by Dr Suk Cho May 08, 2018


(JoyNutritionals) - Periods of voluntary abstinence from food, aka fasting, has been practiced since the earliest days by people around the globe. There are many ethnology and religion describing a variety of fasting practices.  Intermittent fasting is a form of diet which involves cycling between periods of eating and abstinence/fasting from food.

There is renewed interest in intermittent fasting regimens as evidenced by many popular publications and diet recommendations for weight loss and expanding life span.  Mosley and Spencer published a best-selling book titled “The Fast Diet” which touts the benefits of restricting energy intake severely for two days a week while eating normally the rest of the week (aka 5:2 Diet). There are other books that promote various patterns of fasting like Varady’s “Every Other Day Diet”. The internet offers hundreds of fasting-related sites.  Fasting also has been trending in diet circles because celebrities like Beyoncé, Ben Affleck and Nicole Kidman are doing it and more research reveals that the eating pattern may promote weight loss and improve overall health.

What types of intermittent fasting are there?

Types of fasting include alternate day fasting, modified fasting regimen, time restricted feeding, Ramadan fasting, other religious fasting, etc. 

Alternate day fasting (ADF): ADF involves fasting days in which no energy-containing foods or beverages are consumed alternating with days where foods and beverages are consumed.  In 2007, Varady and Hellerstein reviewed alternate day fasting studies in animals and concluded that this fasting regimen was as effective as simple caloric restriction in decreasing fasting insulin and glucose which is a great option for people looking to manage their type II diabetes.   ADF in animals also reduced total plasma cholesterol and triglyceride, and had beneficial effects on cancer risk factors.  The study data suggests that ADF regimens can result in modest weight loss.  These data also show some positive impacts on metabolic parameters.  However, Heilbronn et alnoted that self-reported hunger on fasting days was considerable and did not decrease over time, suggesting that ADF may not be a feasible public health intervention for long term.

Modified fasting regimens (MF): MF generally allow for the consumption of 20–25% of energy needs on regularly scheduled fasting days.  In MF, the term fasting describes periods of reduced energy intake rather than no energy intake. This regimen is the basis for the popular 5:2 diet, which involves energy restriction for 2 non-consecutive days a week and usual eating the other 5 days.

In reviewing MF in humanstudies, most studies reported statistically significant weight loss when compared to a control group.   A majority of studies found significant improvements in lipid profile and insulin resistance as well as improvements in inflammatory markers like c-reactive protein.  Several reviews have compared the results of fasting regimens with continuous or daily energy restriction. The most recent of these reviews found that intermittent fasting regimens in compare to energy restriction demonstrated similar weight reduction after 3–24 weeks. Results from these intervention trials of modified fasting regimens suggest that these eating patterns result in weight loss, with modest improvement in blood glucose, lipids and inflammatory markers.

Time Restricted Feeding (TRF): TRF was based on animal studies with time-restricted feeding.  Twelve studies were reviewed with daily fasting intervals ranging from 12 to 20 hours, in numerous mouse models, with some variability.  Despite the variables of these studies, the authors concluded that in mice, time-restricted feeding was associated with reduction in body weight, total cholesterol, triglycerides, glucose, insulin, and inflammatory markers.

In human clinical trials of TRF-using nighttime fasting, two cross-over studies found significant reductions in weight.  Another cross-over study compared the effect of consuming one afternoon meal per day for 8 weeks and reported 4.1% weight loss when compared to an isocaloric diet (equal macronutrients) consumed as three meals per day.  One meal per day was also associated with reductions in fasting glucose, and improvements in LDL- and HDL-cholesterol.  While clearly limited, results from these studies of time-restricted feeding are consistent with research in animals indicating that incorporation of regular fasting intervals and eating in accordance with normal daily circadian rhythms- daytime hours in humans- may be important for maintaining optimal metabolic function.

Many religions incorporate fasting for both spiritual and physical benefits. And, all published research on these fasting regimens is almost entirely observational and not clinically controlled.

