The concept of intermittent fasting is something that has been around for a long time, but people rarely know what it is exactly, or why it’s effective.
In a nutshell, intermittent fasting is a broad term for a variety of different weight loss approaches that all involve restricting your daily calorie intake to a relatively narrow window of time each day.
While it may sound like a fad, it’s in fact highly effective and an ideal strategy for people wanting to achieve gradual weight loss.
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The 5:2 diet
What: Where calories are restricted to 500-600 calories per day for two days per week, then normal eating is followed for the other 5 days per week. This is a simple method of fasting that suits those who want to make minimal changes, but still see some results. Similar effects have been seen on daily caloric restriction to 1200-1500 cal.
Suits: those who want to feel like they are making a change, but don’t want to have to ‘restrict’ day to day.
Be mindful of: Overdoing it on ‘normal’ days.
The 16:8 diet
What: This method of time restricted fasting is becoming increasingly popular. Eating is kept to an 8 hour window in the day, with a 16 hour fast (14:10 is another popular, very similar method). Skipping breakfast and starting the food day at midday, and finishing by 8pm is the most common window, with usual calorie intake recommended to be consumed within the 8 hour window. This method of fasting is recommended to be higher in protein.
Suits: People with minimal time for meal prep, who don’t spend a lot of time thinking about food.
Be mindful of: Being so hungry by the time you’re ‘allowed’ to eat that more food than is required is consumed.
24 hours and longer
What: Eating is stopped for a 24-hour window, for example consuming nothing other than water from dinner on Sunday to dinner on Monday. Some proponents suggest branched chain amino acids (BCAAs) should be consumed throughout this, though some do not.
Suits: Whilst there is a plethora of case study style evidence available online, this style of fasting is not something dietitians feel comfortable recommending, as there is not enough good quality evidence in humans to support it.
Be mindful of: If you do choose to do it, be mindful of flagging energy levels, and in particularly, minimising any form of physical activity.
Pros and cons of 5:2
When comparing these two methods of fasting it’s not a question of which method is better, rather which method you’ll be able to stick to.
The 5:2 can be extremely effective and has a growing body of evidence to support its use, but it is not easy to do. A 500 calorie diet equates to very little food each day – an egg, a coffee and a small meal of fish and salad – so it’s not for the fainthearted.
Like any diet, results will only be achieved when you can actually commit to the regime and really stick to the 500-600 calorie days. A little cheat which means you eat 800-1000 calories on fasting days will not give you the results the 5:2 can induce when it’s carefully adhered to.
For busy, active individuals who have high energy demands, this regime is especially tough and even inappropriate.
On the other hand, it could be good for those who don’t eat a lot through the day and instead tend to eat a larger meal at night. If they can control the size of their evening meal, the 5:2 can work especially well. Plus, there is the added bonus of not needing to count calories on the other five days each week.
Example of 5:2
Most individuals follow this style of intermittent fasting in one of two ways; either by eating three small meals per day, or two larger meals. For most people, eating ‘whatever you like’ for five days a week and then restricting your calorie intake for two days a week is unsustainable.
Pros and cons of 16:8
Compared to the 5:2, the 16:8 is easier to stick to if you can ward off your morning hunger and not eat until 10am or lunchtime each day. All you then need to do is eat two to three well-balanced meals within an eight hour period.
There is no specific calorie control, you can basically eat a healthy, balanced, filling diet as long as you eat everything within eight hours and still lose some weight.
The 16:8 is a fasting option for those who may have difficulty keeping calorie intake very low, and who don’t have the time, energy or focus to manage their food intake on low-calorie days as required by the 5:2.
It is generally a much easier program to follow long term, across any day of the week.
Example of 16:8
Most people follow this style of intermittent fasting either by skipping breakfast, having a late breakfast, or skipping dinner. This isn’t about cutting back on calories, but fitting your usual intake into a smaller window of time in the day.
