It seems the topic of calories comes up all the time. Everyone thinks that counting calories will cause weight loss. If you burn more than you take in, you'll lose weight. 3,500 Kcal = 1lb of fat, right? After all, you cannot argue with the first law of thermodynamics, right? Which basically states that you cannot destroy energy, conservation of energy is the law. Yes that is true, but maybe we need to have a quick physics lesson. The law states, "The law of conservation of energy states that the total energy of an isolated system is constant" So, is your body an isolated system? (See picture to the left) No, it is not. Also, is your body 100% efficient in turning your food energy into fuel? No, it is not. If your body does not use the fuel it goes out in the form of waste or is stored as fat. So the question is, what kind of calories are you consuming?
Here is an extreme example: Take 1 cup of olive oil and drink it. You'll be getting about 1920 Kcal worth of energy in the 224 grams of fats, 0g carbs. What will happen? Provided you don't vomit, most people know what will happen. You'll get diarrhea, why is that? Your body cannot use all of those calories with perfect efficiency so it dumps any excess. So our body is not an isolated system. Fat uptake is regulated by the pressure gradients and absorbed by the lymphatic system. So if your lipid levels are full, your intestines will let it pass. See Fig.1
Now, let's talk about carbs. These behave much differently because it uses a different metabolic system to harness the energy. If you were to drink 8 20oz bottles of cherry Coke, you'd have 2080 Kcal's via 560g of sugars. Provided you don't vomit or go into shock, what happens to these calories? Your body only needs 5g of sugar in your bloodstream at one time, anything above that destroys tissue. So your pancreas comes to the rescue and pushes the extra 555g of sugar into your fat stores with a rush of insulin. See fig. 2
So if your body gets a large dose of calories, it really depends on what kind they are. Generally speaking, carbs are digested quickly and turned to fuel then deposited into the bloodstream, depending on work being performed are converted into ATP with CO2 as a byproduct. The remaining glucose is transported into adipose tissue (body fat).
Fats are processed differently all together and enter the bloodstream as triglycerides where they are available for muscles to use for fuel as ATP. Any remaining fats that are not needed will not be stored, but eliminated via waste.
All exercise is not created equal. Sprinters use the creatine cycle, they don't tap fats or glycogen stored in the muscles and liver. Middle distance runners who are 2 through 120 minute efforts like 800m to 15,000m are tapping into glycogen stores almost exclusively.
Fig. 3 shows how your body uses the two main fuel systems as you work harder in your workouts. It's pretty fun to see this in action, when you're burning carbs, you produce more CO2, thus you have to breathe harder to eliminate the CO2 from your body. But when you're oxidizing fat, you produce quite a bit less CO2 and can improve your performance with less panting. You also don't feel the burn as quickly into a long steep climb as you would if you're burning carbs for fuel. There is a great article by Dr. Peter Attia on his journey to ketosis as measured in his performance. He proves pretty clearly that ketosis is a much better system for the endurance athlete.
I do not count calories to manage my weight, it seems to make no difference at all. Dr. Steve Phinney has been living in nutritional ketosis for 30 years, his weight has been stable during that time however, his calories can fluctuate from 2,000-6,000 per day.
Here is an example from MyFitnessPal app. It's great except for the assumption that my body is 100% efficient. Also, my lean body mass happens to be 137 lbs. So there might be a little something wrong with their calculation.
Tim & Lynette Jenné are learners first and foremost. We love to ask "why?" We question the status quo. We also love to research and find answers for ourselves. As parents of four adult children, we've learned a few things along the way that may be helpful to others. We love to live & eat clean, simple lives.