Ramadan Fasting: One of the five pillars of Islam is that healthy adult Muslims must fast from dawn to sunset during the holy month of Ramadan. In addition, fluid intake, cigarette smoking, and medications are forbidden.  Depending on the season and the location of the country, day fasting can vary from 11 to 22 hours. Islamic fasting during Ramadan has less frequent intake of food and fluid.

In 2012 analysis of 35 studies examined weight change during Ramadan.  The authors of this review found statistically significant weight loss in 21 (62%) of these studies. When pooled, the studies in this the analysis showed average of 3 lb. weight reduction over the month of Ramadan fasting. Across 16 follow-up studies, subjects regained average of 1.6 lb. in the 2 weeks following Ramadan.

A 2013 analysis of 30 cohort studies including healthy young men and women examined whether Ramadan fasting altered biomarkers in addition to weight. The primary finding of this analysis was that after Ramadan fasting, low-density lipoprotein (LDL) and fasting blood glucose levels were decreased in both sex groups in the entire group compared to levels prior to Ramadan. 

Ramadan is the most common form of time-restricted feeding and results in transitory weight loss, with mixed evidence for improvements in metabolic markers. However, this feeding pattern is in biologic opposition to the human circadian rhythms, and therefore unlikely to be pursued as a desirable weight loss intervention.

Other Religious Fasts: A study of 448 patients from hospitals in Utah found that Church of the Latter Day Saints (LDS) followers who fasted had a lower prevalence of diabetes and atherosclerosis.  Seventh-day Adventists emphasize a healthy diet and lifestyle as part of their faith and live approximately 7.3 years longer than other white adults. This increase in life expectancy has been primarily attributed to healthful lifestyles including not smoking, eating a plant based diet, and regular exercise. 


Is intermittent fasting healthy?

Various forms of fasting have been an integral part in history of mankind.  The natural history man includes the evolution from a time when food was not readily available.  Now, with an abundance of food, processed food mainly, overweight and obesity has reached epidemic proportions in the United States.  This unhealthy metabolic state of Americans is implicated in the development of a variety of chronic diseases and is associated with increased levels of chronic inflammation and oxidative stress.   Intermittent fasting and/or calorie restriction diet studies of various forms have demonstrated modest to significant weight loss as well as improvement in various biological markers associated with chronic diseases.  In addition, both calorie restriction and intermittent fasting have demonstrated increased life span at least in animal studies.   Data from many study indicated intermittent fasting diets aided in weight loss and improved key biological markers.

If you are still hoping to give intermittent fasting a try, there are some things to consider that can increase your chances of reaching your goals.  Also, be sure to check with your doctor to make sure you are healthy and let them know you are starting intermittent fasting and caloric restriction diet before starting any fasting regimen.



Can Intermittent fasting help you live longer?

The jury may be out on whether fasting can help you live longer since it has been only demonstrated in animal studies.  There is some evidence that for calorie restrictions may do this as well.  My argument is that the food that we eat can either help prevent oxidative stress or cause oxidative stress (like fatty processed food).  Many scientists will tell you that the prolonged assault of oxidative stress can shorten life span and trigger disease state conditions.  It is also evident that losing weight and changing to a healthier life style can improve biological markers associated with chronic or metabolic related diseases. 

For the greatest success, you should choose a fasting regimen that best suits your lifestyle, your health conditions, and your ability to sustain fasting.

What types of fasting shall I try?

So, you’ve investigated and decided that you like all the health benefits that intermittent fasting has to offer.  But you are used to eating regularly throughout the day.  You don’t know if you are up for the challenge of fasting. Do you have the willpower?  Well, the good news is that, after the initial effort, your stomach can reset and fasting will seem to require even less effort than daily calorie restriction might. You should also know that there are different approaches to fasting, different fasting patterns, that vary in intensity so you will want to choose the one that will be easiest for you to follow and be successful with.

