ObesityWeek: Intermittent Fasting and Circadian Rhythms

The role of intermittent fasting (IF) and circadian rhythms is a subject of intense interest for people focused on obesity. How can you tell? Just look at the packed hall yesterday at ObesityWeek 2019 for the Blackburn Symposium. In a cavernous room with seating for more than a thousand people you could not find a single empty chair. In fact, people sat on almost every bit of available floor space they could find. They really wanted to hear every word that Courtney Peterson and Frank Scheer uttered.

Intermittent Fasting

This is one of those rare subjects where pop nutrition advice and science are moving (loosely) in parallel. On the science side of things, we have some tantalizing data offering hints that this might be important. Yet definitions are pretty loose. Under some definitions, most adults are fasting intermittently. And then there’s the problem of proving a net benefit to humans. If you’re a lab rodent, it can have marvelous metabolic benefits. But if you’re human, much of the research tells us the difference between intermittent and continuous calorie restriction might be negligible.

In fact, that was precisely the conclusion of a recent review of randomized trials in Nutrients. However, some studies such as this one have found better weight outcomes for IF when you compare it to a matched regimen of continuous calorie restriction. As we said, it’s tantalizing, but there’s more to learn.

Of course, tantalizing is good enough for the hype squad to go nuts with this idea. On Amazon, you’ll find more than 2,000 options for products related to intermittent fasting. You can even find advice on intermittent keto fasting. Sheesh!

Circadian Rhythms

Scheer summed up the science connecting circadian rhythm and food timing to metabolic health. Food timing does matter, he said, especially when circadian rhythms become misaligned with food. It can raise the risk of insulin resistance. It can have an effect on diet-induced thermogenesis. In other words it can affect weight and health by changing how your body uses energy.

Ask any experienced dietitian in obesity care. They will tell you that many, many patients who eat big meals late in the day present with difficult cases of obesity. Yet, we still have more to learn about the cause and effect relationship here.

Food timing matters. Intermittent fasting might be a smart strategy. But beware of people who want to sell you dietary miracles based on this science. It’s not miraculous. It’s merely a subject of intense scientific interest. And that’s why the room was packed yesterday at ObesityWeek for the Blackburn Symposium.

Click here for details of the symposium and here for more perspective from Peterson on IF. For more from Scheer on circadian misalignment, click here.

Intermittent Fasting at ObesityWeek, photograph © Ted Kyle / flickr

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November 7, 2019