Core exercises alone will not flatten your stomach. They strengthen the muscles underneath your abdominal fat, but a visible change in how flat your belly looks depends primarily on reducing overall body fat through a calorie deficit. That said, core training does play a supporting role, and the full picture is more nuanced than a simple yes or no.
Why Crunches Don’t Burn Belly Fat
The idea that you can burn fat from a specific body part by exercising that area is called spot reduction, and for decades, the scientific consensus has been that it doesn’t work in any meaningful way. A recent controlled trial did find that abdominal endurance exercise reduced trunk fat slightly more than treadmill running, about 700 grams (roughly 1.5 pounds) over the study period. But even in that study, the overall fat loss was modest, and participants still needed to be in a calorie deficit to see results.
The core problem is energy math. Core exercises are low-intensity work. A circuit-style workout registers at roughly 2.0 METs (a measure of energy expenditure), which is less intense than slow walking at 3.0 METs. Brisk walking burns nearly three times more energy than a typical floor-based ab routine. Running at a moderate pace hits 8 to 10 METs. So if your goal is to burn enough calories to lose the fat covering your abs, crunches and planks are among the least efficient tools available.
Body Fat Percentage Is What Makes Abs Visible
Your abdominal muscles are already there. Everyone has them. What determines whether you can see them, and whether your stomach looks flat, is how much fat sits on top. For men, a visible six-pack typically requires a body fat percentage in the 10 to 14 percent range. At 15 to 19 percent, you’re unlikely to see much ab definition. Above 20 percent, the midsection will look soft regardless of how strong your core is.
Women naturally carry more body fat and tend to need slightly higher percentages to maintain healthy hormone function. But the same principle applies: visible abdominal definition and a flat appearance come from reducing the layer of fat between your skin and your muscles, not from building bigger muscles underneath it.
What Core Exercises Actually Do
Core training has real benefits. It just doesn’t do what most people hope it will. Strong abdominal muscles protect your spine, improve balance, and help you transfer force during everyday movements like lifting, bending, and twisting. A well-trained core also improves your posture, which can make your stomach appear flatter even without fat loss.
One muscle in particular matters here: the transversus abdominis, which sits deep beneath your outer abs and wraps horizontally around your torso like a corset. When this muscle is strong and properly activated, it pulls your abdominal wall inward and creates a tighter midsection. The “stomach vacuum” exercise, where you slowly draw your belly button toward your spine while breathing normally, specifically targets this muscle. It won’t burn fat, but it can train your deep core to hold your abdomen in more firmly, which creates a visually flatter profile.
Clinical research on core stability training confirms that the transversus abdominis acts as a natural corset, increasing spinal stiffness for stability and tightening the muscles around the waist. For people who have trouble engaging their deep core, regularly practicing stomach vacuums can help activate these muscles during other exercises too.
What Actually Flattens Your Stomach
Reducing body fat requires eating fewer calories than you burn, consistently, over weeks and months. Exercise helps by increasing the “calories out” side of that equation, but the type of exercise matters more than most people realize. Higher-intensity activities like running, cycling, swimming, and resistance training burn far more energy per minute than ab-focused work. Heavy compound movements like squats and deadlifts at 70 percent or more of your max actually activate core muscles at levels similar to, or greater than, isolation exercises like planks and side bridges. So you get core strengthening as a bonus while burning significantly more calories.
That said, isolated core exercises do produce higher peak muscle activation in the rectus abdominis (your “six-pack” muscle) compared to lunges and other integrated movements. If your goal is specifically to build thicker, more defined abs for when body fat is low enough to reveal them, targeted core work has value. It just isn’t the path to a flat stomach on its own.
When Core Exercises Can Make Things Worse
There’s one situation where standard ab exercises can actually make your belly look less flat. Diastasis recti is a separation of the left and right sides of your abdominal muscles, common after pregnancy but also seen in men. If you have it, your belly may stick out or bulge even at a healthy weight. The telltale sign is a visible pooch above or below your belly button that doesn’t go away with weight loss.
Crunches, sit-ups, planks, push-ups, and double leg lifts can all worsen diastasis recti by pushing the abdominal wall outward. Any movement that causes your abs to dome or cone should be avoided. Instead, modified exercises that gently draw the abdominal wall inward, like the stomach vacuum, are typically recommended to help close the gap.
A Realistic Approach
The most effective strategy combines three things. First, a moderate calorie deficit through diet, because you cannot out-exercise a surplus no matter what movements you choose. Second, regular cardiovascular or resistance training to increase calorie burn and preserve muscle mass while losing fat. Third, core-specific work two to three times per week to strengthen the muscles you’ll eventually reveal and to improve the postural tone that pulls your midsection in.
One clinical trial on core exercise in prediabetic women found improvements in several body measurements, but waist circumference did not significantly change from core training alone. This reinforces what the broader evidence shows: core exercises reshape and strengthen the muscle beneath the fat, but the fat itself responds to your overall energy balance, not to which muscles you’re working.