The Truth about Intermittent Fasting: 16:8 or 5:2?

I knew almost immediately after posting my Most Popular Diets for 2019 blog that I had missed perhaps the most talked-about diet besides Keto. Intermittent Fasting. Even the name makes my skin crawl.  It is getting so much attention that Doctor Radio dedicated a whole show to it. I normally love this channel and much of what I hear, but tonight I was really disappointed.

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Intermittent Fasting is one more gimmick to promote weight loss and health. One version is the 16:8 which proposes only eating in an 8-hour window of time and fasting the rest of the time. Another is 5:2 which refers to eating 5 days per week and fasting 2 days per week. We are not talking about religious fasts here, for which I hold no judgment. These are diets.

Of course, it will lead to weight loss at first. Regardless of how you do it, if you eat only a percentage of what you were previously eating, you will lose weight.  Unless of course you binge as a result which can also happen. For those that were previously above their biologically appropriate weight, that initial weight loss can improve health markers such as glucose and blood pressure. There’s no magical formula to this. It isn’t superior to practicing any other form of calorie restriction that leads to weight loss (1). 

We all already fast daily by not eating when we sleep. Any additional fasting just decreases our overall intake and likely our metabolism over time.   We constantly burn energy. The idea that we need to stop eating in order to burn fat is not true. We need to learn how to eat appropriately and stop engaging in spreading further fear of eating. There is enough controversial and contradictory science all over the internet to drive you crazy. And as is touted on some websites, fasting will not improve mental clarity. You will more likely experience lack of energy, mental fogginess, irritability, and possibly hypoglycemia.

Lastly, A woman called into Doctor Radio who had been intermittently fasting and recently had her Cholesterol checked, which, was significantly elevated. The panel recommended she continue fasting in order to lower her Cholesterol. What is often missed, and what I see with my clients who have Anorexia Nervosa is that total circulating levels of Cholesterol can actually increase in the blood stream when we eat too little. Inadequate energy intake can actually increase metabolic syndrome rather than decrease it as is the hope with many of these diets (1,2).

Maybe more important than the potential physiological pitfalls are the psychological ones. Intermittent fasting sounds suspiciously familiar. It is what my clients with eating disorders already engage in. It is a pattern of calorie restriction followed by feasting. Or put another way, dieting and bingeing. It becomes a disordered pattern of eating. It is what eating disorder dietitians try to stop our clients from continuing when they enter our offices feeling defeated and obsessed. It is quite literally disordered eating behavior.  

I spend many hours counseling clients on the benefits of eating adequate (not excessive) amounts of food and proper nutrition. It is particularly hard to meet all of our nutritional needs without eating numerous times throughout the day. We also know that those who eat breakfast have better long-term weight control, better cognitive function, and as students perform better at school (1).  Most of my clients who have obesity almost unanimously skip breakfast. They naturally engage in intermittent fasting. During the short period of time that they do eat, they typically eat far more calories than they need. 


If you are someone who loses control with food, here is what to expect with intermittent fasting:

You will lose more of your permission to eat. You will want to eat during the hours you are not supposed to. You will feel hungry and have strong urges and cravings for food. You will feel like you have failed every time you slip. Your inner critic will tell you that you “can’t even do this right”. That “all you want to do is eat” and “that you are a glutton”. It will lead to eating more during the non-fasting hours and likely to being out of control with food.  You will feel guilty, obsessed, and you might binge.


If you are someone who over-controls your intake, or have been diagnosed with a restrictive eating disorder, here is what to expect with intermittent fasting:

You will find one more rule to adhere to, which, at first will feel safe. This rule will become law. You will lose more of your permission to eat. You will further lower blood pressure, heart rate, physiological and psychological functioning. It will become difficult to eat during non-fasting hours in the future. It will cause you anxiety, guilt, and angst. It will strengthen your eating disorder. It has the potential to make you very ill.


I’ve come to learn that many people just want to be told what and when to eat. They don’t want to do the more difficult thing. Learning to connect, listen, and trust the body is hard and often confusing. Educating yourself about sound, proper, sustainable nutrition and implementing that on a daily basis takes motivation, effort, and energy. It is easier to be told “don’t eat this, don’t eat that”, or now, “don’t eat during these times”. 

It’s time we stop the madness and take a stand against the ever-growing, powerful, mind-conditioning diet culture.

Take back your right to eat. 


For more on this topic check out this great article on the Washington Post: ‘The key to glorifying a questionable diet? Be a tech bro and call it ‘biohacking.’

Marlena Tanner1 Comment