Ab workouts alone won’t flatten your stomach in most cases. The layer of fat covering your midsection is what determines how flat (or not) your belly looks, and losing that fat requires burning more calories than you take in. Crunches and planks build the muscles underneath, but they don’t burn enough energy to meaningfully shrink the fat sitting on top. That said, core training does play a supporting role in how your midsection looks and functions, just not in the way most people expect.
Why Ab Exercises Don’t Burn Belly Fat
Your body doesn’t pull fat preferentially from the area you’re exercising. When you do crunches, your abdominal muscles contract and use energy, but that energy comes from your whole body’s fuel supply, not specifically from the fat wrapped around your waist. To lose fat anywhere, you need to be in a state of negative fat balance: burning more fat than you consume over a sustained period. Ab exercises simply don’t burn enough total calories to create that deficit on their own.
One 2023 study in Physiological Reports did find a modest form of localized fat loss. Overweight men who performed abdominal endurance exercises (not traditional crunches, but sustained aerobic core work) lost about 1,170 grams of trunk fat over 10 weeks, roughly 7% of their trunk fat mass. That was more trunk fat than a comparison group lost doing treadmill running, even though both groups lost similar amounts of total body fat. So there’s some evidence that working a specific area can nudge fat loss in that region. But the effect was small, and the key word is “aerobic.” These weren’t sets of sit-ups. The participants were doing continuous, heart-rate-elevating abdominal work for extended periods.
The practical takeaway: a few sets of crunches after your workout won’t produce a visible change in belly fat. The calorie burn is too low and the duration too short.
What Actually Reduces Belly Fat
A caloric deficit is the single most reliable way to lose fat from your midsection. A landmark trial known as CALERIE compared people who cut calories through diet alone versus diet plus exercise, both targeting a 25% energy deficit. After six months, both groups lost approximately 10% of their body weight, 24% of their total fat mass, and 27% of their deep abdominal (visceral) fat. The results were nearly identical between groups. When the calorie deficit was the same, adding exercise didn’t change where or how much fat people lost.
This doesn’t mean exercise is useless. It means the deficit is what drives fat loss, and you can create that deficit through eating less, moving more, or both. Exercise has clear benefits for heart health, insulin sensitivity, and muscle preservation while losing weight. But if your only goal is a flatter stomach, your diet matters more than any specific workout.
Cardio vs. Strength Training for Belly Fat
Not all exercise affects abdominal fat equally. A study comparing aerobic training (like jogging or cycling) to resistance training in overweight adults found striking differences. Aerobic exercise reduced visceral fat by about 16 square centimeters, subcutaneous abdominal fat by 25 square centimeters, and also improved liver fat levels. Resistance training, by contrast, reduced subcutaneous abdominal fat only slightly and didn’t significantly reduce visceral fat at all.
Visceral fat is the deeper fat packed around your organs. It’s metabolically active, linked to higher disease risk, and tends to push the belly outward. Subcutaneous fat is the softer layer you can pinch. Aerobic exercise appears to be more effective at clearing both types, making it the better choice if your primary concern is reducing your waistline. That said, resistance training preserves muscle mass during weight loss and raises your resting metabolic rate, so combining both with a caloric deficit is the most effective overall strategy.
How Ab Training Helps Your Appearance
Even though ab exercises won’t burn the fat away, they do contribute to a flatter-looking midsection in two important ways.
The first involves your deepest abdominal muscle, the transverse abdominis. This muscle wraps horizontally around your torso like a natural corset. When it contracts, your belly pulls slightly inward. Exercises that train this muscle, like hollow holds, dead bugs, and the “drawing in” maneuver (pulling your navel toward your spine), can improve your resting abdominal tone over time. A well-trained transverse abdominis holds everything in more tightly, even when you’re just standing around.
The second involves posture. An anterior pelvic tilt, where your pelvis tips forward and your lower back arches excessively, pushes the stomach outward and makes it appear larger than it is. Weak core muscles contribute to this tilt. Strengthening your abs (along with your glutes) can help correct pelvic alignment, pulling your belly back into a more neutral position. For some people, this postural correction alone makes a noticeable difference in how flat their stomach looks.
Body Fat Thresholds for Visible Abs
If your goal goes beyond “flat” and into visible six-pack territory, the limiting factor is almost always body fat percentage, not muscle size. For men, abs typically become visible somewhere between 10 and 14% body fat. At 15 to 19%, you might see faint upper ab outlines but little definition below the navel. Above 20%, abdominal muscles are generally not visible at all.
For women, the thresholds are higher because women carry more essential body fat. Visible abs typically appear below about 20% body fat, though genetics and fat distribution play a significant role. Some women see definition at 22%, while others need to get closer to 17%. It’s worth noting that very low body fat percentages (below 14% for women) can disrupt hormone function and menstrual cycles, so chasing extreme leanness comes with real trade-offs.
Building larger abdominal muscles through training does help them show through at slightly higher body fat levels. But no amount of muscle size will overcome a thick layer of subcutaneous fat. The muscle has to be there and the fat has to be low enough to reveal it.
A Practical Approach
If you want a flatter stomach, prioritize a moderate caloric deficit through your diet. Add regular cardio (even brisk walking counts) to increase your total energy expenditure and target visceral fat. Include ab training two to three times per week, focusing especially on exercises that engage the deep transverse abdominis: planks, dead bugs, Pallof presses, and hollow body holds. These won’t melt the fat, but they’ll improve your posture, tighten your abdominal wall, and ensure the muscles underneath look defined once the fat comes down.
The stomach-flattening effect people hope to get from crunches actually comes from the combination of all three. No single piece works alone, and the one most people skip, the dietary component, is the one that matters most.