Intermittent Fasting - familydoctor.org (2024)

You may have heard of the term intermittent fasting. It’s a popular topic nowadays. Some people talk about it when looking for a way to lose weight. Others talk about it as a way to improve their overall health. But what is intermittent fasting? Is it good for your body? What are the benefits? Are there side effects? Is it right for everyone?

Path to improved health

Intermittent fasting is not a diet plan. While it may have some of the same health benefits as a diet, it’s really an eating pattern. It means you fast (don’t eat) during a certain period of time each day (usually an extended period of time). You then eat during another period of time each day (usually a smaller period of time). While you’re fasting, you can drink beverages that don’t contain calories, including water, black coffee, and unsweetened tea.

How fasting and eating is divided each day is called an eating schedule. One of the most common, easy-to-follow schedules is 16:8. This means you fast for a 16-hour period of time and eat your daily meals during an 8-hour period of time. For example, you may want to fast from 7 p.m. until 11 a.m. the next day. You would then eat a healthy lunch and dinner between 11 a.m. and 7 p.m. You wouldn’t eat anything after 7 p.m. until 11 a.m. the next day. This is just an example of times. You can select any 16-hour and 8-hour block of time that works best for your schedule. But it’s important to keep your eating window at the same every day.

Other intermittent fasting schedules include 18:6 (when you fast for 18 hours and eat for 6 hours) or alternating days. With alternating days, you fast for 24 hours, then eat a healthy diet for the next 24 hours, then fast again for the following 24 hours. This schedule continues using the every-other-day format. Another schedule option is 5:2. This is when you fast for two days a week, and eat a normal, healthy diet the other five days. This is a little different, though, as this schedule allows you eat one small meal of 500 to 600 calories on your fasting days.

The time you’re allowed to eat is called your eating window. During your eating window, focus on eating a healthy diet and maintaining portion control. Don’t eat too many calories and avoid junk food and fast food. While you don’t need to eat anything in particular, you do need to make sure you’re getting the nutrition you need. Some people choose to use the Mediterranean diet as a guideline for what to eat. This plan focuses on fruits, vegetables, beans, whole grains, and fish. You can also choose lean proteins and healthy fats.

How intermittent fasting works

Fasting for at least 12 hours changes how your metabolic system works. Your metabolic system is how your body changes the foods and beverages you consume into energy. Most of the time, your body gets its energy from a sugar called glucose. Glucose is found in the foods you eat and beverages you drink. When you eat three meals during a day, your body maintains a steady glucose level because you’re eating and drinking frequently.

However, when you fast for more than 12 hours, your body’s glucose levels start to dip because you’re not eating as frequently. When your body doesn’t have the glucose it needs for energy, it taps into your body’s fat for energy. When this happens, the fatty acids in your body are absorbed into your blood. They produce a chemical called ketones. Your body then uses the ketones as its energy source. This is called a metabolic switch. Your body is switching from glucose to ketones.

When your body uses ketones instead of fat, you may lose weight. But, behind the scenes, the ketones also may be having a positive effect on your body’s organs and cells.

To get the benefits of intermittent fasting, you need to fast for at least 12 hours. That’s how long it takes your body to switch from using glucose for energy to using fat for energy. Additionally, it will take your body a while to get used to this new eating schedule. So don’t expect results right away. You may need to wait between 2 and 4 weeks to see or feel any results.

Health benefits of intermittent fasting

While researchers are still studying intermittent fasting, some research has shown it offers some health benefits. For starters, it’s common to lose weight when following intermittent fasting. That’s because your body is using fat—not glucose—as its energy source. Additionally, if you make wise food choices when you do eat, you’re likely eating fewer calories than before you started intermittent fasting. If you add exercise to the mix, it’s a great combination for not only weight loss, but also improved health benefits. Intermittent fasting may help people who have cardiovascular disease, neurological disorders, and some cancers. Intermittent fasting may also help lower your bad cholesterol and improve symptoms of arthritis.

Be sure to talk with your doctor before you begin intermittent fasting. They will help you decide if it’s a good fit for you. They will consider your current health, medicines, and health history when making their recommendation. If you have certain chronic health problems such as diabetes or heart disease, you may need to adjust or monitor your eating patterns.

Intermittent Fasting - familydoctor.org (2024)

FAQs

Intermittent Fasting - familydoctor.org? ›

Path to improved health. Intermittent fasting is not a diet plan. While it may have some of the same health benefits as a diet, it's really an eating pattern. It means you fast (don't eat) during a certain period of time each day (usually an extended period of time).

Why don t doctors recommend intermittent fasting? ›

Intermittent fasting is safe for many people, but it's not for everyone. Skipping meals may not be the best way to manage your weight if you're pregnant or breast-feeding. If you have kidney stones, gastroesophageal reflux, diabetes or other medical problems, talk with your doctor before starting intermittent fasting.

