Diet fads come and go faster than fashion trends. The details may vary, but whatever the diet of the moment may be, it typically involves cutting out – or at least severely limiting – some or other type of food. (Fat and carbohydrates are often casualties.) Intermittent fasting (IF) takes a different approach – counting hours rather than calories. And with the likes of Beyoncé, Halle Berry, Jennifer Lopez, Hugh Jackman and Chris Hemsworth among its numerous A-list devotees, it may be onto something.

What is intermittent fasting?

“Intermittent fasting is not a diet, and it does not mean starving yourself. It’s more about when you eat than what you eat,” explains registered dietician Kirby Hendricks. You cycle between periods of fasting and periods of eating. The goal is to give the body structured periods of rest from digestion, which may support metabolic health, insulin sensitivity and weight regulation.

Jae Braun, registered dietician, wellness coach and host of the Wellness Is Everything podcast, explains that during fasting periods, the body may switch from burning sugar to burning fat – although the long-term effect of this “metabolic switch” is still being studied.

READ: 5 food myths dieticians wish would go away 

Types of intermittent fasting

There’s more than one way to do intermittent fasting – all of them involve blocks of time when you’re not allowed to eat, but some methods are more flexible than others. Jae shares some of the most common approaches:

• 16/8 method: This is a form of time-restricted eating (TRE). You fast for a certain number of hours a day and have a dedicated time window during which you’re allowed to eat. The 16/8 method (16 hours fasting; eight hours to eat) is the most popular pattern.
• 12/12 method: A gentler approach to TRE, with 12 hours of fasting and 12 hours of eating.
• 5:2 method: Eat normally for five days a week, and limit calories to 500–600 on two non-consecutive days.
• Alternate-day fasting: Switch between fasting days and eating days. A modified version allows for a small amount of food on fasting days.
• Periodic fasting: This involves longer fasts (e.g. two to five days of only drinking water) but you do them occasionally – once a month, or a few times a year.

While the methods differ, Jae notes that “the choice of intermittent fasting method should be based primarily on personal preference, lifestyle compatibility and individual health considerations.”

 

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What happens to your body on IF?

In the short term, IF can lead to modest weight and fat loss, particularly for people with obesity. “Some studies suggest IF may help regulate blood sugar levels, lower inflammation, improve blood pressure, and even support cell repair processes,” says Kirby.

According to Jae, many of these benefits are similar to what you’d see when limiting calories the traditional way. The difference: timing your meals may improve insulin sensitivity and encourage fat burning – at least in the beginning. Over time, however, the initial advantages tend to level out. “The long-term sustainability of IF is similar to other dietary approaches,” Jae notes, “and the body tends to adapt to the new eating patterns.”

In both the short and long term, IF seems to help decrease waist circumference and improve lipid (fat) profiles. However, the key to success is still that you’re creating a consistent, sustainable calorie deficit – not just skipping breakfast.

READ: What’s the deal with high-protein diets? 

Does IF work for weight loss?

Intermittent fasting can support weight loss – but not for the reasons many people assume. “With a shorter eating window, people often snack less or skip a meal they might not have needed in the first place,” explains Kirby.

Jae agrees that IF can reduce overall calorie intake but cautions that it’s not a magic bullet. “It’s not a licence to consume unlimited calories during eating windows,” she says. In other words, you should still be eating predominantly healthy food, not guzzling cake and chips.

As with any eating pattern, what matters most is consistency and fit. Kirby says, “IF tends to work well for people who aren’t hungry in the mornings or prefer structure to help reduce snacking.” If you don’t enjoy weighing your food and counting calories, it may feel less onerous to limit your eating window rather than to measure every meal.

Understand IF before you try it

Not everyone thrives on intermittent fasting. “Some people feel amazing on it, while others feel tired, moody, or headachy – especially at the start,” says Kirby. She recommends easing in gradually and making sure you eat well during your eating window.

IF also isn’t suitable for everyone, particularly people with diabetes, low blood pressure, a history of disordered eating, or those who are pregnant or breastfeeding. Always check with a health professional first.

Ultimately, nutrition isn’t one-size-fits-all. Whether IF works for you will depend on your body, lifestyle and goals – and the best way to figure that out is to consult a registered dietician.

This information is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition.