Discovering intermittent fasting and time-restricted eating
Since BBC journalist and TV doctor Michael Mosley’s Horizon: Eat, Fast and Live Longer aired in 2012, there has been growing interest in what’s called intermittent fasting, or IF.
As fasting has recently become an accepted concept, Mosley explores how we can change the way we live using no pills or medicines, but simply fasting. He points out that following the Great Depression average lifespan actually increased by six years, and introduces a 101-year-old Indian marathoner who has never had surgery or taken medicine and has subsisted on the restricted eating of nutritious foods.
Though continual calorie restriction in traditional weight loss diets can positively impact cardiovascular and metabolic health, it is difficult to maintain. Intermittent fasting has arisen as an effective, practical option that can potentially extend life, helping prevent chronic diseases such as cancer and diabetes, and even improve cognitive ability.
In short, researchers are discovering that intermittent fasting and when we eat may be as important as what we digest.
RELEARNING HOW WE EAT
One good reason for intermittent fasting is to reboot the body’s hunger control mechanism. Says author and media figure Madelyn Fernstrom, Ph.D., CNS of the University of Pittsburgh School of Medicine, “Part of this strategy is to connect your mind and body, to focus on true biological hunger to drive eating, rather than eating from boredom, stress, or just for fun.”
Assistant professor Courtney Peterson, Ph.D. at the University of Alabama’s Nutrition Obesity Research Center goes further, “It doesn’t seem like the number of meals per day that you eat affects weight loss or your health in general, so unlike what you see on magazine covers. If you eat lots of small meals throughout the day it’s not going to rev up your metabolism.”
John Trepanowski, Ph.D. of Stanford University’s Prevention Research Center, who himself is involved in much of the ongoing research on IF, states there are increasing studies suggesting that this method is a viable approach to weight loss for some. He believes IF has broad appeal because people can lose weight “but still have guilt-free days of eating what they want on a regular basis.”
There appear to be three popular types of IF: alternate day fasting; a method called 5:2, proposed in Michael Mosley, MD’s The Fast Diet; and time-restricted feeding, or TRF. The first two methods involve what’s otherwise known as calorie cycling or intermittent energy restriction.
In alternate day fasting, a person eats one day, less than 600 calories the next (500 for women), and so forth. In 5:2, one eats for five days followed by two days at just 25 percent of regular caloric intake.
Time-restricted feeding typically involves consuming daily calories within a window of six to 10 hours. Trepanowski explains that TRF is designed to (theoretically) harmonize our eating pattern with our circadian rhythm so that we eat at appropriate times to allow for optimum health. Continuous eating, on the other hand, disrupts this internal clock and metabolism, leading to weight gain and elevated insulin, for example. Weight loss in TRF could result from either this newly synced eating behavior or fewer consumption opportunities, he says.
One of the more notable forms of TRF is 8:16, or the eight-hour diet, whereby one consumes daily calories within an eight-hour window and fasts for 16.
This option tends to be the form of TRF most recommended by medical professionals, while popularized by guru Martin Berkhan’s “Leangains” program.
GAINING MORE BY GOING WITHOUT
The science behind IF is steadily building.
At PubMed.gov, there are over 800 studies on intermittent fasting and nearly 200 on alternate-day fasting, though only one with the 5:2 method. This particular study, comparing conventional calorie restriction versus 5:2, showed overall similar effects in 107 overweight women ages 30–45 over a six-month period; weight loss of about 5 percent of body weight; reduced cholesterol, triglycerides, leptin (i.e., increased sensitivity of this hunger-suppressive hormone), C-reactive protein (an inflammation gauge), and other health marker improvements; with slightly better insulin reduction/sensitivity from 5:2 (important in eliminating sweet cravings).*1 Research conducted at the University of Alabama, Dr. Peterson reports that for the first time in humans, early time-restricted feeding has demonstrated the ability to reduce daily hunger swings and promote nighttime fat burning. The UA study showed that eating earlier, between 8 a.m. and 2 p.m. in this case (i.e., 6:18), promoted greater fat oxidation during sleep.*2
Dr. Peterson says that many aspects of metabolism are most active during the morning. Thus, aligning eating habits with this internal clock may positively impact health.
