The Benefits and Risks of Intermittent Fasting

Although the very notion of intermittent fasting may imply adjusting one’s eating according to a pre-determined timetable, it does not come with an “everything-you-nom-is-OK-in-the-afternoon” card.

Whether it’s Leangains, the 8-hour diet, the IF eating schedule, the 5:2, or the Warrior diet, there has been a lot of hype in the past five years about the way in which we can improve our weight by modifying our eating schedule. In fact, you can say that we’ve been paying more attention to nutrition in these first two decades of the 21st century than humanity has done in its entire history. We have witnessed a pronounced shift from a diet-oriented mentality towards a healthy eating one.

Not surprisingly, everyone quickly found out that replacing all of your food with Master Cleanse, grapefruit, or by breathing in plain air is not a healthy way towards sustainable fitness. On the other hand, the particularly attractive element of eating schedules is their intrinsic loop-hole of not-giving-up-on-anything, but rather eating it all in a small timeframe during the day. Does the diet that “lets you eat all you want half the time” sound familiar? Of course it does. It’s viral. Well, that is not intermittent fasting (IF).

The Notion of Intermittent Fasting

Although the very notion of IF may imply adjusting one’s eating according to a pre-determined timetable, it does not come with an “everything-you-nom-is-OK-in-the-afternoon” card. In fact, these misconceptions and misunderstandings of what IF actually is have led to numerous health concerns and risks being erroneously associated with it as a result of uninformed, medically unsound practices.

You will often find articles about how IF causes stress, headaches, results in binge eating or other eating disorders, causes rebound weight, muscle loss, and so on. When you come across such an article, verify its claims. Is it based on a clinical investigation or is it just a review? Is the study rigorous—did it involve a control group, monitor participants via blood tests, and use a body composition examination? How old is it? Were newer studies published since? And, last but not least, are there declared or potentially undeclared conflicts of interests?

Throughout this article, I will scrutinize a particular IF (the 16/8) program more carefully in order to outlay its benefits, risks, and how to use the program. I will attempt to rely on as little speculation as possible, and include scientific information, while also giving my personal account. I wholeheartedly invite you to step up and conduct your own nutritional experiment with IF. Afterwards, share your story with us!

The Faces of Intermittent Fasting

As I’ve mentioned in the beginning, there are quite a few interpretations of what IF means. Some people refer to the 5:2 as an IF. The 5:2 program is actually an example of modified fasting regimen (MFR), wherein for five days you consume foods and beverages as usual, while in the remaining two you restrict yourself to around 500 calories, or 25% of your total energy needs. Energy restriction has always been a common way of getting things done in terms of overall weight goals. As expected, a maximum of 14% and an average of around 3-5% reduction in weight was reported after 24 weeks on a MFR when physical exercises were also involved.1 The studies, however, did not identify other metabolic changes and the weight loss efficiency is significantly lower without physical activities.

Objectively speaking, modified fasting regimens are not the best way to lose weight or improve your fitness, although they may show promising results terms of the former. Personally, I have never consciously employed a modified fasting regimen, nor do I believe, as a seasoned coach with a great deal of personal experience in nutrition, that deliberately alternating between eating very large and very small quantities of food will help out in the long run. Your ultimate goal should be ensuring that you lose excess fat, rather than a combination of water, fat, and muscle.

Next up is alternate day fasting, or ADF. This could be described as the “eating everything you want every other day” concept. The same synthesis of research I referenced above found even less clinical evidence to suggest that alternate day fasting promotes sustainable, long-term weight management in humans—although moderate weight loss is often reported alongside marginally improved cholesterol and inflammatory markers. In terms of a diet change with the purpose of weight management, you’d be better off eating less meat and sugar and increasing your intake of vegetables, nuts, and seeds.

In obese individuals, ADF had “minimal adverse outcomes.”2 Take a look at the study results: when they say minimal, they mean it. More importantly, ADF can lead to several unhealthy eating habits, irritability, and deprivation of essential nutrients, which is why the Harvard Health Blog referred to it as a “fad diet.”3 I’d go with them on this one. I never bought into the nothing today, everything tomorrow philosophy.

