Which is best, regular calorie restriction, intermittent fasting, or time-restricted fasting? A meta-analysis reveals surprising answers.
A group of researchers from Colorado must have gotten sick of going to family outings and having to listen to Cousin Dwayne drone on about the success of his intermittent fasting and/or time-restricted diet and how, in soft lighting, you could maybe, from a certain angle and if your eyes were a little watery from hay fever, possibly see the faint outline of some abs.
Their response was to examine whether all this hoopla about intermittent energy restriction (IER) diets was worth it; to see if these trendy diets worked better than traditional calorie restriction diets where you just say "no" to some tater tots or some cheesecake without regard to day or time of day.
In order to figure it out, they reviewed all studies over 8 weeks in duration involving overweight adults that compared the effects of these IER diets (both intermittent fasting or time-restricted feeding) to continuous energy restriction (CER) diets.
It turns out that restricting your eating to certain days of the week or weird, arbitrary hours of the day, like between the first showing of a Golden Girls rerun on Hallmark Channel East and the second showing, three hours later, on Hallmark Channel West, doesn't work any better than good ol' fashioned every-day, all-day dieting.
What They Found
There are an untold number of diet strategies, but the most common is simply reducing daily caloric intake. For most people, this approach results in weight loss of about 5 to 10% (when sustained for over a year). Unfortunately, adherence to these types of diets typically declines within 1-4 months.
This relative ineffectiveness has caused creative people all over to devise different strategies. One such approach is to simply go longer between meals (intermittent energy restriction). Other types of IER include restricting food intake to 8 to 10 hours a day (intermittent fasting) or restricting food intake 2-3 days a week (or on alternate days) while eating normally the rest of the time.
The rationale was and is that dieters who follow these schemes don't fully compensate for the calories they spurned during the fasting periods.
Dietitians and people in the know also hoped that these IER diets would have beneficial effects on body comp, energy expenditure, and substrate oxidation that surpassed those of conventional diets where you just eat less all the time.
Unfortunately, 9 of the 11 studies the Colorado researchers examined failed to show any significant differences between intermittent fasting protocols and continuous energy restrictions diets. Two outlier studies did, however, show some additional benefit from IER diets.
The first of these outliers involved a two-day-a-week intermittent fasting regimen and while it didn't result in any significant differences in weight loss between the two groups, the IF group lost more body fat.
The second outlier study involved subjects who participated in alternate-day modified fasting where the participants on the fasting side got breakfast before 8 AM and then had to ride out hunger pangs for the next 24 hours before eating again, three non-consecutive days a week.
The alternate-day fasters showed greater weight loss and fat loss than the conventional CER method. That's promising, but again, the study was an outlier in that it showed different results than the other comparable studies.
What to Make of This Info
Despite what these comparison studies say, there's some evidence that the timing of meals has an effect on weight loss. For instance, people who eat more calories in the morning than they do in the evening tend to lose more weight. Likewise, eating more at night is linked to obesity.
That being said, it really doesn't seem to matter what type of calorie-restriction diet you follow – they all have the potential of taking you where you want to go. Granted, none of the studies the researchers were able to find involved he-man bodybuilders and it's possible that their different levels of activity and presumably different metabolic characteristics would yield different results.
Not only that, but bodybuilders typically avoid diets where they risk losing valuable muscle from not eating any protein for any significant time period.
Regardless, there's one fact that supersedes the data and personal requirements for regular doses of protein: Intermittent fasting or time-restrictive eating are probably a lot easier to stick with than the monotony of continuous energy restriction.
After all, keeping your hands out of the cookie jar for just a few hours a day, or for one or two days a week, seems infinitely easier than avoiding the cookie jar altogether.
- Corey A. Rynders, Elizabeth A. Thomas, Adnin Zaman, Zhaoxing Pan, Victoria A. Catenacci, Edward L. Melanson, "Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss," Nutrients 2019, 11(10), 2442.