So, if you skip breakfast, your day should look like…
- Morning: Black coffee or tea, or water
- Midday: Quinoa and lentil salad with plenty of leafy greens
- Afternoon snack: Fruit + raw nuts
- Dinner: Grilled fish with sautéed veggies and sweet potato
- Supper (pre 8pm): Yoghurt with fruit
And if you have a late breakfast…
- Morning: Black coffee, tea, or water
- 10am: Omelette with spinach and tomato and sourdough toast
- Midday: Fresh fruit with nuts and seeds
- 2pm: Sashimi with edamame and miso soup
- 5.30pm: Chickpea salad with leafy veggies and grilled chicken
And if you skip dinner, your day should look like…
- 8am: Poached eggs, smoked salmon, avocado, mixed veggies and sweet potato or quinoa
- Mid-morning: Fresh fruit and raw nuts
- Midday: Sautéed veggies with brown rice, chicken and a drizzle olive oil
- 2pm: Yoghurt and fruit.
1. Helps with weight loss
It’s the number one reason people opt to fast – and it all comes down to your body lowering insulin levels, which helps stimulate lipolysis. This is what helps your body break down fat.
Lowering the amount of insulin in your body will not only help break down fat faster, but it will help keep your insulin levels low when you break your fast.
It can also lead to the consumption of fewer calories overall, which with help with weight loss.
While thousands of people worldwide have experienced firsthand the weight loss benefits of intermittent fasting, science has backed this up time and time again.
The most recent study published in the journal Nutrition and Healthy Ageing showed a 16:8 diet is the most effective in helping with weight loss.
Researchers from the University of Illinois at Chicago, examined 23 obese volunteers who had an average age of 45 and an average body mass index (BMI) of 35. Participants were put on the 16:8 diet, a form of intermittent fasting, whereby they were only allowed to eat during an eight-hour window between 10am and 6pm. They were then only allowed to consume calorie-free drinks, such as water, for the 16 hours in-between.
The scientists measured various factors, including the participants’ blood pressure, cholesterol and glucose levels, and fat mass. The data was then compared to the results from a separate weight loss trial carried out between 2011 and 2015.
After a period of 12 weeks, the results found that the participants consumed approximately 350 fewer calories, which resulted in a three per cent weight loss.
The researchers suggested that that 16:8 approach is a more maintainable form of intermittent fasting compared to the 5:2 diet – where individuals consume less than 500 calories for two days of the week and consume a normal amount of calories for the other five days.
2. Improved heart health
Heart disease is the world’s biggest killer.
It’s known that there are various health markers associated with an increased or decreased risk of heart disease. Now, a 2016 review found intermittent fasting had a significant effect on helping prevent and improve these markers – including blood pressure, total and LDL cholesterol, blood triglycerides, inflammatory markers and blood sugar levels.
3. Improved brain health
Fasting may cause your body to go into survival mode, forcing your brain to have greater focus on certain tasks at hand. The changes that happen in your brain during fasting mimic the changes to your brain when you’re exercising.
One study published in PLOS One found mice that were put on an intermittent fasting diet had better learning and memory than mice that had free access to food.
Fasting also increases levels of a brain hormone called brain-derived neurotrophic factor (BDNF), a deficiency often associated with depression and various other brain problems.
Further research in animals suggest fasting can reduce the risk of neurological disorders, including Alzheimer’s disease, Parkinson’s disease, and stroke.
However, more research is necessary to examine whether these results apply to humans.
4. May help prevent cancer
According to the Australian Cancer Research Foundation, 1 in 3 Australian men and 1 in 4 Australian women will be diagnosed with cancer before the age of 75. Furthermore, there is an average of 367 diagnoses each day in Australia alone.
Cancer is a diverse group of several hundred diseases in which some of the body’s cells become abnormal, and multiply uncontrollably. These cells invade and damage the tissue around them, creating tumours that cause further damage, which eventually leads to death.
However, a series of recent studies in animals has indicated that restrictive diets like intermittent fasting could delay the onset of tumours. The only problem is, no current studies have established links between intermittent fasting and cancer in humans.
For people going through chemotherapy, intermittent fasting has also been shown to help suppress many of the side effects.
Additionally, obesity plays a huge role in the onset of different cancers, so the weight loss aspect of intermittent fasting could be responsible for the reduced risk of cancer studies have shown.
5. Lowers risk of type 2 diabetes
280 Australians develop diabetes every day – that’s one person every five minutes. However, a recent study published in the journal BMJ Case found planned intermittent fasting could help reverse type 2 diabetes and eliminate the need for medication.