Last, but not least, there is time-restricted feeding (TRF). This is what I will be focusing on, as it seems to have the most scientific data coming from research conducted both on animals and on humans. I have also attempted a TRF experiment in my personal diet over the past several weeks, partly because of the evidence that I am about to present and partly because I was curious what it would do to my body and mind.

Less a diet and more of an eating schedule, TRF means that you restrict your eating to a daily timeframe. In some places, it is known as the Leangains method, first promoted by the Swedish trainer and nutrition expert Martin Berkhan. It does not, in any way, mean restricting your daily calories, eating only a certain type of food, or eating less, for that matter. Obviously, maintaining an adequate balance of proteins, good fats, and carbohydrates from healthy, unprocessed foods continues to be a top priority. TRF programs often vary from 12 to 20 hours, while some advocate for just one meal per day, as in the case of the Warrior diet.

While I did not manage to find evidence for other TRFs, eating my daily caloric needs as a regular weightlifter with the 16 hour fast, 8 hour eating frame was stress-free. In fact, the 16/8 does not vary much from our everyday routine, except for no breakfast, nor late snacks. You can easily have three healthy meals, at 1:00, 5:00, and 8:00pm. It works similarly to a ketogenic diet, in that it forces your body to tap into those stubborn fat reserves, but it differs in that it does not come with the necessity to abide by a high-fat, low-carb eating configuration.

There are numerous theoretical benefits of having an established eating pattern as a result of maintaining a healthy circadian rhythm. These advantages include lower risk of obesity, cardiovascular diseases, diabetes, and neurodegenerative illnesses.4

The Benefits of 16/8 TRF

In overweight and obese patients, the above mentioned study, led by a researcher at the Johns Hopkins University School of Medicine, found that TRF significantly improved the effectiveness of weight loss therapy. A particular concern for me, as a trainer, was whether the 16/8 might negatively impact endurance, vigor, or strength. Two, separate randomized control trials, one employing resistance, the other weight training, showed that TRF was not associated with lower muscular mass, endurance or strength.5,6 In both TRF trials, active individuals gained slightly more lean mass, while losing more fat. IGF-1 and testosterone were a bit lower, which would normally suggest an adverse effect on hypertrophy—in reality they did not, in any way, impact the ability to maintain lean body mass during TRF. This means that the relationship we commonly entertain between certain hormones and muscle gain is not as simple as we envision it.

In addition, the study found that insulin resistance, blood glucose, bad cholesterol, and several other health markers greatly improved with the 16/8 TRF, leading all of the involved researchers to unequivocally support that these eating schedules may be an important concern for public health and that more research is needed in terms of assessing their long-term impact. Moreover, the underlying metabolic changes that come with a ketogenic diet made epilepsy much easier to control. For instance, IF promotes autophagy, the cleansing and detoxification of damaged cells within our system in order to make room for new, healthy ones. Besides epilepsy, IF was associated with better management of chemotherapy side-effects4, as a result of a stronger, more responsive immune system. In addition, autophagy-related benefits led researchers to hypothesize that this eating schedule might actually better protect lean mass in the long run.

My interest was piqued. Does this mean that we are far better off eating according to a more or less fixed schedule, during a specific timeframe, rather than whenever we feel like it? The Johns Hopkins paper, directly, and the two studies on active individuals, indirectly, certainly affirmed so.

In an attempt to find similarly rigorous research on women, I came across a trial conducted at the University of Ontario. Despite their overall scarcity, this pilot study found that active women experienced substantial fat loss on the 16/8 schedule, one of them 3.2 kg (7 pounds) in just four weeks.7 In all trials, the program seems to work better if no calories whatsoever are ingested during the fasting period (from 8:00pm to noon the next day), although the Ontario study had permitted zero-calorie drinks, like coffee and diet sodas.

The extended fasting period allows the body to enter that golden ketogenic state when fat is the primary target for more energy, damaged cells are no longer fed by a steady supply of nutrients and energy, but cleansed and replenished instead. It is extremely important that individuals maintain adequate levels of hydration, since there is arguably less food for the body to rely upon to secure its much needed fluids. Given this, don’t be afraid to drink more water than usual, sugar-free tea, or an occasional black coffee.

