About the same. Across 54 trials that compared them head to head, interval training and steady cardio changed fat mass and lean mass by the same amount; intervals took far less time each week, but harder effort3.
The bigger surprise in the same data is how little either one moved fat on its own. Here is what was compared, what the numbers say, and where a newer review sees a small edge for intervals.
What was compared
Two ways of doing cardio, defined by how the effort is spread out:
- Steady cardio (researchers call it moderate-intensity continuous training): one longer bout at a moderate, even effort, below about 80% of peak heart rate or aerobic capacity.
- Interval training: several short, hard bouts with easier recovery in between. HIIT (high-intensity interval training) uses hard efforts above about 80%; sprint interval training uses all-out sprints3.
The main source is a 2021 meta-analysis, a study that pools many studies into one answer. It was preregistered, meaning the plan was published before the analysis3. Every included study was a randomised trial that compared the two directly and measured body composition with a validated method such as a DXA scan.
| What | Number |
|---|---|
| Trials analysed | 54 |
| Median age | 30 years |
| Median BMI | 28.3 |
| Untrained groups | 97% |
| Median length | 12 weeks |
| Groups with a calorie deficit | 5% (3 of 60) |
| Interval groups that were HIIT | 75% (the rest sprint intervals) |
In plain terms: mostly untrained adults with overweight, about three months, and almost no diet changes. This is cardio alone.
What the studies found
Head to head, no difference. For fat mass, the difference between intervals and steady cardio was a Hedges' g of −0.02 (95% confidence interval −0.07 to 0.04)3. Hedges' g is a standardised effect size; 0.2 is usually called small, so −0.02 is a tenth of small. The confidence interval is the range the true value most likely sits in, and it is narrow and centred on zero. The authors rated the certainty of this result as high. Body fat percentage showed the same (g −0.04).
Lean mass, no difference either. Fat-free mass differed by g −0.0004 (−0.05 to 0.05), also rated high certainty3. Neither style ate into muscle more than the other.
Time is where they differ. The median weekly dose was about 28 minutes for intervals and 120 minutes for steady cardio3. In the authors' words, interval training "requires less time but more effort".
Median weekly exercise time in the trials, by style · min/week
Sticking with it was the same. People completed about 89% of sessions in both styles; dropouts were 16% with intervals and 20% with steady cardio3. The idea that hard intervals are too unpleasant to keep up did not show in these trials.
An earlier 2017 review of 13 trials in adults aged 18 to 45 with overweight or obesity reached the same verdict: both reduced whole-body fat mass, with no significant difference, and HIIT needed about 40% less training time1.
In plain terms: same fat, same lean mass, same adherence. Intervals trade minutes for effort.
The part most people miss: how small the effect is
Against groups that did no exercise, both styles lowered fat mass, but only a little. Intervals averaged −0.20 kg (95% CI −0.34 to −0.06) and steady cardio −0.25 kg (−0.39 to −0.11) over the trials' typical 12 weeks3. The authors called these reductions "unlikely to be clinically or aesthetically meaningful".
Change in fat mass against no exercise, by style · kg
Their explanation is dose. A median of 28 or 120 minutes a week does not use much energy, and people may eat a little more or move a little less the rest of the day to make up for it3. They concluded that it is "much easier to create an energy deficit from dietary restriction", and that exercise is an important partner to it, helping keep lean mass while eating less.
That matches what the fitness tracker rarely says: the energy used by a workout is smaller than it feels (see why exercise burns fewer calories than the tracker says). How eating and moving add up is in calories in, calories out. Any deficit has limits: the calculator on this site caps it at 35% of TDEE and never sets a target below its calorie floor (1,500 kcal for men, 1,200 kcal for women on the standard setting), as how big a calorie deficit should be explains.
In plain terms: the choice between intervals and steady cardio matters far less than the choice to pair either with the way you eat.
What about the afterburn?
