Intermittent fasting and weight loss: A closer look at the evidence

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Intermittent fasting (IF) represents an intriguing alternative to traditional calorie-restricted diets, particularly in managing obesity.

Obesity is a pressing health issue in Canada and globally, with few effective treatments available in a typical office setting.

Data Sources

An extensive literature review was conducted, involving a search on MEDLINE and EMBASE databases from January 1, 2000, to July 1, 2019.

Using keywords like fasting, time restricted feeding, meal skipping, alternate day fasting, intermittent fasting, and reduced meal frequency, approximately 1200 results were yielded.

Study Selection

Out of the results, 41 articles describing 27 trials were relevant, focusing on weight loss in overweight and obese patients.

The studies included 18 small randomized controlled trials (level I evidence) and nine trials that compared post-IF weight to baseline weight without a control group (level II evidence).

Most studies were short-term, ranging from 2 to 26 weeks, with low enrolment numbers (10 to 244 participants); only two studies had a duration of one year.

The protocols varied greatly, and only five studies included patients with type 2 diabetes.


All 27 IF trials reported weight loss ranging from 0.8% to 13.0% of baseline weight, with no serious adverse events.

Twelve studies comparing IF to traditional calorie restriction diets found equivalent results in weight loss.

Importantly, the five studies that included patients with type 2 diabetes showed improvement in glycemic control.


Intermittent fasting appears promising as an obesity treatment strategy. However, most studies to date have been small and short-term.

More long-term research is required to understand the sustainability and long-term effects of IF as a weight loss strategy.

Given the initial results, there is a compelling argument for further exploration of IF’s potential in obesity management.

How to do intermittent fasting effectively

Intermittent fasting (IF) can be an effective method for weight loss and health improvement when done correctly. Here’s a step-by-step guide on how to do intermittent fasting effectively:

  1. Choose the Right Fasting Method for You

There are several types of intermittent fasting methods. These include:

  • 16/8 Method: This involves fasting every day for 14-16 hours and restricting your daily eating window to 8-10 hours. For example, you might eat only between noon and 8 p.m.
  • 5:2 Diet: With this method, you eat normally five days a week. On the other two days, you restrict your calories to around 500-600.
  • Eat-Stop-Eat: This involves a 24-hour fast once or twice a week.
  • Alternate-Day Fasting: As the name suggests, you fast every other day.

Consider your lifestyle, daily schedule, and health needs when choosing the method that suits you best.

  1. Start Slow

If you’re new to intermittent fasting, start slow. You might begin with a 12-hour fast and gradually increase the fasting duration over time.

  1. Eat Balanced Meals

During your eating periods, it’s important to consume balanced meals. Ensure you’re getting a mix of protein, fats, and carbs, and that you’re eating plenty of fruits and vegetables for vitamins and minerals.

  1. Stay Hydrated

During fasting periods, you’re allowed to consume non-caloric beverages. Water, black coffee, or tea can help curb hunger and keep you hydrated.

  1. Listen to Your Body

Everyone’s body reacts differently to fasting. Pay attention to how you’re feeling. If you’re feeling weak or unwell, it may be best to eat and try fasting again another day.

  1. Combine Fasting with Exercise

Physical activity can boost the effectiveness of intermittent fasting. But remember to listen to your body and adjust your workout intensity based on how you’re feeling.

  1. Consult a Health Professional

Before starting any new diet plan, it’s a good idea to consult a healthcare provider or dietitian. They can guide you to make sure the plan you’re choosing is safe and suitable for your specific needs.

Remember, intermittent fasting isn’t for everyone. People with certain health conditions, pregnant women, and those with a history of eating disorders should avoid it unless guided by a health professional.

The research was published in Canadian Family Physician.

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