💥 Choose a PN program for FREE—when you join the PN Nutrition Certification for $59/month


💥 Choose a PN program for FREE—when you join the PN Nutrition Certification for $59


Become a Certified Nutrition Coach

  • Join for only $59/month
  • Make a great living helping people transform their health
  • Choose a PN Specialist Program for FREE ($697 value)

Calorie restriction and intermittent fasting:
Is the Fountain Of Youth really in your kitchen?


Is living longer a simple matter of eating less? Here we look at two increasingly popular diets and their potential effects on longevity.


As a species, we’ve been after the Fountain of Youth for thousands of years. Ask your doctor what the secret to living beyond 100 is, and he or she will probably have a chuckle and tell you to eat healthy, stay active, and cross your fingers — a lot of it is luck and genetics.

But you’ve probably heard whispers about certain diets that promise longer, healthier lives.

People on the fringe — and I’m not offending them here, because they’re proud to be on the fringe — who practice calorie restriction and intermittent fasting believe that eating a lot less may help you live a lot more (and better).

Should we all be shrinking and/or skipping meals if we want to live long enough to see time travel and flying cars?

Let’s find out.

What is aging, and why does it happen?

Fascinating fact: The molecular clock in our germline cells — those from which our offspring are made when egg and sperm combine — is kept at zero. If it weren’t, babies would actually be born at Mom or Dad’s age!

If ageless cells already exist, this means we could be immortal one day. It’s possible at least in theory.

Why, then, do we age?

We don’t completely know for sure.

What we do know is that it takes a lot of energy to maintain cells and repair the damage that occurs throughout a lifetime. Wear and tear takes a toll. Cells break down, much like cars.

DNA damage in our cells’ nuclei and mitochondria start to accumulate. Meanwhile, the older we get, the harder it is to repair things. At a certain point, the damage is bad enough, and widespread enough, that our cells can’t fix it.

This means our cells (and our tissues) oxidize, become inflamed, and/or fill up with waste. Which leads to chronic diseases like cancer, metabolic disruptions, and/or neurodegenerative disease.

And — in case you haven’t noticed — this functional decline ends in death.

Naturally, we’d all like to find a way to delay that.

It may not be as far-out as it seems (and, no, we don’t have to wait for robotic avatars to replace the human body).

If the mechanisms that cause us to age and die are closely associated with the factors behind chronic disease, then to delay aging and death, we can focus on preventing the cellular damage and health problems that cause them.

Pretty nifty.

Obviously, if you want to age well, start with a healthy diet. But you may be able to take it a step further. Evidence shows that prudent and well-designed dietary restriction can help.

Before we get into the details, let’s take a step back and define longevity.

How are we doing, anyway?

Thanks to advancements like improved sanitation, vaccination, the use of antibiotic and antiviral drugs, and life-lengthening treatments for cancer and heart disease, over the past few decades average life expectancy has steadily gone up.

Babies born in 2013 can expect to live to an average age of 78.7. That’s five years longer than the at-birth life expectancy in 1980. One study suggests that, assuming progress in medicine continues, life expectancy at birth could be about 90 by 2050.

Given this upward trend, why should we even care about aging?

Well, while our life expectancy may be increasing thanks to modern medicine, our health span — the number of years we’re healthy and disease-free — is shrinking.

According to the World Health Organization, more than a third of the U.S. population is obese. About the same proportion will be diabetic by 2050, if current lifestyle trends continue.

Sure, as a population, we live longer.

And thankfully, we think that’s important now. Nobody floats us out to sea on an iceberg or leaves us behind to fend for ourselves the moment we become enfeebled.

But we don’t always live better.

We survive, held together by the duct tape of pharmaceuticals and surgery. We get around as best we can with assistive devices and lifestyle kludges.

We survive… but don’t necessarily thrive.

Luckily, there are other options.

By improving our diets and getting more active, we can live longer… and better.

Caloric restriction

Researchers define caloric restriction (CR) as reducing food intake while avoiding malnutrition.

In animal studies, this usually means consuming 30-40 percent fewer calories than the standard daily requirement. That’s the equivalent of limiting daily intake to around 1,200 calories for women and 1,400 for men.

CR has prolonged life in dogs, rodents, worms, flies, yeast, different kinds of bugs, and (arguably) non-human primates by 30 to 50 percent.

Wow! If that’s the case, then why aren’t we all restricting calories like crazy?

(Well, besides the fact that most of us love to eat.)

First of all, this is animal research we’re talking about here. And just because something’s true for an animal kept in laboratory conditions doesn’t mean the same will be true for a human “in the wild.”

