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Can intermittent fasting help you lose weight?

Intermittent fasting continues to top weight management trends spurred on by celebrity converts and new reincarnations of the diet. But does it actually work and where does the science stand on this to help you manage your weight? We explore everything you need to know before you miss a mouthful of food. 

What is intermittent fasting? 

There are a lot of weight management programs that now fall into the category of intermittent fasting including the high profile 5:2, the 16:8 and alternate day fasting. 

The 5:2 diet hit the headlines thanks to British journalist Dr Michael Mosley and his New York Times bestseller The Fast Diet. This style of intermittent fasting includes eating normally for 5 days a week and dramatically limiting calories for two days a week. 

The aim is to drop calorie intake on fasting days to just 25% of the norm. So, if on average you ate 8,400 kilojoules (2,000 calories) a day, on fasting days this would be limited to 2,100 kilojoules (500 calories). 

We’ve since seen the rise of the 16:8 diet. In this case, the numbers refer to hours - eat what you like for 8 hours a day and fast for 16. 

There are many other fasting variations too.  

But does intermittent fasting work?  

In our fast-paced lives where many of us eat on-the-go, intermittent fasting forces us to put on the brakes. Several studies show that intermittent fasting can help with weight loss (at least over the short term), primarily through restricting the hours in which a person can eat, reducing the amount of food that is consumed and therefore overall energy intake. It’s really a change of when to eat, rather than what to eat. 

While intermittent fasting can help with weight management and weight loss, most studies run for short timeframes and are unable to determine its long-term sustainability. Overall studies show that it is no more beneficial in the long term than non-time restricted general healthy eating.  

But above all, if you want to try intermittent fasting and get results from it, it’s important to plan ahead and to be consistent with whatever approach you decide to take. 

Why is breakfast still important?

Don’t fall into the common trap of skipping brekkie if you want to give intermittent fasting a try. Try extending your overnight fast by bringing forward your last meal (e.g., having dinner earlier in the evening) and aim to have most of your calories earlier in the day.  

Evidence consistently shows that we have better insulin and glucose control during the day compared to the evening. There is also emerging evidence that eating more in line with your sleep and wake cycles (known as chrono-nutrition) can have beneficial impacts on our gut microbiome and may be associated with lower risk of type 2 diabetes. Think of the old saying - “breakfast like a king, lunch like a prince, and dinner like a pauper”. 

There’s a lot of evidence suggesting that eating breakfast helps regulate your appetite, manage your weight, bump up your nutrient intake as well as helping with cognition. It makes sense that your body needs fuel to function - especially after breaking the fast.  

What are the pros and cons of intermittent fasting?


  • One reason for the growing legion of 16:8 fasting fans is that you can forget calorie counting. This style of intermittent fasting does not involve fixating about what you eat, just when you eat. 
  • Advocates of intermittent fasting also say that it can provide benefits that may extend beyond weight management. Early studies with animals suggest alternate day fasting may help lower the risk of certain chronic diseases, such as type 2 diabetes, cardiovascular disease, and cancer. However, to date, there’s been no extensive studies in humans, and more research is needed before we can say whether intermittent fasting has benefits other than short-term weight loss. On the flipside, there is also evidence that delaying your first meal of the day may be associated with an increased risk of type 2 diabetes – another reason not to skip brekkie even if you want to give intermittent fasting a try.  


  • One of the biggest pitfalls of an intermittent fasting diet is sticking to it. Fasting is hard, even if it is only for two days a week. Researchers have even noted high drop out rates on fasting diets. 
  • In addition, intermittent fasting, like many other restrictive diets, can lead to certain nutrient deficiencies. Anyone considering fasting should first discuss it with a doctor and dietitian to make sure that they are getting enough nutrients from their diet. 
  • There are also certain people which intermittent fasting is unsuitable for. These include children and teenagers, individuals with a history of disordered eating and people with chronic disease or taking medication that is dependent on food intake e.g. diabetes. If you are unsure if intermittent fasting is suitable for you, consult your doctor or dietitian.  

Can you exercise while fasting? 

If you’ve googled intermittent fasting, there’s no doubt you will have seen stories of the battle to manage fasting with a regular exercise routine. Certainly, some people struggle to exercise when fasting, noting increased fatigue, muscle loss and difficulty recovering. 

It’s important to plan your exercise based on the intermittent fasting diet you are following. If you’re on the 5:2 diet, plan your big sweat sessions for non-fasting days and line up light exercise, or rest days, for fasting days. 

If you’re on the 16:8 diet, plan your exercise for your 8-hour eating window and what works best for your body. Some people prefer to work-out on an empty stomach, while others need to fuel up first. There’s also evidence to show brekkie before burpees can help burn more carbohydrates through the day. 

Either way, try to include protein after exercising. Aim for 20-25g of protein for muscle growth, tissue repair and recovery. And don’t forget to stay hydrated!