Why Am I Losing Weight in My Buttocks?

Buttock volume depends on two tissues stacked together: a layer of subcutaneous fat and the gluteal muscles underneath. Losing either one makes the area look flatter, and most people experiencing this are losing some of both. The causes span a wide range, from hormonal changes and normal aging to crash dieting, prolonged sitting, certain medications, and a few medical conditions that specifically target fat or muscle in the gluteal region.

What Your Buttocks Are Actually Made Of

The shape and fullness of your backside comes from a surprisingly complex arrangement of tissue. Beneath the skin sits a series of subcutaneous fat compartments. Anatomical dissection studies have identified at least seven distinct deep fat compartments in the gluteal region, grouped into medial, central, and lateral clusters.¹ These compartments don’t all behave identically; some gain or lose fat faster than others depending on your hormones, genetics, and age.

Underneath all that fat sits the gluteus maximus, one of the largest and most powerful muscles in the human body, along with the gluteus medius and minimus. Together these muscles provide the rounded contour people associate with a full backside. When you lose volume back there, the culprit is usually fat shrinking, muscle wasting, or both happening at once. Understanding which one is driving the change matters because the solutions are different.

Hormones and Fat Redistribution

Estrogen is the single biggest reason women tend to carry more fat in the hips, thighs, and buttocks before midlife. The hormone actively directs fat storage toward subcutaneous deposits in the lower body while limiting fat accumulation around the organs.² This pattern is sometimes called a “pear-shaped” distribution, and it’s not just cosmetic. Subcutaneous fat in the lower body is metabolically less harmful than visceral fat packed around the abdomen.

When estrogen levels drop during perimenopause and menopause, that protective pattern reverses. Fat migrates away from the buttocks, hips, and thighs and relocates to the abdomen, creating what’s often described as an “apple shape.” Research estimates that up to 90% of perimenopausal women experience a meaningful increase in body fat percentage alongside this redistribution, with the buttocks visibly flattening as fat shifts upward.³ If you’re in your 40s or 50s and notice your pants fitting differently despite the scale not changing much, this hormonal shift is a very likely explanation.

Men experience something analogous but less dramatic. Testosterone gradually declines with age, and because testosterone helps maintain muscle mass and influences where fat is stored, lower levels can contribute to reduced gluteal fullness over time. The effect is less sudden than menopause but follows a similar direction: less muscle support, less regional fat, a flatter profile.

Age-Related Muscle Loss

Even without hormonal upheaval, aging itself steadily chips away at muscle mass throughout the body, and the gluteal muscles are no exception. Research on hip fracture patients found that noticeable muscle decline begins around age 61, with a sharp acceleration after 75.⁴ That accelerated phase is especially relevant for the buttocks because gluteal muscles are large and heavily relied upon for walking, climbing stairs, and standing up from a chair. When they shrink, you feel it and see it.

Part of what makes this worse is that aging muscle doesn’t just get smaller; it gets infiltrated by fat. Studies using imaging to measure pelvic muscles have found that both muscle size and the amount of fat marbled within the muscle tissue correlate with age.⁵ This fat-within-muscle phenomenon, sometimes called myosteatosis, means the muscle looks bulkier on a scan than it actually performs. Your gluteal muscles can appear to maintain some volume while steadily losing their ability to generate force or hold shape.

Research into the cellular machinery behind this process has pointed to mesenchymal progenitor cells, which normally help maintain healthy muscle fibers. As these cells age, they become more prone to turning into fat cells instead of supporting muscle. In animal studies, reversing this switch actually reversed sarcopenic changes, suggesting that age-related gluteal wasting is not simply inevitable wear and tear but a specific biological process that might eventually be treatable.⁶

The Sedentary Trap

You don’t need to be elderly to lose gluteal volume. Spending most of your day sitting is remarkably effective at shrinking the muscles back there, even if you’re otherwise healthy. Bedrest studies have shown that just five weeks of inactivity produces measurable atrophy in the gluteal region, along with more severe wasting in the thigh and calf.⁷ The gluteal extensors lost around 2% of their mass in that timeframe, which sounds modest until you realize the study also found a substantial drop in hip extensor strength, suggesting the functional impact outpaces the visible shrinkage.

