Looking to tack a few years on to the end of your life, or enjoy your golden years with vigor, good health, and youthfulness? Research on animals shows a restricted-calorie diet may have these effects and slow the hands of time.
Now, practitioners of calorie restriction are hoping that human beings can also drink from the fountain of youth. While only time will tell if it actually works, experts and believers weigh in on the science behind the theory, and the pros and cons of a restricted-calorie diet.
With evidence dating back to 1935, when Cornell scientist Clive McCay unexpectedly discovered that rats on a calorie-restricted diet lived nearly 30% longer than those on "normal" diets, according to a Cornell press release, scientists have been testing the impact of a calorie-restricted diet on everything from mice and worms, to flies, spiders, guppies, dogs, and primates.
"There seem to be two mechanisms by which a restricted-calorie diet increases life span," says Mark Mattson, PhD, chief of the Laboratory of Neurosciences at the National Institute on Aging. "First, it reduces free radical production, or the production of highly damaging forms of oxygen, and the second is that calorie restriction increases the resistance of cells to stress. We think that both of these are important in protecting against a number of different diseases that have a negative impact on life span, such as cardiovascular diseases and cancer."
A restricted-calorie diet has been shown to reduce cholesterol levels and improve blood glucose levels in animals, but the burning question, now, is will a restricted-calorie diet have any long-term benefits for humans?
"There is a lot of evidence to support the benefits of a restricted-calorie diet in rats and mice and other species," says Mattson. "And we can assume that because calorie restriction is important in mice and rats, it's probably important in humans as well, because rats and mice have the same physiology as humans -- they get diabetes and cancers and many of their causes of death are the same as humans."
So it might work, but what's the cost?
The underlying premise of calorie restriction, according to the Calorie Restriction Society web site, is, "to eat fewer calories, while not consuming fewer vitamins, minerals, and other components of a healthy diet, and by doing so achieve a longer and healthier life."
The bottom line? The average male in the U.S. consumes about 2,745 calories every day, and the average female 1,833 calories, according to the CDC. A calorie-restricted diet, depending on how severe a person wants to practice, takes that number and, over time, reduces it by more than one-third.
In 2000, Dean Pomerleau, at 35 years old, 5 feet 8 inches and 172 pounds, described himself as pretty typical.
"My weight was creeping up and I was beginning to see the signs of my own mortality," says Pomerleau, who lives in Pittsburgh. "I was on the downhill side of my youth, and then I heard about the calorie- restriction diet, and the science behind it intrigued me -- that it had a real serious potential for health and longevity. I ended up giving it a try and it really agreed with me."
Four years later and 51 pounds lighter, Pomerleau practices a rigid form of calorie restriction that balances lower calorie intake with proper nutrition.
"I eat the same thing twice a day, seven days a week, 365 days a year," says Pomerleau, of his diet of 1,200 calories a day. "It's a lot of veggies with olive oil-based salad dressing, a lot of mixed fruits, almonds and hazelnuts, and flaxseed oil for omega-3 fatty acids."
Along with a rigorous exercise plan, Pomerleau believes this is adding longevity and quality to his life.
"The animal data, if we can extrapolate, which is pretty extensive all the way up to dogs and primates, suggest that for every calorie you forgo, you can add about 30 seconds on to your life span," says Pomerleau. So in essence, "If you have a slice of pizza, you give up three hours of life. If you skip that slice, you'll get that three hours back. Would you rather have the pizza, or live for three more hours? But it's not just about longevity, there are a number of health and psychological benefits that are here now that are at least rewarding for me than as is the potential for life span expansion."
While adding health and longevity to life may be a result of calorie restriction, Brian M. Delaney, president of the Calorie Restriction Society, also looks at the bigger picture.
"There is substantial evidence that suggests relatively mild versions of this diet lower fasting glucose levels, which will radically reduce the probability that a person will get type 2 diabetes," says Delaney, who practices a more moderate form of calorie restriction. "There is also substantial evidence, though not quite as direct, that someone on a mild form of this diet will reduce his chances of cardiovascular diseases. And, there is evidence, although it's the least direct, that the probability of someone on a restricted-calorie diet getting cancer goes down."
Based on this evidence, explains Delaney, "If around 10% of Americans went on this diet, it would create a reduction in the incidence of these diseases, and reduce nationwide total healthcare costs significantly."
Societal impact aside, Delaney suggests the benefit of calorie restriction is not the possibility of living to 120, but living better, longer.
"There are different groups of people on a restricted-calorie diet," says Delaney. "There are a few life extensionists who are on the diet solely to live longer, others who want to lose weight, but most people just want to be more youthful, longer."
Low Cal, High Nutrition
So how can you do calorie restriction right? The trick is to make sure you're getting adequate nutrition.
"If you're cutting calories and not paying attention to how you eat, there could be some severe health consequences," says Susan Moores, spokeswoman for the American Dietetic Association. "From affecting your immune system to affecting your bones, to affecting your concentration and ability to focus, it's all how you plan your foods. However, if you're only eating 1,000 calories a day and you're eating well, there may be no noticeable changes."
Moores, who is a registered dietitian in St. Paul, Minn., recommends a diet similar to what Pomerleau eats.
"Definitely fruits and vegetables -- there's not a bad one on in the bunch," says Moores. "Also, whole grains, oats, barley, lean sources of protein -- lean red meat, fish, poultry, and eggs, and legumes, which are very power-packed and often forgotten."
"No matter how many calories you cut, you won't reach the fountain of youth without physical activity, without exception," says Moores.
If you're interested in trying calorie restriction, there are steps that can help you test the fountain of youth waters:
Moores strongly recommends working with a dietitian, so an expert can make sure you are getting proper nutrition and making each calorie count.
Pomerleau recommends finding your baseline. "The first thing is to get some blood work done ahead of time to know where you are," says Pomerleau. "Have your cholesterol and blood glucose levels checked so you can track your improvements."
Next, don't overdo it. "Don't make dramatic changes to your diet," says Pomerleau. "Start by cleaning up your diet and substituting refined carbs for healthy fruits and veggies."
Find a support system. "The Calorie Restriction Society is a tremendous resource," says Pomerleau. "For people who are new to the diet, as well as people who have been on it for years."
With a multicenter trial looking at the physiological effects of a restricted-calorie diet underway, researchers hope to pinpoint the impact of this diet in humans. But, only a year in length and looking at factors such as cholesterol and glucose levels, the study will not answer the question practitioners of the diet are longing to know: Will it really increase their life spans?
Nonetheless, Pomerleau and others hope their vigilance pays off.
"The bottom line is that for someone starting calorie restriction around the age of 35, practicing at the level I and keeping it up until they get into old age, they're likely to add -- if the animal evidence can be extrapolated -- from eight to 10 years to their life span," says Pomerleau.
And with a little help from advances in technology, maybe even longer.
"We fully expect there to be substantial improvements in medical technology over the coming decades that could dramatically extend a person's life span," says Pomerleau. "And the target for calorie-restriction practitioners, such as me, is to be around to benefit from them."