By Sahil Handa. Sahil is a student at Harvard University as well as a health and fitness aficionado.

For several years, the nutrition industry has been plagued by the myth that eating 7-8 small meals a day is the best way to reduce fat, improve health, and limit hunger. “Breakfast is the most important meal of the day.” It will “kick-start your metabolism” and leave you a “fat burning machine all day.” And in addition to all that, the thermic effect of food means that the more frequently you eat, the better you’ll feel. All sound familiar? Well, today I want to tell you about a diet practice that claims to have refute every one of these ideas; intermittent fasting.

Intermittent fasting, or time restricted eating, is not a diet. It’s an eating pattern based on the idea that reducing your daily eating window to a limited number of hours per day can dramatically improve health, body composition, and mental well-being.[1] How does it work? The most common approach to IF was popularized by Martin Berkhan, the bestselling author of The LeanGains Method, and it involves refraining from eating for roughly 16 hours a day.[2] All calories for the day are consumed within an 8-hour window at any time that suits your individual schedule. For example, a person could wake up at 7am, begin eating at 2pm, and finish their last meal at 10pm. And that’s just one example of how it can be implemented. Other forms of IF include 14-10 fast/feeding windows, 18-6 fast/feeding windows, and day-long fasts followed by regular eating patterns.[3]

You don’t need me to tell you that eating all your food within a small window might make it difficult to eat as much in a day. What you might also be thinking, however, is that you’d never be able to follow a schedule that prevents you from eating for the majority of the day. Let’s have a look at why IF advocates would tell you that you’re wrong.

The Body Adapts, and the Fat Begins to Crack

The human body tends to get hungry at the same times every day. Ghrelin, a hormone that increases appetite, is secreted when the body expects to receive an intake of food – usually at breakfast, lunch, dinner, and frequent snack-times. When a person shifts to intermittent fasting, the body recognizes that it needs to readjust.[4] Over time, it learns to stop secreting ghrelin at regularly meal times and instead releases more of a hormone called leptin, an appetite suppressant. The result? A decrease in appetite during the fasting window.

In addition to these hormone changes, intermittent fasting has a record of decreasing insulin resistance among subjects; in other words, the body becomes less subject to the rapid changes in insulin levels that usually come with eating various foods.[5] Bringing these facts together, we can see why it’s no surprise that followers of the practice commonly cite decreased appetite after less than a week of adherence. The bottom line is that intermittent fasting can help reducing overfeeding, limiting overall caloric intake. Along with the insulin levels dropping and human growth hormone increasing during a fasted state, this helps the body burn fat for fuel.

The Health Claims

Perhaps you are wondering why any of these effects matter; getting hungry less often isn’t necessarily good for you and losing fat might not improve any of your health markers. But claims about the benefits of intermittent fasting don’t stop at weight loss. Greater focus, improved cardiovascular health, and reduced blood pressure have all been associated with the practice.[6] More controversially, recent studies on rats have shown that fasting diets may contribute to longevity, decreased cancer risk, lowering cholesterol, and increased lifespan.[7] The idea that three or more meals a day is essential to proper functioning has been proven wrong repeatedly. Recent research by Salk Institute Professor Sachin Panda has even attempted to align IF eating windows with natural circadian rhythms, with fascinating results.[8] This involves shifting the eating window to earlier in the day and fasting throughout the evening and early morning. In addition to increased muscle mass and improved endurance, clients report better sleep, alertness, and general mood.[9]

Before we get carried away

The research on intermittent fasting is difficult to judge, because the majority of studies do not control for caloric restriction. In simple terms, this means that the number of total calories that a person is consuming often acts as a confounding variable in experiments. Caloric restriction has already been shown to increase longevity, reduce cancer risk, and lower cholesterol, so it’s difficult to distinguish whether improvements have been caused by a fasting protocol or a low-calorie diet.[10] In addition, the fat loss benefits from IF have not been shown to have an advantage over other forms of caloric restriction in humans. In mice studies, a restricted feeding window was shown to contribute to greater muscle mass, improved cardiovascular healthy, and decreased body fat retention.[11]  In humans, however, no such connection has been shown.[12]

So, should you do it?

The truth about intermittent fasting is that, like most approaches to nutrition, whether or not it’s for you comes down to your lifestyle preferences and health goals. If you are currently enjoying your eating habits, are relatively healthy, and are progressing towards your fitness goals, then there might not be a need to make a dramatic change to your daily routine. If, on the other hand, you are dissatisfied and looking for something different, then there’s no evidence to suggest that you’d do yourself any harm by experimenting with fasting. Countless anecdotal studies have attested to intermittent fasting making weight loss much easier and new research continues to be published every day suggesting that there may be concrete biological reasons for this fact. Our ancestors certainly didn’t eat three meals a day, let alone the constant snacking and feeding common in Western society today. Rather, they ate until they were truly satisfied and then gave their body the time to metabolize that food. They exposed their body to hunger in the short term in order to accustom themselves to that kind of stress in the long term.

Think about your mindset

It’s worth noting the mental advantages and disadvantages that can come with intermittent fasting. One of the main reported benefits is the added concentration during the fasting period, in which subjects don’t have to use up mental energy thinking about food and eating choices. Equally important, however, are the eating disorders that can arise while following this kind of diet. It’s imperative that a person consume a sufficient number of calories during their eating window. If you want to lose fat you may not be eating enough to cover the caloric intake of three large meals, but you should eat enough to make sure that your weight loss is slow and consistent; not rapid and short-lived. The point of intermittent fasting is not the strictness of the window; taking an hour off or adding an hour onto your fast is not going to hurt you. If you are the type of person who wouldn’t allow yourself this room for adjustment, it might be best to stick to your current schedule.[13]

On a more positive note, intermittent fasting can, if done with the right mindset, bring a remarkable level of flexibility to dieting. Many people on strict food group diets cite a frustration with having to eat the same boring meals every day in order to keep their appetite down. The nature of a smaller eating window is that it allows you to incorporate more calorically dense foods into your diet. That doesn’t mean you start making the majority of your intake pop tarts and fries; what it does mean is that you can eat that scoop of ice cream once in a while without feeling like you’ve ruined your diet.

Experimenting is Healthy

Cultivating this type of relationship with food is not only good for your body, but it’s good for your mind. The acceptance most people have nowadays that they couldn’t last more than five hours without an insulin spike is unnecessary and extremely harmful. Fasting, alongside all of the potential physical benefits, puts you in control of your body and can even make your food taste a million miles better. There’s no harm in a few weeks of experimentation; diet is extremely individual, and people can have all kinds of different responses to the same stimuli. The only way is to try it out, and, in the case of intermittent fasting, that might end up being the best nutrition decision you’ve made in a while.

[1] http://www.burnfatnotsugar.com/test/IntermittentFasting.pdf

[2] https://leangains.com/the-leangains-guide/

[3] https://www.nerdfitness.com/blog/a-beginners-guide-to-intermittent-fasting/

[4] https://idmprogram.com/fasting-ghrelin-fasting-29/

[5] https://www.alimillerrd.com/insulinresistance/

[6] https://www.healthline.com/nutrition/10-health-benefits-of-intermittent-fasting#section10

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2249073/

[8] https://www.foundmyfitness.com/episodes/satchin-panda

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

[10] https://www.ncbi.nlm.nih.gov/pubmed/26384657

[11] https://www.ncbi.nlm.nih.gov/pubmed/12771340

[12] https://alanaragon.com/aarr/

[13] https://www.ncbi.nlm.nih.gov/pubmed/25943396/