Flank fat, commonly known as “love handles,” is adipose tissue stored on the sides of the waist, extending from the bottom of the rib cage to the hips. This localized deposit is a mix of subcutaneous fat, located just beneath the skin, and deeper visceral fat surrounding internal organs. While flank fat accumulation results from consistently taking in more energy than is expended, the location of that excess energy is determined by specific biological signals. The body’s propensity to store fat in this central region involves a complex interplay of inherited tendencies and metabolic processes.
Genetic Predisposition and Body Shape
Genetic makeup establishes the blueprint for where the body preferentially stores fat during a caloric surplus. This explains why individuals consuming the same diet may gain the same weight but exhibit distinctly different body shapes. Some are genetically predisposed to store fat in the hips, thighs, and buttocks (a “pear” shape), while others accumulate fat centrally around the abdomen and flanks (an “apple” shape).
This predisposition is reflected in somatotypes, where an endomorphic body type tends toward a higher percentage of body fat and a greater propensity for central fat accumulation. Studies suggest the heritability of abdominal visceral fat, which is closely related to flank deposits, can be as high as 56%. These inherited differences are the baseline factor influencing how the body distributes excess energy.
The Influence of Hormones on Fat Storage
Hormones are chemical messengers that instruct the body on where to store energy, significantly contributing to flank fat accumulation. Cortisol and insulin are two hormones that play a major role in directing fat toward the midsection.
Sustained elevation of cortisol, the body’s primary stress hormone, results from chronic stress and poor sleep. Elevated cortisol promotes the redistribution of fat stores from the extremities to the central abdominal area. This occurs because fat cells in the abdominal region have a higher concentration of cortisol receptors.
Insulin also drives central fat storage, especially when cells become resistant to its action, known as insulin resistance. When cells fail to respond effectively, the pancreas releases excessive amounts, causing chronic hyperinsulinemia. This high circulating insulin signals midsection fat cells to store energy and actively inhibits lipolysis, the process of breaking down stored fat.
Dietary Patterns and Chronic Energy Surplus
The fundamental cause of any fat gain, including flank fat, is a chronic energy surplus—a consistent intake of more calories than the body burns. Specific dietary components, however, exacerbate the hormonal and metabolic environment favoring central fat accumulation.
Refined carbohydrates and simple sugars, such as those in processed snacks, are absorbed quickly, causing a rapid spike in blood glucose. This forces the pancreas to release a large surge of insulin, reinforcing the hyperinsulinemia that drives fat storage in the flank area. A diet high in these high-glycemic foods promotes long-term fat deposition around the waist.
Alcohol consumption contributes to central fat accumulation via its caloric content and metabolic effects. When alcohol is metabolized, the body prioritizes processing it, suppressing the oxidation of fat from other food consumed simultaneously. This “fat-sparing” effect ensures that meal fat is more likely to be stored, often directed toward the abdomen and flanks.
A sedentary lifestyle facilitates the chronic energy surplus manifesting as fat gain. Prolonged sitting reduces the activity of lipoprotein lipase, an enzyme important for lipid metabolism. This diminished physical activity lowers overall energy expenditure and reduces insulin sensitivity, creating an ideal environment for central fat accumulation.
How Aging Shifts Fat Accumulation
The natural process of aging causes a physiological shift in where fat is stored, even without changes in diet or activity. A central factor is sarcopenia, the progressive, age-related loss of skeletal muscle mass. Since muscle tissue is highly metabolically active, this loss reduces the basal metabolic rate (BMR), meaning the body burns fewer calories at rest. This lower resting energy expenditure promotes fat accumulation for a given caloric intake.
Changes in sex hormones further dictate the new fat distribution pattern. In women, the sharp decline in estrogen during and after menopause alters fat storage preference. Because estrogen typically directs fat toward the lower body, its reduction causes fat to shift toward the trunk and flanks, contributing to an “apple” shape. Men also experience a gradual decline in testosterone, which supports lean muscle mass, favoring increased visceral and central fat storage.