Does Intermittent Fasting Work For Weight Loss?

Intermittent fasting (IF) has become popular in recent years, and advocates claim it is beneficial for weight management and various other health concerns. Researchers have been busy investigating whether or not intermittent fasting lives up to the hype.

Read on to find out if there is evidence that IF supports weight loss and how it compares with other commonly used weight-loss diets.

What is intermittent fasting?

IF is an eating pattern that alternates periods of fasting with periods of eating. IF is not so much about what you eat as when you eat. Rather than counting calories, the focus is more on eating during certain times and fasting at others.

How does intermittent fasting help weight loss?

The rationale behind IF is that after time spent fasting, your body switches from burning sugar for energy to burning fat — a process called intermittent metabolic switching. A beneficial decrease in insulin levels accompanies this switch-up. In addition, a person doing IF may end up regularly eating fewer calories, which will also contribute to weight loss.

Types of intermittent fasting

There are three common fasting patterns:

16:8 fasting

The 16:8 fasting method requires you to fast for 16 hours, then allows you to eat for the remaining eight hours of your day.¹ How you time the fasting period is up to you and can depend on your lifestyle preferences.

5:2 fasting

In the 5:2 fasting method, you eat for five days of the week without restricting your calories. Then, you reduce your calorie intake to one-quarter of your daily requirement for the other two days of the week.

So, if your usual daily calorie intake is 2,000 calories, this approach would mean reducing your calorie intake to just 500 calories per day for two days of the week.

Alternate-day fasting

Alternate day fasting (ADF) is precisely what it sounds like. You alternate fasting days with days that you eat normally. Some people follow a modified version of this form of fasting in which they eat restricted calories (usually limited to 500 calories per day) on their fasting days. Then they return to eating, as usual, the following day.

Is there evidence that intermittent fasting can help you lose weight?

A systematic review published in 2020 looked at the evidence for using IF as a weight-loss strategy. This review examined 27 trials in which overweight or obese participants followed an IF plan. Results showed that intermittent fasting does show promise for the treatment of obesity. However, the article concludes that larger, more long-term studies are needed to validate these results and see whether IF-related weight loss is sustainable.²

A 2019 review of time-restricted eating assessed the benefits of alternate-day fasting and the 16:8 and 5:2 fasting methods. Not only was weight loss observed, but there were also other reductions in cardiovascular risk factors, including lowered blood pressure, positive changes in lipid profiles, and reduction in atherosclerotic plaque formation (the buildup of fats and cholesterol in the arteries).³

Deciding to combine your IF with exercise may also enhance weight loss benefits. A study comparing alternate-day fasting combined with endurance exercise versus alternate-day fasting or endurance exercise alone found that the combined intervention was more effective for weight loss and improvements in body composition.⁴

How does intermittent fasting compare to other diets?

You might be wondering how IF stacks up against other diets so that you can make an informed decision about which diet will work best for you for weight loss goals.

Although few studies directly compare IF to specific diet regimens, several studies compare IF-based weight loss results with conventional dieting by calorie restriction. In these studies, IF produced equivalent or superior weight loss than daily calorie restriction did.⁵ ⁶ Alternate-day fasting delivered a similar decrease in weight and body composition. In a follow-up 24 weeks later, there was no significant weight regain for those in the fasting group.⁷

Can intermittent fasting be dangerous?

The impact of intermittent while breastfeeding or during pregnancy hasn’t been adequately studied yet. So, you should speak to your doctor before making any changes. A 2018 study monitored pregnant women fasting during Ramadan and concluded that “clinicians and other pregnancy healthcare providers cannot make firm recommendations that fasting has no adverse consequences for mother or infant.”⁸

Anyone with an eating disorder or a history of an eating disorder should avoid fasting.

If you have diabetes, it is crucial to ask your doctor about the feasibility of IF before starting, as it can affect your sugar levels and the timing of insulin requirements.

Pitfalls of intermittent fasting

Many people find that IF is an easy eating plan because it focuses on time rather than calorie counting or limiting certain foods. There are, however, some pitfalls that you need to avoid to lose weight by fasting.

During periods of eating, try not to overeat — eat to feel satisfied. It’s also important to focus on healthy eating choices during your eating period. If you gorge yourself on junk food during your eating time, you may undo all the excellent work achieved during your fasting period.

Drink enough water during fasting to keep hydrated. Some people find that drinking an electrolyte solution during the fasting period can help maintain your energy levels. 

The lowdown

IF shows promise as a viable weight loss alternative to dieting. Weight-loss outcomes in studies comparing IF with continuous daily calorie restriction were equivalent or superior. However, more long-term studies are needed. Fasting provides flexibility and is adaptable to your schedule and lifestyle.

If you decide to test out IF, be sure that you still consume plenty of nutritious food during your eating times.