Intermittent Fasting: A Complete Beginner's Guide (Types, Benefits & How to Start)

Intermittent fasting is an eating pattern that alternates periods of eating with periods of fasting, which may last from about 12 to 24 hours. Common approaches include the 16:8 method and one meal a day, with water, unsweetened tea, and black coffee generally allowed during fasting periods.

Current evidence suggests that intermittent fasting may support weight loss and improve some markers of metabolic health, such as blood sugar, triglycerides, cholesterol, and blood pressure. Its effects can vary depending on the fasting schedule, overall diet, physical activity, and individual health conditions.

Although intermittent fasting may offer health benefits, longer fasting periods can increase the risk of side effects such as weakness, dehydration, or low blood sugar. Medical guidance is especially important for people with diabetes and those taking blood sugar-lowering medications.

Benefits of intermittent fasting

The potential benefits of intermittent fasting include:

1. Regulating cholesterol levels

Intermittent fasting may help improve cholesterol and triglyceride levels in some people, especially when combined with a balanced diet that is low in added sugar and saturated fat and high in fiber.

These dietary changes may help reduce overall calorie intake and improve blood lipid levels.

2. Helping with weight loss

Intermittent fasting may help with weight loss because going for a long period without eating lowers insulin levels and encourages the body to use stored energy, including glycogen and body fat.

To support weight loss while practicing intermittent fasting, it is also important to exercise regularly, such as by walking or strength training. When appropriate, exercise can be performed with guidance from a certified personal trainer.

3. Supporting metabolic health

During intermittent fasting, reduced food intake can lower blood glucose and insulin levels, encouraging the body to use stored energy.

Intermittent fasting may therefore improve some markers of metabolic health, although its effects on metabolic rate can vary depending on calorie intake, fasting duration, body composition, and physical activity.

Long periods of fasting can slow down how your body uses energy and should only be done with medical supervision.

4. Improving blood pressure

Intermittent fasting may help modestly lower blood pressure in some people, especially when it leads to weight loss and improvements in overall metabolic health.

It may also improve certain cardiovascular risk factors, although its effects on LDL, or "bad," cholesterol and HDL, or "good," cholesterol are not consistent across studies.

5. Preventing diabetes

Intermittent fasting, especially when combined with a balanced diet that limits added sugar, may help improve blood glucose control and insulin sensitivity in some people.

However, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), fasting while taking insulin or certain other blood sugar-lowering medications can increase the risk of hypoglycemia. People with diabetes should therefore talk to their healthcare provider before starting intermittent fasting.

6. Preserving muscle mass

Intermittent fasting can cause changes in hormones involved in energy metabolism, including growth hormone.

However, maintaining muscle mass during weight loss depends mainly on adequate protein intake, resistance exercise, overall calorie intake, and other individual factors. Intermittent fasting alone does not prevent loose skin or muscle loss.

7. Supporting cellular repair

Fasting causes metabolic changes that may support the way cells repair and recycle damaged components.

However, there is not enough evidence in humans to say that intermittent fasting ‘detoxifies’ the body. The liver and kidneys naturally process and remove many waste products from the body.

8. Lowering the risk of heart disease

According to the American Heart Association, some forms of intermittent fasting may support weight loss, lower triglycerides, and improve blood pressure when they lead to sufficient weight loss, although their effects on cholesterol appear to be limited.

Following a balanced diet that is rich in fiber, vitamins, minerals, and antioxidant foods is also important for heart health.

However, more research is needed to determine whether intermittent fasting itself can reduce the long-term risk of cardiovascular diseases such as heart attack, stroke, or atherosclerosis.

9. Supporting healthy aging

Reducing added sugar and excess saturated fat while prioritizing foods that are rich in fiber, vitamins, minerals, and other nutrients can support overall health.

Intermittent fasting is also being studied for its possible effects on biological processes associated with aging. However, there is not enough evidence to conclude that intermittent fasting prevents premature aging in humans.

10. Promoting autophagy

Fasting may stimulate autophagy, a natural process in which cells break down and recycle damaged or unnecessary cellular components.

During periods of nutrient restriction, cells may increase the recycling of certain cellular components to help maintain normal cell function.

However, the amount of fasting time needed to significantly increase autophagy in humans has not been established, and much of the detailed evidence on fasting-related autophagy comes from laboratory and animal studies.

How to intermittent fast

To practice intermittent fasting, periods of restricted food intake are alternated with periods when eating is allowed.

For people who have never fasted before, a shorter fasting period may be easier to tolerate. For example, some people may begin with about 12 hours of fasting and gradually increase the fasting period based on their tolerance and medical guidance.

Longer fasting periods are not necessary for everyone and may increase the risk of side effects such as dizziness, headache, weakness, dehydration, or low blood sugar.

Before starting a fasting period, eating a balanced meal that contains protein, fiber, healthy fats, and nutrient-rich carbohydrates may help you feel full for longer.

During the first several hours after eating, the body continues to use energy from the most recent meal before gradually relying more on stored energy.

What is allowed during fasting?

During the fasting period, water and noncaloric beverages such as unsweetened tea and black coffee are generally allowed.

Check out this intermittent fasting meal plan for help getting started.