WARNING!
This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.
By Dr. Mercola
If you're looking for the proverbial fountain of youth, most researchers and scientists will likely agree that calorie restriction is about as close as you can come.
Research shows that you can slow down aging and significantly increase your lifespan simply by lowering your caloric intake. The effects have been observed in a variety of species from worms and yeast to rats and fish, and there's evidence that calorie restriction has a similar effect on the human lifespan, as well.
Despite its simplicity and proven merit, calorie restriction remains a strategy few people are willing to embrace, but what if you found out the beneficial effects happened rapidly, allowing you to potentially slow down and even reverse the aging process after just a few days or weeks?
Calorie Restriction Provides Anti-Aging Benefits, Fast
Calorie restriction is known to alter the expression of hundreds to thousands of genes, some of which are related to longevity and some of which play a role in metabolism, cell growth, reproduction, immune response, and more.
What is perhaps most exciting is the speed with which these beneficial changes occur. We're not talking about an effect that takes decades to occur, we're talking about benefits that begin virtually immediately. According to one recent paper in regard to calorie restriction in fruit flies, the beneficial changes occurred within days of restricting calories:1
"…diet switches rapidly alter age-specific mortality… Remarkably, when flies are shifted from a rich diet to just a relatively restricted diet, within days the cohort adopts the same trajectory of low age-specific of adults continuously maintained on restricted diet (and vice versa for cohorts switched from restricted to rich diets).
…These observations suggest that the molecular, cellular and physiological changes caused by DR [dietary restriction] to extend lifespan must occur within a short time frame after adults experience an alternative diet."
Other animal studies have similarly found that the life-extension effects of calorie restriction not only happen rapidly but also occur among old animals that have never been on a calorie-restricted diet before.2
What this implies for humans, of course, is that it may lead to rapid changes in genetic expression that promote longevity – even if you're new to calorie restriction. According to researcher Stephen Spindler, Ph.D.:3
"I think the conclusion you can reach from the paper is that even in very old animals, caloric restriction will very rapidly produce most of the gene expression effects that you see in long-term calorie-restricted animals.
That means, I think, that even in the short-term, older people may be able to benefit rapidly from switching to a calorically-restricted diet, and that fits with some of the information that has been in the literature for years.
For instance, type II diabetics improve when they start under-eating. Their blood glucose levels improve. Their insulin sensitivity improves. Their general health improves, even before the fat mass, for instance, is depleted. So, there have been some hints that underfeeding could produce positive effects rather rapidly…"
Short-Term Calorie Restriction May Fight Cancer
In addition to offering anti-aging and longevity benefits, research suggests that strategically restricting your calories may also be an effective form of cancer prevention and treatment, again with results appearing in a matter of days or weeks.
For instance, one animal study tested what would happen when mice with lymphoma were fed a regular diet or a calorie-restricted diet (75 percent of their normal intake) along with a targeted therapy to induce cancer cell death (known as ABT-737).4 The study showed that calorie restriction did improve survival when done along with the treatment. Specifically, median survival was 30 days in the control group that received a regular diet and no treatment, compared with:
- 33 days in mice that received a regular diet and treatment with ABT-737
- 30 days in mice that received a reduced-calorie diet without treatment
- 41 days in mice that received a reduced-calorie diet and treatment with ABT-737
Furthermore, the number of circulating lymphoma cells was reduced in the calorie-restricted/ABT-737 mice, which suggests that the cancer cells had been sensitized to the treatment. As explained by the American Society of Hematology:5
"When humans and animals consume calories, the body metabolizes food to produce energy and assist in the building of proteins. When fewer calories are consumed, the amount of nutrients available to the body's cells is reduced, slowing the metabolic process and limiting the function of some proteins.
These characteristics of calorie restriction have led researchers to hypothesize that reducing caloric intake could potentially help inhibit the overexpression of the protein Mcl-1, an alteration associated with several cancers."
Reducing Your Calories Benefits Your Gut Health Too
There is an emerging consensus that most disease originates in your digestive system, and this includes conditions that impact your brain, your heart, your weight, and your immune system, among others. There's also evidence that the microorganisms present in your gut can affect how well you age,6 and this ties in directly with the latest research on calorie restriction and longevity.
