Does Intermittent Fasting Really Work?

Two registered dietitians weigh the pros and cons of intermittent fasting as a diet method

Does Intermittent Fasting Really Work?

Live longer. Gain Muscle. Lose weight. It’s your standard tagline for the latest fad diet. Or is it? Fasting is hardly a new concept, with cultures participating in it for religious reasons for centuries (such as Ramadan), and the medical community recommending it to help treat various disorders, like diabetes and epilepsy, starting in the early 1900’s.

In the last few years there’s been a rise in diet books touting the weight loss effects of intermittent fasting, and even scientific evidence suggesting that periodically slashing calorie consumption can reduce your risk of chronic disease, increase lifespan and help drop excess pounds. But not everyone is in agreement with it as a way to eat or to slim down.

Too Many Choices

Picking which intermittent fasting technique to try is a challenge, as there isn’t one ‘right’ way to do it. The most popular is the 5:2 diet where you eat normally for five days and then fast for two consecutive days. During the fasting days you limit yourself to 500-600 calories. There’s also alternative fasting where you consume 500-600 calories every other day. Another style is time-restricted eating where you fast for 16 hours, giving yourself an 8-hour window to consume all of your calories for the day.

When it comes to deciding what approach is right for you Toronto-based registered dietitian, Leslie Beck suggests choosing a method that’s right for your lifestyle, but admits the 5:2 approach is ‘the most palatable to many people’ since it limits fasting to only a couple times a week.

The flexibility of the diet is also appealing, but on the flip side you may need to do some trial and error before picking a style that you can realistically maintain in the long run.

A Healthy Focus

‘On the days that you are fasting and taking in only 500 calories or so, I would make every bite count,’ says Jessica Tong, a Vancouver-based registered dietitian. ‘I would also recommend a multivitamin or even a fiber supplement.’

It’s essential to choose nutrient dense foods on the days when your calories are low, so your body is getting the nutrition it needs to function properly.

Beck agrees, ‘If you’re going to do it, do it correctly. It doesn’t mean that you can be eating a fast-food diet five days a week and then you go down to salads on the other two days.’

Like any healthy lifestyle, eating lean protein, fruits and vegetables, and whole grains are necessary on both your regular and fasting days. And if you’re not sure what that involves, Beck suggests consulting with a registered dietitian to ensure your diet is nutrient packed.

Not for Beginners

Even though the data backs up the weight loss benefits, intermittent fasting is not ideal for people who are trying to lose weight for the first time. The diet is restrictive and it can be challenging to adopt.

‘There are much better methods to lose weight than intermittent fasting if you are just starting out,’ admits Tong. ‘I would try reducing calories overall or choosing healthier, more balanced food throughout the day.’

However, it can be an option for those looking to bust through a plateau, particularly if that person is already eating very healthy and working out regularly. ‘If you want to try the method to lose that extra five pounds for a wedding or a trip, sure,’ says Tong.

There are Side Effects

Ever skipped a meal or two and wound up with a splitting headache? That’s just one of the many side effects fasting can have on the body. You’ll also need to shift your exercise schedule to avoid heavily exerting yourself on days when your calories are low.

‘When you’re starving and exerting yourself you may not be able to push yourself as much,’ warns Tong. ‘You run the risk of being dizzy or fainting because your blood sugar is low.’

Even if you’re not working out, stomach aches, vomiting, irritability, fatigue or even difficulty sleeping can be uncomfortable side effects. Beck says most eventually diminish over time. If not, then it’s a sign to stop. Pregnant or breastfeeding women, children, diabetics or those suffering from hypoglycemia should avoid intermittent fasting all together.

The psychological side effects can be difficult to adjust to as well. ‘The first few times that people experience those fasting days, they may feel hungry and tempted with whatever is around them,’ admits Beck. Meaning a strong willpower is required to say no to those sprinkled donuts at the office.

For some people, fasting can trigger binges or a preoccupation with food, making it a difficult diet to maintain in the long term. Some experts, including Tong, also feel regular fasting can put you in starvation mode, forcing your body to not be as efficient in burning calories when you do eat. She also says when your body is starving for a long period of time it will break down muscle tissue to use as energy, another reason she’s skeptical about fasting.

Many proponents of intermittent fasting, including Beck, believe weight loss is merely a bonus side effect. The true benefit of the diet is longevity and health.