threats looming today. To what extent that implicates life expectancy remains to be seen. More important to realize, however, is the fact that health-promoting diet and lifestyle choices contribute to the quality of life at any age and become even more significant as we grow older.

Timi Gustafson R.D. is a registered dietitian, newspaper columnist, blogger and author of the book “The Healthy Diner – How to Eat Right and Still Have Fun”®, which is available on her blog and at amazon.com.  For more articles on nutrition, health and lifestyle, visit her blog, “Food and Health with Timi Gustafson R.D.” (www.timigustafson.com).