The popular argument for HIIT is the "afterburn": extra oxygen use in the hours after a hard session, called excess post-exercise oxygen consumption. The 2021 authors address it directly: the extra energy it adds is modest and "unlikely to be of practical meaningfulness from a fat loss standpoint"3. Their pooled result, no difference in fat mass, is consistent with that.
Where a newer review sees an edge
A 2024 umbrella review, a review of reviews, pooled 79 randomised trials of apparently healthy adults from 16 earlier meta-analyses4. Against steady cardio, interval training lowered body fat percentage by an extra 0.77 points (95% CI −1.22 to −0.32) across 40 trials. For fat mass in kilograms and every other outcome, there was no significant difference between the two. The body fat edge was larger in trials lasting 12 weeks or more (−1.10 points) and in people with overweight or obesity (−0.74), and the authors concluded that the findings support interval training for reducing body fat4.
So the two big analyses agree more than they disagree. One sees a trivial difference; the other sees a small difference in one measure and none in the rest. Most of the reviews it pooled were rated low or critically low in quality, which the authors flag as a limit4.
For fat around the organs, a 2018 meta-analysis of 39 HIIT studies (617 people) found HIIT reduced total, abdominal and visceral fat, with running more effective than cycling2. That review looked at HIIT on its own, not HIIT against steady cardio. Whether cardio of any kind beats lifting for fat is a separate question, covered in our article on cardio or weights for fat loss.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Wewege et al., *Obes Rev*1 | 13 trials, adults 18 to 45 with overweight or obesity | Both lowered fat mass; no significant difference; HIIT about 40% less time | 2017 |
| Maillard et al., *Sports Med*2 | 39 studies, 617 adults, HIIT only | HIIT lowered total, abdominal and visceral fat mass | 2018 |
| Steele et al., *Sports*3 | 54 trials, mostly untrained adults, median 12 weeks | Fat mass difference trivial (g −0.02), high certainty; 28 vs 120 min a week | 2021 |
| Poon et al., *Sports Med*4 | Umbrella review, 79 trials, healthy adults | Intervals −0.77 points body fat % vs steady; no difference in fat mass | 2024 |
| Deng et al., *BMC Sports Sci Med Rehabil*5 | 18 trials, adults with obesity, 8 to 16 weeks | HIIT of 75+ min a week ranked first for body fat % vs control | 2026 |
Limits worth knowing
- Almost no diets. Only 3 of 60 groups in the 2021 analysis ate less, so it cannot say whether one style works better alongside a diet3.
- Almost no lifting. Only one group added weight training.
- Who. Mostly untrained, younger to middle-aged adults with overweight; few athletes, few older adults.
- Short. A median of 12 weeks.
- Not matched for work. In 57% of groups the two styles were not matched for total work, so "same fat" partly reflects different amounts of exercise.
- Review quality. Most reviews in the 2024 umbrella were rated low or critically low4.
- Abstract only for the reviews from 2017, 2018 and 2026. The 2021 analysis reports no funding.
Latest research
The newest study we opened is a 2026 network meta-analysis of 18 trials lasting 8 to 16 weeks in adults with obesity5. Against no exercise, HIIT of at least 75 minutes a week lowered body fat percentage by about 3 points and ranked first for that outcome; it also appeared to lower BMI and body weight more than most other regimens compared. The authors rate the evidence moderate to low certainty and describe HIIT as "a time-efficient option for modest fat loss", with steady cardio of at least 150 minutes a week as an alternative. We read its abstract only. It does not overturn the 2021 finding; it adds that the weekly dose matters within each style.
The short version
- Head to head, intervals and steady cardio changed fat mass and lean mass by the same amount.
- Intervals took about 28 minutes a week against 120, with harder effort.
- Adherence was the same, about 89% of sessions.
- Either style alone moved fat mass by only about a quarter of a kilogram on average in three months.
- The style that gets done matters more than the style on paper.
Educational overview only — not medical advice.
