Intermittent fasting (IF) is an umbrella term, used to define a variety of types of fasting. IF was introduced in science as a way to see if restricting calories intermittently was easier to adhere to compared to continuous calorie restriction. For example, scientists wanted to find out if someone who eats 500 calories a day for 2 - 3 days per week will be easier than eating ~1200 calories every day.
In other IF diets, you have a small window when you can only eat (usually around 8 hours), and you fast for the remainder of the day. These fasts usually happen overnight (while you sleep), ranging from 16 hours to a maximum of 24 hours.
So, what is Intermittent Fasting, really?
In general, IF involves restricting your calorie intake for 1 - 3 days per week, and then freely eating on the alternate days (without restriction). I'll delve into IF regimes in more detail below:
1. Alternate day fasting
This type of fasting is the most-studied form of IF - where people are required to alternate between feeding and fasting days. While on a fasting day, you are either fasting completely (that is, not having any food intake), or alternatively, some programs allow one meal in the day where ~25% of your total caloric needs are met. This typically happens for 1 - 2 days per week, while all the other days you are free to eat what you like.
An example of this program is the well-known 5:2 diet. This is where the 5 represents the number of alternate days you eat normally, and the 2 represents the number of non-consecutive days you have to restrict calorie consumption to 25% (500-600 calories) of your total daily energy expenditure calories.
2. Time-restricted fasting
This is the more 'lenient' way of IF, where you fast for a specific number of hours each day. A better researched way of time-restricted fasting is when you abstain from any calorie intake for 16 to 20 hours, and you have a window of 4 - 8 hours of eating allowed. There are no set protocols on 'calories' allowed during the allowed eating phase.
An example of time-restricted fasting is the 16:8 diet, where you would be abstaining from food intake between 8:00pm to 12:00 noon the next day; that is, your first meal would be lunch. There are no set protocols on how often you would do this per week, but many do recommend it every day of the week.
Now that we know a little bit more, let's talk about the pros and cons
Here are the pros
1. Weight loss
The reason any weight loss diet works is because it reduces your total calorie intake. This means you’ll burn more calories than you consume (caloric deficit), leading to weight loss. Studies have also shown that IF is just as effective for weight loss when compared to continuous calorie restriction - which may be good news to those who have been on low-calorie diets before.
This eating pattern is easily implemented, and for those who like routine, it can be adhered to pretty easily (compared to the traditional calorie restriction that may be hard to follow in the long-run). For some people, it may be easy to incorporate IF into current routine and while not having to worry about limiting the types and amount of food you eat on feeding days.
3. More food in a shorter time frame
Some people may like this part the most because you get to consume more food at once, leaving you feeling more full and satisfied, and you wouldn’t have to worry about eating later. In a way, IF may help prevent the typical night-time binges after not eating all day at work, or the binges resulting from those calorie-restricted diets that are difficult to keep up with for long run.
Although all this seems positive, we still need to think of the negatives. And there are a few.
1. Limited sustainability, especially for those who like to be social
Eating is very much a social activity. Since this new style of eating is very different from the typical daily eating patterns of most people, it may interfere with social hangouts which usually involve food. The shortened time frame you have for eating can makes it difficult when everyone else is eating and sipping on beverages, making you awkwardly stand out from the crowd.
2. Lowered energy and productiveness
We are all well-aware that life is unpredictable and can throw something at you out of the blue! So when changes in our life occur, we might get hungry and be much less productive, especially if you are used to eating lots of snacks or meals throughout the day, and all of sudden, you can’t.
Studies have found that some IF participants experienced adverse reactions when fasting, like feeling cold, constipated, fatigued, bad tempered and reduced concentration. For those who enjoy vigorously working out, this could be bad news - lack of energy and concentration may reduce your ability to work out to the level you want.
3. You set yourself up for a binge
In IF, you only have a limited amount of time reserved for eating, some people may take these "feasting” periods as an opportunity to eat more calories than they usually would. The chair of the department of Nutrition at Harvard said that "It's human nature for people to want to reward themselves after doing very hard work, such as exercise or fasting for a long period of time, so there is a danger of indulging in unhealthy dietary habits on non-fasting days."
Obviously, when you’re hungry, or you anticipate a period of fasting coming up, it can be very tempting to go crazy at the first sight of food. If the fasting element were to create some sort of caloric deficit, it’s very possible that the feasting period can easily undo it. Let’s also remember that the foods we choose to eat can have a significant impact on our health - and IF does not differentiate 'whole foods' from other foods - they treat any calorie, as a calorie. Which is something I do not endorse.
4. It's certainly not for everyone
Skipping meals and severely limiting calories can be dangerous for people with certain conditions like diabetes (massive blood glucose drops can be very dangerous). People who take medications for blood pressure or heart disease also may be more prone to electrolyte abnormalities from fasting.
If you are one of those people who feel nauseous or just don’t feel great going too long without eating, IF may not suitable for you. It’s also important to note that if you have ever had a history of an eating disorder – this is definitely not for you. IF promotes eating a lot of food in a short amount of time, so it may exacerbate potential disordered eating patterns such as a “binge-eating” mentality. This will definitely have adverse effects on your relationship with food and your body’s physical health.
5. Weight GAIN
Reducing calorie intake too severely can lead to the body responding with physiological adaptations that can cause weight regain after losing the weight during fasting. This means that it is very likely that individuals will not maintain their weight loss after extreme restriction of food and in fact, can gain even more weight. Obviously, that’s not ideal. But this claim is not confirmed, because there have not been any long term studies testing the sustainability of this diet.
For many others, a better weight-loss approach may be eating several small meals throughout the day, which stabilises our insulin levels and blood glucose, preventing any sort of ravenous meal gorging at the end of the day. It has been found that eating 6 times a day may even help maintain your lean muscle mass (which means faster metabolism!) compared to eating less frequently.
So what can you do with all this information?
It is very important to know that there is no conclusive evidence in IF research. As of now, this way of eating can be seen as a more flexible alternative to the traditional calorie restricted diet. In the end, each person has their own way of eating and their own “diet personality,” which means that there is no one-size-fits-all, perfect diet that is suitable for everyone. What’s most important is that you assess your own eating habits and find out what approach works best for you.
Food and dieting are very complex areas with adverse reactions to the human body if not done with caution. So, if you do decide you want to go ahead with IF, or you need more support to help you make that decision, speaking to myself or another experience Accredited Practising Dietitian can be a much safer route for you to take. Click here to contact us!
Love and light,
Joyce Haddad, Director of A Dietitian's Mission, is an Adelaide based Dietitian, Nutritionist and Master Personal Trainer with a passion for health and wellbeing. ADM aims to help the public make informed and realistic nutritional choices and ensure everyone has a healthy relationship with their body and with food.