How much weight can you lose in 2 weeks of intermittent fasting? ›

Effective Diet Plans for Rapid Weight Loss
Diet PlanHow much can I lose in 2 weeks?Example
Low-carb diet5-10 poundsAtkins, Ketogenic
Low-fat diet3-6 poundsOrnish, Pritikin
Intermittent Fasting4-8 pounds16/8 method, Eat-Stop-Eat
Sep 23, 2023

What is the best intermittent fasting to lose the most weight? ›

A 2023 review of research found that the 16/8 method and 16/8 combined with restricting calories were effective strategies for weight control in adults with overweight or obesity. An eating window starting before noon led to greater weight loss than one that began after noon.

How long does it take for 16:8 intermittent fasting to work? ›

In one study, women over the age of 60 saw an average body fat loss of 2 kilograms — about 4.5 pounds — after 6 weeks of following a daily 16/8 intermittent fasting plan. In other research, people with overweight followed alternate-day fasting for between 8 and 12 weeks.

What are the negatives of intermittent fasting? ›

As much as IF is filled with benefits, there are mild side effects that can happen during fasting, which do not generally require medical or surgical treatment. Possible side effects can include dizziness, nausea, insomnia, headache, weakness, etc.

Why is 16 hours the magic number for fasting? ›

During the 16-hour fast, your body undergoes a process known as autophagy, a process where the body destroys old or damaged cells in the body. Autophagy recycles the cells that help in the reduction of inflammation in the body and reduces diseases.

Is fasting from 7pm to 7am good? ›

Many people find that a moderate fast, finishing all food by 7pm and then waiting until 7 or 8am the next day before eating breakfast can offer a more sustainable approach, while still reaping some of the perceived benefits.

How many hours should a woman over 50 do intermittent fasting? ›

The daily method typically follows a 16/8 or 18/6 rule. That means eating regular, healthy foods during a 6- to 8-hour window each day, then fasting for the remaining 16 to 18 hours. Many people find this to to be the most sustainable way to fast. You can use shorter variations of timing to get started.

What is the healthiest intermittent fasting schedule? ›

Depending on your lifestyle and when you can manage to stop eating, the best hours for intermittent fasting include the 16/8 or 14/10 fasting periods. Intermittent fasting is hailed by many as the new mantra of weight loss, disease prevention, and reversal of aging.

What foods won't break a fast? ›

Foods you can eat while fasting
  • Water. Plain or carbonated water contains no calories and will keep you hydrated during a fast.
  • Coffee and tea. These should mostly be consumed without added sugar, milk, or cream. ...
  • Diluted apple cider vinegar. ...
  • Healthy fats. ...
  • Bone broth.

How can I speed up weight loss on intermittent fasting? ›

A person needs to decide on and adhere to a 12-hour fasting window every day. According to some researchers, fasting for 10–16 hours can cause the body to turn its fat stores into energy, which releases ketones into the bloodstream. This should encourage weight loss.

How to lose belly fat by fasting? ›

Best Intermittent Fasting Method For Subcutaneous Belly Fat
  1. 16/8 Method: Fast for 16 hours and have an 8-hour eating window daily. ...
  2. 5:2 Method: With the 5:2 method, you consume your regular diet five days a week and consume around 500-600 calories for two remaining fasting days.
Jul 30, 2023

What foods should you avoid during intermittent fasting? ›

It's best to limit ultra-processed foods like packaged snacks, deep-fried items, sugary drinks, and most frozen meals. These negate the positive effects of 16/8 intermittent fasting. To begin 16/8 intermittent fasting, choose an 8-hour window and limit your food intake to that time span.

Can I eat whatever I want while intermittent fasting and still lose weight? ›

It's not a diet, so unless you have individual dietary restrictions, you can eat whatever you want within the eight-hour time frame. But the plan will work best for weight loss if you are already making smart, nutrient-rich choices, said NBC News health and nutrition editor Madelyn Fernstrom, Ph.

Why intermittent fasting is not recommended? ›

Longer periods without food, such as 24-, 36-, 48- and 72-hour fasting periods, are not necessarily better for you, and may be dangerous. Going too long without eating might actually encourage your body to start storing more fat in response to starvation.

What is the controversy with intermittent fasting? ›

Research presented this week immediately drew doubt and critiques from experts by suggesting that eating within an eight-hour window or less was significantly associated with a 91% increased risk of dying from cardiovascular disease, when compared with eating over a 12- to 16-hour period.

Is intermittent fasting hard on your heart? ›

The scientists found that people who followed a 16:8 diet, or ate only within an eight-hour window, had a 91% higher risk of dying from cardiovascular disease compared to people who ate across 12 or 16 hours.

Is 12 hour fasting as effective as 16? ›

Both 12-hour fasting and 16-hour fasting can be effective for weight loss, but 16-hour fasting may be more effective because it may lead to a greater reduction in overall caloric intake (through a more condensed eating window) and promote more significant reliance on fat burning.

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