Protein is the most satiating and most thermogenic of the macronutrients. That’s science speak for “it’s a less efficient fuel.” In other words, substitute protein calorie-for-calorie in place of carbs and/or fat and the metabolism will burn off more energy. Protein is the hardest macronutrient to store as fat.
Carbs are the next most satiating and thermogenic, and they’re highly variable. Carbs with lots of fiber are very inefficient. More refined carbs with less fiber are more efficient. Glycemic index and insulin kinetics related to carbs can be viewed as an efficiency measure.
Also, starches can have varying degrees of resistant starch. A cold potato eaten whole with the skin on is more inefficient compared to a hot mashed potato without the skin. One interesting study showed the useable calories in rice can be reduced by 50% when cooked with coconut oil, cooled, and reheated again. This is an example of making food more inefficient in the cooking process.
Despite what the popular pseudoscience and biased blogosphere says, fat is the least thermogenic and least satiating macronutrient. In other words, calorie for calorie, it’s the most efficient fuel you can eat and store. However, when combined with protein, its satiating potential is more pronounced and this combination flips the switch to metabolic inefficiency.
Two more interesting and emerging pieces of info related to metabolic efficiency have to do with toxins and bacteria living in our colon (what is euphemistically referred to as “bugs”).
I hate the word toxins because it means nothing without clarification. In the context of metabolic efficiency, I’m talking about POPs or persistent organic pollutants.
These compounds accumulate in the environment (pesticide residues, plastic leaching, industrial pollutants, etc) and concentrate in the fat tissue of animals. This is known as bioaccumulation, where animals eat the plants that harbor the compounds and end up with the highest concentrations. This is the same reason the large predatory fish of the ocean have the highest mercury levels.