Maintenance calories, often referred to as Total Daily Energy Expenditure (TDEE), represent the number of calories your body burns in a 24-hour period while maintaining a stable weight. This energy expenditure is not a fixed number but is a dynamic figure that shifts due to internal and external factors. TDEE is the sum of the Basal Metabolic Rate (BMR), the energy used for physical activity, and the Thermic Effect of Food (TEF). Since these components are subject to change, the maintenance calorie requirement also changes. The body continually tries to achieve energy balance, meaning calories consumed must equal calories burned to keep weight stable.
The Impact of Body Mass and Composition Shifts
The most fundamental change that alters maintenance calories is a shift in overall body mass. A larger body requires more energy, and the Basal Metabolic Rate (BMR), which accounts for 60% to 75% of total daily calorie burn, is directly correlated with body weight. When weight is lost, the amount of tissue that needs to be supported decreases, causing a corresponding drop in BMR.
A change in body composition—the ratio of fat mass to lean muscle mass—can have a significant effect even if the scale weight remains the same. Muscle tissue is more metabolically active than fat tissue, meaning it burns more calories at rest. Each pound of muscle burns approximately 6 to 10 calories per day, whereas fat burns only a fraction of that amount.
A person who loses muscle mass, which can happen with age or insufficient protein intake during dieting, will see their BMR decrease. Conversely, maintaining lean muscle mass is linked to preserving a higher BMR. Two people with the exact same weight and height may have different maintenance needs based on their muscle-to-fat ratio. Losing weight causes a drop in BMR because the body is smaller, but the composition of that weight loss determines the magnitude of the metabolic shift.
Fluctuations in Physical Activity and Energy Output
Daily energy expenditure is highly dependent on physical activity, which is split into two categories: Exercise Activity Thermogenesis (EAT) and Non-Exercise Activity Thermogenesis (NEAT). EAT refers to structured, planned exercise like running or weightlifting.
NEAT encompasses all the energy expended for activities that are not sleeping, eating, or formal exercise, including walking, fidgeting, maintaining posture, and typing. For most people, NEAT is a highly variable component of TDEE and changes significantly from day to day.
NEAT has the power to alter maintenance needs substantially. A person with a desk job who spends a weekend doing yard work or standing all day will naturally have a higher TDEE for those days than a sedentary day. Even small movements, like fidgeting, can increase energy expenditure above resting levels by 20% to 40%.
Adaptive Thermogenesis and Metabolic Rate Changes
A more complex factor influencing maintenance calories is adaptive thermogenesis. This occurs when the body responds to prolonged calorie restriction by reducing its energy expenditure beyond the reduction caused by the loss of body mass. This adaptation makes it harder to continue losing weight or maintain a new, lower weight.
Adaptive thermogenesis involves changes in hormone levels and nervous system activity, which suppress resting energy expenditure. Prolonged caloric deficits lead to decreased levels of the hormone leptin, which signals energy status to the brain. This drop in leptin triggers a reduction in the activity of the sympathetic nervous system and the hypothalamic-pituitary-thyroid (HPT) axis.
The resulting depressed HPT axis activity leads to lower concentrations of bioactive thyroid hormones, which determine the metabolic rate. This hormonal cascade reduces the energy required for basic functions, lowering the BMR and subsequently the TDEE. After significant weight loss, the body may require hundreds fewer calories than predicted by standard formulas to maintain the new weight because the body has become more efficient.
Practical Strategies for Tracking and Adjustment
Since maintenance calories are dynamic, a fixed number calculated by an online tool should only be treated as a starting point. The most accurate approach relies on using real-world data by consistently tracking food intake and monitoring weight trends over several weeks. Daily weighing provides data points, and monitoring the weekly average weight helps smooth out daily fluctuations caused by factors like water retention.
If weight consistently decreases over a two- to three-week period while eating a specific calorie target, that target is below the current maintenance level. Conversely, if weight consistently increases, the target is above maintenance, and a calorie reduction is necessary. Adjustments should be made slowly, adding or subtracting small amounts, typically 50 to 100 calories at a time, and then observing the weight trend for another two weeks.
For individuals coming out of a period of weight loss, calories should be increased gradually, perhaps by 200 calories per day every few weeks. This allows the body time to adapt and find the true new maintenance level.