HIIT: do you really lose more fat than with traditional cardio?

Does high-intensity interval training (HIIT) melt more fat than conventional cardio? It causes fat loss, including belly fat, roughly as much as continuous moderate-intensity cardio, in significantly less time. Its advantage on fat itself is small, and not all studies find it. The famous "afterburn" effect accounts for almost none of it. Here is what twenty-two studies measure.

As much fat lost, in less time

In trials, HIIT (short, intense efforts interspersed with recovery, sometimes sprints lasting a few tens of seconds) is generally compared to continuous moderate-intensity endurance, steady-pace jogging or cycling. A 2017 meta-analysis in overweight adults finds that both lower fat mass and waist circumference, with no difference between them for any body composition measure, but with about 40% less training time for HIIT. Another meta-analysis, from 2022, reaches the same finding for liver fat: a moderate drop with both, with no difference between them.

Other reviews lean slightly toward interval training. The one from 2019, titled "is high-intensity interval training the magic bullet?", finds 28.5% more fat mass lost with interval training, especially with sprints. A 2023 meta-analysis in young and middle-aged adults gives an advantage to HIIT for waist circumference and fat percentage. And compared to a non-exercising group, another 2023 meta-analysis quantifies the effect of HIIT at −1.86 kg of fat mass, −1.53 percentage points of fat, and +0.51 kg of lean mass.

What about belly fat?

A 2018 meta-analysis finds a drop in total, abdominal, and visceral fat (the fat surrounding organs) with HIIT. Compared to continuous cardio, trials are divided. In young obese women, for equal work, visceral fat dropped as much with HIIT (−9.1 cm²) as with continuous training (−9.2 cm²). In overweight postmenopausal women, weight and total fat dropped in all groups, but abdominal and visceral fat dropped significantly only with HIIT, with or without weight training; added weight training did not cause more fat loss, but increased the muscle share.

Even at estimated equal energy expenditure, cycling sprints in overweight young women caused total fat mass to drop by 3.6%, versus 0.6% with continuous cycling, and belly fat by 6.6% versus 0.7%, without weight changing. The weight on the scale can therefore stay stable while fat melts: it is body composition that you need to track, not just weight.

In this 2018 trial, very short sprints caused as much visceral fat loss as longer interval training, with the difference not being significant, using less time and a lower training load. Subcutaneous belly fat, however, dropped less with sprints. Less is therefore not always just as good.

How many sessions, and which exercise?

In women, a 2020 meta-analysis finds clearer effects before menopause, and more effective programs beyond 8 weeks at three sessions per week. On exercise choice, reviews contradict each other: the 2018 one finds running more effective than cycling for total and visceral fat, whereas the 2020 one and the 2023 one give the advantage to cycling. Pick the one you will stick to.

Short programs are enough to see an effect in healthy people: in active women, six weeks of running sprints at three sessions per week caused fat mass to drop by 8% (from 15.1 to 13.9 kg) and waist circumference by 3.5%, while lean mass increased by 1.3%. In overweight young men, twelve weeks of HIIT without any diet caused waist circumference, BMI, and fat percentage to drop.

The "afterburn" effect: a stubborn myth

We read everywhere that HIIT burns calories for hours after the session. In 12 men, for equal total work, post-exercise oxygen consumption (EPOC) was neither stronger nor longer after intervals than after continuous exercise. What changes with training is slightly the ability to burn fat during exercise: a 2022 meta-analysis finds +0.08 g per minute after weeks of interval training, and barely 0.03 g per minute more than with continuous cardio.

A 12-week trial in obese individuals points in the same direction: HIIT and continuous cardio matched for energy expenditure produced the same drops in weight, waist circumference, and fat, and even a HIIT session matched for half the expenditure did just as well.

And appetite after the session?

Intense effort suppresses appetite slightly in the moment. In a 2013 trial, appetite and the hunger hormone (ghrelin) dropped during exercise, more so with short sprints than with endurance, but the amount eaten afterward did not change. Result: over 24 hours, only endurance created a true deficit (15.7% less than without exercise), because it had burned more during the session; short sprints did not. In overweight men, hunger dropped after HIIT, and the fats eaten afterward decreased by 16%, whereas they increased by 38% after moderate-intensity intervals.

The takeaway: a few-minute session does not offset a heavier meal. It is the weekly balance that counts; for cardio done on an empty stomach, see fasted cardio, and for everything that actually causes weight loss, weight loss: what really works.

In summary

In practice: choose the cardio you will do regularly, interval training if you are short on time, continuous if you prefer, and set your deficit with the calorie calculator. To track what really matters, your fat and not just your weight, use the body fat calculator. And for endurance itself, see how to improve your cardio.

Every figure in this article comes from a study you can open: the underlined mentions lead to the summary of the work it is taken from, written solely from the abstract. Trials are often small and short, and HIIT protocols vary greatly from one study to another. Informative content, which does not replace the advice of a healthcare professional.