High-intensity interval training—think fast sets of burpees and squat jumps—has been gaining popularity in fitness for decades.
And time-restricted eating, which people may find less tedious than counting calories, has been attracting notice for almost as long.
But new research finds that when overweight women combine the two approaches, they may get an unexpectedly big boost in health.
The study tracked more than 130 sedentary and overweight women for seven weeks, dividing them into four groups. A control group did nothing different.
One group did three 35-minute HIIT workouts each week. Researchers supervised the exercise sessions, making sure participants worked hard enough to reach 90% of their maximum heart rate.
A third group used a time-restricted eating approach, consuming all their calories within a 10-hour window. (For example, they’d eat only between 10 a.m. and 8 p.m.)
A fourth group added HIIT workouts and time-restricted eating.
The exercise-only and restricted-eating groups saw health gains, including reduced fat mass and visceral fat.
But the group that did both—exercise and restricted eating—made more dramatic changes, losing twice as much fat. And they did significantly better in improving their long-term glycemic control.
The combination of a diet and exercise program seemed more appealing than either approach on its own.
That’s fantastic news for the tens of millions of women struggling with their weight and health, said Jessica Corwin, a registered dietitian at Corewell Health’s Women’s Health & Wellness Center.
“It’s especially important for women hitting perimenopause and menopause,” she said. “That’s when their weight is creeping up, and for many, their sugar levels are hitting the danger zone.”
It’s especially exciting that the study focused entirely on women.
“That is quite rare in randomized controlled trials,” she said.
Make HIIT work for you
Words like “high intensity” are likely to scare off gym-o-phobes. But Corwin is quick to point out that it’s all relative.
“You are working out super hard, but only for brief periods,” she said. “And that intensity is measured against your heart rate, not some elite athlete.”
While there are almost infinite variations, the basic premise remains: Quick bursts of hard work raise your heart rate. Shorter periods of rest allow your heart rate to slow down.
That might mean sprinting from one telephone pole to the next on your morning walk, then walking, and then running again.
At the gym, it might mean short bursts of jumping jacks or squat jumps, followed by very brief intervals of rest.
“There’s no need to try and run a six-minute mile,” she said.
Hard and sweaty? Yes. But the joy of it, she said, is that it’s only for 30 minutes, three times a week.
“There’s no need to spend hours at the gym if you don’t enjoy that,” she said.
“And plenty of research shows that even shorter HIIT workouts—some as quick as 15 minutes—are beneficial. You can really get your heart rate up.”
One caveat, she said, is that for the many women with Hashimoto’s disease or other thyroid issues, HIIT may be problematic.
“It can tax the adrenal glands and make weight loss more difficult,” she said.
Not sure about the state of your thyroid?
“It’s a good idea to ask for your provider about a full workup at your next checkup, especially if you’re having problems with weight gain or fatigue,” Corwin said.
Time-restricted eating
A 10-hour window for eating is “quite realistic,” Corwin said.
Start with time-restricted eating by choosing a time window that most easily lines up with your lifestyle.
People are often unaware of how much grazing they do all day and all evening, often without feeling satisfied.
The shorter time window often helps focus on three better meals each day, with 20 to 30 grams of protein at each of those meals.
“There’s so much evidence that adequate protein boosts satiety, preventing those sugary cravings later in the day and keeping our energy up all day,” Corwin said.
With those solid meals under your belt, “it’s easy to stop eating at 7 p.m. and not again until 9 a.m. the next day,” she said. “And even going from 7 p.m. to 7 a.m. is an incredible start.”
Black coffee and tea are fine.
“But bear in mind that adding anything—even a zero-calorie sweetener like Stevia or Splenda—ends the fast,” Corwin said. “It tells your body something sweet is coming, and it starts to crank out insulin.”
The key: Adjust the window to suit your life, whether that involves cooking for a family or working different shifts.
Another reason it works so well, she said, is that it’s very forgiving.
“So maybe one night you go out to dinner outside that window or have a glass of wine later in the evening,” she said. “Just reset the clock and start over again the next day.”
While the research study looked at the impact of this eating style on metabolic health, “it also helps with heartburn, which is a big problem for many women,” Corwin said.
Additionally, she likes how it encourages women to listen to their bodies differently, promoting a more mindful, intuitive approach to nutrition.
“You may say, ‘I’ve always been a big breakfast person,’ and then discover you like waiting until 10 a.m.,” she said. “And our bodies are different every day, especially for women with a menstrual cycle.
“For many, it helps them get in touch with what it they’re body is saying, and what they are hungry for.”
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