Until recently, most IF research has been on sedentary and overweight populations. But in 2016, a study in the Journal of Translational Medicine showed similar benefits in younger males performing weight training exercise using the 8:16 method versus a traditional normal control group.*3
In the eight-week study, TRF participants consumed roughly 2,800 calories (about 55 percent carbohydrate, 25/fat, and 20/protein) spread over three meals: 1 p.m., 4 and 8 p.m. versus 8 a.m., 1 p.m. and 8 p.m., in the control group. TRF adherents showed reduced body fat while maintaining muscle and strength, elevated adiponectin (a hormone involved in glucose regulation and fat burning), and decreased insulin-like growth factor 1 (important in longevity). Control subjects ate roughly 3,000 calories daily with the same nutrient profile and showed no change.
While the subjects’ fat loss may have been partly due to the slight calorie deficit, there are many weight loss anecdotes of IF and TRF, including people who had plateaued on traditional diets.
Mark Mattson of the National Institute on Aging says IF improves disease indicators, reduces oxidative stress, and preserves learning and memory—possibly as an adaptive stress response.*4
Not eating for 10–16 hours, he says, releases fat stores for energy called ketones which have a protective effect on the brain.4
LIVING IN THE FAST LANE
Alternate day and 5:2 fasting may not be for everyone, as very low-calorie days would likely need to coincide with low scheduled activity. TRF seems most practical, involving minimal lifestyle changes for most people.
Though Berkhan and others skip breakfast, as in the study above, UA research suggests it’s better to move up dinner, eating two to three meals per day in all. Thus, one would have an eating window of 8 a.m.–2 p.m., as in the UA study, or 8 a.m.–4 p.m./6 p.m., for example, with no snacking before bed.
Eat normally during feeding periods, allowing three to five hours for digestion between meals; and include exercise, with weight training to help preserve lean tissue.
As John Trepanowski notes, TRF’s main drawback is the temptation from easy access to food. So removing any temptation is essential (i.e., “stimulus control”).
Natural appetite suppressants such as green tea and conjugated linoleic acid (CLA) can help the body switch to its fat reserves, possibly making falling asleep on an empty stomach easier. (Valerian root can also help with sleep.) Otherwise, beginning one’s eating window at noon or 1 p.m. is recommended.
Beverages should be zero-calorie before bedtime.
IF becomes second nature once hunger hormones have readjusted, say those who have tried it.
Many believe that a Mediterranean-style diet coupled with intermittent fasting is the best approach to optimum health.
JUST ANOTHER FAD?
Fasting is nothing new.
The practice has a long Biblical history for not only encouraging more profound spiritual connectedness but promoting self-discipline and physical well-being.
However, IF could become another passing trend, says Eat Stop Eat author Brad Pilon.
Fasting may not be for everyone, and there are legitimate precautions: possible risks to pregnancy, those with eating disorders, and diabetics, for instance.
In the Canadian Medical Association Journal, Roger Collier points to possible binge eating behavior during feeding windows and insufficient human studies.*4
Still, while the research is inadequate for recommending IF as a health intervention, it does show benefit when done sensibly.*5
With the approval of one’s healthcare provider, you may have everything to gain and nothing to lose. H
1 Harvie, M.N., Pegington, M., Mattson, M.P. et al. (2011, May). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity (London), 35(5), 714-27.
2 Pope, A. (2017, January 9). Time-restricted feeding study shows promise in helping people shed body fat. UAB News.
3 Moro, T., Tinsley, G., Bianco, A. et al. (2016). Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine, 14(1), 290.
4 Collier, R. (2013, June 11). Intermittent fasting: the science of going without. Canadian Medical Association Journal, 185(9), E363-64.
5 Home, B.D., Muhlestein, J.B. & Anderson, J.L. (2015, August). Health effects of intermittent fasting: hormesis or harm? A systematic review. American Journal of Clinical Nutrition, 102(2), 464-70.
Rob Saint Laurent, MEd is a health writer and editor.
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