Medically Reviewed by Dr. Bryan Seigel D.C., P.L.C.
Intermittent fasting is nothing new. When food was scarce in Paleolithic times, our ancestors simply went without it.
Fasting kept early humans lean and metabolically flexible. During a fast, they would burn body fat. Later, after a successful hunt, they would add it back.
Today, most people don’t practice intermittent fasting. And when we feed 24/7, our bodies store fat like a black bear preparing for an extended winter slumber.
But since you’re reading this article, you’re not most people. You’re interested in intermittent fasting, and you want to learn more. That’s a solid foundation for success.
What Is Intermittent Fasting?
Intermittent fasting (IF) just means taking regular breaks from calories. These breaks span anywhere from 12 to 36 hours, depending on the protocol. Fasts beyond 36 hours are generally considered extended fasts.
An intermittent fast needn’t be a total fast. Certain regimens, for instance, allow limited amounts of calories on so-called “fasting” days. Usually, however, fasting means zero calories.
Here’s how fasting works. When you take a break from calories, your body senses an energy deficit. And since food isn’t coming in, energy must be found elsewhere.
That elsewhere is body fat. Even a lean person has tens of thousands of fat calories, just waiting to be unleashed and burned for energy.
How do you unleash body fat? By keeping the hormone insulin low[*]. When you eat, your pancreas secretes insulin to process and store the incoming nutrients. When you don’t eat, insulin levels fall.
By Suppressing insulin through fasting, you don’t constantly store fat. You store it sometimes, burn it other times. That’s called being metabolically flexible.
Health Benefits of Intermittent Fasting
Over the past decade or so, the literature on fasting benefits has grown, but it’s still early days. Let’s review four of those benefits.
#1: Weight loss
Most people pursue intermittent fasting to lose weight. But does IF actually work for this purpose? Let’s see what the science says.
According to a 2018 review published in the journal Cureus—a review that looked at multiple forms of IF—“intermittent fasting was found to be efficient in reducing weight, irrespective of the body mass index”[*].
It makes sense. When you shorten your feeding window, you tend to eat less food. This mild caloric deficit can promote sustainable fat loss.
#2: Stable energy
Remember insulin? It’s the hormone that tells your body whether to store or burn fat.
Fasting keeps insulin low. That’s fat-burning mode.
Fat-burning mode means stable energy. When you rely more on fat for energy, you rely less on the fluctuating ups and downs of blood sugar. Now you’re on the smooth and steady fat train—energetically speaking.
#3: Mental acuity
Burning body fat doesn’t just produce energy (ATP) directly. It also produces molecules called ketones that fuel the brain. In one study, higher ketone levels were linked to better mental performance in older adults[*].
#4: Healthy Blood Sugar
Lowering blood sugar is a primary therapeutic goal for type 2 diabetics, and nothing lowers blood sugar like eating nothing. In his Toronto clinic, Dr. Jason Fung has pioneered fasting therapy for type 2 diabetes with excellent results[*].
Types of Intermittent Fasting
There are many flavors of intermittent fasting. Here are the most popular.
- 12/12. If you’ve ever gone 12 hours without food, you’ve practiced 12/12. It’s the ideal starting regimen.
- 16/8. When you practice 16/8, you compress your daily feeding window to 8 hours. (12 PM to 8 PM, for example).
- OMAD. OMAD stands for one meal a day. To optimize your circadian rhythm—the 24-hour wake-sleep cycle that regulates a huge chunk of your genome—eat this meal while the sun is shining[*].
- 5:2. This protocol entails two non-consecutive fasting days (0-25% of normal calories) per week. The other five days you eat normally.
- ADF. To practice alternate day fasting, you eat 0-25% of your normal calories every other day. Simple, but not easy.
The trick is to start slow when choosing a fasting regimen. A 12 hour overnight fast should be easy enough, and still has metabolic benefits. From 12/12, work your way up to longer fasts one hour at a time.
Who Should Be Careful With Fasting?
Fasting isn’t for everyone. Some groups should be careful with IF, and others should avoid it entirely.
Careful With Fasting
- Diabetics. Supervision is essential to avoid complications with blood sugar-lowering medications like metformin.
- Athletes. High-intensity or strength athletes may need longer feeding windows to fuel their rigorous training regimes.
- Stress. Fasting is a stressor. If you’re more stressed than a squirrel in late November, it’s probably not the best time to try IF.
- Children. Fasting-related calorie deficits can stunt growth, especially during puberty[*].
- Those with eating disorders. For obvious reasons, fasting is not recommended for those with anorexia, bulimia, or other eating disorders.
- Underweight people. If someone is underweight, food (not fasting) is the best medicine.
With these caveats in mind, understand that humans evolved to thrive on intermittent feeding schedules. Some fasting is generally healthy.
Intermittent Fasting Tips
Now that you’ve learned the basics of IF, it’s time to get practical. Follow these tips and you’ll be well prepared for fasting success.
Tip #1: Take electrolytes
When we fast, our body excretes more fluids and electrolytes[*]. Plus, we’re consuming fewer electrolytes through diet. To prevent electrolyte deficiencies and feel your best, take a zero calorie electrolyte supplement to support your fasts.
Tip #2: Drink non-caloric beverages
Coffee, tea, lemon water, and bone broth curb hunger without derailing a fast. Take advantage.
Tip #3: Eat a nutrient-dense diet
When you compact your feeding window, you have fewer chances to get vitamins, minerals, proteins, and other essential nutrients. Make your meals count by eating nutrient-rich foods like meat, fish, eggs, fruits, and vegetables. Bonus points if you like beef liver. It’s nature’s multivitamin[*].
Tip #4: Don’t fear hunger
Hunger is inevitable during a fast, but it doesn’t spiral upwards to infinity. Instead, the research suggests your hunger hormones stabilize over time[*]. Hang in there.
Hunger is normal, but if you’re feeling shaky or dizzy, don’t push it. You might have dangerously low blood sugar (hypoglycemia), which means you should break the fast.
Tip #5: Track your progress
Why are you fasting? To lose weight? To clarify your mind? To be an uber-productive human?
Whatever your goals, be sure to track them, preferably in a daily journal. This not only helps you stay motivated, but also provides tangible feedback that you’re moving in the right direction.
Our ancestors were fasting pros, but they didn’t have this capability. They didn’t have articles giving them helpful advice either. Advantage: You.