The shape of your buttocks is determined by a combination of bone structure, muscle mass, fat distribution, and hormones. While no shape is inherently “better” than another, the way fat and muscle sit on your frame can offer real clues about your hormonal balance, metabolic health, and how your body may change with age.
The Four Common Buttock Shapes
Most buttocks fall into one of four general categories: square (or H-shape), round (or O-shape), heart (or A-shape), and inverted V. These aren’t medical diagnoses. They’re visual patterns created by where your body places fat and how wide your pelvis is relative to your waist.
If the line from your hip bone to your outer thigh is more or less straight, you likely have a square shape. This is common in people with prominent, high hip bones or minimal fat padding around the sides. Some people with square shapes notice “hip dips,” those small inward curves between the hip bone and thigh. A round shape indicates fairly even fat distribution across the entire gluteal area, with fullness in the center and sides. The heart shape (sometimes called pear) is widest at the lower portion of the buttocks and tapers toward the waist, reflecting fat storage concentrated in the lower glutes and upper thighs. The inverted V shape is narrower at the bottom and wider at the top, often seen when there’s less fat in the lower glutes and more volume near the waist or upper hips.
What Actually Determines Your Shape
Three things work together to create your buttock shape: your skeleton, your muscles, and your fat.
Your pelvis provides the frame. The ilium, the largest pelvic bone, is a broad, curved bone that wraps around the sides of your hips. The width and angle of this bone, along with the angle of your femur (thighbone), set the underlying silhouette before any soft tissue is added. Wider-set hip bones tend to create a rounder or heart-shaped base, while a narrower pelvis leans toward a square or V shape. This is genetic and not something exercise or diet changes.
On top of that skeleton sits the gluteus maximus, the single largest muscle in the human body and the primary contributor to surface contour. The gluteus medius and minimus sit underneath and along the sides, filling out the upper and lateral portions of the buttocks. When these muscles are well developed, they add roundness and lift. When they’re underdeveloped or have lost mass, the shape deflates or flattens, especially in the lower portion.
Finally, subcutaneous fat fills in the remaining contour. Where your body deposits that fat, whether it favors your lower glutes, your flanks, or your upper hips, is largely driven by hormones and genetics.
How Hormones Direct Fat Storage
Estrogen is the primary hormone responsible for directing fat to the buttocks and thighs. It activates specific receptors in gluteal and femoral fat cells that promote fat uptake and storage in those areas. This is why premenopausal women tend to carry more fat in the hips, thighs, and buttocks rather than the abdomen.
When estrogen levels drop, as they do during and after menopause, the ratio of androgens (like testosterone) to estrogen shifts. Androgens promote fat storage in the abdomen instead. The result is a visible change in body shape: fat migrates away from the hips and thighs and accumulates around the midsection. A person whose buttocks were once round or heart-shaped may notice them becoming flatter or more V-shaped over time, while their waistline thickens. This isn’t just cosmetic. It reflects a fundamental shift in where your body is storing energy, and abdominal fat carries significantly more metabolic risk than gluteal fat.
Why Gluteal Fat Is Metabolically Protective
Fat stored in the buttocks and thighs behaves differently from fat stored around the organs in your abdomen. Research published in Frontiers in Nutrition identified three key reasons why gluteal fat is protective against insulin resistance and cardiovascular disease.
First, fat cells in the buttocks are highly resistant to being broken down. They release stored fat into the bloodstream at a much slower rate than abdominal fat cells. Abdominal fat cells are roughly 40 times more responsive to the chemical signals that trigger fat release. This matters because when fat floods the bloodstream too quickly, it can damage blood vessels and interfere with insulin signaling.
Second, gluteal fat acts as a buffer. It has a high capacity for absorbing excess fatty acids from the blood, thanks to elevated levels of an enzyme that pulls circulating fats into storage. By soaking up those extra lipids, it prevents them from spilling over into abdominal fat or accumulating in the liver and muscles, where they cause inflammation and metabolic damage.
Third, gluteal fat releases higher levels of adiponectin, a hormone that improves insulin sensitivity and reduces inflammation. People with more hip and thigh fat tend to have higher adiponectin levels, while people with more abdominal fat have lower levels. At the same time, gluteal fat produces less of the inflammatory compounds that visceral (deep belly) fat pumps out. One inflammatory marker is found at five times higher levels in visceral fat compared to subcutaneous fat in obese individuals.
What Your Shape May Signal About Health
An inverted V shape or a noticeable shift from a rounder shape to a flatter, top-heavy one can reflect declining estrogen, reduced muscle mass, or both. Research presented by the Radiological Society of North America found that changes in the shape of the gluteus maximus are significantly associated with type 2 diabetes. In men with type 2 diabetes, the muscle showed shrinkage. In women, the muscle appeared enlarged, likely due to fat infiltrating the muscle tissue itself. These shape changes may reflect early functional decline and metabolic compromise.
Your waist-to-hip ratio offers a more precise health signal than shape alone. For women, a ratio above 0.85 is considered abnormal; for men, the threshold is 0.90. A higher ratio means proportionally more fat is stored around the waist compared to the hips, which correlates with increased risk of heart disease, type 2 diabetes, and metabolic syndrome. If your buttock shape suggests a narrow lower body relative to your midsection, tracking this ratio over time gives you useful information.
How Shape Changes With Age
Buttock shape is not static. Starting around age 30, skeletal muscle mass declines at a rate of 3 to 8 percent per decade. Women develop this age-related muscle loss earlier than men, and the decline accelerates after menopause. The gluteus maximus, being a large muscle that many people underuse in sedentary daily life, is particularly vulnerable. As it shrinks, the buttocks lose their lift and projection.
Simultaneously, the hormonal shifts of menopause redistribute fat away from the gluteal-femoral region and toward the abdomen. Postmenopausal women tend to have higher total body fat, a higher fat percentage overall, and a clear shift toward central fat accumulation. The combination of less muscle and less gluteal fat means the buttocks flatten and lose volume, while the waist thickens. This is the transition many people notice as moving from a heart or round shape toward a squarer or V-shaped profile.
Resistance training that targets the glutes can counteract some of this change by maintaining or building muscle mass, which preserves both shape and the metabolic benefits of keeping the gluteal muscles active. The underlying bone structure won’t change, but the ratio of muscle to fat on that frame is something you have meaningful influence over at any age.