Understanding Intermittent Fasting

Intermittent fasting has been a topic on the nutrition trend radar for a while now. Originally, this way of eating blew up in the fitness and weightlifting community, now filtering down to the general public. It quotes benefits like weight loss, improved blood sugars and mental clarity. Diets like The 5:2 Diet, The 16/8 Method, Leangains, The Warrior Diet, and several others have recently emerged as popular fasting diets.


Intermittent fasting involves alternating periods of fasting and eating. Intermittent fasting doesn’t tell you what to eat, but rather it tells you when to eat. There are several ways to practice intermittent fasting, but the most popular form of IF is time-restricted fasting.

16/8 and 14/10 methods are common examples of time-restricted fasting. This means restricting for 16 hours and eating within an 8-hour time-frame, or restricting for 14 hours and eating within a 10-hour time-frame. You’re “allowed” to drink water, tea, and coffee and take supplements during the fasting period, as long as they’re all non-caloric (AKA skip the cream and sugar). Putting it simply, you cannot eat anything during the fasting cycle.

Other forms of IF include:

  • The 5:2 diet – This type involves eating 500-600 calories for two days of the week but eating normally the other 5 days.
  • Eat-Stop-Eat: This form of intermittent fasting is practiced with one or two 24-hour fasts per week.
  • Alternate-day fasting:  Fasting every other day, either by not eating anything or only eating a few hundred calories.
  • The Warrior Diet: Eating only small amounts of vegetables and fruits during the day, then eating one huge meal at night.
  • OMAD: One meal a day – not eating during the day and having all your caloric intake in 1 meal. 

The Research

Despite the recent popularity of intermittent fasting and associated weight loss claims, the supporting evidence base in humans remains small. Most studies have been done in animals, not being able to generalize the results to humans. Some trials of alternate day fasting for eight weeks in obese people did find improvements in heart disease risk markers, however, revealed increases in insulin resistance within 24 to 72 hours of initiation of fasting.

For those with IBD and other digestive issues, there has been some new research coming out to give the digestive system a rest. This area is still under research but there might be something there. 

Prolonged fasting may negatively impact athletic abilities or exercise stamina. It’s not clear to what degree intermittent fasting impacts our physical performance. It also may impact everyone differently, as some people likely adapt more quickly to fasting than others.

The Special Case of Female Health

Experimenting with fasting as a one off seems tiny to many women. Unfortunately — for some women— it seems like small decisions can have big impacts. It turns out that the hormones regulating key functions like having your period are incredibly sensitive to your energy intake and nutrient timing. Fasting for even a short period of time 2-3 days can cause a chain reaction in the female body. There’s even some evidence that missing a single regular meal can start to put the female body on alert. Any sort of psychological or physiological stress can throw female hormones off balance including too little food, poor nutrition, too much exercise, too much stress, illness, infection, chronic inflammation, and too little rest and recovery. Fasting falls under this umbrella. 

Top Factors to Consider

  • The research on this diet is spotty. Most studies are done in animals
  • People with any history or predisposition to eating disorders or disordered eating of any kind should not attempt this diet.
  • Pregnant women, diabetics, or anyone who takes medications shouldn’t attempt this diet.
  • This diet could be good if you have lost your hunger cues through overeating/indiscriminate eating and need to reset them. You’ll quickly remember what it feels like to be hungry.
  • Women who get hungrier at certain times of the month will find fasting at those times, very challenging.
  • Don’t expect to exercise on the day you fast or on the following day. Your energy levels will me all over the place. For this reason, I do not recommend the diet if you are active or are an athlete of any kind
  • Don’t expect to look normal, energetic, full of live and clear skinned when you’re fasting. You’ll probably look (and feel) like a corpse.
  • This diet may lead you to eat foods that you never eat, just because they are low calorie. Diet soda, low calorie processed foods, artificial products… 
  • This diet has been noted to make people feel guilty about eating beautiful, whole foods on a day when they have been fasting. Guilt has no place in nutrition and eating.
  • If you travel a lot for business or have a lot of business functions, this diet may not work for you. You can’t fast during a business dinner. That would be weird.


As someone who works with many people who have disordered eating patterns and are trying to work on their relationship with food, I don’t think its for every where. Waking up and wondering if you are “allowed” to take your omega-3 supplement because it contains calories or put almond milk in coffee could ultimately add more stress to many people’s life.

Many people practice IF simply as an excuse to skip breakfast in hopes of cutting calories, rather than practice it for the potential health benefits. Yes reducing calories could be the part of your goals but it goes beyond that giving your digestive system a break, working on satisfaction after a meal and regulating blood sugar control.

Whatever the research says, the effectiveness of any diet ultimately relies on how long you’re actually going to be able to sustain it, which is why diets don’t usually work. Is intermittent fasting sustainable? And if it is for a person, how would it make you feel, both physically and emotionally? Would you end up overeating the day after fasting? Would you really lose weight? The work hangry rings through my mind. Some people may be able to handle this diet. If you’re the sort of person who eats to live and sees food as fuel (versus lives to eat, like many of us do), you might find this diet easier. 

When considering a diet to be sustainable, a question comes down to flexibility and whether you can maintain it with your daily lifestyle. A diet such as carb cycling which optimizes energy intake around training and activity, allows you to enjoy your favourite foods, and stresses whole real foods may be a better option for you to be successful in the long term. 


Antoni R., Johnston, KL., Collins AL., Robertson MD. (2016). Investigation into the acute effects of total and partial energy restriction on postprandial metabolism among overweight/obese participants. Br J Nutr;115(6):951-9. 

Bhutani S, Klempel MC, Berger RA, Varady KA. (2000). Improvements in coronary heart disease risk indicators by alternate-day fasting involve adipose tissue modulations. Obesity (Silver Spring);18(11):2152-9. 

De Bond JA., Smith JT., (2014). Kisspeptin and energy balance in reproduction. Reproduction;147(3):R53-63.

Dubost J. (2014). Intermittent fasting: A good approach? Academy of Nutr Diet. http://www.eatright.org/resource/health/weight-loss/your-health-and-your-weight/intermittent-fasting 

Fry JR, Sinclair D, Piper CH, Townsend SL, Thomas NW. (1999). Depression of glutathione content, elevation of CYP2E1-dependent activation, and the principal determinant of the fasting-mediated enhancement of 1,3-dichloro-2-propanol hepatotoxicity in the rat. Food Chem Toxicol;37(4):351-5. 

Jane L., Atkinson G., Jaime V., Hamilton S., Waller G., Harrison S. (2015). Intermittent fasting interventions for the treatment of overweight and obesity in adults aged 18 years and over: a systematic review protocol. JBI Database System Rev Implement Rep;13(10):60-8.

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