The 5 Health Benefits of Intermittent Fasting, Explained

What are the health benefits of intermittent fasting? Can intermittent fasting solve existing health problems?

The five health benefits of intermittent fasting are promoting weight loss, improving body function, elevating cognitive function, enhancing workouts, and encouraging better sleep. Understanding these benefits in detail can help your confidence in trying an intermittent fasting program.

Learn what the health benefits of fasting are and how to make the most of an intermittent fasting routine.

Health Benefit #1: Fasting Promotes Weight Loss

The health benefits of intermittent fasting include promoting weight loss. Fasting helps you lose weight by switching your body’s energy source from glucose to fat. When you fast, your body runs out of glucose from food, so it starts burning fat instead. It converts your fat into energy molecules called ketones, which also suppress your hunger. When your body burns fat as its primary energy source, you’re in a state called ketosis.

(Shortform note: When you stop consuming glucose, it takes some time before your body starts burning fat as its primary fuel source. In The Obesity Code, Jason Fung says ketosis kicks in after two to three days of fasting.)

Health Benefit #2: Fasting Improves Your Body Function

Apart from promoting weight loss, fasting also helps your body function more cleanly and optimally. Here are several ways fasting improves your physical health:

1. Fasting triggers autophagy. This is your body’s natural way of cleansing itself by getting rid of toxins and damaged cell parts. This helps your body function more effectively, slows aging, and reduces inflammation, which is your body’s response to illness or injury. While inflammation helps heal an acute problem (like an ankle sprain), it can be harmful if the response lasts too long. He argues that many modern foods contain harmful toxins that keep your body in a constant state of inflammation. Fasting and autophagy help you clear out those toxins and soothe your inflammation.

(Shortform note: Being able to stimulate autophagy might become increasingly important as we age. In Ageless, Andrew Steele explains that as time passes, our bodies accumulate leftover protein fragments that can interfere with autophagy. He notes fasting as one method to trigger autophagy, but he also writes about a potential alternative: drugs called dietary restriction mimetics. These drugs mimic the effects of calorie restriction and help boost autophagy without requiring you to make dietary changes. According to other experts, you can also trigger autophagy in simpler ways—such as by exercising, restricting your calories, or following a ketogenic diet.)

2. Fasting balances your insulin levels. When you eat, your body turns food into glucose that your cells can use for energy and releases a hormone called insulin to help your cells absorb the glucose. However, eating too much processed food overloads your body with more glucose than it can use, which can make your cells less responsive to insulin (a condition called insulin resistance, which can result in type 2 diabetes). By depriving your body of calories when you fast, you make your body use its stored sugar and fat instead. This stabilizes your glucose levels and lowers your insulin production, which keeps your cells sensitive to insulin.

(Shortform note: In addition to fasting from food, you can also pay attention to what you eat to prevent insulin resistance. Experts recommend you eat foods with a low to medium glycemic index—a rating system that measures how different foods affect your blood sugar levels. Further, in addition to eating a diet of processed foods, other factors can put you at risk for insulin resistance, such as obesity, age, physical inactivity, certain medications, and hormonal or genetic conditions.)

Health Benefit #3: Fasting Elevates Your Cognitive Functioning

Fasting has two important benefits for your brain—it helps it function better and it improves your mental health:

1. Fasting enhances your focus, memory, and learning. When you fast, your senses become sharper. This is because evolutionarily, when in a fasted state, our ancestors needed heightened focus to find food. Fasting also helps you think more clearly by reducing inflammation in the brain, clearing out toxins in your bloodstream, and directing energy your body normally uses for digestion to your brain instead.

2. Fasting lifts your mood. During a fast, your body produces chemicals such as dopamine and adrenaline that enhance your mood and energy. These chemicals allowed our ancestors to survive: They gave them energy when they were hungry and helped them stay motivated to hunt for food.

Health Benefit #4: Fasting Enhances Your Workouts

Another benefit of fasting is that it enhances your workouts by making your body more metabolically flexible and resilient. Asprey explains that normally when you work out, your body first turns to carbohydrates—derived from food—for energy. When you fast, however, you don’t have a supply of carbohydrates to use as fuel, so your body burns fat instead. This has two advantages for your workouts: First, fats provide more energy than carbohydrates. Second, fats are anti-inflammatory, so they speed up your muscle healing with less ache and soreness.

(Shortform note: Working out while in ketosis can not only help you burn more fat and recover post-workout, but it can also improve your body composition by optimizing your hormones: In particular, fasting while sprint-training raises human growth hormone (HGH) production and insulin sensitivity, which gives you a more youthful and lean body. However, experts caution that your performance may dip at first until your body gets used to burning fat and not carbohydrates for fuel. It could take up to six months before you become metabolically flexible and have adapted to using fat as a fuel source.)

Health Benefit #5: Fasting Improves Sleep

Fasting can improve the quality of your sleep, which can have a number of benefits for your health: Sleep reduces stress and inflammation, accelerates healing, increases your sex drive, helps with weight loss, and improves your memory and thinking. 

(Shortform note: In Why We Sleep, Matthew Walker agrees that there’s a long list of benefits quality sleep can bring. Walker notes, further, that sleep deprivation can lead to a host of negative health outcomes, including not only the opposites of sleep’s benefits but also decreased emotional control and an increase of many diseases not typically associated with sleep, such as cancer and heart disease.)

Improper eating habits can interfere with your body’s sleep patterns. If you eat close to your bedtime, your stomach will signal to your body that it’s still time to be awake, and you’ll have trouble sleeping soundly. This is not only because your digestive tract is actively consuming energy but also because your blood sugar and insulin levels are increasing, which can cause you to awaken during the night.

Experts recommend that you stop eating at least three hours before going to bed. This gap of time allows for enough digestion that your blood sugar won’t be overly elevated as you settle down for the night.  

(Shortform note: Most experts agree with the recommendation to refrain from eating a large meal before bedtime and to allow around three hours to pass after eating before you go to sleep. However, some caution there are exceptions to this advice. If you struggle to maintain a stable blood sugar level, eating a small, nutrient-dense snack before bedtime may help you sleep better as it can prevent your blood sugar from either rising or falling sharply during the night. In addition, some nutritionists contend that an evening snack of foods rich in melatonin (such as cherry juice), magnesium (like almonds), or anti-inflammatory antioxidants (like kiwi fruit) can improve your sleep.)

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Here's what you'll find in our full Fast This Way summary:

• Why intermittent fasting is more than just a way to lose weight
• How our modern eating habits differ from our bodies' natural eating patterns
• An intermittent fasting method that makes it easier and more enjoyable

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