Understanding the Role of Metabolism

Most of us talk of metabolism in a loose sense linking it with gain and/or loss of weight. In a real sense, digestion and metabolism are important and fundamental functions of the human body by which ingested food is converted into energy vital for the sustenance of life. Scientists believe that the human body contains approximately 37 trillion cells. Each cell is a living entity where the absorbed nutrients undergo complex biochemical reactions to either produce energy (catabolism) or synthesize products (anabolism) that are necessary for life.
Most of us however are familiar with terms such as fast metabolism or slow metabolism referring to Basal Metabolic Rate (BMR) – meaning the amount of energy or calories used to maintain bodily function on a day-to-day basis.
Glucose, a major component of most of the carbohydrates we consume is the key that on degradation releases energy. Excess glucose is converted into glycogen and stored in the liver or further converted into fats to be stored in adipose tissues.
Similarly, food proteins undergo biochemical processes that are responsible for the synthesis and catabolism of proteins and amino acids. Amino acids are basic units used by cells to synthesize structural proteins as well as enzymes, hormones, nucleoproteins, antibodies, and many other compounds that perform specific functions. As the body can’t store protein, any extra is converted to glucose for energy production, and finally to fats.
Lipids (fats) also undergo degradation and synthesis for energy and for the synthesis of structural and functional lipids for use in cell membranes. Excessive intake of carbohydrates, proteins, and fats is stored as fats. Proteins digestion and metabolism consume more energy in comparison to carbohydrates and fats. Consumption of foods with appreciable amounts of proteins leads to healthy levels of muscle mass and an increase in BMR.
In general, our metabolism declines with age peaking in our 20s. Our food intake pattern dictates our metabolic rate.  Ingestion of certain foods has been shown to marginally increase metabolic rates but has no measurable overall impact.  Metabolism is commonly referred to be the cause of losing or gaining weight but weight gain and /or loss depends mostly upon the intake and burning of calories.  
I will cover the fundamentals of weight gain and loss in a separate blog. My book on the Science of Food Nutrition and Health provides you with detailed information on food digestion and metabolism.

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