By Dr. Mercola
Is it a good idea to “starve” yourself just a little bit each day? The evidence suggests that yes, avoiding eating around the clock could have a very beneficial impact on your health and longevity.
What we’re talking about here is generally referred to as intermittent fasting, which involves timing your meals to allow for regular periods of fasting.
It takes about six to eight hours for your body to metabolize your glycogen stores and after that you start to shift to burning fat. However, if you are replenishing your glycogen by eating every eight hours (or sooner), you make it far more difficult for your body to use your fat stores as fuel.
It's long been known that restricting calories in certain animals can increase their lifespan by as much as 50 percent, but more recent research suggests that sudden and intermittent calorie restriction appears to provide the same health benefits as constant calorie restriction, which may be helpful for those who cannot successfully reduce their everyday calorie intake (or aren't willing to).
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.
Three Major Mechanisms by which Fasting Benefits Your Health
While fasting has long gotten a bum rap for being one of the more torturous ways to battle the bulge, it really doesn’t have to be an arduous affair. We’re NOT talking about starving yourself for days on end. Simply restricting your daily eating to a narrower window of time of say 6-8 hours, you can reap the benefits without the suffering. This equates to 16-18 hours worth of fasting each and every day — enough to get your body to shift into fat-burning mode.
Many studies have evaluated daily intermittent fasting, and the results are compellingly positive. Three major mechanisms by which fasting benefits your body, as it extends lifespan and protects against disease, include:
- Increased insulin sensitivity and mitochondrial energy efficiency – Fasting increases insulin sensitivity along with mitochondrial energy efficiency, and thereby retards aging and disease, which are typically associated with loss of insulin sensitivity and declined mitochondrial energy.
- Reduced 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.
- Increased 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.
Is Daily Fasting the Key to Permanent Weight Loss?
As reported by George Dvorsky1 in a recent article, one of the most important studies in support of daily intermittent fasting was published just last year by biologist Satchidananda Panda and colleagues at Salk's Regulatory Biology Laboratory. They fed mice a high-fat, high-calorie diet but altered when they were able to eat.
One group had access to food both day and night, while the other group had access to food for only eight hours at night (the most active period for mice). In human terms, this would mean eating only for 8 hours during the day. Despite consuming the same amount of calories, mice that had access to food for only eight hours stayed lean and did not develop health problems like high blood sugar or chronic inflammation2. They even had improved endurance motor coordination on the exercise wheel. The all-day access group, on the other hand, became obese and were plagued with health problems including:
- High cholesterol
- High blood sugar
- Fatty liver disease
- Metabolic problems
This suggests that your body may benefit from the break it receives while fasting, whereas constant eating may lead to metabolic exhaustion and health consequences like weight gain. Researchers said their latest work shows it's possible to stave off metabolic disease by simply restricting when you eat with periodic fasting, or even by just keeping to regular meal schedules rather than "grazing" off and on all day. They concluded:
"[Time-restricted feeding] is a nonpharmacological strategy against obesity and associated diseases."
What the Research Says about Intermittent Fasting
Dvorsky highlights other research into fasting that point to similar conclusions, such as:
- Research by Valter Longo3 at the University of Southern California's Longevity Institute shows that intermittent fasting has a beneficial impact on IGF-1, an insulin-like growth factor that plays a role in aging. When you eat, this hormone drives your cells to reproduce, and while this is good for growth, it’s also a factor that drives the aging process. Intermittent fasting decreases the expression of IGF-1, and switches on other DNA repair genes. In this way, intermittent fasting switches your body from “growth mode” to “repair mode.”
- 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, which is known to benefit health and longevity. Animal studies using alternate-day fasting4 have shown it lowers the risk of diabetes, at rates comparable to caloric restriction. Alternate-day fasting has also been shown to reduce cancer rates by reducing cell proliferation.
