What is the TEF of protein, and why is it higher than other macros?

The Thermic Effect of Food (TEF), also known as diet-induced thermogenesis (DIT) or specific dynamic action (SDA), refers to the increase in energy expenditure above the basal metabolic rate that occurs for several hours after consuming food. It represents the energy your body uses to digest, absorb, metabolize, and store the nutrients from your meals. TEF is typically expressed as a percentage of the calories consumed.

Here's the approximate TEF for each macronutrient:

•  Protein: 20-30%
•  Carbohydrates: 5-15%
•  Fats: 0-5%

As you can see, protein has a significantly higher TEF compared to carbohydrates and fats. This means that for every 100 calories you consume from protein, your body burns approximately 20-30 calories just to process it. In contrast, you might only burn 5-15 calories processing 100 calories of carbohydrates and very few, if any, calories processing 100 calories of fat.

Why is the TEF of protein higher than other macronutrients? 

The higher TEF of protein is primarily due to the more complex metabolic pathways involved in its digestion, absorption, and utilization. Here's a breakdown of the reasons:

1.  Breaking Peptide Bonds: Proteins are made up of long chains of amino acids linked by peptide bonds. Breaking these bonds during digestion requires more energy compared to the simpler breakdown of carbohydrates into glucose or fats into fatty acids and glycerol.
2.  Gluconeogenesis: A portion of dietary protein can be converted into glucose through a process called gluconeogenesis. This metabolic pathway is energy-intensive.
3.  Urea Synthesis: When amino acids are metabolized, nitrogen is produced as a byproduct. The body needs to convert this nitrogen into urea, which is then excreted in the urine. Urea synthesis in the liver is an energy-requiring process.
4.  Protein Turnover: The body is constantly breaking down and rebuilding proteins (protein turnover). This process requires energy. A higher protein intake can stimulate protein synthesis, thus increasing energy expenditure.
5.  Slower Digestion and Absorption: Protein generally takes longer to digest and absorb compared to carbohydrates and fats. This prolonged digestive process leads to a sustained increase in metabolic rate.

In summary, the body has to work much harder to process protein due to the complexity of its structure and the metabolic pathways involved in its utilization and disposal. This increased "work" translates to a higher number of calories burned during digestion and metabolism compared to fats and carbohydrates. This is one of the reasons why high-protein diets can sometimes be beneficial for weight management, as a larger portion of the consumed calories is used for processing.