Ask the Doctors

Dear Doctor: I want to lose 15 pounds but have had no luck cutting calories or carbs, or even trying that crazy (IMHO) keto diet where you eat mostly fat. What about that new diet where you only eat during certain hours? How does it work?

Dear Reader: We think you're referring to time-restricted eating, which is also called "early time-restricted feeding" or "intermittent fasting." No matter the language, these approaches all boil down to the same basic concept. That is, all of your calorie intake, including meals, snacks and beverages, takes place within a limited period of time. Instead of reducing the calories you take in each day, or limiting the types of food you eat, it's the timeframe in which calories are consumed that is strictly defined.

Before we go any further, we'd like to point out that this isn't a weight-loss regimen per se. Initial studies looked into the potential health benefits of the practice, such as blood sugar control. However, in studies done, as well as in anecdotal evidence from everyday participants, it has emerged that weight loss often takes place.

Restricted eating is based on a growing body of evidence that humans do best when we live in sync with our circadian rhythms, which are guided by the built-in "body clock" that operates within us on a 24-hour cycle. We already know that circadian rhythms influence a number of behavioral and physiological processes. These range from the obvious, such as our sleep/wake cycles, to the unseen, like body temperature, hormone secretion, enzyme function and even the speed at which wounds will heal.

So it's not that surprising to discover that nutritional intake would also have a spot on the list. There's no doubt that we've come a long way from the days of our primitive ancestors, when the rigors of hunting, gathering and preparing food, to say nothing of the challenges of storage, strictly limited mealtimes. These days, however, the average American eats from early morning until well into the night.

One of the thoughts behind restricted eating is that, over time, this type of behavior wreaks havoc on our circadian cycles, which use hormones and enzymes to prep the body in myriad ways for nutritional intake in the morning and afternoon. Then, during the subsequent fast, these processes rest. By front-loading our food consumption, as our ancestors presumably did, we allow our inner clocks to sync up for optimal operation. In a study in which men with pre-diabetes limited caloric intake to a six-hour period for five weeks, researchers saw a drop in participants' blood pressure and lower insulin levels.

There's no single formula for restrictive eating. Some plans suggest an eight-hour window for eating, while others stretch that to 10 hours. The one constant is that during the fasting period, nothing caloric -- and this includes the milk in your morning coffee or that handful of nuts at night -- passes your lips. It also appears that reversing the size of meals -- large breakfast, moderate lunch, light dinner -- helps with hunger management. If you do decide to move forward with a restricted eating plan, please check in with your primary care physician for advice and guidance.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

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