Humans live a lot longer than the animals used for CR experiments. A mouse that spends 12 months on a calorie-restricted diet has just devoted half its life to the cause.

Plus, reducing calories by 30-50 percent in the modern human diet could easily lead to malnutrition, since the processed foods many have come to heavily rely on aren’t exactly nutrient-dense. In that case, CR would actually decrease your health span (and, potentially, life expectancy) instead.

In short, you are not a rat.

However, there is some real-world evidence that restricting calorie intake by just 15 percent over the long term may be effective in humans. Let’s take a closer look.

The Okinawa “experiment”

Maybe you’ve heard of the Japanese island of Okinawa. Fifty people out of every 100,000 in Okinawa live to be at least 100 years old.

That’s five times as many as in the U.S.

Naturally, researchers are all over this. What makes Okinawans live so long?

Here’s what one study revealed:

  • Okinawans had 80 percent lower mortality from coronary heart disease and 40 percent less from cancer than folks in the U.S.
  • Older Okinawans consumed 1,780 calories daily — 11-15 percent fewer than would normally be recommended to maintain their body weight.
  • Adult BMI averaged 21 (compared to 29 in the U.S.), and people reached peak body weight in young adulthood.
  • The older folks ate a diet low in protein and rich in “functional” foods — ones  believed to promote health (potentially adding to the effects of calorie restriction).
  • Younger Okinawans who did not follow a CR diet had higher BMIs at all ages, as well as higher incidence of type 2 diabetes and higher risk of heart disease.

Note that this study was not a controlled clinical trial. So the significance of these results is still debated.

Still, these findings are interesting because they involve human subjects.

Also, the younger population, who eat more like typical modern humans, served as sort of a “negative” control. It showed that Okinawans are not a naturally long-lived population for genetic or other reasons.

Could the Okinawans’ calorie-restricted diet be their trick for avoiding chronic disease?


But there’s a key factor that can’t be overlooked: protein.

Is it just all about the protein?

Sure, the older Okinawans don’t eat much. More specifically, though, they don’t eat much protein.

Controlled studies on humans confirm that living longer depends on lower levels of the hormone “insulin-like growth factor,” or IGF-1. How do you reduce IGF-1? Eat less protein.

This suggests that unless we cut back on protein, reducing calories won’t really affect how long we live. (It works differently in rodents. One more bit of proof that you are not a rat.)

Thus, in essence, effective caloric restriction in humans is really caloric restriction plus protein restriction.

So, should we do like the Okinawans do and reduce dietary protein to reach the big 100?

Not necessarily.

First, IGF-1 plays an important role in childhood growth. It is no surprise, then, that Okinawans tend to be on the small side. Even smaller than the rest of the Japanese population.

In adulthood, we need IGF-1 for building muscle mass.

This is why reducing protein and trying to maintain (or gain) muscle are mutually exclusive goals.

Which might give you pause if you are hoping for a six pack — or even simply improved strength.

Drawbacks of CR

As it turns out, that’s not the only potential drawback of a prolonged calorie- and protein-restricted diet. With such a diet, we also risk:

  • Depleting our growth, insulin, and thyroid hormones
  • Age-related muscle wasting (aka sarcopenia)
  • Having less bone mass and more osteoporosis
  • Poor cardiac health (IGF-1 helps maintain the heart muscle)
  • Amenorrhea (missing menstrual periods)
  • Weaker immune systems and slower healing
  • Lowering our libidos and fertility
  • Worse athletic performance and less strength
  • Anemia
  • Getting more forgetful with reduced cognitive function

So how come the Okinawans seem to escape these problems?

Their nutrient-rich diet probably helps. Certain aspects of their environment and lifestyle could also play a role. Plus, they’ve been eating this way for generations, so it’s possible they’ve evolved to handle it.

Luckily for those of us who would like to increase our health span and maintain our fitness, caloric restriction is not the only path.

Intermittent fasting

Intermittent fasting (IF) may sound technical. But all it really means is going for extended periods without eating.

Throughout the world there are many tribes who naturally experience some form of IF. Among them, many show no signs of age-associated problems like cancer, neurodegeneration, diabetes, cardiovascular disease, or hypertension.

The reality is that fasting is an intrinsic part of human life. IF in its most basic form is called… sleeping.

There are many ways to do IF on purpose, including meal skipping, alternate day fasting, Eat Stop Eat, and more. For a full rundown, check out PN’s popular free e-book on the topic, Experiments with Intermittent Fasting.

