By Dr. Mercola
Over the years, many theories have been advanced about how much you should eat and when you should eat it to achieve optimal health.
Research reveals many Americans eat all day long, as frequently as 15 out of the 24 hours.1 Most also consume a majority of their daily calories late in the evening. Such dysfunctional eating patterns are a recipe for metabolic upset and weight gain.
Unique diets and diet advice abound. In recent years, intermittent fasting has been promoted as a means of preventing your risk of chronic disease, as well as a potential avenue for adding years to your life.
While you may cringe at the thought of skipping meals or limiting your eating to certain hours of the day, there is a growing body of evidence to suggest the health benefits of doing so could have a dramatic, positive effect on your sense of well-being.
Particularly if you're overweight and accustomed to "grazing" throughout the day — eating meals and snacks every hour or two — you may want to give intermittent fasting a try.
Intermittent fasting gives your body more time to effectively digest what you are eating and eliminate waste. Many biological repair processes take place when your body is in the "rest," not the "digest," mode, which is why all-day grazing is a bad for you.
Biologically, your body is not designed to run optimally when it is continuously fed. Therefore, you should seriously consider intermittent fasting.
What We Can Learn From the Calorie-Restricted Diets of Monkeys
A recent study,2 published in Nature Communications, demonstrates calorie-restricted diets play a role in aging and health for rhesus monkeys.
Because many anatomical and physiological aspects of rhesus monkeys parallel human beings, it is thought the study's outcomes may be helpful in understanding the role of calorie restriction on humans.
As would be the case when evaluating the effectiveness of human diet programs, the study noted that a monkey's age and gender, as well as the type of diet eaten, influenced the research outcomes. There was no one-size-fits-all approach.
The current research re-evaluated data gathered in two previous studies: one conducted by the University of Wisconsin-Madison (UMW) in 2009 and the other by the National Institute on Aging (NIA) in 2012. The combined research analyzed nearly 200 monkeys, but produced conflicting results.
In the new study, the groups examined the previous body of work with an eye to uncover reasons for the differing outcomes of the reported results. They ultimately agreed that variables such as the age of the monkeys and their food intake were important factors that drove the results.
Scientists offer the following explanations for the differences reported in the earlier studies:3
• Age: The animals in the two studies had their diets restricted at different ages, and comparative analysis suggests adult primates benefit more from calorie restriction than younger animals do
• Food intake: The monkeys in the controls groups for each study ate different amounts of food, which seems to have contributed to improved survival for the monkeys that ate less
• Type of diet: Monkeys in the NIA study were fed naturally sourced foods, while UWM monkeys ate processed foods with higher sugar content, which demonstrated that eating habits affect fat mass and body composition
• Sex: Key differences were identified between male and female monkeys related to the relationship between diet, obesity and insulin sensitivity, with females seeming less vulnerable to the adverse effects of obesity than males
The findings suggest that calorie restriction does benefit rhesus monkeys, and following a calorie-restricted diet resulted in fewer health problems.
For example, the monkeys in the UWM study4 lived significantly longer than the control monkeys: two years longer for calorie-restricted males and nearly six years longer for calorie-restricted females. Notably, these monkeys also evidenced lower rates of cancer and heart disease.
In terms of aging, four of the NIA monkeys that began dieting as adults broke longevity records by living beyond age 40. The typical lifespan for rhesus monkeys is around 30 years.5
While it is too early to tell if calorie restriction works the same way in humans, it does seem there are positive effects to be had from limiting your food intake, given the research validation that aging can be targeted by fasting.6
"The main take-home is what you eat, and how much you eat, absolutely influences how you age," said Rozalyn Anderson, UWM associate professor of geriatrics and one of the study authors.
Do Calorie-Restricted Diets Work for Humans?
While calorie-restricted diets promote both weight loss and longevity in studies involving animals, they generally have only mixed results with humans. The thought of undertaking a "starvation diet" causes most people to cringe. Very often, this type of diet is considered as a desperate attempt at weight loss when other approaches have failed.
Unfortunately, you may have experienced personally that people who pursue "starvation diets" eventually return to their old habits — sometimes weighing even more after the diet than before!
The latest thinking about fasting supports the belief that you can get most of, if not all, the same benefits, and more, with intermittent fasting. In its most basic form, intermittent fasting involves reducing your food intake in whole or in part, either a few days a week, every other day or daily.
Eating less often better aligns us with our ancestors, who did not have access to food around the clock; but rather, had periods of feast and famine. The detrimental effects on the human body related to a food supply that was once hunted and gathered, but is now readily available 24/7 from the local grocery store, are profound.
My Favorite Type of Intermittent Fasting
The type of intermittent fasting I recommend and personally use involves restricting your daily eating schedule to a specific window of time. Based on the experimenting I have done in recent years, I suggest a six- to eight-hour timeframe in which to consume your daily food intake.
For example, if you skip breakfast and make lunch the first meal of your day, you might restrict your food intake to the hours of 11:00 a.m. and 7:00 p.m. If breakfast serves you better, your window could be between 8:00 a.m. and 4:00 p.m.
The key is to eat only two meals, and to ensure you eat the last meal at least three hours before bedtime. When you eat three or more meals a day, you rarely, if ever, empty your glycogen stores, mainly because it takes about eight to 12 hours to burn the sugar stored in your body as glycogen. Intermittent fasting will dramatically change the way your body processes food for fuel.
