Dukan, Paleo, Atkins. Some diet plans seem to explode into our consciousness and onto the pages of glossy magazines in a flash of publicity (and sometimes controversy), only to quickly disappear from the headlines, making way for the next dietary fad.

One trend that has consistently intrigued the scientific community, however, is a diet that has existed for many years but has never become mainstream. Perhaps because it’s difficult to adhere to its rules. This diet plan is known as Caloric Restriction with Optimal Nutrition (CRON, or sometimes just CR). Its ultimate aim is not to help proponents lose weight, but rather to make them live longer — much longer. The central premise of the diet is very simple: the dieter only has to eat approximately 25 percent less than the recommended daily allowance. Sounds simple, right?

Well, it is no surprise that many people refer to CR as the “starvation diet.” Yet, the idea is not to starve, but to exist just above that level and to live off a highly nutritious diet that consists of very few calories. Its supporters have pointed out that human biology has evolved over millennia to cope better with very little, rather than a lot.

A typical man on a CR diet, therefore, would consume 1,700 to 1,900 calories a day, which is almost half of what the average U.S. male currently consumes. Some proponents of caloric restriction adhere to the diet plan by choosing to essentially eat nothing for two-to-three days a week, usually on alternate days.

The History Of CRON

CRON was pioneered by Dr. Roy Walford, the author of The 120-Year Diet . Walford, a medic who served in the Korean War, promised from the outset that following his diet plan would retard the rate of aging, leading to an increased lifespan (up to perhaps 150 to 160 years, depending on when one started the diet and how thoroughly one held to it) and a marked decrease in susceptibility to most major diseases.

In 1991, Walford became physician to the crew of Biosphere 2, an enclosed three-acre bubble in the Arizona desert designed to test if space colonization might be possible. After crop yields inside the sealed greenhouses proved disappointing, Walford convinced his fellow “econauts” (as the inmates were called) to follow his radical diet. When they emerged from the experiment two years later, they not only displayed substantial weight loss (14 percent), but also lower blood pressure and cholesterol, more efficient metabolisms, and enhanced immune systems.

Walford, who was a renowned pathologist at the University of California, Los Angeles, spent much of the last 30 years of his life following a calorie-restricted regimen. He died of Lou Gehrig’s disease (a neurodegenerative disorder) in 2004 at the age of 79 years. Rather poignantly, however, recently published work reported that long-term caloric restriction hastens disease progression and shortens lifespan in a Lou Gehrig’s disease mouse model.

So, is caloric restriction an anti-ageing elixir that has always has been, albeit unknowingly, readily available to us? Or is it a hazardous pseudoscience thrown into the already murky mix of quick-fix dietary “advice,” at a time when contradictory messages regarding both obesity and eating disorders are on the rise?


The theory that intentionally depriving the body of energy may actually be of benefit originated in 1935. Dr. Clive McCay, a nutritionist at Cornell University in New York, reported that mice who consumed 30 percent fewer calories lived about 40 percent longer than their free-grazing laboratory mates. The dieting mice were also more physically active and far less prone to the diseases of advanced age.

McCay’s experiment was successfully completed in a variety of species over the following decades, including in fruit flies, roundworms, and mice. These studies concluded that lowering energy intake could switch biochemical pathways on or off, resulting in greater insulin sensitivity (sugar sensitivity), enhanced cardiovascular functioning, and reduced age-related muscle wastage, to list just some of the benefits. In addition to allaying the normal aging process, caloric restriction has been shown to greatly reduce the incidence of age-related diseases, such as diabetes and cancer.

Arguably the best study of the CRON diet ever performed on animals yielded headline-grabbing findings at the start of this decade. This study involved 20 years of applied CR to our genetic “neighbors,” the rhesus monkeys, and was carried out at Wisconsin National Primate Research Center in Madison.

Rhesus Monkeys on CR Diet
In a 2009 study, 27-year-old rhesus monkeys were put through a CR diet. Photos A and B show a monkey on a normal diet, while photos C and D show a younger, healthier looking monkey on a CR diet. Science Magazine

According to the report, which was published in the esteemed scientific journal Nature , approximately 20 percent of normally fed monkeys had evaded age-related mortality 31 years after they were born. In contrast, this number was almost doubled in CR-fed animals. The appearance of the monkeys was even more astonishing, as the non-treated set reportedly looked visibly older, even to the untrained eye.

Following the CR diet as a general practice has its supporters within the scientific world, with Dr. Luigi Fontana, research associate professor of medicine at Washington University, St Louis, being one notable proponent. Fontana told School of Medicine magazine that although animals on calorie-restricted diets still die eventually, they do not suffer from illness before they die. Indeed, calorie restriction goes further by also affecting markers associated with primary aging.

This also appears to hold true in the human population. For example, ultrasound examinations have revealed that the hearts of people on calorie-restricted diets are more “elastic” and efficient than those of age- and gender-matched control subjects. These patients also have lower markers of inflammation. The changes seem to be related to the CR diet, rather than to body weight.

Fontana was quick to clarify that many of the changes observed were due to lower energy intake, rather than to leanness. He further stated: “We’ve found that although exercise helps prevent many problems that can cut life short — such as obesity, diabetes, and cardiovascular disease — only CR appears also to influence primary aging.”


All of this research seems universally positive. However, CR has its detractors and the science behind it also has its shortcomings. Current epidemiological data does not largely support the conclusion that those who are thinnest live longest, while back in 2009, a long-term study of middle-aged and elderly people by Tohoku University’s Graduate School of Medicine showed that people who were a little overweight at age 40 lived six to seven years longer than very thin people.

In addition, the Japanese study also addressed one theory that held that thin people’s lives were short because many of them were either sick or they smoked. But the difference was almost unchanged, even when these factors were eliminated.

There is great suspicion of the unknown in medical research, specifically the dangers of what caloric restriction might mean to those at various stages in the life cycle and to those who carry other conditions such as, for example, the aforementioned Lou Gehrig’s disease.

There is also a fear that CR may encourage possible psychological issues in vulnerable people: the diet may endanger its proponents to anorexia or other eating disorders. This charge, however, has been flatly rejected in the past by Brian M Delaney, president of the Calorie Restriction Society.

One might presume that a diet plan that promises to extend longevity would see us all signing up en masse , but perhaps CR takes a special kind of commitment that is beyond most of us. Those of us who love our grub might find a calorie-restricted existence to be rather joyless. It seems a universal truth that most things that are good for us are generally not much fun. Maybe someday, scientists will point to the health benefits of watching box sets of Game of Thrones with a six-pack of beer. Until then, however, we will have to aspire to the CR diet.

Dr. John Carrigan is a biochemist from Dublin, Ireland with over 10 years experience in both the biotech and research environments. He has worked in such diverse fields as engineering enzymes for diagnostic kits and analyzing the metabolic effects of cancer. More recently, he has been focused on the potential for algae oil as a food source. When away from the lab he likes to write, drink Guinness, and bet on horses.