Maintenance calories, or Total Daily Energy Expenditure (TDEE), represent the total number of calories your body burns in a 24-hour period to maintain your current weight. This value is highly unique and is not a fixed universal number. While online calculators offer a starting estimate, your body’s actual energy needs are influenced by complex, individual factors, which can sometimes result in an unexpectedly low maintenance calorie requirement.
The Role of Basal Metabolic Rate
The single largest factor determining your daily calorie burn is your Basal Metabolic Rate (BMR), which accounts for approximately 60% to 75% of your TDEE. This is the energy your body requires just to perform fundamental life-sustaining functions while at rest, such as breathing, circulating blood, and maintaining organ function. A naturally low maintenance number often begins with a lower BMR, which is primarily influenced by static, biological characteristics.
Body Size and Composition
One of the most significant determinants of BMR is body size, as a smaller body requires less total energy to maintain its mass than a larger one. Furthermore, the ratio of muscle mass to fat mass plays a major role. Muscle tissue is significantly more metabolically active than fat tissue, so a person with a lower percentage of muscle mass will inherently have a lower BMR.
Age
Age is another factor that causes a gradual decline in BMR over time, typically starting after the age of 20. This metabolic slowing is mainly attributed to the natural, progressive loss of muscle mass that occurs with aging. The main structural reasons for a low baseline calorie burn are having a smaller overall frame and a lower proportion of lean muscle mass.
Underestimating Sedentary Time
Beyond the internal, biological factors of BMR, your daily behaviors contribute substantially to your TDEE, and a low maintenance number can result from an overestimation of activity levels. Many people focus intently on Exercise Activity Thermogenesis (EAT), which is the calories burned during structured, intentional exercise. EAT often makes up a relatively small portion of the total energy expended throughout the day.
Non-Exercise Activity Thermogenesis (NEAT)
A much larger and more variable component of your TDEE is Non-Exercise Activity Thermogenesis (NEAT). This is the energy burned by all movement that is not planned exercise, including standing, walking around the house, performing chores, and fidgeting. A highly sedentary job or lifestyle, involving long periods of sitting, can severely depress your NEAT, even if you perform a dedicated workout once a day.
The difference in NEAT between two people of similar size can be hundreds of calories per day, demonstrating its significant impact on TDEE. If you spend eight hours a day seated at a desk, the caloric burn from that hour of exercise may be largely offset by the low level of movement during the rest of the day. A low maintenance calorie number often reflects a lower-than-expected multiplier applied to your BMR due to minimal consistent daily movement.
Metabolic Adaptation from Dieting History
One of the most common reasons a person’s maintenance calories are lower than predicted is Adaptive Thermogenesis, often referred to as metabolic adaptation. This is the body’s powerful survival response to prolonged periods of calorie restriction or significant weight loss. When the body senses a persistent energy deficit, it downregulates energy expenditure to conserve fuel.
This adaptation means your body is burning fewer calories than a standard formula would predict for a person of your current weight who has never dieted. The reduction in energy expenditure can be seen in a lowered BMR, as well as a subconscious reduction in NEAT. You might instinctively move less, feel less inclined to fidget, or become more fatigued, all of which save calories.
This metabolic slowdown is the body’s attempt to defend its current body weight. Hormonal signals, particularly a drop in thyroid hormone and leptin—a hormone that regulates appetite and energy balance—help drive this reduction in metabolic rate. For individuals with a history of chronic dieting or substantial weight loss, this adaptation can leave them with a maintenance calorie requirement that is notably lower than their peers.
Underlying Health and Hormonal Influences
In some cases, an unusually low maintenance calorie requirement may point toward an underlying medical condition impacting metabolic function. The thyroid gland produces hormones that act as the primary regulators of the body’s metabolic speed. An underactive thyroid, a condition known as hypothyroidism, can directly cause a substantial decrease in BMR.
When the thyroid does not produce enough hormones, the body’s cellular processes slow down, leading to symptoms like persistent fatigue, cold sensitivity, and unexplained weight gain. Other hormonal imbalances, such as high levels of the stress hormone cortisol, or certain medications, can also negatively influence metabolism and energy expenditure. If your calculated maintenance calories are severely low and accompanied by other physical symptoms, consult a healthcare professional.