- Research by Mark Hartman and colleagues5 indicates short-term fasting can trigger production of human growth hormone (HGH) in men, and reduce oxidative stress that contributes to disease and aging; benefits brain health, mental well-being, and clarity of thought
Review Debunks Myths about Weight Loss, Obesity
Intermittent fasting is one of the latest weight management strategies to get a lot of press. Meanwhile, other weight loss myths are being debunked. Dr. David B. Allison, director of the Nutrition Obesity Research Center at the University of Alabama, and colleagues recently published a paper on Myths, Presumptions, and Facts about Obesity6, stating:
“Many beliefs about obesity persist in the absence of supporting scientific evidence (presumptions); some persist despite contradicting evidence (myths). The promulgation of unsupported beliefs may yield poorly informed policy decisions, inaccurate clinical and public health recommendations, and an unproductive allocation of research resources and may divert attention away from useful, evidence-based information.”
The team identified:
- Seven obesity-related myths concerning the effects of small sustained increases in energy intake or expenditure, establishment of realistic goals for weight loss, rapid weight loss, weight-loss readiness, physical-education classes, breast-feeding, and energy expended during sexual activity. These include:
- Small things make a big difference. Walking a mile a day can lead to a loss of more than 50 pounds in five years.
- Set a realistic goal to lose a modest amount.
- People who are too ambitious will get frustrated and give up.
- You have to be mentally ready to diet or you will never succeed.
- Slow and steady is the way to lose. If you lose weight too fast, you will lose less in the long run.
- Six presumptions that have yet to be proven true or false about the effects of regularly eating breakfast, early childhood experiences, eating fruits and vegetables, weight cycling, snacking, and the built (i.e., human-made) environment, such as:
- Diet and exercise habits in childhood set the stage for the rest of life.
- Add lots of fruits and vegetables to your diet to lose weight or not gain as much.
- Yo-yo diets lead to increased death rates.
- People who snack gain weight and get fat.
- If you add bike paths, jogging trails, sidewalks and parks, people will not be as fat.
- Nine evidence-supported facts that are relevant for the formulation of sound public health, policy, or clinical recommendations, including:
- Heredity is important but is not destiny.
- Exercise helps with weight maintenance.
- Weight loss is greater with programs that provide meals.
- Some prescription drugs help with weight loss and maintenance.
- Weight-loss surgery in appropriate patients can lead to long-term weight loss, less diabetes and a lower death rate
What I feel is missing here is the focus on an all-around healthy lifestyle pattern. Can you lose weight on prescription drugs? Yes. Does the research support this as “fact”? Yes. But this does NOT automatically mean that recommending diet drugs is good public health policy! Will diet drugs have a beneficial impact on your health in the long run? Do potential side effects of the drugs outweigh the benefit of losing weight?
Ditto for bariatric surgery. Does it lead to weight loss? Yes! But the side effects can be severe, including death, and several studies have shown the long-term outcome in terms of overall health is not that great...
Some of the items listed as myths and presumptions are simply common-sense guidelines and “helpful tips” that can help you maintain a healthier lifestyle, which will inevitably form the foundation of good health. So I would advise you to differentiate between “established scientific fact” (such as: weight loss surgery leads to weight loss) and what amounts to holistic healthy lifestyle guidelines, as the two are not necessarily interchangeable.
If your goal is to promote health, then supporting the addition of bike paths in your communities is not a crazy idea at all. In fact, some of these myths and presumptions are sort of silly, as when you talk about things like “can adding jogging trails and parks promote healthier weight?” You also have to consider the fact that there is social conditioning at work, and people have to start to rethink how they live their daily lives in order to see a change. This can take time. Having a public policy that tells you to get bariatric surgery instead of going for a walk every day is nothing short of crazy if you really think about it...
Clinical Trial to Be Conducted to Test Whether Skipping Breakfast Leads to Weight Loss
According to the New York Times7:
“... people often rely on weak studies that get repeated ad infinitum. It is commonly thought, for example, that people who eat breakfast are thinner. But that notion is based on studies of people who happened to eat breakfast. Researchers then asked if they were fatter or thinner than people who happened not to eat breakfast — and found an association between eating breakfast and being thinner. But such studies can be misleading because the two groups might be different in other ways that cause the breakfast eaters to be thinner. But no one has randomly assigned people to eat breakfast or not, which could cinch the argument.
... The question is: ‘Is it a causal association?’ To get the answer, he added, 'Do the clinical trial.'
