A very frequent question that has been posed to me in the last several years is my stance on the concept of intermittent fasting (IM). This approach has several variations, but all include the concept of eating “normal” for most days of the week and on alternate days, having a markedly reduced caloric intake (500 calories or less per day). Most approaches suggest a “5 days normal/2 days fasting” or “4 days eating normal/3 days fasting” schedule.
Studies have shown that people doing IM will, in fact, lose weight to the same degree as those that follow a reduced caloric intake every day. However, in the studies comparing both approaches, there was a far greater dropout in the IM group compared to those following an everyday caloric restriction approach.
On the medical side, I believe that IM is not as safe as an everyday prudent dietary plan. For those taking blood pressure or diabetic meds, there may fluctuations of the blood pressure and/or blood sugar that may not be safe for those people. Electrolyte changes may occur as well. Also, if a person is an everyday exerciser, the fasting days may provide more of a challenge to do as much intense exercise.
From the psychological standpoint, there are many people that, after the “fasting day” will feel the “right” to indulge the next day. This may lead to overeating on the non-fasting days.
I have been a doctor for almost 40 years and have seen many “diets” come and go. I believe IM will suffer the same fate. It is a fad that, due to the dropout rate, plays little-no role in long term weight control. If a person’s motivation to lose weight is to get into a certain outfit for an upcoming event several months down the road, IM will get you there. However, if the goal is to lose weight and keep that weight off long term, I suggest that you should take a pass at IM.