By now, you have likely heard some of the buzz surrounding intermittent fasting. On the surface, it seems a bit drastic. After all, isn’t it obvious that skipping meals would be associated with weight loss? That can’t possibly be a good idea, right? Research shows, however, that intermittent fasting may be more than just another fad diet.
Simply put, intermittent fasting is deliberately refraining from eating in a given period of time. This period can vary, though it is subsequently followed by a duration of time in which food is consumed.
Although this craze may seem relatively new, intermittent fasting is not a recent phenomenon. In fact, certain cultures and religions have incorporated various forms of fasting for centuries. Regardless of belief systems, many are unknowingly enforcing a period of fasting when they sleep. Upon awakening, breakfast is strategically designed to allow for a break in the previous evening’s fast.
Not all Fasting Regimens Are Alike
There are three commonly described intermittent fasting protocols: time-restricted feeding, alternate-day fasting and whole-day fasting.
Time-restricted feeding is probably the most widely discussed. It involves a time frame designated for eating while the remainder is dedicated to fasting. Regimens that may be used include a 16:8 or 20:4 split. The larger number represents the fasting period and the smaller is the interval in which food is consumed. For example: If you fast for 16 hours, you’d consume your food during the following eight-hour time period.
Alternate-day fasting is precisely what it sounds like — a day of food consumption, followed by a day of fasting. Fasting days commonly include consuming a single meal that allows for 25 percent of your caloric needs.
Whole-day fasting is similar, though fasts are limited to one or two days each week (with a single 500-calorie meal on fasting days). The 5:2 split would be five days of unrestricted eating with two non-consecutive days of fasting.
Water consumption is vital during both fasting and non-fasting periods. Dietary recommendations on non-fasting days are typically not described, though most suggest eating as you normally would. Keep in mind this is not an excuse to splurge, however. “The current literature is devoid of any support suggesting that you can consume whatever you want,” says Rocklend Davis, a postdoctoral research fellow at Concordia University.
What Does the Research Say About Intermittent Fasting?
The weight-loss effects of intermittent fasting continue to be extensively researched. In rodent models, intermittent fasting has been demonstrated to be as effective or superior to more conventional methods of calorie restriction — such as daily calorie restriction — when it comes to weight loss and other desirable health effects.
While the results in mice do not necessarily mean that humans can expect the same benefits, the research is promising. In 2015, one study reviewed the best available literature to date and found that intermittent fasting was an effective means of weight loss.
“Available literature seems to point to intermittent fasting as a viable weight-loss option, comparable to daily calorie restriction,” Davis says.
Is Intermittent Fasting More Than Just a Weight-Loss Method?
This is where the topic becomes even more interesting. The short answer is yes … in rodents. Despite at times comparing apples to oranges (in terms of study design), there seems to be agreement regarding the many desirable metabolic effects of intermittent fasting. Numerous mouse models have demonstrated reductions in cholesterol, triglycerides, glucose and insulin levels, protection from certain forms of cancer and even enhanced longevity. These effects appear to occur regardless of weight-loss achievements.
While animal models have highlighted the potential benefits, these conclusions are more challenging to elucidate in human subjects. Most intermittent fasting regimens seem to be associated with weight loss, though robust literature underlining the key metabolic effects remains sparse. This is due largely to the fact that studies have included varying fasting protocols, making it challenging to practically apply these findings. Nonetheless, there is some evidence of positive effects on clinical markers such as cholesterol, triglycerides and glucose in humans.
How Are These Effects Possible?
Generally speaking, the effects from intermittent fasting are thought to arise by allowing transition from the fed to the fast state. When we eat, a hormone called insulin allows our bodies to appropriately use the sugar obtained from food. Like a squirrel, insulin diligently works to store sugar for a rainy day. As storage is limited, excess sugar is converted to fat in the liver. Some is stored here, though much of it is shipped off to bolster the various fat deposits in our bodies (love handles, for example).
As undesirable as this sounds, without insulin the sugar would hang out in our bloodstream, causing elevated glucose levels (i.e. diabetes). When we fast, the opposite occurs. Insulin takes the hint, punches its timecard, and allows for our energy stores to be utilized. We have enough sugar to last about a day or so, after which the body turns on the fat burners.
So Which Intermittent Fasting Regimen is Superior?
The short answer is, we don’t know. Recent reviews included studies that incorporated a 5:2 split and found them to be effective means of weight reduction. The alternative-day regimen was not shown to be superior to traditional daily caloric restriction. Subjects assigned to a 16:8 split lost more fat mass compared to those eating throughout the day, though after only eight weeks. Strong, long-term evidence is lacking with regards to comparison of these three protocols to one another.
Davis believes research will be heading this way “sooner rather than later.” He adds, “Studies will look to characterize the importance of nutrition and activity timing among the most popular intermittent fasting protocols.”
Is Skipping Meals Safe?
“Generally, yes,” says Davis. He believes a 16:8 split is likely a better starting point for those without experience fasting. “Eight hours is plenty of time to get the recommended dietary allowances, while a person’s body will respond more predictably when half of the 16-hour fast is during sleep,” he says.
Though there does not seem to be literature describing the harm associated with intermittent fasting, it may not be for everybody. Diabetics and those that have challenges controlling blood-sugar should avoid fasting as it may be associated with unsafe drops in glucose levels.
Others who should avoid fasting include adolescents, pregnant and nursing women, those who have wounds that are healing, and those on medications that require ingestion with food as well as those with a history of eating disorders or underweight individuals.
So Are You Ready to Jump on the Bandwagon?
While intermittent fasting is cheap, easy to implement and generally safe, a medical opinion should be sought prior to initiation. Though we have yet to clearly delineate the optimal fasting regimen and its true metabolic benefits, ample evidence in mice models point towards a myriad of health benefits above and beyond just weight loss.
When asked about the downfall of most fad diets, Davis believes the answer is simple: “Sustainability.” The picture can become clouded after you reach your goals with daily caloric restriction, often resulting in putting the weight back on.
A better way of approaching intermittent fasting is as a lifestyle change, Davis says, making it part of a comprehensive plan for overall health that includes daily physical activity.