One important thing to remember about the microbes in your gut is that they are not static. They can change profoundly throughout your life, for better or for worse, and one of the biggest influences on this change is your diet.
Indeed, research has shown that life-long calorie restriction in mice "significantly changes the overall structure of the gut microbiota" in ways that promote longevity.7 So it appears that one reason why calorie restriction may lengthen lifespan is because it promotes positive changes to the microorganisms in your gut. However, even if you're not keen on the idea of sacrificing a significant number of your daily calories for the rest of your life, there's a way to get the benefits that this dietary strategy has to offer.
Intermittent Fasting May Work Even Better Than Calorie Restriction (And It's Easier to Stick With)
The primary problem with calorie restriction is the compliance or willingness of anyone to stick with this painful depriving strategy is extremely low. My guess is that less than 1% of people would be willing to do this. Besides it is needlessly painful and uncomfortable as newer strategies that replicate ancestral eating patterns are likely to provide the same benefits and result in naturally reduced desire to eat excess calories.
Krista Varady with the University of Illinois has been researching the impact of fasting on chronic diseases like cardiovascular disease, type 2 diabetes, and cancer. Her work also compares the effects of intermittent fasting with caloric restriction. Animal studies using alternate-day fasting have shown it lowers the risk of diabetes at rates comparable to caloric restriction.8 Alternate-day fasting has also been shown to reduce cancer rates by reducing cell proliferation. So what exactly is intermittent fasting, and how is it different from calorie restriction?
Calorie restriction involves reducing your daily calories by a certain percentage at every meal. Unfortunately, hunger is a basic human drive that can't be easily suppressed, so anyone attempting to implement serious calorie restriction is virtually guaranteed to fail. Fortunately, you don't have to deprive yourself as virtually all of the benefits from calorie restriction can be achieved through properly applied intermittent fasting.
There are many different variations of intermittent fasting. If you are like 85 percent of the population and have insulin resistance, my personal recommendation is to fast every day by simply scheduling your eating into a narrower window of time each day. I find this method to be much easier than fasting for a full 24 hours or more, twice a week, as some people suggest.
In order to understand how you can fast daily while still eating every day, you need to understand some basic facts about your metabolism. It takes most people 8 to 12 hours for their body to burn the sugar stored in your body as glycogen. Now, most people never deplete their glycogen stores because they eat three or more meals a day. This teaches your body to burn sugar as your primary fuel and effectively shuts off your ability to use fat as a primary fuel.
Therefore, in order to work, the length of your fast must be at least eight hours. Still, this is a far cry from a 24-hour or longer fast (or chronic calorie restriction), which can be quite challenging. I believe that, for most people, simply restricting the window of time during which you eat your food each day is far easier. For example, you could restrict your eating to the hours of 11am and 7pm. Essentially, you're just not eating anything for three hours before bed, skipping breakfast and making lunch your first meal of the day instead. This equates to a daily fasting of 16 to 18 hours—more than twice the minimum required to deplete your glycogen stores and start shifting into fat-burning mode.
The Quality of Your Calories Matters When Applying Intermittent Fasting
Please keep in mind that a proper nutrition plan becomes even more important when you're fasting and/or cutting calories, so you really want to address your food choices before you try any form of fasting. You need to make the calories you do consume count. Simply relying on fast food and processed foods during your non-fasting hours will not give you the longevity benefits you're after. So when you do eat, make sure to minimize carbs like pasta, bread, and potatoes.
Instead, exchange them for healthy fats like butter, eggs, avocado, coconut oil, olive oil, and nuts—essentially the very fats the media and "experts" tell you to avoid. You may also want to restrict your protein a bit if you're typically a big meat eater. I strongly suggest eating only high-quality pastured protein, and limiting it to about one gram of protein per kilogram of lean body mass (about one-half gram of protein per pound of lean body weight) may be appropriate for most people. (Note: if your body fat mass is 20 percent, your lean mass is 80 percent of your total body weight.) These kinds of food choices, in combination with intermittent fasting, will help shift you from carb-burning to fat-burning mode.