Using 16/8 TRF

To experiment with time-restricted eating, keeping a food and exercise diary, as well as measurements of your body mass and composition will greatly help out. In my instance, three weeks into the 16/8 I experienced visible contouring around my abdomen and obliques, where I personally get the most headache from stubborn fat. From my measurements, I had managed to lose around 0.7 to 0.9 kg of fat, without trying anything special. Although I did not strictly abide by the fasting period (sometimes I had late workouts and delayed protein shakes), my stress levels and my overall mood experienced a noticeable boost. I did, however, consult with my general practitioner (family doctor for some of you) before trying any of this. If you decide to try a TRF, it is crucial that you do the same.

Because I didn’t have to worry about eating, I could dedicate the morning entirely to the work that I had planned to get done throughout the day. Just something to keep my mind off those alluring, luscious pastry fragrances. In the first few days, I admit that it was quite difficult to get my mind off of food, especially with everyone around me generously offering the odd glazed donut, buttery croissant, or freshly squeezed fruit juice—my particular weakness. A neat trick that I developed was to keep some of these generous contributions for later.

The Risks of 16/8 TRF

The most important aspect about trying out the 16/8 TRF, or any other plan, for that matter, is that you consult with your medical practitioner beforehand. As it currently stands, more medical data is needed to confirm the long-term impact of IF on various clinical outcomes like diabetes or cardiovascular diseases. The data currently available is promising, but not enough. This is normal for a phenomenon that has recently caught the attention of medical research and is just now being given the importance it deserves.

Many individuals have reported increased levels of stress as a result of trying one type of IF or another. In a sense, the 16/8 TRF is a minor stressor on the human organism. Instead of giving it what it’s used to, when it’s used to, you are trying to get it accustomed to a more or less rigorous eating schedule. Moderate amounts of stress are good for us8, and they are the cause of positive developments within our bodies. Whether 16/8 represents too much stress, ultimately, is a matter for you and your GP to decide.

Intermittent Fasting May Be Worthwhile

Medical research has shown that IF programs, like the 16/8 eating schedule, hold numerous benefits for our health, mainly because they help align our eating with the natural, circadian rhythms of the human body. Everything you would have to worry about while trying TRF would be losing fat and staying hydrated, as the 16/8 showed that endurance, strength, and overall muscle mass will grow at a slightly better rhythm than eating from 9am to 10pm.

Before conducting your own diet experiment, check in with your family doctor to ensure that your personal trial is medically approved. This step is vital towards ensuring your own health, as well as your credibility when asserting the benefits of TRF to others.


1. Ruth Patterson et al, “Intermittent Fasting and Human Metabolic Health”, Journal of the Academy of Nutrition and Dietetics, no. 115(8):1203-1212, accessed April 27, 2018.

2. Kirstin Hoddy et al, “Safety of alternate day fasting and effect on disordered eating behaviors”, Nutrition Journal, no.14 (44), accessed April 27, 2018.

3. Monique Tello, “Eat only every other day and lose weight?”, Harvard Health Blog, 31 May 2017, accessed April 27, 2018.

4. Mark Mattson et al, “Meal frequency and timing in health and disease”, Proceedings of the National Academy of Sciences of the United States of America, accessed April 27, 2018.

5. Grant Tinsley et al, “Time-restricted feeding in young men performing resistance training: A randomized controlled trial”, European Journal of Sport Science, no. 17 (2):200-207, accessed April 27, 2018.

6. Tatiana Moro et al, “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, no. 14 (290), accessed April 27, 2018.

7. Siobhan Smith, Jordan LeSarge and Peter Lemon, “Time-Restricted Eating in Women – A Pilot Study”, Western Undergraduate Research Journal, no. 8(1):1-6, accessed April 27, 2018.

8. Mark Patterson, “Hormesis Defined”, Ageing Research Reviews, no. 7(1):1-7, accessed April 27, 2018.