Bioenergetics 101

Fred invited me to write a little about bioenergetics and macronutrients in this article. At the beginning I thought this was piece of cake, until the moment he said “Filipe no geek talk, just simple plain stuff that anyone can read”. Well I have to say this kind of made me rethink my entire speech.  I now have to explain some very complex issues with simple and accurate words, I was never good at that… Just hope for now I can be successful.



Bioenergetics is basically applying Thermodynamics to biological systems. The basic law we all invoke is the 1st law, in which we state energy is conserved and cannot be destroyed or created. Basically we state that energy is transferred between thermodynamic systems and its surroundings. Now everybody has heard the theory that all nutritionists love: if you eat it you have to burn it or you will store it. I believe in this corollary what I do not believe is that we are calculating calories in food the right way (in which concerns human body). You see the 2nd law says that using energy also consumes energy, so in the end… energy available in human body is not the energy that a bomb calorimeter will give you. Oh… and by the way don’t invoke the Attwater factors because they were made with a sample of 3 individuals (n=3) yes you heard it right! They were written almost 120 years ago with a sample of 3 individuals that by the way were Attwater’s lab technicians… No I’m not crazy… go check it yourself! In case you want to know a bit more about this stuff on calories, ask me or Fred and we will be glad to forward you an article full of geek stuff, now you have to be ready to go on a geek safari!

Well getting back to Bionergetics…

Our body gets energy from the chemical bonds in macronutrients, it stores this energy in triglycerides (one molecule of glycerol attached with 3 fatty acids), glycogen (several units of glucose) and debatably protein in skeletal muscle (our body can breakdown proteins into amino acids for energy).  This energy that is used to perform work is called in Thermodynamics Gibbs free energy. Now, I promised Fred this wouldn’t be geek stuff, so our body is more a less like a combustion engine, we use fuel (carbohydrates, protein, fat, alcohol) as fuel and after combustion, work and heat is produced. Almost all these reactions are made in the presence of oxygen since this gas is the primary acceptor for electrons in biological reactions. This capacity for storing energy is huge! We can survive several days without eating (if water is provided). We can survive one day without food easily… if you can’t… you are a Golden-crowned Kinglet and you weight about 5 grams J (this is true for these small birds).

Golden-Crowned Kinglet, these little fellows really have quite an appetite

Golden-Crowned Kinglet, these little fellows really have quite an appetite


Simple approach of matter and energy (7)



Energy… How do we get it?

In the pursuit of ATP molecules (adenosine triphosphate) which are the only chemical molecules that our body uses to perform work we can use several pathways. In order to avoid some really boring and nasty chat I will resume this, pay attention folks this stuff is really important!

ATP and CP (phosphocreatine)=This is a very fast but very limited source of energy, it can last only a few seconds.

Glycogen=It’s broken down to glucose, glucose ends converted to lactate in the absence of oxygen and you also get lactic acid build up (if this pathway is sustained to long). Lactic acid loses one H+ and you get its salt, lactate.  This is a fast energy source, does not require oxygen and is limited.

Triglycerides (β-oxidation)=Fatty acids are cleaved from the glycerol molecule and are used as energy in the mitochondria (they are actually converted into acetyl-CoA and enter TCA cycle). In the end you get CO2. This is a very slow process you need a lot of O2 but you have almost unlimited energy (I said almost!).

Skeletal muscle protein=They are broken down into amino acids, amino acids are then used to produce ATP (for example pyruvate from alanine). The end product can be CO2, keep in mind that this pathway is rarely used and can only supply about 5-7% of TEE (total energy expenditure). If you do not replace these, you can say goodbye to your muscle mass.


Glucose and ATP are balanced between spontaneous and nonspontaneous reactions (7)

Before I move to macronutrients, let me clarify this..! The information provided is based on conventional biochemistry and exercise physiology, last time I wrote about this, TBI’s technical manager Carlo Buzzichelli presented me one paper that showed different thresholds for energy systems involved in exercise. Just to be clear, I don’t dare to think that I’m 100% right about this, so probably in 10 years I will be wrong… too bad this is the way science goes!


Now… How much fuel does an athlete need?



The electron transport chain (ETC) in the inner membrane of the mitochondria (image from wikipedia)

5-7 g/kg/day=moderate duration/low intensity training.

7-12g g/kg/day=moderate to heavy endurance training.

10-12 g/kg/day=extreme exercise program (professional athletes).


This is a very controversial topic!

In endurance athletes it should not exceed the 1.6 g/kg/day.2

In strength athletes it is recommended 1.33 g/kg/day.3 In my opinion it should be between 1.5-2.0 g/kg/day.3,4


Well it’s not different from the regular person, meaning 30% of the caloric intake.

If you want to reduce body fat:

0.5-1.0 g/kg/day5,6

That’s it folks, I tried to resume this to what really matters… Hope you enjoyed.

Important: I would like to thank Fred Koch (TBI’s International Director) for all his support and especially for his invitation to work with TBI. Fred is a practical person with a lot to teach, he may not use fancy words or quote important papers, but his knowledge is priceless, you can’t find it in any book or journal!

Thank you,

Filipe Teixeira

Director of Nutrition – Tudor Bompa Institute International

1. Burke LM, et al. Carbohydrates and fat for training and recovery. J Sports Sci 2004;22:15-30.
2. Tarnopolsky M. Protein requirements for endurance athletes. Nutrition 2004;20:662-668.
3. Lemon PW et al. Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders. J Appl Physiol 1992;73(2):767-775.
4. Kreider RB. Effects of protein and amino acid supplementation on athletic performance.Sportscience 1999. Available at:
5. Kreider RB et al. Overtraining in Sport: terms, definitions, and prevalence. In: Overtraining in Sport. Champaign, IL: Human Kinetics; 1998.
6. Miller WC et al. A meta-analysis of the past 25 years of weight loss research using diet, exercise or diet plus exercise intervention. Int J Obes Relat Metab Disord 1997;21:941-947.
7. Scott CB. A Primer for the exercise and Nutrition Sciences – Thermodynamics, Bioenergetics, Metabolism. New Jersey:  Springer; 2008.

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