Recent research shows that IF, when done properly, might help regulate blood glucose, control blood lipids, reduce the risk of coronary disease, manage body weight, help us gain (or maintain) lean mass, reduce the risk of cancer, and more.

Now, these studies are still in their early stages, so there’s plenty of room for skepticism. Still, the findings indicate that IF could have a significant impact on our health span.

That means that IF may be a more effective method for lengthening your life, because it:

  • provides similar metabolic benefits as long-term CR
  • lacks many of the negative side effects of CR
  • is more manageable psychologically, and, therefore, easier to adhere to
  • won’t necessarily help you lose weight (a plus if that’s not your goal), but will still protect you from metabolic damage

Finally, there’s related protocol called periodic fasting, or PF. The idea here is the same, except that fasting cycles are longer (typically 2 or more days) and separated by at least one week to allow for any lost weight to be regained.

According to research, PF tends to produce more pronounced changes in growth factors and metabolic biomarkers, indicating that it may provide greater health benefits than IF. But it remains to be seen which is truly better for longevity.

Overall, we file IF and PF’s health benefits under “Inconclusive…but Really Interesting.”

IF isn’t for everyone

Intermittent fasting is not a healthy option for everybody.

Active women, in particular, should be cautious. We just don’t know whether IF’s benefits in exercising women outweigh the possible risks.

And we don’t advise IF at all if:

  • you’re pregnant
  • you have a history of disordered eating
  • you’re chronically stressed (which covers a lot of us in the 21st century)
  • you don’t sleep well
  • you’re new to diet and exercise

There are plenty of other measures you can take to improve your health span if any of these describe you. Focus on those before you consider fasting.

What’s the role of exercise?

It goes without saying that we should all be doing some sort of conditioning exercise a few times a week.

But the combination of exercise and IF, in particular, has synergistic effects on insulin sensitivity and inflammation.

Though we have little scientific evidence that working out can directly extend lifespan on its own, the proven health benefits of exercise — including aerobic capacity, muscle mass, strength, and improved bone density — are enough to convince most.

Add physical activity to your life, and you may protect yourself from heart disease, diabetes, and osteoporosis. And to this day exercise is the best intervention for age-related muscle loss that we know of. No drug comes close.

What do animal studies say about exercise and IF? You might be interested to know that our most frequently used exercise model — Mus musculus, or the common mouse — does not die of the same ailments as we Homo sapiens. They most often fall to kidney disease and cancer. So exercise will do very little for Mickey’s quest to live forever.

What did I tell you? You are not a rat.

What to do next

As it stands, we don’t have enough evidence to safely recommend long-term CR as an anti-aging strategy.

Remember: CR can put you at risk for malnutrition. And because it appears to require protein restriction, CR’s health risks probably outweigh the potential benefits.

Not to mention that CR is a major commitment that would be tough to balance with any kind of social life.

All in all, IF seems like a better bet than CR for those hunting for the Fountain of Youth (and those comfortable with self experimentation).

Which IF protocol to choose?

Given that even different types of mice respond variably to different modes of dietary restriction, the optimal IF approach for you may be that one that best fits your lifestyle. (And genetics—but we’re not there yet with the science.)

We do know that when we fast, our bodies can begin a famine-type response as soon as glycogen (our stored energy) is depleted — generally in just 12-24 hours.

So the most balanced solution for most may be a slightly extended overnight fast, which might provide similar benefits to the more extreme IF regimens while having virtually no impact on our daily schedules.

Best advice: Take it easy (remember, this is intermittent fasting, not intermittent eating).

Here’s how to get started:

  • Be flexible with how you define IF for yourself. A good starting point is to try to resist eating late into the night and take a bit longer to make breakfast in the morning.
  • Next, experiment with skipping breakfast a few times per week.
  • Once you’ve determined how the longer fast makes you feel, consider instituting an honest nightly fast of 12 to 16 hours.
  • Once you do break the fast, have a plan. Eat healthy, whole foods. Binging on Oreos won’t net you any health benefits.
  • Keep active, exercising regularly.
  • If you are underweight, type I diabetic, or have extreme hypertension, make sure you consult with your doctor before attempting any form of dietary restriction, including this one.

Again, intermittent fasting is not for everyone. But for some people, it may help to improve fitness and act as a fountain of youth.


Click here to view the information sources referenced in this article.

Eat, move, and live…better.©

The health and fitness world can sometimes be a confusing place. But it doesn't have to be.

Let us help you make sense of it all with this free special report.

In it you'll learn the best eating, exercise, and lifestyle strategies – unique and personal – for you.

Click here to download the special report, for free.