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Ask the Diet Doctor: The Pros & Cons of Fasting for Weight Loss

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Fasting for weight loss seems to be one of the hottest diet trends right now. But despite its current popularity, fasting has been used for thousands of years for various purposes. (It can even boost your memory, according to Intermittent Fasting: Not Just for Weight Loss?.) Because of its popularity with celebrities, people have come to believe that intermittent fasting for weight loss has an advantage over traditional diet and exercise approaches. It doesn’t. While it can be a safe weight loss strategy (if done correctly!), it doesn't actually yield better results than other fat loss methods.

Today, there are a variety of ways that people use intermittent fasting for weight loss. Here are two of the most popular approaches.

24-hour Fasts: This protocol popularized by Brad Pilon in his book Eat, Stop, Eat. (He really introduced me to the science behind intermittent fasting for weight loss). Brad’s approach is very simple—just don’t eat for two non-consecutive 24-hour periods each week.

16/8: This fasting protocol requires you to shorten your ‘eating window’ each day so that you are fasting for 16 hours and eating for eight hours. For many people, this means that breakfast starts at noon or 1 p.m., then they stop eating at 8 or 9 p.m. each day.

Regardless of which protocol you choose, there are three universal components to weight loss that people often overlook when they turn to fasting as a weight loss strategy. Here's how they could impact your success with intermittent fasting for fat loss:

You need to maintain a calorie deficit: At its most basic level, intermittent fasting requires prolonged periods of no eating so that when you are eating, you can eat normally and not worry about eating less to create a caloric deficit. Here's a practical example:

Traditional dieting approach: You burn 1750 calories per day, so you eat 1250 calories per day to create a 500/day calorie deficit. Over the course of the week, you will have a total caloric deficit of 3500 calories, which yields approximately 1 pound of weight loss per week.

Intermittent Fasting Approach: You burn 1750 calories per day and, instead of eating less each day, you opt to fast for two non-consecutive 24-hour periods during the week. The rest of the week, you eat as much as your body needs (1750 calories/day). This creates a weekly calorie deficit of 3500 calories, which yields approximately 1 pound of weight loss per week.

You need to exhibit self-control: Self-control is a must during periods of fasting and not fasting. Calorically rewarding yourself for a successful fast counteracts what you are trying to accomplish. Pilon advises, “When you finish your fast, you need to pretend that your fast never happened. No compensation, no reward, no special way of eating, no special shakes, drinks or pills.” This is harder than it sounds, but crucial to your fasting for weight loss success. Fasting for several hours does not give you permission to eat whatever you want in whatever quantities that you want.

You need to be consistent: Consistency is the trump card for long-term weight loss success. You can’t fast for a couple days, then switch to a low carb diet for a week, then go back to fasting or a high carb approach. The people that I have have the most success with fasting for weight loss adopt it as a long-term approach to losing and maintaining their weight—not a quick fix to drop weight fast. The more consistently that you fast (not the duration of the actual fast, but the days, weeks, months that you employ intermittent fasting), the more benefits you will reap. As time goes on, your body will have the time to ramp up the right enzymes and pathways to maximize fat burning during your fasted state. (Rake note of The 10 Most Misunderstood Diet and Fitness Strategies.)

So, should you fast?
Fasting for weight loss works, but so do a lot of other approaches. No dietary approach is magic. Some research suggests that a very low carbohydrate diet yields the exact same benefits of fasting—without requiring you to stop eating. If you have find yourself overeating after a fast or if you get shaky and light-headed while fasting (signs of hypoglycemia), fasting probably isn’t a good approach for you. Know your body and select the appropriate diet plan accordingly.

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