Fasting, especially intermittent fasting, is all the rage now for “weight loss tips and tricks.” It’s said to harness the body’s natural biology to help you lose weight and improve overall health. But does fasting help reduce belly fat? And how should you fast to get rid of fat?
What Is Intermittent Fasting?
First, what intermittent fasting (or IF) isn’t is a diet—it can be combined with a variety of diets. Instead of what you eat, IF is about how you eat. That is, by restricting eating to specific times (such as between 8 and 12 hours and then fasting the other 12 to 16 hours—including overnight as you sleep). And this way of eating has ancestral roots. That is, humans have likely been eating this way for thousands of years. 1
According to some experts, because food was scarce, our hunter-gather ancestors went through long periods of famine between feasts, so our bodies are well adapted to switching fuel sources. Now, of course, most people in Western societies have access to unlimited quantities of cheap “foods.” Yet, there are numerous potential benefits of a fasted state. For example:
- Metabolism (the rate the body burns calories) increases during short-term fasting. (Extended fasts for longer than 48 hours, however, can slow metabolism to prevent starvation and conserve energy.)
- The body switches from burning mostly glucose (from carbohydrates) to burning more fat (from body fat).
- You give your digestive system a break to allow your body to perform other important functions like breaking down fat and removing old, disordered cells and toxins (aka autophagy).
- Helps increase fat burning and weight loss—even from more stubborn areas like the belly as it’s a fairly easy way to reduce calorie consumption. (Just remember to continue eating healthy whole foods and skipping highly processed junk foods when you do eat to keep calories and appetite in check.)
- Improves metabolic flexibility by retraining the body to shift between carb-burning and fat-burning mode.
- Lowers insulin levels, which may support fat loss as well as mental clarity.
- Preserves lean muscle mass to improve overall body composition, especially when combined with weight training two to four times per week.
- Improves metabolic health, including a reduced risk of type 2 diabetes, heart disease, and neurodegenerative disorders (like Alzheimer’s).
- Supports brain functioning, including thinking and memory.
Types of Intermittent Fasting
There are several popular ways to intermittent fast. Perhaps the most common is the 16:8 method, where you fast for 16 hours and eat over an 8-hour window. Another popular form is the 5:2 diet, where you eat normally five days a week and then reduce calories to one-quarter of your plan two days per week. So, for example, if you consume 2,000 calories per day on average, 2 days a week, you would drop down to 500 calories per day.
Eat-Stop-Eat from Brad Pilon is another common method. Just pick two non-consecutive days per week to fast for 24 hours. Similarly, alternate-day fasting allows you to alternate eating whatever you want every other day with fast days. You can also modify this diet to allow 500 calories on fasting days.
The Warrior Diet, created by Ori Hofmeler, is allegedly based on ancient warrior eating patterns and is one of the most extreme methods of IF. You eat very little for a full 20 hours during the day but can eat as much as you want during a four-hour window in the evenings. For example, during the day, you subsist on small portions of hard-boiled eggs, raw vegetables and fruits, and dairy products. Once your eating window hits, you can eat as much as you want—just as long as it’s unprocessed and healthy. Organic foods are recommended.
Intermittent Fasting and Metabolic Hormones
Not only could fasting help reduce belly fat and weight, but it may have positive effects on metabolic hormones. This is due to how the body changes to make stored energy more available during a fast. For example, during a fast, insulin levels can decrease drastically. And lower insulin levels may encourage fat burning. Your body can also send more noradrenaline (or norepinephrine) to fat cells to help break them down to be burned for energy.
On the other hand, human growth hormone (HGH) levels can also increase during fasting. This can signal the body to conserve energy, boost appetite, and slow metabolism—to potentially slow fat loss and calorie burning.
What to Eat When Fasting
You’re skipping meals, so you can eat whatever you want during your eating window, right? Wrong! If you’re skipping meals, what you choose can be even more important as you want to eat enough healthy foods to get the nutrients you need. When selecting meals, go for quality. That is, eat mostly whole foods like vegetables, fruits, lean meats, and healthy fats like avocado and olive oil. The Mediterranean diet offers good guidance.
While you don’t need to count calories, they do still count. Be careful not to overcompensate for skipped meals by overindulging at your next meals.
Will Fasting Get Rid of Fat?
Studies do support that IF can lead to fat loss. For example, a review of the research has found body weight can be reduced by up to 8% over 3 to 24 weeks. 2 While there are many benefits of fasting, the main reason fasting is recommended to help lose belly fat is because when skipping meals, most people naturally eat fewer calories. And indeed, much of the research has shown a 4 to 7% reduction in waist circumference. So, if you have the average waist size of an American woman (38.7 inches), IF could lead to a 1.5-inch to 2.7-inch loss. That’s a good indication that you’re losing belly fat.
Is Intermittent Fasting Right for You?
While there are benefits to intermittent fasting, it isn’t right for everyone. For example, some people find it leads to uncomfortable levels of hunger or decreased energy levels. It’s also not recommended for people who have experienced disordered eating, pregnant or nursing moms, teenagers, or those with diabetes or blood sugar issues.
If you don’t feel good when fasting, then don’t. Studies have found that simply creating a calorie deficit throughout the day can be as effective for losing belly fat as intermittent fasting. So, choose what works best for you—what leads to greater feelings of health, well-being, and energy levels as well as decreasing belly fat.
That said, many people do find that intermittent fasting leads to greater brain clarity, focus, improved health status, and weight loss. It can also make eating healthy easier and more convenient. Simply by eating fewer meals throughout the day, you can save time and energy on preparing and eating food.
If you do want to try intermittent fasting to lose belly fat, it can help to ease into it. For example, start by waiting an extra hour before eating breakfast in the morning and then add on more time as your body adapts. For example, if you usually eat dinner at 7 p.m. and then have breakfast at 6 a.m., make sure you don’t have any nighttime snacks and then wait until 7 a.m. before eating breakfast for a few days. Then wait until 7:30, 8, etc., until you have extended your fasting window to the 16-hour mark. It can take time, patience, and practice to make it work, but gradually increasing the fasting window is easier for most people.
At the end of the day, the best eating pattern for you is the eating pattern you’ll stick with, long-term—whether that’s intermittent fasting or another healthy eating regimen.
1. Intermittent Fasting: What is it, and how does it work? [Internet]. 2021 [cited 13 March 2021].
2. Barnosky AR, Hoddy KK, Unterman TG, Varady KA. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research. 2014 Oct 1;164(4):302-11.