Doctors at Scarborough Hospital, Ontario, put three patients, aged between 40 and 67, on the diet.
Prior to starting intermittent fasting, the patients were injecting at least 70 units of insulin daily, and all had high cholesterol and high blood pressure.
Two of the men fasted every second day for a full 24 hours, and the third fasted on three days a week.
On their fast days, the patients were allowed to consume water and very low calorie drinks like tea, coffee or broth, and were allowed to eat a very low-calorie meal in the evening.
On non-fasting days, the men had lunch and dinner and were encouraged to eat low-carbohydrate meals.
The participants also attended a six-hour nutritional training programme before starting the diet, where they were informed on how to manage their chronic condition through diet and a healthy lifestyle.
Within a month, all three participants had stopped injecting themselves with insulin. Two were able to stop all their other diabetes medication, while the third dropped from four drugs to one.
Additionally, their blood sugar levels, and weight and waist measurements were recorded ten months after starting the eating plan. The results showed they had lost 10 to 18 per cent of their weight (around 10-11kg), and their waist circumference had reduced by 10 to 22 per cent.
While the study provides hope for those with the chronic condition, the researchers stress the fact that the study only included three men, and therefore further research needs to be conducted to determine whether all-day fasting can treat type 2 diabetes.
6. Improves sleep quality
Intermittent fasting in many ways helps the body stay well aligned for sleep. This is because the timing of meals can affect our 24-hour circadian rhythm, which significantly influences our quality of sleep.
Eating heavily near bed time is proven to worsen sleep quality, making sleep more restless and less refreshing. But when you are fasting, your digestive system quiets down and your body goes into energy saving mode earlier in the night. This makes for a stronger, more synchronized body clock, and means you’ll have easier time falling asleep, staying asleep and waking feeling refreshed and energized.
The best thing about intermittent fasting is that it provides a wide range of positive health benefits without requiring a massive lifestyle change – it’s super convenient. In saying this, it’s still important to provide your body with all of the essential nutrients and vitamins it needs to function at its best.
Technically, consuming any food or drink that contains a significant amount of calories will break the fast. This includes coffee with milk, protein shakes, bulletproof coffee or a piece of fruit. While these foods are relatively low in calories, they still offer 50-100 calories per serve, which will have an impact on the hormones that influence glucose levels, thus ceasing the beneficial metabolic processes that justify fasting.
What is a significant number of calories?
The true answer to this we do not know, but there is one frequently mentioned study that is said to have examined the impact of including BCAA’s (Branch Chain Amino Acids) in a morning fast, which equated to 50 calories – and it was found that there was no significant effect on weight loss.
While the source of this information or study is unknown, this is largely where the rationale comes for an insignificant number of calories equated to 50 or less.
In food terms, this would also suggest that tea or coffee enjoyed with a dash of milk, a few berries, or some plain vegetables such as cucumber or carrots, will disturb the metabolic processes that give fasting its benefits, especially if it fends off hunger.
What about zero calorie sweetened foods?
This would then suggest that foods that have zero calories, as is the case with diet products that use artificial or natural sweeteners to achieve sweet tasting foods (minus a significant number of calories), can be consumed freely during the fasting period. However, while this may sound reasonable, there is some evidence to show that artificially sweetened foods in particular can result in a release of insulin, the hormone that controls fast metabolism and drives hunger.
This means that while the drink or jelly may not technically contain calories, it may still disrupt the fast and directly impact your appetite – and as such is best avoided.
Are you focusing on the type of food you’re eating?
When undertaking intermittent fasting, the 5:2 approach reduces calories on 2-days a week and the 16:8 approach has you only eating in 8-hour windows each day. What I like about this is you typically reduce your calorie intake and most of us eat too much. However, it is too simplistic and not a balanced perspective when it comes to nutrition to just think of food as a calorie number.
It’s very common for people to only eat two meals when they’re following the 16:8 approach and sometimes this means they’re not eating enough calories required for the human body to perform at an optimum level.
You’re not getting enough nutrients
By having a shortened period of eating, or having to restrict calories on certain days, it can mean you’re not getting the amount of nutrients your body needs.
