By Smiljka Kitanovic Ph.D, Vladimir Rodic and Nenad Rodic,
posted 04/05


We live in the age of excess and quick fixes. Our diets perhaps reflect this sad attitude more than anything else. On one side we have people with insatiable appetites and funny eating habits. And on the other side we have “experts” trying to fix their problems. As a result we had the FAT-FREE CRAZE and lately, the CARB-FREE CRAZE. These two diets are so radical that they actually claimed the lives of their credulous followers.
Atkins’ diet advocates claim that it is in our nature to eat a lot of protein just because in the past 40 000 years, human diet consisted mainly of prey. If you’re going to use evolution as evidence, however, do not forget that millions of years ago our ancestors ate the same foods that today’s big apes eat (bananas and other plants).
As for the carb-free diet, not all carbohydrates are created equal. Simple sugars and complex sugars (starches, cellulose) are all carbs, but the effects they have on our bodies are not the same. Starches are an important source of energy. Simple sugars, however, are one of the major culprits to human health. They are contained in highly processed and favorite foods such as cookies, cakes, chocolate, and ice cream.


Macronutrients required for sustenance of life are carbohydrates, fats, and proteins.

Carbohydrates are the most common macronutrient in the human diet. We find them in abundance in wheat products, potatoes, and other vegetables. They are also the most available source of energy: easy to find, easy to digest, and quick to metabolize. All this makes carbohydrates the main source of energy for daily life and sport.

One gram (g) of carbs contains 4 kcalories (Cal) or 16.8 kJ (kilojoules). In the body carbs are stored as glycogen in muscle cells and the liver. Studies show that glycogen stores last about two hours if an athlete is exercising at 65ml/kgmin (world record marathon pace). Continuous exercise at 70-80 % of VO2max causes the greatest degree of muscle glycogen depletion. However, training can increase the amount of glycogen stored in muscles from 14 g per kg of muscle to up to 36 g per kg of muscle.
Glucose taken by mouth does not reduce the degree of muscle glycogen utilization but slows down or replaces the use of liver glycogen. It is essential to keep liver glycogen at safe levels since its depletion will cause hypoglycemia (fall of blood glucose levels), which impairs brain function and leads to exhaustion (bonk). The optimum amount of carbs needed to fill glycogen stores is 500 g a day, three days preceding the race. This should be done only in conjunction with controlled depletion via energy-demanding training 72 hours prior to race (super compensation). Daily amounts of carbs taken should vary depending on your needs. *

Extra calories from carbs are quickly stored as fat. If this process is slowed down, some of these extra calories may be burned when the need for energy arises, instead of becoming storage fats. The simplest way to prevent fast conversion of carbs into fats is by balancing your meals. Never eat just one macronutrient at a time; include them all in your diet. There are weight-loss diets based on single macronutrient meals that are very effective, but the health aspects of such nutritional regimens represent a separate issue.
*More on these issues on pre race and race nutrition pages

Proteins are the building blocks of every cell, and therefore very important for our well-being. However, the body has very low needs for this nutrient as a source of energy, unless exposed to starvation. Only certain components of proteins, essential amino acids, are required in our diet because human bodies cannot produce them. Bodybuilders and some power-sport athletes take up to 450 g of protein a day. That is completely unnecessary, since excess protein is a big burden for kidneys and liver. Due to increased blood and muscle cell damage that athletes experience, it is recommended to take about 1.5 g of protein per kilogram (2.2 lbs) of body weight. If you’re taking more than that it is likely that you’re wasting protein and money since protein-rich food is usually the most expensive. Every food product is labeled nowadays and tells you how much protein it has. I find some dairy products to be the best sources of protein (unless you’re lactose-intolerant). There are also a variety of supplements that are excellent sources of protein (whey designer 95 or more % protein powder). Beware of artificial sweeteners in supplements since these are more toxic than FDA and manufacturers would care to admit.

