Is intermittent fasting that great?

If you’ve ever been very sick, very busy, stressed and anxious or on a demanding work deadline or otherwise preoccupied you’ve probably done so-called intermittent fasting.  For a day or two, you eat very little.  Then you go back to normal eating.  What happens to people all the time, due to circumstances, now has a sciency name and is promoted as a weight loss miracle diet.  The basics go like this: you eat normally on one or two days, and then you eat very little on the days in between.  The eventual result is that you’re eating fewer calories overall and you lose weight.  Intermittent fasting devotees claim that it’s there’s something magical and different compared to just regular low calorie diets.   They believe those fasting days boosts weight loss and provide other benefits.  The other benefit is that on normal eating days, you don’t think about calories or restricting food, which for some people can be a positive.

But does this method really result in more weight loss?  A new study suggests it doesn’t.  The study divided the obese subjects into 3 diet groups:

  1. Low Calorie Group: restricted to 75% of their usual calorie intake every day
  2. Intermittent Fasting Group: alternated between eating 25% of usual calorie intake on fast days and 125% on alternate daye
  3. Control Group: was given no special diet instructions

The subjects were provided with all their meals for the first 6 months of the study, to insure they followed the calorie restrictions.  For the second 6-month period, they were told to maintain weight, and were tested to assess calorie intake, but were not provided food.  The average target calorie intake for the fasting days was 450.  The average for the non-fast days was 2100.  The low calorie group target was 1500 calories/day.

How did they do?

Weight loss was not different between the fasting and low calorie groups after 6 months.  Other metabolic measures were not significantly different either.  One significant difference: the dropout rate for the fasting group was significantly more than for the low calorie or control groups.  People just didn’t want to follow that plan.  Another unexpected result: on the non-fast days, when people were allowed to eat 125% of their usual calorie intake, they didn’t eat that much.  Actual intake averaged 1500 calories, not the permitted 2100.  And even at that, eating fewer calories overall than permitted, the fasting group did not lose significantly more weight.

Fasting true believers will undoubtedly find something to criticize, or they’ll just claim that the diet works for them and is wonderful.  And the study authors did not discount the possibility that this system may be a good fit for some people.  But the high drop out rate suggests it’s not a great choice for a lot of people, and that simple calorie restriction is just as effective.

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