When this happens for a sustained period of time, it can lead to deficiencies and manifest as a number of symptoms or complaints.
If something doesn’t seem right, it may be time to get back to regular eating habits. Be sure to consult a doctor or healthcare practitioner if anything is out of the ordinary.
It’s impacting other areas of your life
Sometimes when we just look at the numbers, things make sense. But the real world in which we live in isn’t about numbers. It involves stress, emotion and temptation and there are practical realities that can cause such a restrictive way of eating to cause potential problems.
Are you stressed about what to eat or when? Are you obsessing over calories consumed during your eating windows? If what is meant to be a good thing for your health is causing an unnecessary amount of stress or an unhealthy obsession, you need to ask yourself: ‘is this right for me?’
1. Non-starchy vegetables
Veggies are the bee’s knees when it comes to filling up for little energy cost. Veggies like carrots and cucumber (not potato, peas and corn) are super low calories – with 41 and 23 calories per vegetable respectively. Another bonus is that they’re high in fibre, so you can eat a lot of them and feel full without going overboard on energy.
2. Cauliflower rice
I’m not against carbs at all – eating rice (particularly long grain brown rice) is perfectly healthy and fine by me. But if you’re watching calories, switching to a vegetable-based ‘rice’ can be a game-changer. One serve of cauliflower ‘rice’ (75 grams) contains 19 calories.
3. Zucchini noodles
Along the same veggie tone, swapping your usual noodles for ones made out of zucchini (hence: ‘zoodles’) can be a wise choice, too, with one zucchini coming in at 30 calories. Use them raw for salads or as a bed for bolognese sauce.
I don’t really believe in superfoods, but if I had to pick, eggs would be one. That’s because they’re an excellent source of high-quality protein, are packed with micronutrients and are super easy to use. Plus, they’re cheap as chips! A couple of eggs will set you back 112 calories.
5. Rice cakes
A low-energy base for lunch with 50 calories per thick cake, you can top these babies with your usual sandwich fillings. I’d encourage you to opt for a brown rice variety to get the wholegrain benefit. Note that rice cakes can have a high glycaemic index, so you’ll need to add lots of fibre-rich veggies and lean protein to get that fullness factor.
Before I expand on this, let me clarify one thing, first: all fruits are good for you, no matter how many calories or how much natural sugar they contain. If you’re trying to stick within a calorie budget, however, berries and citrus fruits are lighter choices than tropical fruits. One cup of mixed berries, for example, has just 51 calories, while a banana has 90 calories.
7. Grilled fish
For a protein punch, white fish can be a great low-calorie choice with just 96 calories per 100 gram fillet. Be careful of the way you cook it, though, as frying fish in loads of oil will send the calorie count skyrocketing – so baking is usually the best method.
Anything veggie-based is a good idea for a light meal, but beware of creamy soups and skip the buttery bread. You can bank on roughly 30 calories from one cup of store-bought veggie soup.
A great idea for in-between meals, popcorn is actually classed as a wholegrain and so provides a decent amount of fibre and micronutrients. If you steer clear of the buttered and sugary varieties, you’re in for just 28 calories per cup.
10. Lean mince
Another one on the protein bandwagon, 65 grams of lean beef mince has 111 calories. An even leaner option is lean turkey mince, with 94 calories in the same amount. Not only is mince high in hunger-busting protein to keep you feeling full, but micronutrients like energising iron and zinc to support immune function.
There is a growing body of evidence to show that fasting, even occasionally is exceptionally good for us. It helps to get us reacquainted with our natural hunger, helps is to eat less overall and supports weight loss.
There are no hard and fast rules when it comes to IF. You don’t have to turn your life upside down if you want to benefit from it – do it as much, or as little as you like. Never forget that fasting is an extreme process on the body. Don’t feel disappointed if you can’t commit to fasting every day, sometimes work commitments or dinners with friends get in the way.
The key step in getting fasting to work for you is to choose the type of fasting that you are ultimately able to stick to and to then stick to it for a good period of time. In eight-12 weeks you will see the results.
Fasting is not a quick fix diet solution, rather a lifestyle choice that can help with weight control. The key to success is sticking to it.