Slow Down as You Consider Fasting

A Professor's Perspective On Current Events

Professor Kimberlee Bethany Bonura, Ph.D.
By Professor Kimberlee Bethany Bonura, Ph.D.

Slow Down as You Consider Fasting. A better and more holistic approach for dietary cleansing is to fill your day-to-day diet with cleaner foods

Fasting is trendy: juice fasts, the cayenne-pepper-and-maple-syrup fast, whatever fast the Kardashians are currently doing. I’m not a fan. I tried them all when I was in my 20s. I know from first-hand experience that the nutritionists are right: you mostly lose water weight (and you might lose muscle, which you don’t want to lose), you don’t have much energy, you end up hangry and cranky and generally irritable.

Fasting advocates say they are great for cleansing. A better and more holistic approach for dietary cleansing is to fill your day-to-day diet with cleaner foods: lots of fresh water, whole grains, fresh produce, and lots of the green vegetables that provide both fiber and vitamins, minerals, and micronutrients.

But the research on intermittent fasting is far more compelling. Intermittent fasting isn’t about starving yourself for two weeks while you live on juice. Instead, it’s about giving up the snacking-all-day-long habit and giving your digestive system an occasional break. Research by Dr. Mark Mattson, a Neuroscientist at the John Hopkins School of Medicine, shows that what we eat impacts brain functioning and aging. Every time we eat, glucose is stored in the liver as glycogen.

If we snack and eat all day long, our bodies have a constant streaming source of glycogen for energy, because it takes 10 to 12 hours after eating to deplete glycogen levels in the liver.

If your glycogen levels get depleted, then your body burns fats, which are converted to acidic chemicals called ketones, which are used by the neurons in the brain for energy. Ketones improve brain health. Your body only creates them when you deplete your glycogen levels.

One strategy to deplete glycogen levels on a regular basis is a time-restricted diet. If you eat all your meals within an eight-hour period during the day, then your body has 16 hours until your next meal to burn through your glycogen stores and begin using fat stores.

This article is part of our Professor’s Perspective series—a place for experts to share their views and opinions on current events.

In practice, this means that if you eat breakfast at 9 am, you eat an early dinner about 4:30 pm, and quit eating for the day by 5 pm. You might remember that the origin of the word “breakfast” is to “break” the “fast.” And that’s exactly the intent of a time-restricted diet – to go back to a way of eating in which food is not ever present – where you don’t snack all day and into the night.

In research studies, fasting yields benefits like improved insulin levels and reduced asthma symptoms. Prior research found health-promoting benefits with calorie restriction diets, but being perpetually hungry is hard to sustain. A time restricted diet, in contrast, doesn’t mean you must eat less. You can still eat about 2000 calories per day – you just eat it in a more limited period. (To estimate how many calories you should be eating each day, based on your age, gender, and activity levels, click here for a tool from the National Institutes of Health.)

Previously, I wrote about the benefits of eating earlier in the day versus later. Click here to read that post on The Great Courses Daily. Looking at time effects and fasting effects together, it makes good sense to eat dinner early and then close your kitchen. Who knew that health and clean counters went together?

To learn more about intermittent fasting, you may want to read this article in Scientific America (which covers both pros and cons, and some of the details of animal research) and this interview with Dr. Mattson at John Hopkins.

For more with Professor Bonura, check out “How to Stay Fit as You AgeWondrium!