The question of how many calories the body burns during menstruation is common, often fueled by noticeable changes in appetite and energy levels throughout the monthly cycle. Menstruation is the shedding of the uterine lining, signaling the end of a cycle when pregnancy has not occurred. Understanding the true energy cost requires examining the subtle but significant shifts in the body’s baseline metabolism that occur over the full month, not just during the days of bleeding. The perception of increased energy expenditure during the period often misinterprets hormonal effects on energy intake and changes in resting caloric needs in the preceding weeks.
Basal Metabolic Rate Fluctuations Across the Menstrual Cycle
The energy expenditure of the human body at rest is measured by the Basal Metabolic Rate (BMR), which accounts for the vast majority of daily calorie burn, fueling processes like breathing and circulation. This baseline rate shifts in response to fluctuating reproductive hormones, providing the mechanism for caloric changes in the cycle. The most significant metabolic change happens not during the period itself, but in the week or two leading up to it, during the luteal phase.
Following ovulation, the hormone progesterone begins to rise, directly linked to a slight but measurable elevation in BMR. Progesterone is thermogenic, meaning it slightly raises the core body temperature, which requires the body to expend more energy. Studies indicate that BMR can increase by approximately 5% to 10% during this late phase compared to the follicular phase. This elevation in resting metabolism translates to an increased caloric need, often falling within the range of an extra 100 to 300 calories per day.
This metabolic boost is a temporary physiological event driven by hormonal signaling, preparing the body for a potential pregnancy. The BMR typically reaches its peak just before the onset of menstruation when progesterone levels are highest. Once pregnancy has not occurred, progesterone levels drop sharply, causing the BMR to return to its lower baseline level characteristic of the follicular phase. This means the body’s highest rate of calorie burn occurs before the period starts, not during it.
Direct Calorie Expenditure During the Menstrual Phase
The physiological event of menstruation, involving the shedding of the uterine lining, does not constitute a significant energy-burning activity. The actual caloric cost of bleeding and the muscular contractions known as cramps is negligible. The body does not undergo a massive metabolic spike during active bleeding that would require a substantial increase in fuel.
During the menstrual phase, BMR typically decreases from its luteal phase peak and stabilizes at the lower follicular phase levels. For some individuals, the resting metabolic rate may even drop slightly below the pre-luteal baseline before gradually rising again. The overall change in calorie burn on any given day of the period, compared to the follicular phase, is generally marginal, often less than 50 calories.
The intense feeling of discomfort from uterine contractions can create the illusion of high energy expenditure. However, the work done by the uterine muscles to expel the lining is not metabolically demanding like sustained physical exercise. The idea that the body is performing a large-scale caloric feat during the period is a common misconception, as the energy required for this process is minimal in the context of total daily expenditure.
Hormones, Appetite, and Energy Intake Changes
The noticeable feeling of increased hunger and specific food cravings experienced around the period are often confused with the body burning more calories. These changes result from hormonal shifts influencing appetite and satiety, relating to energy intake, not expenditure. The fluctuation of hormones like estrogen and progesterone directly affects the regulatory systems that control hunger.
As progesterone rises during the luteal phase, it can stimulate appetite, leading to a natural desire to consume more food. This effect is compounded by the drop in serotonin levels that often occurs in the late luteal phase just before the period begins. Serotonin is a neurotransmitter that affects mood, and its decrease can trigger cravings for energy-dense foods, particularly those high in carbohydrates and fats, which the body uses to temporarily boost mood.
The combination of a slightly elevated BMR and hormonal signals for increased food intake explains why many people report eating an extra 100 to 300 calories per day during this time. Cravings for specific items, such as chocolate or refined carbohydrates, are the body’s attempt to meet a small increase in energy demand and address chemical changes in the brain. Understanding this clarifies that the body is signaling a need for more fuel, which is a behavioral response to hormonal shifts, not solely the result of the physical act of bleeding.