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How intermittent fasting can help you lose weight (and even live longer!)

By Dr. Mary James, ND

When you first hear about it, intermittent fasting might sound like an impossible feat or a miserable experience. But once you learn the secrets, you’ll be surprised at how easily you can do it.

An alarm clock on a plate in a table setting

The truth is intermittent fasting can be done in several different ways, yet each can result in weight loss – along with other benefits. It’s all about finding the right approach for you.

You can lose belly fat with intermittent fasting

Intermittent fasting works to shed belly fat by training your body to burn fat (as ketones) for energy more than glucose. This swap happens naturally when you take longer breaks from eating – anywhere from 12 hours to an entire day.

Once your body adjusts to this schedule, you’ll start to see your belly fat and overall weight go down. Plus, you’ll likely see a real improvement in every measure of your metabolism. That means intermittent fasting can help whether you have high glucose, high insulin, pre-diabetes or type II diabetes, insulin resistance, high triglycerides, or similar issues.

Intermittent fasting improves digestion

Another big advantage of intermittent fasting is how it heals and resets your digestive process. In researching my own digestive issues, I’ve learned that a really important part of digestion can only occur when you’re in a fasting state.

During this time, the migrating motor complex in the smooth muscle of the small intestine acts like a sweeper to clear food out of it and into the large intestine. If you’re eating too frequently (more often than every 4 hours), this process stalls. And that contributes to bacterial overgrowth in the small intestine, where very few bugs should normally reside. Bacterial overgrowth leads to inflammation that damages the microvilli (little cellular protrusions) responsible for absorbing important nutrients from your food. This is a big factor in the development of “leaky gut syndrome,” and intermittent fasting helps that heal.

Fasting can even slow down the aging process

I’m seeing more and more science showing major benefits of intermittent fasting, so this way of eating is definitely more than a trend. It’s also fascinating that so many animal studies have consistently shown that caloric restriction, which includes fasting, slows aging and extends life span.

No wonder scientists became so curious about the effects of fasting in humans!

Fasting isn’t one size fits all

There are several ways to do intermittent fasting, and they all yield similar benefits. So choose the one that seems easiest for you:

  • Alternate-day fasting: You move back and forth between one complete fasting day (no eating or drinking of energy-containing foods; water and tea are allowed) and one day eating and drinking as you normally would. For example, if you eat on Monday, you fast on Tuesday and eat again Wednesday and continue this way through the week.
  • Modified fasting: You severely restrict how many calories you eat and drink for two days a week (not in a row). On the other days of the week, you eat and drink normally. You may have heard of the popular “5:2 diet,” which follows this format. For example, on Monday and Thursday you would only eat 500 calories (including foods with healthy fats), while on the rest of the days of the week you would eat normally.
  • Time-restricted eating: Each day you only eat and drink within a specific timeframe; the rest of the time you’re fasting. If you usually eat a late breakfast and early dinner, you are already close to this schedule. Try to restrict all of your calorie intake to an eight-hour period. For example, you might eat only between the hours of 12 noon and 8 p.m. every day.

If you’re just starting out

I suggest trying the time-restricted approach first, and going at a slow pace to let your body adjust.

One simple way to keep track of when to eat and when not to eat is to plan on eating your meals only during the daylight hours. When it’s light out, eat as you need to in order to not feel hungry. But once the sun sets, don’t eat. Your body will immediately experience the benefits, and over time you’ll likely start noticing them.

Lots of people find it helpful to start with a cup of “bulletproof coffee” in the morning, and then refrain from eating till afternoon. Of course, the fat in the coffee contains some calories. But it’s a helpful way to start, and many people still lose weight with this approach. Just don’t add milk or sugar!

How much should you eat during non-fasting hours?

When you do eat during IF, you don’t have to worry about being super restrictive. Of course, eating like every day is Thanksgiving doesn’t make a lot of sense if you are trying to lose weight, whether you’re fasting intermittently or not. Instead, focus on eating enough that you don’t feel physically hungry between meals.

Some researchers note that people generally don’t overeat during the non-fasting hours, especially once it becomes part of a routine. You should always make sure you continue to drink plenty of water, which not only keeps your system hydrated but also helps you feel less hungry.

Before you get started, check with your healthcare practitioner to see if intermittent fasting is a good idea for you. This is especially important if you’re severely underweight, taking blood sugar-lowering drugs, or are experiencing adrenal insufficiency. Right now, I know my adrenal health is not where it should be. If I go a long time without eating, my blood sugar drops too low and I can get spacey, shaky and irritable. That’s why, for now, I’m holding off on more rigorous fasting than time-restricted eating.

Part-time intermittent fasting?

I’ve been asked by a coworker somewhat jokingly about “part-time” intermittent fasting. I think my answer surprised her. I said that if you can fast like this only once in a while, then once in a while is still better than never!

Remember, there’s no single way to incorporate intermittent fasting into your life – the way that works best for you is the one to choose.

  • Patterson, R. E., Laughlin, G. A., Sears, D. D., LaCroix, A. Z., Marinac, C., Gallo, L. C., … Villaseñor, A. (2015). INTERMITTENT FASTING AND HUMAN METABOLIC HEALTH. Journal of the Academy of Nutrition and Dietetics, 115(8), 1203–1212. https://doi.org/10.1016/j.jand.2015.02.018

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Last Updated: September 28, 2023
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