Category: Bioenergetics

According to Oregon State University's animal nutrition guide, metabolizable energy is the energy remaining after losses from feces and urine have been accounted for. So, is metabolisable energy the same as digestible energy? The short answer is no, and understanding the distinction is crucial for proper animal diet formulation and performance.

Over 70% of the body's energy expenditure at rest comes from the metabolism of fats. In energy systems, a substrate is the initial molecule that is broken down through metabolic pathways to produce adenosine triphosphate (ATP), the body's primary energy currency. The type of substrate utilized depends heavily on the intensity and duration of activity.

Approximately 2,803 kilojoules (or 686 kcal) of energy are released when one mole of glucose is completely oxidized. This energy, however, is not a simple, single value for a lone glucose molecule but is released through a complex, multi-stage process called cellular respiration, resulting in the production of the cell's usable energy currency, adenosine triphosphate (ATP).

The energy an animal derives from its food is a critical metric in nutrition, and approximately 19% of a ruminant's digestible energy may be lost before it can be fully metabolized. Digestible energy (DE) quantifies the portion of an animal's dietary energy that is actually absorbed, excluding the energy lost through feces.

Over 65% of the cost of raising livestock is attributed to feed, making energy the most expensive component in an animal's diet. This is why understanding exactly how we measure the amount of energy in feed is crucial for formulating cost-effective rations and optimizing animal health and productivity.

In animal nutrition, over 40% of the gross energy in some fibrous feeds is lost in feces alone, highlighting a critical distinction. Understanding this key difference between net energy and gross energy is essential for accurately evaluating a food source's true nutritional value for an organism.

A single gram of fat yields more than double the amount of ATP as a gram of carbohydrate, making fat the macronutrient with the highest energy density for cellular fuel. This deep dive explores why your body's energy production is most efficient with fat, even though carbohydrates are the quickest fuel source. By understanding what type of food will yield the most ATP, you can optimize your dietary energy strategy.

Research indicates that when carbohydrate stores are significantly depleted, the body upregulates the ketogenic pathway to produce energy. This metabolic shift, known as ketosis, allows the body to efficiently burn fat for fuel by producing alternative energy molecules called ketones.

Despite containing more than double the calories per gram, fats are the slowest source of energy for the body. This is because the body must go through a more complex and time-consuming metabolic process to break down and convert fats into usable energy compared to carbohydrates.

The human body converts approximately 40% of the energy from glucose into usable energy, known as ATP, with the rest being released as heat. This conversion is a complex and highly regulated process, and the true efficiency of carbohydrates depends on numerous metabolic factors, not just a single percentage.