What is Metabolism? Metabolism refers to the biochemical processes in which our bodies convert food and drink into energy. This energy is then used to fuel bodily functions such as breathing, circulating blood, and repairing cells. Metabolism is divided into two categories: Catabolism: Catabolism is the set of metabolic pathways that break down molecules into smaller units to release energy. It involves the breakdown of complex molecules such as carbohydrates, fats, and proteins into simpler ones like glucose, fatty acids, and amino acids. This breakdown process releases energy, which is captured in the form of adenosine triphosphate (ATP), the primary energy carrier in cells. In simple terms, catabolism is the breakdown of molecules to obtain energy. Anabolism: Anabolism is the set of metabolic pathways that construct molecules from smaller units. These biosynthetic processes require energy, which is often derived from ATP produced during catabolic reactions. Anabolism is responsible for the growth and repair of tissues, the storage of energy, and the production of molecules necessary for cellular functions. In simple terms, anabolism is the synthesis of compounds needed by the cells. How Does Metabolism Maintain Weight? Our body weight is determined by the balance between the calories we consume and the calories we expend. Metabolism plays an important role in this balance: Basal Metabolic Rate (BMR): This is the amount of energy expended while at rest. It accounts for about 60-80% of daily calorie expenditure and includes the energy required for vital functions like breathing and keeping the heart beating. Thermic Effect of Food (TEF): This is the energy required for digestion, absorption, and removal of ingested nutrients. It accounts for about 10% of daily energy expenditure. Physical Activity: This includes all movements, from exercise to daily activities like walking or cleaning. It can vary greatly among individuals and is the most variable component of our energy expenditure. What Happens to Our Metabolism When We Lose Weight? When we lose weight, several changes occur in our metabolism: Reduction in BMR: Loss of Lean Body Mass: During weight loss, especially if it’s rapid or involves severe calorie restriction, some of the weight loss can be from lean muscle mass. Since muscle tissue is more metabolically active than fat tissue, a decrease in muscle mass leads to a reduction in BMR. Smaller Body Size: A smaller body requires fewer calories to maintain. As you lose weight, your body mass decreases, and thus the energy required to sustain basic bodily functions also decreases. Adaptive Thermogenesis: Metabolic Adaptation: The body responds to caloric restriction and weight loss by becoming more energy-efficient. This means that for a given level of activity, the body will burn fewer calories. This adaptive thermogenesis is believed to be a survival mechanism developed during periods of food scarcity in human history. Decreased Energy Expenditure from Physical Activity: Reduced Body Mass: When you weigh less, the energy cost of physical activities decreases. For instance, walking or running requires less energy if you are lighter. Why Steady Weight Loss is Better than Rapid Weight Loss Steady, gradual weight loss is generally considered more effective and sustainable than rapid weight loss for several reasons we just mentioned: Preservation of Lean Muscle Mass: Slow weight loss helps preserve lean muscle mass, which is crucial for maintaining a higher metabolic rate. Sustainable Habits: Gradual weight loss encourages the development of healthy, sustainable habits rather than quick fixes that are difficult to maintain. Also, keep in mind that rapid weight loss can lead to nutrient deficiencies, as it often involves restrictive diets that may lack essential nutrients. This can cause deficiencies that may impact overall health, energy levels, immune function, and more. It’s imperative that we focus on adequate intake of lean proteins, healthy fats, and complex carbohydrates in addition to vitamins and minerals to maintain our metabolism. Also, slow, steady weight loss is associated with a lower risk of regaining the lost weight compared to rapid weight loss. How GLP-1 Receptor Agonists Affect Metabolism GLP-1 (glucagon-like peptide-1) receptor agonists, such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) help with weight loss and affect metabolism. They work by: Increasing Insulin Secretion: GLP-1 agonists increase insulin secretion in response to meals, which helps regulate blood sugar levels. Reducing Appetite: These medications help reduce appetite and increase feelings of satiety, leading to lower calorie intake. Slowing Gastric Emptying: GLP-1 agonists slow the emptying of the stomach, which prolongs the feeling of fullness after eating. When we lose weight, it can have both positive and negative effects on metabolism: Positive Effects: ...