Outside of bedrest, a more insidious version of the same problem affects people with desk jobs. The concept of “gluteal amnesia” describes a state where the gluteal muscles stop firing properly because they’re almost never asked to do anything. Prolonged sitting keeps the hip flexors shortened and the glutes stretched in a lengthened, inactive position for hours at a time. Research on sedentary women found that this impaired neuromuscular activation of the gluteal muscles contributed to low back pain and functional disability, and that targeted glute exercises significantly improved both strength and symptoms.⁸ So if your job chains you to a chair eight hours a day, your gluteal muscles are slowly atrophying whether you realize it or not.

Dieting and Caloric Deficits

Losing weight through dieting almost always means losing some muscle along with fat, and the gluteal region gets hit from both sides. The fat layer thins because you’re in a caloric deficit, and the muscle layer thins because your body breaks down protein for energy when calories are scarce. How much muscle you lose depends heavily on how aggressive the diet is and how much protein you’re eating. Research has found that inadequate protein intake during a calorie-reduced diet significantly worsens the loss of lean body mass.⁹

Very low-calorie diets pose a particular risk. While they can produce rapid weight loss, concerns have been raised repeatedly about their impact on lean mass, with reviews noting that the risk of losing muscle is a real trade-off of these approaches.¹⁰ If you’ve been on a strict diet and noticed your buttocks flattening faster than other areas, it’s likely a combination of regional fat loss and muscle wasting from insufficient protein and calories. Eating enough protein and incorporating resistance training are the standard recommendations for minimizing this, though they don’t eliminate the problem entirely.

GLP-1 Medications and Rapid Weight Loss

The rise of semaglutide and tirzepatide for weight management has introduced a new and widely discussed source of gluteal volume loss. These medications are highly effective at reducing body weight, but the weight that comes off is not all fat. In clinical trials, lean soft tissue loss made up roughly a quarter to 40% of total weight lost.¹¹ That’s a substantial chunk of muscle disappearing alongside the fat.

One study specifically measured the psoas muscle (a deep hip flexor) in people taking semaglutide and found its volume dropped by about 9% over 24 weeks.¹² Interestingly, physical function didn’t decline significantly despite the muscle shrinkage, which suggests the remaining muscle was working more efficiently. Separate research confirmed that semaglutide leads to significant reductions in both fat and lean mass, though the muscle tissue that remains may actually function better at the cellular level.¹³

Still, the cosmetic result is hard to miss. People on these medications frequently report that their face, arms, and buttocks look deflated. The term “Ozempic butt” has entered the popular vocabulary for a reason. The case series data does suggest that some individuals manage to preserve or even gain lean tissue while taking these drugs, but those people are typically combining the medication with resistance exercise and high protein intake.¹¹ Without that effort, losing muscle alongside fat is the default outcome.

Medical Conditions That Target Gluteal Tissue

In rarer cases, losing volume in the buttocks points to a specific medical condition rather than lifestyle or aging. Lipodystrophy syndromes involve selective loss of fat tissue from certain parts of the body, often including the gluteal area. These conditions can be genetic or acquired and are characterized by varying degrees of fat loss combined with metabolic complications like insulin resistance and high triglycerides.¹⁴ The genetic forms involve mutations that disrupt how fat cells develop or maintain themselves, leading to selective disappearance of subcutaneous fat from specific body regions.¹⁵ If you notice dramatic fat loss in the buttocks and limbs while your midsection stays the same or grows, lipodystrophy is worth discussing with a doctor.

Cushing’s syndrome, caused by prolonged exposure to high cortisol levels, produces a different pattern: fat accumulates in the face, upper back, and abdomen while the limbs and buttocks can lose tissue. The most common cause is long-term use of glucocorticoid medications like prednisone.¹⁶ If you’ve been on corticosteroids for months and notice your body shape changing in this distinctive way, the medication is the likely culprit.

