# Anaerobic nutrient expenditure

Doing some research into different forms of exercise and energy systems and I realized something odd about the way we talk about energy.

When we eat, we take on macronutrients that are broken down into their smaller components, but on it's face the assertion is that:

Fat = 9 Calories/gram
Carbs = 4 Calories/gram
Protein = 4 Calories/gram


However, when you look at the Krebs cycle, one acetyl sugar molecule generates 32 ATP molecules. Contrast that against Anaerobic metabolism and the Cori cycle, 1 sugar molecule generates 2 molecules (at a cost of 6 ATP in the liver later).

There are all sorts of fitness calculators out there, most of the calculations are based on the Assessment of Physical Activity and Energy Expenditure: An Overview of Objective Measures book, most of which was put together through measuring oxygen in put versus carbon dioxide output (in conjunction with heat radiation. The clear problem with associating that with weight training and other anaerobic activities is that the other activities don't immediately create CO2 and don't immediately require O2. Some attempts have been made to make estimates based on lactate production in the blood stream, but I'm not confident in those results.

My question is, when there is anaerobic activity taking place, are we actually "burning" more base ingredients than we are exercising aerobically?

In other words, even if I'm only burning 100 Calories lifting weights, would I actually be burning the equivalent of 1,600 Calories based on the glucose I would have converted to ATP aerobially?

• The Urea cycle doesn't generate energy and it doesn't break down amino acids. It uses energy to convert ammonia and carbon dioxide to urea. The Cori cycle isn't a metabolic pathway generating energy as you imply. It's a system whereby lactate produced in muscle exercise is goes into the blood and is taken up by the liver, converted back to pyruvate and then to glucose which goes back into the bloodstream. There is no net generation of energy. The liver expends energy so that muscle can use it. You need to sort your question out. – David Mar 28 '16 at 23:04
• @David Removed the bit about the Urea cycle. I used the Cori Cycle as a shorthand for anaerobic metabolism and the Cori cycle. As stated in the question, not only is there not a net generation of energy, there's a net loss in energy, the muscles create energy at 16 times lower rate than oxidation and the liver expends energy making more glucose, which is the driving factor in the question. – Snowburnt Mar 30 '16 at 1:39