Intermittent fasting refers to the practice of only eating between certain hours of the day, or in some versions, alternating normal diet days with days when you severely restrict the number of calories that you eat.

It certainly works if you’re an overweight rat. On one hand, there are scores of studies showing that they lose weight and their blood pressure, cholesterol, and blood sugars improve. On the other hand, the initial studies that were done on people, while they showed that intermittent fasting was safe and effective, couldn’t prove that it was any more effective than any other calorie restricting diet and many people found it tough to stick to.

New research may help. We’ve evolved to be in sync with the day/night cycle. Our metabolism is therefore adapted to daytime food, nighttime sleep. Nighttime eating is associated with a higher risk of obesity and diabetes. A study from the University of Alabama took this into account. Intermittent fasting with all food between 7 a.m. to 3 p.m. (an 8-hour period) was compared to fasting but spread out over 12 hours (between 7 am and 7 pm). Both groups maintained their weight, but after five weeks, the “eight-hour group” had significantly lower insulin levels, improved insulin sensitivity, lower blood pressure and, even better, the “eight-hour group” weren’t starving.

In other words, by changing the timing of meals — eating earlier in the day and extending the overnight fast — there was an important change in metabolism even in people who didn’t lose a single pound.

Should everyone go on an intermittent fasting diet? No. As with any medical act we need to use common sense. People with diabetes who are on medication for it; people with a history of eating disorders (for example: anorexia nervosa, bulimia); and, pregnant or breastfeeding women should not, unless under they do it under the close supervision of a physician who can monitor them.

So, if you want to improve your metabolism and lose weight:

  • Avoid sugars and refined grains and follow a plant-based, Mediterranean diet with mainly fruits, vegetables, beans, lentils, whole grains, lean proteins (fish and fowl), and healthy fats.
  • Don’t snack. By avoiding snacking and being active throughout the day, your body will burn fat between meals.

If you are going to intermittently fast, limit the hours of the day when you eat. It’s best if you start earlier and end earlier in the day, for example: between 7 a.m. to 3 p.m, or 10 a.m. to 6 p.m. And do not eat in the evening before bed or at night.

Dr. Mitch Shulman is an Assistant Professor, Dept. of Surgery, McGill Medical School and an Attending Physician, Emergency Department, McGill University Health Centre. He’s also the CJAD AM 800 Medical Consultant.

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