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

Background: Understanding the Basics
Intermittent fasting (IF) may sound technical. But all it really means is going for extended periods without eating.

Throughout the world there are many tribes who naturally experience some form of IF. Among them, many show no signs of age-associated problems like cancer, neurodegeneration, diabetes, cardiovascular disease, or hypertension.

The reality is that fasting is an intrinsic part of human life. IF in its most basic form is called… sleeping. There are many ways to do IF on purpose, including meal skipping, alternate day fasting, Eat Stop Eat, and more.

The idea behind intermittent fasting is that by limiting your eating either to a certain number of hours per day (such as in the 16/8 method where you only eat for an 8-hour window) or to a certain number of days per week (5:2 Diet), you ideally eat less calories overall. Fasting also burns off the liver’s energy stores from carbohydrates, and therefore switches the body’s fuel supply from glucose to fat.

Intermittent Fasting – 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. There is only one published systematic review examining the health benefits of this approach and it does not conclude successful weight loss.

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. Even skipping breakfast for 14 days was found to raise LDL cholesterol (he bad kind) and produce insulin resistance throwing your blood sugars out of wack.

Other human studies show 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 2-3days 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.

Conclusion
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.

References
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?

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.