He decided to do it himself, with university research funds. A few hundred people will be recruited and will be randomly assigned to one of three groups. Some will be told to eat breakfast every day, others to skip breakfast, and the third group will be given vague advice about whether to eat it or not."
Is Intermittent Fasting Right for You?
If you're already off to a good start on a healthy diet and fitness plan, then intermittent fasting might be just the thing to bring you to the next level. However, you need to pay careful attention to your body, your energy levels, and how it makes you feel in general.
Please keep in mind that proper nutrition becomes even MORE important when fasting, so addressing your diet really should be your first step. Common sense will tell you that fasting combined with a denatured, highly processed, toxin-rich diet is likely to do more harm than good, as you're not giving your body proper fuel to thrive when you DO eat.
If you're hypoglycemic, 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. Others categories of people that would be best served to avoid fasting include those living with chronic stress, and those with cortisol dysregulation.
Signs and Symptoms of Hypoglycemia
Hypoglycemia is a condition characterized by an abnormally low level of blood sugar. It's commonly associated with diabetes, but you can be hypoglycemic even if you're not diabetic. Common symptoms of a hypoglycemic crash include:
As your blood glucose levels continue to plummet, more severe symptoms can set in, such as:
- Confusion and/or abnormal behavior
- Visual disturbances, such as double vision and blurred vision
- Loss of consciousness
One of the keys to eliminating hypoglycemia is to eliminate sugars, especially fructose from your diet. It will also be helpful to eliminate grains, and replace them with higher amounts of quality proteins and healthful fats. However it will take some time for your blood sugar to normalize. You'll want to pay careful attention to hypoglycemic signs and symptoms, and if you suspect that you're crashing, make sure to eat something. The ideal food would be coconut oil as it will not worsen your insulin levels and is metabolized relatively quickly for energy. You can try some coconut candy, for example. Ideally, you should avoid fasting if you're hypoglycemic, and work on your overall diet to normalize your blood sugar levels first. Then try out one of the less rigid versions of fasting and work your way up.
Fasting While Pregnant is Not a Good Idea...
As for pregnant and/or lactating women, I don't think fasting would be a wise choice. Your baby needs plenty of nutrients, during and after birth, and there's no research supporting fasting during this important time. On the contrary, some studies8 suggest it might be contraindicated, as it can alter fetal breathing patterns, heartbeat, and increase gestational diabetes. It may even induce premature labor. I don’t think it’s worth the risk.
Instead, my recommendation would be to really focus on improving your nutrition during this crucial time. A diet with plenty of raw organic, biodynamic foods, and foods high in healthful fats, coupled with high quality proteins will give your baby a head start on good health. You'll also want to be sure to include plenty of cultured and fermented foods to optimize your — and consequently your baby's — gut flora. For more information, please see this previous article that includes specific dietary recommendations for a healthy pregnancy, as well as my interview with Dr. Natasha Campbell-McBride.
Finding a Lifestyle Plan that Works for You Requires Trial and Error
While intermittent fasting can provide valuable health benefits, remember that fasting does not mean abstaining from ALL food for extended periods of time. Rather it involves a dramatic reduction of calorie intake at regular intervals — whether you opt for a 16, 20, or 24 hour fast once or twice a week, or fasting every other day, or simply delaying certain meals, such as skipping breakfast.
Just remember, it takes about six to eight hours for your body to metabolize your glycogen stores and only after that do you start to shift to burning fat, but only if you are already adapted to burning fat by having your fat burning enzymes upregulated by the strategy discussed above, which takes anywhere from a few weeks to a few months, depending on how healthy you are.
Always listen to your body, and go slow; work your way up to 16-18 hour fasts if your normal schedule has included multiple meals a day. Also be sure to address any hypoglycemic tendencies, as it can get increasingly dangerous the longer you go without eating to level out your blood sugar.
If you have already addressed your diet, cutting out fructose and grains and replacing them with healthful fats, then intermittent fasting could further boost weight loss and provide additional health benefits. If you’re engaged in a regular fitness program and feel like you’ve hit a plateau, then working out in a fasted state might help rev things up. For more information about exercise while fasting, please see this previous article.