THE WASHINGTON POST – Whether you consider a six-pack a goal or a beverage is beside the point when it comes to extra fat at your waistline. Abdominal adiposity – excess stomach fat – is associated with increased mortality risk, regardless of body mass index.
Although the exercise community has long known that it’s impossible to “spot train” to reduce inches anywhere on your body, some trainers have been touting high-intensity interval training (HIIT) as the best way to target stomach fat. The workout, which includes short bursts of intense work followed by short rest periods (think 30 seconds on, 30 seconds off), can take as little as 20 minutes. Before you start alternating burpees and jumping jacks with recovery intervals, however, let’s look more closely at that claim.
To understand HIIT’s role in health and longevity, you need to first understand that all fat is not created equal.
Two types of belly fat, subcutaneous fat and visceral fat, accumulate in your abdomen, but they look and act very differently. Subcutaneous fat is stored just underneath the skin, said Connecticut-based exercise physiologist and fitness consultant Tom Holland.
It’s visceral fat, however, that you should be concerned about. Nestled deeper in your abdomen, adjacent to your organs, it’s “almost like an endocrine organ” that poses serious health risks, Holland said.
Unlike belly fat, visceral fat is “metabolically active”, said Director of the Weight and Metabolism Management Programme at Mount Sinai Hospital and Endocrinologist Reshmi Srinath. It produces molecules known as adipokines that can increase inflammation in various organ systems. Such inflammation is associated with chronic conditions, such as insulin resistance, higher glucose levels, diabetes, heart disease and fatty liver disease.
Your waistline measurement is generally an accurate predictor of excess visceral fat and the health risks associated with it. According to Srinath, who is board certified in endocrinology and obesity, women whose waists measure 35 inches or more and men whose waists measure 40 inches or more are at increased risk of conditions including heart disease, diabetes, hypertension, hyperlipidemia and obstructive sleep apnea.
But although a larger waist circumference and excess visceral fat generally “go hand in hand”, Holland said, this isn’t always the case. According to physician assistant and athletic trainer at Redefine Healthcare in New Jersey, Evan Jay, some thin people who don’t appear to carry extra weight in their abdomen do have visceral fat. Meanwhile, there are people with larger waistlines who don’t have excess visceral fat.
The only way to know for sure what kind of fat you’re carrying in your stomach is through imaging, which, Srinath said, isn’t typically done in clinical practice. Instead, in addition to looking at waist circumference, your health-care provider will note clinical markers indicative of visceral adiposity, Jay said. These include low HDL cholesterol, high triglycerides, high blood pressure and high fasting blood glucose, all of which are associated with excess visceral fat.
Can HIIT reduce stomach fat? The answer is yes, according to a 2018 meta-analysis, which looked at 39 studies involving 617 subjects.
“HIIT significantly reduced total (p = 0.003), abdominal (p = 0.007), and visceral (p = 0.018) fat mass,” the study’s authors said.
What the authors did not say is that HIIT reduced fat better than other forms of exercise.
And, in fact, studies have not found a difference in fat loss between HIIT and moderate-intensity continuous exercise in laboratory trials or in the real world.
“From a clinical perspective, there’s really no difference” between HIIT and moderate exercise, Srinath said. “The real benefit of HIIT,” she added, is its efficiency.
Holland agrees. The “true beauty of a HIIT workout”, he said, is how little time it takes compared with moderate-intensity exercise, such as brisk walking, leisurely swimming or biking on a flat surface at a conversational pace. “When you look at a lot of studies,” he added, “you’re getting the same results with high-intensity interval training in half the time”.
And that, he said, helps people maintain their routine: “It’s, ‘Hey, I’m getting the same results – and in half an hour rather than an hour. I’m more likely to be consistent’.”
HIIT training also has potential cardiovascular health benefits. A 2019 meta-analysis reviewed 22 researched articles comparing HIIT training with moderate-intensity training. The authors found that when subjects’ total energy expenditure was equal, HIIT and moderate training produced similar reductions in weight, body fat, total cholesterol and cardiorespiratory fitness, all of which reduce the risk of cardiovascular disease. However, the HIIT subjects spent less time working out than their counterparts; their sessions were about 10 minutes shorter than the moderate exercisers’ sessions.
Also, because HIIT workouts tend to be shorter, participants may be more likely to avoid “compensatory eating”, said Holland. In other words, you might be less prone to “rewarding” yourself with a bigger portion or a dessert after a 25-minute HIIT session versus a 45-minute jog.
In fact, because fat loss depends on an overall caloric deficit, exercise alone won’t necessarily drive results. According to Jay, fat reduction has more to do with your meals than your workouts. Anybody interested in starting a HIIT programme who hasn’t started looking at their diet, he said, “should take all that energy and redirect it”.
None of this is to say that you shouldn’t give HIIT a try. There are many ways to do it; the type of exercise doesn’t matter, as long as you get your heart rate into the “red zone”, Holland said. Common moves include compound (multi-joint) movements, such as variations on burpees, squats and lunges, “due to their relative difficulty and concomitant high heart rate response”.
If arthritis or other mobility issues preclude you from high-impact movements, you can turn any low-impact workout, such as cycling, swimming or using the elliptical, into a HIIT workout. All you need are a timer and some motivation.
According to the American College of Sports Medicine (ACSM), the work periods should range from five seconds to eight minutes and be performed at 80 per cent to 95 per cent of your maximum heart rate. The time commitment varies, but it can take as little as 20 minutes.
If you don’t know your maximum heart rate or don’t have a heart-rate monitor, Holland suggests going by feel, or rate of perceived exertion (RPE). On a zero to 10 RPE scale, shoot for eight, nine or 10 during your work intervals. To maintain the intensity throughout the session, he suggests shorter intervals, ranging from 20 seconds to a minute. “You’re outside your comfort zone, but you’re not staying there very long.”
Pace yourself, so by the time your work interval is complete, you’re out of breath. “And right at that point where you finally catch your breath, it starts again,” Holland said. Your ratio of work to recovery time can be adjusted to accommodate your fitness level, but it should generally range from 1:4 to 1:1. This might look like a minute of burpees followed by two minutes of recovery or 20 seconds of jump squats followed by a minute of recovery.
Although you might be tempted to minimise your recovery time in pursuit of a more intense workout, that strategy can be counterproductive. “If you cut (your recovery) too short,” Srinath said, “you can’t go at a high intensity for the next interval”.
Holland said a 25-minute HIIT session might include five one-minute rounds of high-intensity exercise, each followed by two minutes of recovery, sandwiched between a five-minute warm-up and a five-minute cool-down.
Regardless of what moves and time intervals you use, it’s important to vary your routine. As you get fitter, your body becomes more efficient – and you burn fewer calories. “Our bodies are very smart machines,” Holland said, so “we need to mix it up”.
To avoid injury and burnout, Srinath suggests incorporating HIIT into your routine two to three times a week; on other days, you can insert strength training and low-impact aerobic exercise, such as walking or swimming. Although the workout is appropriate for any age, if you’ve been diagnosed with a heart condition, you should exercise with medical supervision, Srinath said.
HIIT is an excellent choice for anyone who has time constraints and wants to optimise their long-term health – in other words, just about everyone, including beginners. No matter what your HIIT workout looks like, it will be done before you know it.