How does the body burn calories?

Did you know you can burn calories without exercise? Our bodies have a variety of amazing ways it expends energy throughout the day... some of which may be a surprise! If you have ever tried to lose weight or know someone who has, you have likely heard the phrase "calories in equals calories out". When we eat foods containing energy-yielding nutrients (carbohydrates, fat, and/or protein), our bodies convert these into units of energy called calories or kilojoules. This energy is used by the body for a variety of essential functions such as cell growth and repair, heart rate, respiration, digestion, and filtration of waste products. Inadequate energy intake from not eating enough calories to support our basal metabolic rate ("metabolism") may lead to weight loss as well as our bodies running on empty and not functioning to its fullest. Meanwhile, excess energy intake without adequate energy expenditure generally results in weight gain and may contribute to chronic diseases.

Our bodies have a variety of amazing ways it burns calories throughout the day.

1. Basal Metabolic Rate or Resting Metabolic Rate

Let's imagine that you are lying in bed all day, just resting and not moving. While you are awake and in a completely resting state such as this, your body burns a certain amount of calories to maintain essential functions such as breathing, maintaining body temperature, regulating heart rate and blood pressure. This energy expenditure, known as the Basal Metabolic Rate or Resting Metabolic Rate or "metabolic rate", is generally about 40-70% of our body's daily energy expenditure for the day. It is also the minimum amount of calories your body needs to perform basic function well. Body size, gender, and genes all play a role in metabolic rate. In general, women need a minimum of 1200 calories per day and men need a minimum of 1500 calories per day to support daily bodily functions. Every human being has an individual basal metabolic rate that can be estimated by a Registered Dietitian and/or can be calculated with indirect calorimetry metabolic testing tools. Doing strength-training and aerobic exercise, staying physically active, getting adequate sleep, eating nutritious foods with adequate protein, drinking green tea and black coffee, and eating spicy foods have been shown to boost metabolic rate. Losing weight too quickly through calorie-restricted diets or fad-diets, losing muscle mass, being more sedentary, and going through menopause are things that lower metabolic rate. Thyroid conditions also impact metabolic rate.

2. Thermic Effect of Food

When we eat food, it costs our body energy for the digestion, absorption, transport, storage, and disposal of nutrients consumed. The Thermic Effect of Food (TEF) is the increase in the metabolic rate that occurs after eating a meal to provide energy for the metabolism of carbohydrates, protein, and fat. The TEF is estimated to be about 10% of our caloric intake. Evidence suggests that it is increased by larger meal sizes, intake of protein, low-fat plant-based diets, and exercise. Dietary fat is higher in calories per gram than protein or carbohydrates and also has less of a thermic effect, making it more likely than protein or carbohydrates to lead to weight gain. This idea has fueled high-protein diets as well as myths touting "negative-calories foods". Eating raw celery has often been touted as burning more calories than the celery itself contains, but this has not been backed by science.

3. Non-Exercise Activity Thermogenesis (NEAT)

Non-exercise activity thermogenesis dubbed "NEAT" is just a fancy term for unintentional movements that burn calories. It involves energy expended through involuntary movements such as fidgeting, spontaneous muscle contraction, maintaining posture when sitting up, typing, pacing, and tapping fingers. Even these small, insignificant movements help to increase metabolic rate and make up a majority of an individual's non-resting calorie needs. Research suggests that NEAT may be important in weight management and may enhance or inhibit weight gain or weight loss efforts.

4. Periods of Growth (Infancy, Childhood, Adolescence, Pregnancy, Lactation)

During periods of growth, energy is required for the growth of new tissues. Infancy is a period of substantial energy expenditure, requiring frequent feedings every 3-4 hours to fuel growth. Childhood, adolescence, pregnancy, and lactation are additional periods of growth requiring additional energy intake to support growth. During these periods, energy needs are higher due to increased energy expenditure from fueling bodily changes. A Registered Dietitian can best estimate calorie needs during these changing times.

5. Physical Activity

Physical activity is defined as any bodily movement produced by skeletal muscle that results in energy expenditure. Physical activity is categorized by intensity, from light intensity activity to moderate to vigorous. The intensity of the physical activity corresponds to heart rate and breathing. Examples of light intensity activity include housework such as sweeping, vacuuming, ironing, dusting. Moderate intensity activities such as brisk walking, water aerobics, tennis may be characterized by the "talk test". If you can carry a conversation but not sing, you are performing moderate intensity activity. High-intensitvy activity is characterized by not being able to say more than a few words without pausing to catch a breath. Examples of this include jogging, running, bicycling, and hiking uphill. Not only are calories burned through physical activity, but staying more physically active and less sedentary can also boost metabolic rate.

6. Exercise

Exercise is a subcategory of physical activity defined as a voluntary, planned, structured, and deliberate activity performed for anticipated positive effects. These positive effects may be physical, such as strengthening muscle, improving range of motion, or losing weight. They may be psychological, such as for stress-relief or improving sleep and energy levels. They may additionally be social well-being. Exercise may be further categorized as endurance training or muscle-strengthening resistance-training. Endurance training is the repetitive and dynamic use of large muscle groups such as swimming, walking, running, bicycling, dancing. Resistance-training is repetitive use of muscle designed to increase muscle strength and power. By increasing muscle mass and improving body composition, resistance-training can boost metabolic rate. Balance and stretching actives enhance physical stability and flexibility to reduce risk of fracture and injuries. Endurance training improves cardiovascular health and blood sugar levels.

No matter what form of movement you voluntarily or involuntarily participate in, moving more and staying less sedentary is essential for health and wellness. If you feel it is difficult to get moving or need assistance reaching your activity goals, speaking to a Registered Dietitian may help!

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