Intermittent fasting: does it work, and is it right for you?

A friend swears by 16:8. Someone at work does 5:2. Your feed is full of people skipping breakfast and feeling great about it. So does intermittent fasting actually work, and is it worth trying?

The short answer: healthdirect says intermittent fasting can lead to weight loss, mostly because people end up eating less overall. Healthdirect says many of the other benefits people claim haven't been confirmed in studies on humans yet, and that it isn't safe for everyone. If you're curious, it's worth a chat with your GP first, and worth watching how it fits with your sleep, energy and mood.

Here's what intermittent fasting is, what the research says, who should skip it, how to try it sensibly, and how the Thrive Health Band and the Thrive by Optihealth app can help you see how it's really going.

What is intermittent fasting?

Healthdirect describes intermittent fasting as setting specific times when you eat normally and times when you eat little or nothing. There are no foods you must or mustn't eat. The rules are about timing, or about how much you eat on certain days.

The common types are:

Time-restricted eating, like 16:8. You eat within an 8-hour window each day and fast for the other 16 hours. For example, eating between 10am and 6pm.
The 5:2 diet. You eat normally five days a week, and on two days you have only a small amount of food.
Alternate day fasting, or eat-stop-eat. Longer fasts of about 24 hours, once or twice a week or more.

You can drink water at any time, including during a fast.

Does it work?

For weight, it can. Healthdirect says intermittent fasting usually means eating less food over a day or week, and that it can lead to weight loss. It's also linked to better cholesterol levels and lower blood pressure.

The catch is what's doing the work. Healthdirect notes that some research has found the benefits come from eating fewer kilojoules, and that the timing may not make much difference. Recent research in humans also suggests you don't get the same health benefits as from some other eating plans that cut kilojoules while making sure you still get the nutrients you need.

There's some early research suggesting that eating at set times of day may help your metabolic response and blood pressure, even without eating less. Healthdirect is clear that more research is needed, and that much of the original work was done in animals.

Healthdirect also points out that regular meals and avoiding lots of late-night eating or snacking seem good for your health. For some people, a time-restricted eating window is simply a tidy way to do that.

So intermittent fasting isn't magic, but it isn't nonsense either. It's one way to eat a bit less, and it suits some people's routines better than others.

What to expect in the first weeks

Healthdirect says that when you first start, you'll feel hungry and you may get headaches, and that your body is likely to get used to it over time. Diabetes Australia notes that headaches early on can happen and that drinking enough water can help.

Because some of your daily fluid normally comes from food, you may need to drink more water than usual. Healthdirect suggests stopping and talking to your doctor if you feel weak, anxious or irritable, can't concentrate, or can't do your usual activities.

It's also worth thinking about your week. Diabetes Australia mentions how a fasting plan fits with the people you live with and your social life. A plan that clashes with family dinner every night is hard to keep up.

Who should skip it

Healthdirect says intermittent fasting isn't recommended if you:

are underweight
have, or have had, an eating disorder
are pregnant or breastfeeding
are a child or teenager
are an older adult
take a daily medicine that has to be taken with food

If you're in your 50s or older, healthdirect's advice is a good reason to talk to your GP before trying it.

If you take medicines for diabetes or are having cancer care, healthdirect says to talk to your doctor first. Your doctor may need to change your medicines. Diabetes Australia adds that blood pressure medicines may need a review too.

How to try it sensibly

If your GP is happy for you to give it a go, these steps can help:

Start gently. A 12-hour overnight gap, like 7pm to 7am, is a softer start than jumping straight to 16:8.
Pick a window that suits your life. If you train in the morning or love a family dinner, plan around that.
Make the meals count. Healthdirect says to focus on nutritious food when you do eat. Protein and fibre help you feel fuller. See how much protein you need as you get older and how much fibre you need a day.
Drink water through the day.
Watch your sleep. A late, big dinner to squeeze in your kilojoules can affect how you sleep. Our piece on food and mood covers the link.
Check in after a few weeks. If you're hungrier, flatter or sleeping worse, it may not suit you, and that's fine. A dietitian can help you find another plan.

If you're thinking about training while fasted, read our piece on exercise on an empty stomach first.

See how fasting is really going with Thrive

How you feel on a new eating plan is often easier to see in your trends than in the moment. Thrive can help you see the bigger picture.

Log your meals in seconds. In the Nutrition tab you can log Breakfast, Lunch, Dinner and Snacks. The Food Logger lets you search Australian foods, Scan Photo or scan a Barcode, and shows your calories, protein, carbs and fat for the day. You can track your water there too.

Know your eating window. From your logged meals, Thrive picks up your usual meal timing as part of what's normal for you.

See your nights and days. Wear the Thrive Health Band to bed. It has no screen and up to 14 days of battery. Thrive shows your hours slept along with Quality, Quantity, Regularity and Timing, and your Daily Check-In lets you rate your mood, stress and energy.

Over time, Thrive learns what's usual for you right across your health, from sleep, heart, temperature and activity to mood, meals, medications and body composition. Your Health Fingerprint is ready after about 30 days of wear. Then you can ask Ask Thrive questions like:

"Has my sleep changed since I started eating earlier?"
"Do I have more energy on days with a shorter eating window?"
"How much protein am I getting on my fasting days?"

Before you start, you can show your Thrive trends to your GP, and again a few weeks in.

Before you buy

Thrive Health Band: A$589 for the band including 12 months of the Thrive plan, paid upfront. Prices are in AUD and include GST.

Free shipping. Your 12 months start when you activate your Band, and there's no automatic renewal.

At renewal: a new band plus 12 more months for A$589.

Or keep your band and renew the plan for A$240 a year.

Or A$29 a month with no lock-in.

One size, IP68, up to 14 days battery, 12-month warranty, not a medical device, no Apple Health sync. The app is Thrive by Optihealth on iPhone and Android.

See today's price on the Thrive store

Consumer guarantees under Australian Consumer Law always apply. See Returns if something is wrong with your purchase.

Common questions

Is intermittent fasting good for weight loss?

It can help, mostly because you tend to eat less overall. Healthdirect notes the timing itself may not make much difference.

Can I drink coffee or water while fasting?

Healthdirect says you can drink water at any time, including during a fast. Check with your GP or a dietitian about other drinks.

Is 16:8 safe?

It can be safe for some people, but not everyone. Healthdirect recommends talking to your doctor before you start.

For more answers, see Questions.