Protein: Magic Ingredient for Intermittent Fasting?

MagicianIntermittent fasting has some enthusiastic fans. While some studies have shown impressive benefits, others have found little benefit. On top of that, virtually all of the research on this type of dietary intervention has been of a short duration. Compliance with intermittent fasting can be a challenge over time. So the fan base will surely welcome a new study published in Obesity. It appears to show that all you have to do is add some protein to intermittent fasting and presto! Intermittent fasting is clearly superior to mere calorie restriction.

But two little problems get in the way of a full embrace of this study that seems too good to be true. First, it’s a very brief intervention – only eight weeks. Second, the study is pretty small – only 41 patients.

Randomized and Controlled

On the plus side of the ledger is the fact that this is a randomized, controlled study. The intermittent fasting group actually consisted of  two slightly different intermittent fasting regimens. One regimen had the subjects consume only 400 calories for one day a week. The other had them consume only 500 calories daily for two consecutive days each week. Both of these groups also received “protein pacing” to assure that 35 percent of their calories throughout the study came from protein. These two groups were randomly assigned and then combined in the final analysis of intermittent fasting versus continuous calorie restriction.

In the control group, subjects received a similar number of calories per week, but without intermittent fasting or protein pacing. So they received only 21 percent of their calories from protein.

After eight weeks, the investigators report that the combined intermittent fasting group with protein pacing lost more weight and also improved their body composition more than the control group. Quite reasonably, they conclude that dietary interventions to promote weight loss should emphasize both the quantity and quality of food – emphasizing adequate protein and fiber while reducing sugar and salt.

Is It the Protein or the Fasting or Both?

But we’re not so sure that they’ve proven intermittent fasting itself is superior to simple calorie restriction. With this study design, it could be that the protein, not the fasting regimen, is what’s making the difference. We cannot know if both the fasting and the protein pacing were essential for these results because they did not test continuous calorie restriction with protein pacing.

One other thing to consider is that this study was funded by a multi-level marketer of protein supplements for weight loss – Isagenix. About this company, Healthline reports some concerns:

“Despite its popularity, Isagenix failed Healthline’s rigorous vetting process due to concerns about its products, health claims, and business practices.”

Though we do not favor rejecting research findings based on funding sources, we would like to see these finding replicated and validated by other investigators. Evidence of a benefit over much more than eight weeks is necessary as well.

Click here for the study in Obesity, here, here, and here for more on intermittent fasting, and here for more on protein pacing.

Magician, painting by Fernand Khnopff / WikiArt

Subscribe by email to follow the accumulating evidence and observations that shape our view of health, obesity, and policy.


January 6, 2023