Intermittent Fasting vs. Time Restricted Eating: Which One Is Better For You?

Guest post by Jen Johnson

With the rise of obesity, cancer, and diabetes in this country has come a rise in various health trends and diets that claim to resolve them. The trouble with these claims is that it’s hard to distinguish the ones you can trust with a science backing, from the fads that promise you the world but don’t deliver.

However, sometimes a claim that is real and promising will have the facade of a fad alongside the science to back it. Yet, it is cast aside as being just another popular opinion whose spark will die out as quickly as it ignited.

Two of these claims that have been gaining attention in the medicinal world recently are intermittent fasting (IF) and time-restricted eating. On the surface, the two methods of dieting seem strikingly similar.

Both involve a caloric restriction in some fashion, and both rely heavily on the time you eat, not necessarily what you eat. Beneath the surface, these two methods are completely different and have different effects on the body.

So, which one is better for you? Which one will help you lose more weight? Which one will help lower risk of diseases like diabetes? I decided to get to the bottom of those questions that circle the internet so much they make you dizzy.

What Is The Deal With Intermittent Fasting?

There are a number of different takes on intermittent fasting. The idea is to restrict caloric intake by about ⅔ on 1-2 days of the week and eat normally the remaining 4-5 days. Some also advise a one day off, one day on approach. Which days to eat and fast to achieve better results have been debated among scientists and health professionals, but the most popular is the “5:2 diet” (eat normally 5 days: fast 2 days).

The trouble with this is that not enough research has been done on humans, with most studies focusing on implementing these diets in mice and rats. One of the most popular studies done on IF was done by Mark Mattson, senior investigator for the National Institute on Aging, part of the US National Institutes of Health.

Although the results of this study were deemed promising - improving biomarkers of disease, reducing oxidative stress, and preserving learning and memory function - Mattson has called for more human clinical trials to be done.

When it comes down to the validity of these studies, it is hard to determine how accurate the results are because humans are genetically different and respond to changes in diet differently than rodents do. Studies that have been done on humans have shown that a high caloric restriction diet once or twice a week was not much different than a lower caloric restriction every day of the week.

Eating only 500 calories for two days does not have a better or worse effect than eating a few less calories every day. It’s just much more uncomfortable. Studies have also shown that people are more likely to give up IF after an extended period of time due to the difficulty of the fasting period and the tendency to overeat on normal eating days.

The few benefits seen from IF don’t have to do with weight loss, but the stress that your body is under during fasting blocks. Stress tends to have a negative connotation, however, the stress your cells are under while you’re fasting is very similar to the stress they are under when you are exercising. When your cells are stressed, they adapt by “enhancing their ability to cope with stress and, maybe, to resist disease.”

Time Restricted Eating, a.k.a The Circadian Diet

Humans have evolved to be diurnal beings. What this means is that our bodies work on a clock designed to keep us awake and active during the day, and asleep and rested at night. This is also called your body’s circadian rhythm.

When you wake up in the morning, the first thing you put in your body (besides water) activates metabolic functions in your gut and liver that stay working for a 12 hour time period. What the circadian diet attempts to do is align your eating habits with your body’s metabolic clock, thus boosting your metabolism and improving digestion.

It is recommended that you constrict the time you eat during the day to the 12-hour window when your metabolic functions are optimally working. Some research has shown even greater benefits of eating in 8-10 hour windows as well, such as improvement in endurance and muscle gain.

On average, people eat 15 hours per day, starting with a cup of coffee early in the morning and finishing with a late night snack. The problem with that is when you eat past the 12-hour window, your metabolic functions are already shutting down, resulting in fat gain, muscle deterioration, and insulin resistance.

One study from researchers at the University of Alabama was conducted on a group of 8 obese men with prediabetes. They were split into two groups eating either in an 8-hour window early in the day, or a 12-hour window throughout the day.

Both groups were able to maintain their weight over 5 weeks, and the 8-hour group showed dramatically lower levels of insulin and improved insulin sensitivity. They also experienced a decrease in appetite which made it far easier for them to manage the fasting window. They were not dealing with the hunger pangs of starvation commonly felt during the IF diet, and their metabolism improved.

There have been studies that have been done when mice are put on the circadian diet, but the same problem occurs when testing the IF diet on mice: humans and rodents are too different to tell. However, the results seem promising and have led to further studies that are presently being done on humans that seem to be producing positive results. The circadian diet seems to contribute to weight loss, improvements in appetite, energy, and digestion and fighting diabetes.

Which One Is Better For You?

Both diets have their benefits and pitfalls. Both of them need more research done on them than the existing studies on mice and rats. However, it seems that science leans towards the circadian diet as having better and stronger results overall.

Monique Tello, MD, MPH of Harvard Medical School recently published an article claiming that IF is not worth the pain and to stick to eating a diet high in fruits and vegetables to maintain your health. However, she recently revised her opinion with a surprising update, claiming that a circadian diet is a form of IF that does, after all, have proven health benefits.

In the end, the choice is yours. My advice would be: don’t listen to the critics who claim that either diet is essentially allowing you to eat whatever you want (i.e. junk foods like pizza, cake, hamburgers, etc.) during certain times of the day and still lose weight and be healthy. Quality over quantity of food. All in all, a diet rich in fruits vegetables, lentils, beans, and healthy sources of protein, while on a circadian diet, seems to be the winner here.

Of course, you should always consult with your health care provider when making a major diet change. These diets are not recommended for women who are pregnant or breastfeeding or anyone with a history of an eating disorder of any kind.

Sources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680567/

https://www.health.harvard.edu/heart-health/not-so-fast-pros-and-cons-of-the-newest-diet-trend

https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156

http://www.johnshopkinshealthreview.com/issues/spring-summer-2016/articles/are-there-any-proven-benefits-to-fasting