Intermittent fasting (IF) is a type of diet strategy that limits calorie consumption to certain hours within a day, or days within a week. Proponents claim that going without food on a regular basis can reduce disease burden/risk and increase longevity. Some of the more popular types of intermittent fasting are:

1. Time-restricted feeding: requires limiting calorie intake to a certain time period, somewhere between eight and 12 hours per day.
2. Intermittent calorie restriction: calls for reducing daily caloric intake to 800-1,000 calories, for two consecutive days per week.
3. Periodic fasting: requires limiting caloric intake for between three and five days, such that cells are depleted of glycogen stores.

One of the theories behind the health benefits of IF involves an exercise analogy.  Just as high intensity exercise can produce added fitness gains, stressing the body’s cells with occasional starvation causes them to be more immuno-fit, ready to fight off disease and inflammation (such as cancer). Another theory is that IF can reset circadian rhythms in the liver, kidney, and stomach, causing more regular hormone production that improves satiety and results in decreased overall calorie consumption. A third theory is that by starving cells of food for a couple of days at a time, the body switches to burning fat rather than sugar, and any weak or damaged cells die off during the fast, hence stimulating a kind of Darwinian health benefit at the cellular level.

These are interesting hypotheses, but currently there is insufficient human research/evidence of such mechanisms to confirm or deny them.

What We Do Know…

1. Fat loss has health benefits, especially for those who are obese or have obesity-related disease, such as type 2 diabetes, heart disease, or high cholesterol.
2. Fat loss attained via IF techniques can produce these health benefits, but does not seem to be superior to fat loss achieved through general (non-timed) calorie reduction.
3. IF, if it causes rebound binging (where foregone calories are consumed later on), does not produce weight loss or associated health benefits.
4. There are at least 40 published, human research studies measuring the effects of IF, most of which have shown health benefits from weight loss produced by IF, but none has demonstrated that IF is superior (for weight loss efficiency) over continuous calorie restriction.  Questions remain about the lifestyle sustainability of IF, as long term studies are currently lacking.

What I Think…
If the prospect of being constantly hungry is what’s keeping you from losing weight, and you have no medical conditions that would preclude you from trying IF (i.e. diabetes or an eating disorder), then why not give it a try? At least there are some days/times when you will not feel hungry. Keep in mind that you will be very tempted to binge eat on your days/hours off the fast, and that if you do not decrease your overall average calorie intake, you won’t reap the benefits of your efforts.

Although I cannot prove it, I hypothesize that IF may be particularly helpful for those prone to “grazing.” Reducing eating hours may naturally result in overall calorie reduction for those who consume a significant amount of calories due to stress or without mindfulness (e.g. the bowl of candy or nuts at the office).
However, if going without food throws you into a tailspin, where you end up thinking about it all the time and then binging the minute you’re fast ends, this diet strategy is not for you.

The Bottom Line:
The best weight loss strategy is the one that you can sustain for a lifetime. Barriers to fat loss are complex and differ from person to person. If you have medical conditions that might be worsened by fasting, ask your doctor before you embark on a trial of IF. There’s no magic to IF, and so far human studies have not proven it superior for general weight loss than our usual methods. Remember that a healthy diet* is important to maintain, regardless of when you plan to eat. Using IF as an excuse to starve yourself so you can eat all the “bad” foods you’ve been craving (such as deep fried foods, desserts, and low-nutritional-value snacks) is a recipe for disaster.

*My favorite healthy diet is the Mediterranean Diet. See more at the link below.

References
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680567/
http://scopeblog.stanford.edu/2016/07/07/intermittent-fasting-fad-or-science-based-diet/
https://www.medpagetoday.com/primarycare/dietnutrition/70663
https://www.ncbi.nlm.nih.gov/pubmed/26384657
https://endpoints.elysiumhealth.com/the-science-of-fasting-2f5b56a2a65d
Mediterranean diet: https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/multimedia/mediterranean-diet/sls-20077104

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