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The Low-Down on Fasting and Meal Timing

Get the facts about fasting, frequency and if there’s a right time to eat.

Fasting and meal timing

Which is better: eating five or more small meals or fasting for 16 hours a day? Whether you’re trying to lose weight or gain muscle, chances are you’ve asked yourself these very questions. Meal frequency and meal timing have become common terms used to talk about dietary eating patterns.

But all the talk has created a mythology around the “right” way to eat, and it’s time to separate myth from reality by focusing on the science.

Celebrate March’s National Nutrition Month with this information from Michelle Alencar, PhD, certified clinical nutritionist, associate professor in kinesiology and co-founder and chief science officer for inHealth Lifestyle Therapeutics, Inc. Understanding the science of meal timing can make decisions easier, especially as your healthy resolutions for this year may be in the rearview mirror!

Is Fasting Best for Increasing Fat Metabolism?

Intermittent fasting is definitely a hot topic—and controversial when it comes to fat metabolism. So is there a difference between reducing calories evenly throughout the week (calorie restriction) and fasting (reducing intake for an extended duration)?

The Evidence

Anton et al. discuss intermittent fasting as a superior method for overweight adults because of the fat mobilization benefits that kick in as the body switches to fat as a source of fuel. The authors describe this as the “metabolic switch,” which they suggest occurs after about 12 hours of fasting (at the point of negative energy balance). That’s when liver carbohydrates stores are depleted and fat metabolism must take over. The authors describe this adaptation as occurring with habitual intermittent fasting practices. However, there have been reported risks with extended fasting (several weeks or more), including nausea, dizziness, abnormal liver function, decreased bone density and thiamine deficiencies (Anton et al. 2018).

Know that intermittent fasting isn’t the only way to tap into fat metabolism. Caloric restriction has been shown to increase fat mobilization, especially in combination with exercise (Cherif et al. 2016). Your focus should be goal-oriented, with energy metabolism as a secondary consideration. Any potential benefits from fasting can be undone if caloric and macronutrient targets (carbs, fats and proteins) are not adequate.

The Takeaway

We are either storing food energy or burning food energy. Therefore, to manipulate body weight up or down, we need to manipulate the energy balance equation. Overall, both calorie restriction and fasting can considerably reduce caloric intake and bring about similar health benefits. Consider what will work for you over the long run to successfully attain your goals.

See also: Myths About Meal Timing and Frequency


Please share this page with your clients. And let know what other topics would be most valuable for future Handouts.

Meal-Timing Myths Exposed

Here are the facts behind other common meal timing myths:

Meal Frequency. Available literature states that increasing your meal frequency does not have a metabolic advantage. If increasing the frequency of your meals helps you attain calorie goals, great! But if you have a hard time with meal planning and counting calories, this method may do more harm than good.

Hunger. Intermittent fasting is equivalent to continuous energy restriction. Since many factors regulate hunger hormones, it may be best to focus on diet quality and caloric targets instead of eating patterns.

Body Composition. Currently, the evidence does not support an added benefit of increased meal frequency for long-term body composition goals. For a lower-calorie diet, a pattern of eating fewer meals may reduce the risk of underreporting food intake.

Nutrient Timing. This is the cherry-on-top of eating patterns. The first step is to focus on overall energy goals, nutrient aims and exercises that support muscular fitness (for optimal body composition). Then, if you like, you can learn more about the timing of nutrients. (You may want to work with a registered dietitian to explore these topics. Find one at eatright.org.)


Anton, S.D., et al. 2018. Flipping the metabolic switch: Understanding and applying the health benefits of fasting. Obesity, 26 (2), 254–68.

Cherif, A., et al. 2016. Effects of intermittent fasting, caloric restriction, and Ramadan intermittent fasting on cognitive performance at rest and during exercise in adults. Sports Medicine, 46 (1), 35–47.

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