By fasting about 14 to 16 hours a day, you will give your body more than enough time to drain your glycogen stores and shift into fat-burning mode. Once your body shifts from burning sugar to burning fat as its primary fuel, you will find this program is easy to maintain. Because fat is a slow-burning fuel, you will not only have a more balanced energy supply, but you will also avoid the typical sugar "highs" and "lows" that come with typical diets.
If you are overcoming a health problem such as obesity, high blood pressure or high cholesterol, you can maintain this schedule every day until your body begins to overcome those deficits. As an example, if you need to lose 50 pounds, you'll need about six months of intermittent fasting, after which you can return to regular eating, or a fasting variation, as desired.
What I like best about this approach is that you don't need a lot of willpower or enormous amounts of self-discipline to maintain your designated window for eating.
While you will undoubtedly feel hungry on occasion, that is perfectly normal. Once your body adjusts, you may be surprised to discover how much less food you will consume to feel completely satisfied. You'll be amazed, as I was, when you begin to see your food cravings literally disappear once you have regained your ability to burn fat for fuel.
Health Benefits of Intermittent Fasting
Intermittent fasting provides a number of health benefits that most people need, and you and your body are worthy of all of them:
- Gets rid of stubborn weight and sugar cravings by activating your fat-burning mode
- Builds muscle and promotes overall health and wellness
- Enhances brain health and helps prevent neurological disorders like Alzheimer's
- Reduces oxidative stress and fights aging, diseases like cancer and stress
- Delivers an array of physiologic benefits, including lowering triglycerides, reducing inflammation and lessening free-radical damage
While the positive effects of intermittent fasting apply to everyone, athletes may benefit even more from limiting their eating to a defined window of time. A 2016 study that tracked the effects of time-restricted feeding (TRF) on 34 resistance-trained male athletes found restricting their eating to an eight-hour daily timeframe positively affected several health-related biomarkers, while decreasing fat mass and maintaining muscle mass.7
For eight weeks, the participants divided their daily calorie intake across three meals eaten at 1 p.m., 4 p.m. and 8 p.m. They fasted the remaining 16 hours of the day, and completed three weekly sessions of resistance training on non-consecutive days. Among the biomarkers noted, there was a significant decrease in blood glucose and insulin levels for the TRF group as compared to the normal diet group.
While additional studies need to be completed to further investigate the effects of intermittent fasting on athletes, it seems a TRF regimen could be adopted by athletes during maintenance phases of training when the goal is to maintain muscle mass while reducing fat mass.
Making Good Food Choices Is Still Important
One of my strongest cautions about intermittent fasting relates to food choices. Some claim that you can eat whatever you want as long as it is only consumed within your designated eating timeframe. While you may achieve some of the benefits from intermittent fasting simply by respecting the time boundaries, regardless of the foods you consume, I strongly recommend you consume high-quality food.
Regardless of the program you choose, your food choices matter. Since you'll be eating less, it's vitally important that you get proper nutrition from your food. Healthy fats are essential because intermittent fasting pushes your body to switch over to fat-burning mode. Particularly if you begin to feel tired and sluggish, it may be a sign that you need to increase the amount of healthy fat in your diet.
Cutting net carbs (total carbs minus fiber) is equally important. Fructose is particularly troublesome as it activates a key enzyme, fructokinase, which in turn activates another enzyme that causes your cells to accumulate fat and hold onto it. If you're diabetic, insulin-resistant or overweight, reducing your sugar consumption will be a critical component to your success. Regardless of whether you are doing intermittent fasting or not, aim for a diet:
- High in healthy fats, obtaining 50 to 85 percent of your daily calories in the form of avocados, coconut oil, organic grass-fed butter, pastured egg yolks and raw nuts, such as macadamia, pecans and pine nuts
- Moderate amounts of high-quality protein from organically raised, grass-fed or pastured animals, which translates to no more than 40 to 80 grams of protein per day, based on the protein limits I have suggested previously
- Unrestricted amounts of fresh, low-net-carb vegetables, ideally organic
Important Contraindications for Fasting
Although most people could safely benefit from intermittent fasting, it's important to take caution if you have certain health challenges. If any of the following situations apply to you, you should NOT participate in extended fasting of any kind unless approved by your physician.
- Underweight: defined as having a body mass index (BMI) of 18.5 or less
- Malnourished: You need to put your focus on eating healthier, more nutritious food before you can safely fast
- Children should not fast for more than 24 hours because they need nutrients for continued growth; if your child is obese, consider cutting him or her back on refined grains and sugar to promote weight loss
- Pregnant and breastfeeding women put their baby's healthy growth and development at risk when fasting because a consistent flow of nutrients must be shared continually with the baby to ensure its well-being
If You Take Medication Use Caution When Fasting
If you take medication and it must be taken with food to achieve the proper effect, you will need to use caution when fasting. Medications such as aspirin and metformin, as well as any other drugs that may cause stomach ulcers or stomach upset, need to be considered.
Risks are especially high if you're on diabetic medication. If you take the same dose of medication but don't eat, you run the risk of hypoglycemia, which is when your blood sugar drops very low. This can be extremely dangerous. It's important to check with your doctor before adjusting your medication to accommodate fasting. You may need to find a doctor who has some experience with diabetes and fasting so he or she can guide you in how to implement this program safely.
Also, if you have high uric acid, fasting can precipitate gout. Fasting tends to increase your uric acid level because your kidneys increase their reabsorption of uric acid when you don't eat. Most people will not experience a problem with this, but if you have gout you may need to consult your physician before starting a fasting program.