Some traditional fasting patterns, like the “5:2 fasting diet” where you fast for 2 days and eat for the other 5 days each week, can cause people to overeat during non-fasting days.   People in this situation often blame themselves for pigging out, but interestingly, it’s not just human weakness that causes the overeating.  The overeating is in response to an actual physiological change in the body, the release of a hormone called ghrelin.  The hormone sends signals to your brain to encourage you to eat as if you were in starvation mode.  It’s a natural response to fasting!  Aside from eating too much on non-fasting days, there’s the concern about making good choices for nutrition on those days. What should I eat so I don’t undo all my efforts at fasting? A USDA study suggested that most US consumers don’t know what to eat and how much to eat.

The key to successful intermittent fasting is having both a reasonable weight loss goal and having some flexibility in your fasting program.  I have developed the 511 Smart Fasting Program to address some of the shortcomings of traditional fasting diets. My focus was on creating a program that is sustainable for long-term success and flexible for any life style.  511 Smart Fasting uses time-restricted fasting of 1 or 2 days but allows for restricted calorie intake in the form of specific snacks and a special beverage to make the fasting days smoother and, subsequently, the non-fasting days more controlled. Now, what do you eat on the non-fasting days?  In my investigations, I ran across a study that showed that, for consistent calorie intake, meal replacement has a higher success rate than meals prepared at home. With that in mind, I formulated meal replacement shakes that are high in protein and fiber, satisfying, convenient, and delicious.  So, on the non-fasting days, it’s easy to create a habit of having a couple of meal replacement shakes during the day and a planned 400-600 calorie meal in the evenings. The flexibility of the 511 Smart Fasting comes in the form of “Choice Day”.  Once a week, you eat what you choose.  These are guilt-free days built into the plan to allow some flexibility and result in better overall compliance with the program.  Long term success is the goal with the 511 Smart Fasting Program. 


What should you eat during fasting days?

Focus on protein and fiber rich food or supplements for fasting and meal days.  Protein and fiber-rich foods will keep you feeling full and satisfied, which is important when calories are reduced. Healthy fats that contains polyunsaturated omegas derived from nuts and peanut butter can also curb hunger but provide a lot of calories for a small portion size.  Again, fasting days need to be limited calories or restrictive calories, and feeling full is important. 

If you decide to fast for any length of time, adequate hydration is important and should be maintained. Foods such as fruits, vegetables and broth-based soups contain significant amounts of water can help you stay hydrated.  Drinking water or fasting tea during fasting days can be beneficial and minimize symptoms associated with dehydration-like a headache.  I personally have done many types of fasting, first one is always challenging and it becomes easier as you reset your body and begin to eat healthier portions with healthier choice to achieve weight and physiological goals.

What should we eat for non- fasting days?

We are used to eating large portions.  Our expectations for portions are not aligned with metabolism or how much energy we burn-especially in sedentary life many of us lead.   We should eat sensible meals or meal replacement that are high in dietary fiber and high in lean protein.  The research also showed that types of protein matter in keeping lean body mass- this is what helps you burn fat.   The choice of meal need to be consciences but also have “feeling full” sensation because when we are consuming very few calories on certain days, our bodies are going to do everything they can to encourage us to eat a lot when we eat.  Drinking low calorie food or beverage like water or soup can also help expand the fullness sensation as well as consuming lean protein and food that contains dietary fibers.  Overdoing it on a non-fasting day by eating excessive calories may defeat the purpose of a fasting day.  In other words, having pancakes with several strips of bacon for breakfast, a cheeseburger with fries for lunch and a steak with baked potatoes with sour cream for a dinner on a non-fasting day can be detrimental to weight loss and prevent you from reaching your goals.  Being cognizant of how much you eat and what you eat is a battle that one must overcome.

Should you exercise on intermittent fasting days?

Strenuous exercise, long distance running, high-impact aerobics and heavy weight lifting, may not advised on fasting days because the body does not have the fuel available to sustain rigorous activity. Again, this depends on how adaptable you are to fasting and to changes in eating habits.  Initially, you want to do some form of physical activity on those days like walking, gentle biking, stretching or gentle yoga.

If you experience light headedness, dizziness, fatigue, nausea, headaches, difficulty concentrating or any other symptoms that regularly interfere with your daily functioning, you should gradually change your fasting and calorie restrictive diet. 

Dr Suk Cho
Dr Suk Cho

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