Diabetic amyotrophy is another uncommon but relevant condition. It’s a complication of type 2 diabetes that causes painful muscle weakness and wasting in the thighs, hips, and buttocks. Imaging in affected patients reveals muscle swelling and damage in the gluteal muscles bilaterally.¹⁷ Unlike simple atrophy from disuse, this condition involves nerve damage and is typically accompanied by severe pain, so it’s not something you’d mistake for normal weight loss.

Why Some People Lose It There First

If two people follow the same diet and exercise routine and one loses volume in their buttocks while the other loses it from their midsection, genetics is the most likely explanation. Body fat distribution is substantially regulated by your DNA.¹⁸ Large genome-wide studies have identified specific gene variants that influence how fat is distributed to the arms, legs, and trunk, and these effects differ between sexes. In particular, the genetic architecture governing fat distribution to the legs and trunk shows clear sex-specific patterns.¹⁹

This means your tendency to store fat in (or lose fat from) the gluteal area is partly inherited. You can’t control which fat deposits your body taps into first during weight loss. Some people will always notice their buttocks flatten before their belly shrinks, while others experience the opposite. The frustrating reality is that spot reduction of fat doesn’t work, and neither does spot preservation. Your body follows its own genetically influenced priority list when it mobilizes fat stores.

Rebuilding Gluteal Volume Through Exercise

The good news is that unlike fat distribution, muscle growth is something you have direct control over. Targeted resistance training can meaningfully increase gluteal muscle volume, even in populations recovering from surgery or dealing with age-related loss. A study comparing a dedicated gluteal strengthening program to standard care found that the exercise group gained about 7% in gluteus maximus volume over a year, compared to roughly 2% in the control group.²⁰ The gluteus medius showed similar gains.

Not all exercises are equally effective at targeting the glutes. Research measuring muscle activation during common therapeutic exercises found that single-limb squats and single-limb deadlifts produced the highest gluteus maximus activation, roughly 59% of maximum voluntary contraction. That was significantly more than lateral band walks, hip clams, or hopping exercises, which produced activation in the 27-35% range.²¹ For the gluteus medius, single-limb movements were similarly dominant. The takeaway: exercises that force one leg to bear your full body weight are far more effective at building glutes than the lighter isolation movements often featured in social media workouts.

Eccentric exercises, where you slowly lower a weight rather than lift it, appear to be especially potent. In a year-long trial following ACL reconstruction, participants who did early progressive eccentric work saw about a 21% improvement in gluteus maximus volume, compared to about 12% in the standard rehabilitation group.²² These were patients recovering from knee surgery, not healthy gym-goers, which makes the magnitude of the effect all the more striking. Slow, controlled lowering phases during squats, lunges, and hip hinges may be particularly useful for anyone trying to restore gluteal volume.

When Exercise Alone Isn’t Enough

For some people, the volume loss is primarily fat rather than muscle, and no amount of squats will replace lost subcutaneous fat. In these cases, cosmetic procedures are an option. Gluteal augmentation has evolved considerably over the decades. Gluteal implants offer predictable volume but come with surgical risks and a long recovery period. The Brazilian butt lift, which transfers a person’s own fat from one area to another, delivers more natural-looking results and doubles as body contouring for the donor site, but carries its own risks including fat embolism and the gradual reabsorption of some of the transferred fat over time.²³

Injectable fillers like poly-L-lactic acid (sold under brand names like Sculptra) have also been used off-label for gluteal volumizing with less invasive procedures, though the results are more subtle and temporary. None of these options addresses muscle atrophy, so for people losing volume from both fat and muscle, the most comprehensive approach combines resistance training with whatever aesthetic intervention fits their goals and risk tolerance. The realistic expectation is that exercise rebuilds muscle structure and strength while cosmetic approaches address fat-related fullness that training alone cannot restore.