Intermittent Fasting: What is it & how does it work?

Are you thinking of trying intermittent fasting? Let’s dive into the details and look at the key need-to-knows.

What is intermittent fasting? How does intermittent fasting work? 

Intermittent fasting is an approach to eating based on timing which involves fasting for a period of time and eating only during a certain window of the day. 

Different types of fasting

Let’s take a look at some different ways of approaching fasting: 

Intermittent fasting: typically involves restricting food intake to specific time periods of the day.

• The 16:8 method involves fasting for 16 hours and only eating during an eight-hour window of the day. 
• 20:4 involves fasting for 20 hours and only eating during a four-hour window of the day. 
• 22:2 otherwise known as the OMAD diet, One Meal A Day, consuming all of your calories for the day in one meal.

Periodic fasting: fasting for one or two days of the week. 

• 5:2 involves greatly reducing food intake on any two days of the week (down to 500 calories for women and 700 calories for men), and maintaining normal calorie intake on the remaining five days.

What are the benefits of intermittent fasting?

There’s no doubt intermittent fasting has been a hot topic of late, and for good reason! There are health benefits associated with fasting, but it’s also important to discuss the not-so-healthy effects of fasting. And of course, consider if it is actually right for you. 

Metabolic effects 

Fasting isn’t actually anything new; it is part of our physiology and is essential for various cellular functions. When you sleep at night, your body naturally falls into a fasted state. Hence where ‘breakfast’ gets its name from! 

When combined with a healthy diet and lifestyle there is evidence to support the restriction of meals to an eight to ten-hour window of the day in positively affecting metabolic markers (i.e. different measurements that define your health state, such as elevated blood glucose levels)  and supporting the health and function of your cells. 

Intermittent fasting and weight loss 

It’s thought that fasting may support weight loss through lipolysis - the breakdown of fat - whereby fasting over an extended period of time causes fat to be used for energy. 

Studies have shown that intermittent energy restriction interventions (like the 5:2 approach) may be an effective strategy for weight loss in those who are overweight or obese. It’s important to note that participants in some of these studies were provided education and support in addition to fasting such as behavioral strategies, stress management, nutrition, and physical activity, which supported their results. Other study interventions including the 16-hour fast showed promising weight loss results. 

Heart health and cholesterol 

What about other health benefits besides weight loss? Some research has shown that intermittent fasting may reduce low-density lipoprotein and triglyceride levels in both men and women. But what does this mean, exactly?  Essentially, by intermittent fasting for more than 8 weeks using various fasting approaches, there was an improvement in both men and women in their cholesterol.

Intermittent fasting for women vs. men 

To date, there is still minimal research on the effect that fasting has on women, and in particular, on reproductive hormones. What we do know is that women who tend to skip breakfast are more prone to disruptions in the release of cortisol, and persistently high cortisol levels may be linked to a decline or complete stop in the production of normal reproductive hormones. 

Timing food intake to consume earlier in the day versus later in the day may be an appropriate approach to fasting for women with polycystic ovary syndrome (otherwise known as PCOS) as one study revealed that eating earlier in the day may help manage hormone imbalances in women. 

When to approach fasting with caution 

In-house Naturopath Gabbie Watt shares some cautions with fasting, “It’s important to listen to your body when fasting as you may experience side effects such as headaches, nausea, fatigue, a foggy mind, dizziness, changes in mood, or irregular periods. These might be telltale signs that fasting or the type of fast isn’t working for you”, says Watt. 

There is evidence to suggest that intermittent fasting may result in reduced muscle mass, which is why education about healthy nutrition and lifestyle practices, such as adequate dietary protein intake, is important.

There is still a way to go to know exactly how intermittent fasting may affect gut health and the gut microbiome, with the need for further studies. It’s important to remember everyone has a unique microbiome, so while fasting may benefit some, it might not work for everyone. 

A popular starting point for intermittent fasting is to skip breakfast, but be wary of cutting out gut-loving foods (think whole grains, and fruit) and good sources of calcium (such as milk and yoghurt). No matter how you structure your fast, it is essential to incorporate plant-based, high-fibre foods into the diet to ensure good gut health is maintained.

Bottom line?

Like any new dietary approach, fasting should still be approached with caution and ideally with the guidance of a healthcare professional to ensure it is right for you. Intermittent fasting is not just about simply skipping or restricting calories. It’s important that you are still consuming healthy, balanced meals each day to meet your daily nutrition requirements and to find an eating pattern that is sustainable in the long term.

Find your happy weight

If you’re exploring intermittent fasting for weight loss, it's important to understand the physical, emotional and mental effect dieting can have on your wellbeing. Which is why we created our Weight and Wellbeing program. 

This free program combines the expert insight of Glenn Mackintosh, Psychologist, and Lyndi Cohen, Dietitian, to guide you through a holistic approach to ditching the diet mindset and finding your happy weight. Sign up today.

Related:

• What is a fad diet and why do you need to avoid them?
• Are you hungry or thirsty? The link between hydration and appetite
• 4 myths about detox diets

Reviewed by the healthylife Advisory Board December 2022.