This is the ultimate exercise combo, according to science
Published in Body & Soul 26 March 2023 p6-7 ‘The Aussie weight loss breakthrough’ reporting on
Professor John Hawley’s findings [Prof John Hawley, Director of Centre for Exercise and Nutrition
Research Program at the Australian Catholic University]
Groundbreaking Aussie research has shown a specific combination of eating and exercise can have
phenomenal results, minus the deprivation and crazy diets. And it’s easier than you think.
Sydney-based professor, John Hawley, has spent much of the past four decades thinking about
losing weight. Or, more specifically, observing how people try, then miss the mark – often repeatedly
– to shed unhealthy fat.
As director of the Centre for Exercise and Nutrition Research Program at the Australian Catholic
University, and author of more than 300 scientific papers on diet and exercise, Hawley has spoken
with countless people disillusioned at having tried a dozen or more diets, “only to find themselves
back where they started”.
His decades-long mission has been to find a method that works – a plan that is almost effortlessly
simple but brings results in terms of fat lost and health gained. It is the elusive golden carrot of the
diet industry, but in findings he describes as “the most promising” of his career, Hawley has moved
closer to realising it.
In new research, he has discovered that a potent combo of two on-trend powerhouses of the
wellness world – time-restricted eating (TRE) and high-intensity interval training (HIIT) – is better at
blasting fat than any approach he has come across previously. Stick to a few rules and, in as little as
seven weeks, you will shift weight, lose body and belly fat, and shed centimetres from your waist
faster than with other diet programs – and at double the rate you would by employing either of
these approaches alone. Sound too good to be true? The science says otherwise.
Independently, both TRE (which involves eating all of your daily calories within a predefined eating
window) and HIIT (which involves brief, intense activity interspersed with set recovery breathers)
have been shown in studies to reduce internal visceral fat, high levels of which are associated with
insulin resistance and type 2 diabetes, as well as lower blood pressure, boost mood and enhance
sleep. What intrigued Hawley is whether the two are more powerful when performed together.
Working with Trine Moholdt, a research scientist and head of the Exercise, Cardiometabolic Health
and Reproduction Research Group at the Norwegian University of Science and Technology in
Trondheim, and her colleagues, he set about investigating the synergistic effects of the combo with a
group of 131 overweight women in their 20s and 30s. “I didn’t invent either TRE or HIIT, but we were
the first to put them together in a research study,” says Hawley.
Over seven weeks, the women were asked to follow one of four different interventions. One group
did TRE, consuming all of their calories within a 10-hour window; another group did three supervised
HIIT sessions per week; a third group did a TRE and HIIT combo; and the fourth acted as the control
group, with no intervention. For those trying TRE there were no rules about what, or how, they
should eat – no banned foods, carb cutting or calorie counting – which made it the antithesis of strict
and restrictive diets.
The results, published in the Cell Metabolism journal, were a surprise even to the research team. So
effective was the TRE-HIIT combo that it led to a twofold greater reduction in body fat and the risky
visceral fat stored around the organs, compared with TRE or HIIT performed in isolation. And people
had no problem sticking to the 10-hour eating window rules. Even when they relaxed the window
rules for one day during each week, usually on weekends, the weight still came off.
Why it works is intriguing. By its nature, TRE tends to lead to fewer calories consumed inadvertently
each day just because you can’t fit them in. When you are restricted to eating within a defined
window, that late-night chocolate, bag of chips or glass of wine – what Hawley refers to as the
dietary biggies – are automatically off the agenda. It is, he says, these sorts of “subtle changes and
omissions that can make a big difference over time”.
While it’s often confused with intermittent fasting, which advocates periods – days or hours – of
strict calorie restriction, TRE, says Hawley, is “definitely not the same thing”. It plays to our natural
circadian rhythm or body clock, which regulates everything from metabolism to gut health.
“Intermittent fasting doesn’t do that and, in fact, can actually disrupt our circadian rhythm,” says
Hawley. When that happens, hunger and satiety hormones are thrown into disarray, which can lead
to snacking and eventually to an overconsumption of daily kilojoules that leads to weight gain. Not
With HIIT added to the mix, the metabolic and weight-loss outcomes are better than any other
known diet – healthy, safe or otherwise. It’s not even that the workouts were colossal calorie-
burners – each participant in the study expended only an average total of 14,000 kilojoules a week in
doing them – but when they were combined, TRE and HIIT proved to be more potent than the sum
of their parts. In particular, says Hawley, levels of HbA1c, a clinical measure for blood sugar,
improved only with the dual approach.
“The real appeal for people is that TRE is a less tedious method for losing weight than daily calorie
counting,” says Moholdt. “And HIIT is tolerable, time-efficient and safe for even previously sedentary
individuals.” Hawley believes the TRE-HIIT combo is “the brightest thing we’ve had on the horizon”
in terms of weight loss and health. In short? Exciting news that could be a game-changer.
How to do TRE
1. Decide on your own eating window
For the trial, TRE was loosely defined as consuming all daily calories within a 10-hour time window.
“Our only recommendation was that they should not consume food or snacks after 7pm each day,”
says Hawley. “We know that when you bring in your evening meal that little bit earlier, your glucose
concentrations during the night are much lower.”
2. Don't obsess about calories, fat and carbs
There are no rules about how much or what food to consume or avoid. You can eat whatever you
like – chocolate, chips and a glass of wine are fine, provided you have them within your window.
However, you may find your eating habits naturally improve simply because you’re losing weight and
3. Don't add any calories outside of your window
Be strict with yourself and only have black coffee, tea without milk or water outside your eating
window. “Milk and sugar in your drinks count as calories, so they are out,” says Moholdt. The same
goes for that sneaky extra glass of wine in the evening.
4. Eat plenty of fibre
Choosing nutritious food that fills you up is important from the outset. “Nuts, seeds and fresh fruit
and vegetables contain fibre that is filling and nourishing for the gut microbiome,” says Alex Ruani,
researcher in nutrition science at University College London.
How to do HIIT
1. Aim for three 30 minute sessions a week
For two of your sessions, after a warm up, do four minutes of hard running on a treadmill (aiming for
90 per cent of your maximum heart rate or a rate at which you are breathing hard). Follow this with
a three-minute active recovery (slow run or fast walk) at around 60 per cent maximum heart rate.
Repeat this cycle three more times, then end with two minutes of light walking to cool down.
For the third session, which is also on a treadmill, after a warm up complete a 60-second burst of
effort at high intensity, followed by 60 seconds of low-intensity activity such as walking. Do this
routine 10 times, then follow with 10 minutes of light activity to cool down.
2. Pick a cardio method that works for you
If anyone in the trial had knee pain or other issues that stopped them from running, they did the
same training on a stationary bike or rowing machine instead. Simple. You’re not confined to a gym,
either. “Running up stairs can be a HIIT session, as can sprinting outdoors on a football pitch,” says
Moholdt. “Be creative and inventive to make it work for you.”
3. Consider investing in a heart-rate monitor
The trial used polar trackers to be sure everyone worked to the ideal heart rates, but tech isn’t
essential. “You can assume you are making the right amount of effort if you are breathing heavily
and are not able to talk in full sentences during the activity burst,” says Moholdt.
4. Train in the afternoon or evening
Previous studies by Moholdt have shown that aerobic exercise training, including HIIT, done in the
early evening reduced overnight blood sugar concentrations. “But any time of day is always better
than none,” she says. “Just try and fit it in at a time of day when you feel most energised.”