Just the other day, I came across a story about interval training for fat loss, with scientists claiming to have devised a workout that burns three times more fat than regular workouts lasting twice as long
According to news reports, interval training triggers a metabolic response that allows more fat to be burned under the skin and within the muscles.
Can you really lose weight three times faster with only half the exercise?
Let’s take a closer look at what happened in the study…
Australian researchers studied a group of overweight women, putting them through a 20 minute cycling regime in which they sprinted on a stationary bike for 8 seconds followed by 12 seconds of cycling lightly. The women performed the workout three times a week for 15 weeks.
“They lost three times more weight than other women who exercised at a continuous, regular pace for 40 minutes,” says study co-author Professor Steve Boutcher.
Other types of interval training using longer work and rest periods, says Professor Boutcher, are not as effective for overweight people.
As far as I can tell, the work-rest ratio (8-second sprint, 12-second recovery) is based on a previous study by the same researchers showing that short work and rest ratios burn more calories than longer (24-second sprint, 36-second recovery) intervals.
Boutcher thinks the current government recommendations for exercise are largely ineffectual. “Walking for 60 minutes, seven times a week does not result in much fat loss, usually 1.15 kilograms over 15 weeks,” he says. “For a lot of overweight people this is going to be a revolution.”
Is this a revolution in weight loss?
Maybe… if you’ve had your head in the sand for the last 10 years.
Using interval training for fat loss is certainly not a revolutionary idea. It’s a big part of the cardiovascular workouts featured in my Fight Fat and Win programs. And there are plenty of other people who have been writing about it — and using it — for a number of years.
However, even though interval training is both a highly effective and time-efficient way to train, saying that it’ll help you lose weight “three times faster” than regular cardio does paint a rather overly optimistic picture about what to expect.
With all the fuss about interval training and fat loss, you’d think there are dozens of studies to show that it consistently leads to greater fat loss than steady-state cardio. But there aren’t.
It’s true that interval training will increase calorie expenditure in the hours after exercise. But so do other forms of exercise, such as lifting weights or even regular steady-state cardio done at a sufficiently high intensity.
And most studies of interval-style workouts have looked at changes in performance and fitness, rather than weight loss.
Studies to track changes in body composition are few and far between, which is one of the reasons this Australian study caught my eye.
However, when I looked at the research in detail, the results weren’t quite as exciting as they first appeared.
Here’s why…
At the end of the 15-week study, the interval-training group had lost, on average, 2.5 kilograms (5.5 pounds) of fat. The steady-state group gained 0.5 kilograms (1.1 pounds).
The results are shown in the figure below.
The amount of fat lost in the interval training group wasn’t all that great — 5.5 pounds over 15 weeks, which works out at just 0.4 pounds of fat loss per week. This figure doesn’t really grab your attention like “three times greater weight loss.”
In fact, I can’t figure out how the researchers arrived at a figure of “three times greater weight loss,” as the interval training group lost weight while the steady-state group gained it.
Much has been made of the fact that the interval group lost more fat from their stomach. And when you look at the figure below, the first impression you get is that there was quite a dramatic difference compared to the steady-state group.
However, take a look at the numbers down the left hand side. You’ll see that the interval group lost just 0.15 kilograms of abdominal fat. That’s less than half a pound. Which over a 15-week period, is hardly worth getting excited about.
It’s also worth pointing out that subjects in the steady-state group started out cycling for only 10-20 minutes. Over the course of the 15-week study, this gradually increased to a maximum of 40 minutes per workout.
So it’s not true to say that the interval group got better results with “half the exercise” as the steady-state group weren’t actually exercising for 40 minutes from day one.
What about diet? How did that affect the results?
Calorie intake was monitored using 3-day diet diaries that were completed at the start and end of the study.
According to these diaries, the steady state group reported a decrease in their calorie intake over the course of the study in the region of 400 calories per day.
Yet despite this reported reduction in calorie intake, the women in this group actually GAINED weight.
The problem here is that self-reporting is a notoriously inaccurate way to estimate calorie intake. Some studies show that people underestimate their calorie intake by up to 50%. In other words, someone who says they are eating 1000 calories per day may really be eating 2000 calories.
The researchers themselves also point out that their estimates of calorie intake “lack sufficient precision.”
“Our estimates of energy expenditure and intake lack sufficient precision to comfortably conclude that energy balance was unaffected in the [interval training group]. Thus, it is feasible that the change in fat mass that occurred in the [interval group] may have been influenced by unreported changes in diet.”
So, changes in calorie intake might have been primarily responsible for any weight loss. Or they might have had nothing to do with it. We don’t really know for sure.
With all that said, I still think that interval training is a great way to lose fat. It’s something I use myself and recommend to others. The interval training used in this Australian study is similar to the level III workout in my Fight Fat and Win program.
However, interval training alone is not a magic bullet, and I think most people would be disappointed losing less than six pounds of fat after 15 weeks of exercise.
The fact is that there are many different ways to do cardio. All of them have their place at different times and for different people. Don’t be duped by the HIIT “propaganda machine” into believing that interval training is the only way (or even the best way) to drop fat.
For fast muscle building workouts, take a look at Muscle Gaining Secrets.
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