Weight Loss and Intermittent Fasting: Research Update

The science behind weight loss explains why success is not easily found on the simple path of calorie reduction.

Nearly all of us know someone who has tried a weight loss diet—or a few of them—and come away frustrated despite some initial success. 

If you’ve observed this phenomenon, you’re not alone. 

A recent study published in the British Medical Journal analyzed a large number of research trials in an investigation of the results of many popular diets. Their conclusion: 

… researchers analyzed 121 trials that enrolled nearly 22,000 overweight or obese adults who followed one of 14 popular diets, including the Atkins diet, Weight Watchers, and Jenny Craig [a diet focused on low-fat foods], for an average of six months. While low-carbohydrate and low-fat diets both resulted in weight loss of about 10 pounds at six months, most of the lost weight was regained within one year.

A contemporaneous review, published in Experimental Gerontology and titled, “Impact of Calorie Restriction on Energy Metabolism in Humans,” explains one well-documented reason why this might be true. Defining Calorie Restriction (CR) as a sustained reduction in energy intake, the review comes to this conclusion: 

CR induces weight loss and a disproportionate reduction in energy expenditure.

What the science is telling us is that while sustained reduction of calories will result in weight loss,  it also slows the rate at which the body consumes energy, which we commonly refer to as metabolism. And once  metabolism slows, when the dieter goes back to their normal intake of calories, less of those calories will be burned as fuel, leaving more of them to accumulate as fat. 

Does that mean there’s no hope for those who want to lose weight? Not if you pay close attention to the definition of Calorie Reduction as sustained reduction in energy intake. It raises the question, what if the reduction is not sustained, but rather implemented over several relatively short periods of time, which is to say intermittent. 

A third study, published in December 2021 in the Journal of the American Medical Association open network, reviews high-quality research trials involving Intermittent Fasting (IF) with nearly 6900 participants. Their conclusion:  

Our results support the role of IF…in adults with overweight or obesity as a weight loss approach with metabolic benefits.

There have been many studies of Calorie Reduction (CR) and Intermittent Fasting as methods to approach weight loss, in some cases with results conflicting with the above. What distinguishes the BMJ and JAMA papers is the quality of the research that they summarize—they reviewed only gold-standard randomized controlled trials (RCTs)—and the number of participants involved (thousands in each case). 

If you wish to dig further into those studies, keep this in mind: Intermittent Fasting can range from the relatively mild approach of eating only during a 12- or 8-hour period of the day to the more rigorous approaches of fasting for 24 hours, 36 hours or even more, once or twice a week. The type of intermittent fasting being studied is likely to make a big difference in a study result.  

Keep in mind also that there’s a great deal more money to be made in selling special meals than there is in explaining to someone why they should try not eating for a day every so often, which is likely to influence what you read in the news.  

Why, you might well wonder, would the body respond differently to IF than to CR? To answer that question, you’ll want to gain a deeper understanding of exactly how your body manages energy, which you can achieve with several eSavvyHealth guidebooks and courses available on that exact subject. 

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