Available May 16th, 2017


Time-Restricted Eating for Better Hormonal and Metabolic Health


time restricted eating

By Dr. Mercola

I recently interviewed Dr. Mindy Pelz, author of “Fast Like a Girl,” and we both agree that time-restricted eating (TRE) could be one of the best foundational strategies you can implement to boost your metabolic fitness and even balance your sex hormones. However, the devil’s in the details, especially for women looking to implement it.

The Two Energy Systems in Your Body

Your body has two primary energy systems, one of which is activated when you eat. As your blood sugar goes up, your body uses that glucose for energy. After going without food for some time, blood sugar goes down. If you’re metabolically healthy, your body switches over to using ketones derived from fat.

Dr. Pelz noted that the switch to burning fat for fuel occurs around 13 to 15 hours of fasting. During this period, growth hormones rise and inflammation comes down. After 17 to 18 hours of fasting, autophagy kicks in, and at 24 hours, stem cells begin to emerge.

Understanding these two energy systems is key for maximizing the benefits of TRE. In the next sections, I’ll outline different ways you can approach this.

Ketone Drink May Be Helpful for Athletes

Throughout the years, athletes believe that the easiest way to bolster athletic performance is to increase glucose intake. But studies show that a high-ketone diet for athletes provides superior benefits. In experiments, competitive cyclists who were given a ketone drink showed improved speed and endurance. The ingestion of this drink allowed their bodies to use up these ketones instead of fat and glucose.

Although I don’t usually recommend anything from outside the natural food category, there have been studies that show that ketone ester drinks may change your metabolism for the better. Scientists created this ester drink, which contains both (R)-3-hydroxybutyrate and (R)-1,3-butanediol. Reuters says that by ingesting ketonic drinks, the amount of lactate produced by the body is minimized, pulling down the risk of having cramps and soreness after a workout.

Timing Your Eating Window

The core tenet of TRE is compressing your eating within certain hours of the day, and then fasting for the remaining hours. To maximize TRE, here are three rules to keep in mind:

  1. Your eating window should be shorter than 12 hours
  2. Wait at least two or three hours to eat after waking up
  3. Your last meal should be three hours or more before bedtime

Dr. Pelz believes that these rules mimic your ancient ancestors’ feast-famine cycle. On some days, they gorged on food, and then went without food for days after, allowing them to switch between metabolic energy systems. A popular TRE strategy that mimics this is the 16:8 fast, which means fasting for 16 hours, and then eating for eight hours.

Fine-Tuning TRE for Best Results

If you’re not used to the concept of fasting, it’s best to start off slow first. Count the total hours between your first and last meals, and reduce that window by one or two hours. You’ll become a little uncomfortable, but keep pushing it until you get used to 15-hour fasts.

You’ll know you’ve started producing ketones because you suddenly feel you have better energy and your hunger goes away. For most people, that only occurs when you haven’t eaten for 15 to 16 hours.

Once you’ve gotten used to a 15-hour fast, it’s time to vary the TRE. Dr. Pelz advocates the 5-1-1 fast. For five days a week, you’re intermittent fasting for around 15 hours, and then the next day you’ll stretch it further. Then, you’ll have a day without fasting. Based on Dr. Pelz’s experience, varying the fasting hours is important, as it prevents your body from plateauing.

In order to maximize TRE, these other strategies may help improve results:

It can take anywhere from a few weeks to a few months for you to become metabolically flexible. But once you do, you’re not out of the woods yet. You’ll have to increase your eating window for a few hours because your body needs glucose.

If your body doesn’t get enough dietary glucose for too long, it will produce cortisol as well as its own glucose from your liver. Vary the eating window between eight and 12 hours and avoid going lower or higher than that window.

Maximizing Fasting for Women

Men and women differ in the sex hormones that predominate and drive key health processes. For men, testosterone is the primary hormone. In women, testosterone, estrogen and progesterone all play a part. Once a woman reaches 40 years old, her estrogen levels fluctuate, which may cause weight gain and insulin resistance. To mitigate this, you can time your fasting to your menstrual cycle to balance these dips in estrogen.

For the first 10 days, estrogen is building. During this time, you can go into longer fasts — even three-day water fasts. As you reach ovulation, wherein estrogen, testosterone and progesterone are at their highest, you should bring the fast down to 12 to 15 hours.

To help you understand this concept better, you can check out the graphics below from Dr. Pelz’s book:

fasting and menstrual cycle visual 1
fasting and menstrual cycle visual 2
fasting and menstrual cycle visual 3
fasting and menstrual cycle visual 4
fasting and menstrual cycle visual 5

Fasting for Perimenopausal and Menopausal Women

For perimenopausal and menopausal women, Dr. Pelz offers these fasting tips if they’re experiencing any of these symptoms:

To learn more about integrating time-restricted eating into your lifestyle, read my book, “Fat for Fuel,”and the article, “How to Fast for Metabolic Fitness and Hormone Balance.”



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