How Does Intermittent Fasting Work?
Mounting research confirms that when your body becomes accustomed to burning FAT instead of sugar as its primary fuel, you rather dramatically reduce your risk of chronic disease. Becoming fat adapted may even be a key strategy for both cancer prevention and treatment, as cancer cells cannot utilize fat for fuel—they need sugar to thrive. In short, fasting increases insulin sensitivity along with mitochondrial energy efficiency, thereby retarding aging and disease, which are typically associated with loss of insulin sensitivity and declined mitochondrial energy. Two additional mechanisms by which fasting benefits your body include:
- Reducing oxidative stress – Fasting decreases the accumulation of oxidative radicals in the cell, and thereby prevents oxidative damage to cellular proteins, lipids, and nucleic acids associated with aging and disease.
- Increasing capacity to resist stress, disease, and aging – Fasting induces a cellular stress response (similar to that induced by exercise) in which cells up-regulate the expression of genes that increase the capacity to cope with stress and resist disease and aging.
While most people will successfully switch over to burning fat after several weeks of intermittent fasting, you may need several months to teach your body to turn on the fat-burning enzymes that allow your body to effectively use fat as its primary fuel. So if you're using intermittent fasting for weight loss, don't give up! The other benefit to intermittent fasting is that once you've become fat adapted and are of a normal weight, without high blood pressure, diabetes, or high cholesterol, you really only need to do scheduled eating occasionally. As long as you maintain your ideal body weight, you can go back to eating three meals a day if you want to. I restricted my eating to a six- to seven-hour window each day until I got fat adapted and lost about 10 pounds. Now, I still rarely ever eat breakfast, but several days a week, I will have two meals instead of just one.
Compelling Reasons to Give Intermittent Fasting a Try
For most people, the idea of extending lifespan, lowering the risk of chronic disease, and losing weight is quite alluring, even if the idea of calorie restriction is not. Intermittent fasting offers a way for you to glean these benefits without feeling deprived, and it's a strategy I urge virtually everyone to try (see below for a few exceptions). Based on my own phenomenal experience with intermittent fasting, I believe it's one of the most powerful ways to shift your body into burning fat for fuel and improve a wide variety of biomarkers for disease.
For example, research presented at the 2011 annual scientific sessions of the American College of Cardiology in New Orleans showed that fasting triggered a 1,300 percent rise of human growth hormone (HGH) in women, and an astounding 2,000 percent in men.9 HGH, commonly referred to as "the fitness hormone," plays an important role in maintaining health, fitness, and longevity, including promotion of muscle growth, and boosting fat loss by revving up your metabolism.
Additionally, intermittent fasting may trigger your brain to release brain-boosting protein called brain-derived neurotrophic factor (BDNF). Fasting every other day may boost BDNF by anywhere from 50 to 400 percent,10 depending on the brain region.11 This is great news, as BDNF activates brain stem cells to convert into new neurons, and triggers numerous other chemicals that promote neural health. This protein also protects your brain cells from changes associated with Alzheimer's and Parkinson's disease. Other health benefits of intermittent fasting include:
| Normalizing your insulin and leptin sensitivity, which is key for optimal health | Improving biomarkers of disease |
| Normalizing ghrelin levels, also known as "the hunger hormone" | Reducing inflammation and lessening free radical damage |
| Lowering triglyceride levels | Preserving memory functioning and learning |
I believe intermittent fasting is one of the most powerful ways to improve a wide variety of biomarkers for disease. The effects can be further magnified by exercising while in a fasted state. There are a few exceptions to consider if you're thinking of giving fasting a try: if you're hypoglycemic, adrenal fatigued, diabetic, or pregnant (and/or breastfeeding), you are better off avoiding any type of fasting or timed meal schedule until you've normalized your blood glucose and insulin levels, or weaned the baby. Other categories of people who would be better off avoiding fasting include those living with chronic stress and those with cortisol dysregulation.