The human body generally burns more calories at high altitude compared to sea level. High altitude is typically defined as elevations above 8,000 feet (2,400 meters), where decreased atmospheric pressure reduces the available oxygen per breath. This forces the body to work harder to maintain oxygen delivery, directly increasing energy expenditure, even at rest. This effect, compounded by other environmental factors, causes a substantial increase in the total calories consumed daily.
How Low Oxygen Increases Resting Calorie Burn
The primary mechanism driving increased calorie burn at elevation is the body’s involuntary response to reduced oxygen availability, known as hypobaric hypoxia. To compensate for the thinner air, the body initiates compensatory actions requiring extra energy input. This increased effort raises the Resting Metabolic Rate (RMR), the energy needed simply to keep the body functioning at rest.
A major part of this response is an increase in both breathing rate (ventilation) and heart rate. The respiratory muscles and the heart must work harder and faster to process more air and circulate blood quickly to distribute the limited oxygen. This constant, heightened activity consumes more adenosine triphosphate (ATP), the body’s energy currency, leading to a sustained increase in resting caloric expenditure.
This metabolic shift is measurable, with RMR increasing based on the elevation gained. Studies suggest RMR can increase by approximately 5% at 10,000 feet and up to 25% at 15,000 feet during initial exposure. This effect is partly regulated by Hypoxia-Inducible Factor (HIF), which alters cellular metabolism to cope with low oxygen stress. The body also shifts toward less efficient energy pathways, such as glycolysis, forcing it to use more fuel to generate the same amount of cellular energy.
The Added Energy Costs of Cold and Physical Activity
Beyond the internal hypoxic response, the external environment introduces additional energy demands, most notably from cold exposure. Temperatures drop significantly with increasing elevation, forcing the body to expend energy on thermogenesis to maintain a stable core temperature. This process involves shivering and non-shivering heat production, which independently raises the metabolic rate.
The energy cost of maintaining warmth is distinct from the RMR increase caused by hypoxia. This thermoregulatory effort can increase the resting metabolic rate by an additional 10% to 30%. When combined with the hypoxia-driven RMR increase, total resting energy expenditure rises substantially, particularly without adequate shelter or clothing.
Most trips to high altitude involve strenuous physical activity like hiking or climbing, which dramatically increases overall calorie burn. Reduced oxygen makes these activities feel more difficult, increasing the energy cost per unit of effort compared to sea level. Mountaineers can see their total daily energy expenditure increase three- to six-fold over their normal RMR. Carrying a heavy backpack also adds a measurable energy cost, with one study noting an approximate 1% increase in expenditure for every kilogram carried.
Managing Appetite and Calorie Intake at Altitude
While the body’s energy expenditure increases at high altitude, a common physiological side effect is appetite suppression, sometimes called anorexia of altitude sickness. This phenomenon is linked to hormonal changes, including elevated satiety hormone leptin and decreased hunger hormone ghrelin. This often creates a significant negative energy balance where the body burns far more calories than it consumes.
The deficit can be severe; trekkers have been observed to reduce their energy intake by up to 29% while their caloric needs are elevated. This sustained energy gap leads to rapid weight loss, often including the loss of lean muscle mass. For instance, a 16-day trek at high altitude resulted in an average muscle loss of over two pounds per person.
To mitigate muscle wasting and support increased energy demands, intentional nutritional strategies are necessary. A high intake of carbohydrates is recommended to fuel the body efficiently, given the metabolic shift toward less efficient glucose utilization. Adequate protein intake, around 1.4 to 2.0 grams per kilogram of body weight, is important to counteract muscle breakdown. Furthermore, increased breathing and the cold environment accelerate fluid loss. Therefore, a daily intake of 4 to 5 liters of fluid is necessary to ensure proper hydration.