Often maligned and unjustifiably excommunicated as a macronutrient, fat is very important if you want to be a distance athlete. How fast you’ll go will depend on your ability to metabolize fat and your efficiency (aerobic threshold training). Everyone can go hard on glycogen (up to two hours), but after that the body begins to use fat as its main fuel source. The ability of different cells of the body to store carbs in the form of glycogen is slight. Only a few hundred grams of glycogen can be stored in the liver, the skeletal muscles, and all other tissues of the body put together. In contrast, the average person has almost 150 times as much energy stored in the form of fat as compared to glycogen. Good and healthy sources of fats are nuts, olive oil, flax oil, etc. Animal fat should be avoided.
At VO2max effort there is enough energy stored in fat reserves to last you 60 hours. Each gram of fat contains almost 2.5 times as many calories of energy as each gram of glycogen. However, the process of transferring fat into a usable energy source (ATP-Adenosine Tri Phosphate) is very slow, hence the lack of ability to perform above 75 % of VO2max* solely on fat. If you’re working on fat, your body will still keep some glycogen in reserve (liver glycogen). This glycogen can be released when needed and if extra energy is available (from eating during exercise, which keeps the glucose level high in blood).
Fasting can increase the levels of fatty acids in blood, but do not expect to perform at a high level (max and sub-maximal). By training on an empty stomach in the morning after a 12-hour fast, you can quickly use up extra fat since there will be no available glycogen. Your metabolism will then rely on fat exclusively.

Overall energy demands depend on your training regimen. An average human being that does not exercise or work physically can sustain a healthy life at about 1200 kcal/day. Athletes usually have a higher basal metabolism, and spend energy while exercising. These amounts are not as high as you might think. On average, LSD training will burn 500-600 kcal/hour, and super-intense race-like efforts will burn about 1000-1200 kcal/hour (elite athlete level).

*Observing pro cyclists we notice that they are indeed capable of performing close to AT for a very long time. Examples like Tyler Hamilton’s solo breakaway in the 2003 tour with the average speed of well over 40-km/h show that it is possible to put out more power and work over 75 % of VO2max for extended periods of time. This kind of efficiency is what you want to achieve for Ironman racing. It requires careful season planning (refer to triathlon-season planning page), and developing all the necessary systems.


The body obtains water from two major sources:

1) ingested in the form of liquids or water in the food (taken together add about 2100 ml/day, and
2) synthesized in the body as a result of carbohydrate metabolism (about 200ml/day)

Fluid intake is highly variable among different people. Even within the same person fluid intake varies on different days, depends on climate, habits, and level of physical activity.
Daily loss of body water is also variable. Therefore, intake of water must be carefully matched to daily fluid losses. The body loses fluid in several ways:

1) Insensible Fluid Loss which consists of continuous fluid loss by evaporation from the respiratory tract and diffusion through the skin. Together they account for about 700 ml/day of fluid loss under normal conditions.

2) Fluid Loss in Sweat. This form of fluid loss is highly variable, depending on physical activity and environmental conditions, and it accounts for loss of about 100 ml/day normally. However, the volume of sweat in very hot weather and/or during heavy exercise occasionally increases to 1 to 2 liters per hour.

3) Water Loss in Feces is very small. It amounts to 100 ml/day but it can increase to several liters a day in people with severe diarrhea.

4) Water Loss by the Kidneys is a process regulated by multiple mechanisms. It is the most important means by which the body maintains the balance between fluid intake and output, as well as the balance between intake and output of most electrolytes. Kidneys excrete water and electrolytes in the form of urine. There is extreme variability of urine volume and it can be as low as 0.5 liters/day in a dehydrated person or as high as 20 liters/day in a person who has been drinking huge amounts of water. Excretion of body electrolytes (sodium, chloride, and potassium) also shows high variability.
Daily intake and output of water (in ml/day) is summarized in the following table:


Minerals represent a group of inorganic substances. Their specific functions are very diverse, and to list them all would exceed the scope and purpose of this short overview. In general the best dietary sources of minerals for humans are darkly pigmented vegetables. Nuts are also good source of minerals and some contain minerals missing from crops.

Magnesium. Many intracellular enzymatic reactions depend on magnesium as a catalyst, particularly those related to carbohydrate metabolism. If the extracellular concentration of magnesium increases, one can experience depression of both the nervous system activity and skeletal muscle contraction. Normalized skeletal muscle contraction can be achieved by administration of calcium. On the other hand, low magnesium concentration can cause irritability of the nervous system, peripheral vasodilatation, and cardiac arrhythmias.

Calcium. Calcium phosphate in the bones is the main form in which calcium is present in the body. The concentrations of this mineral in extracellular fluids are strictly regulated: both excess and low levels can lead to serious conditions. High concentrations of calcium ions can cause the heart to stop in systole and can also act as a mental depressant, whereas low concentrations can cause spontaneous discharge of nerve impulses resulting in tetany.

Phosphorus. The body contains large amounts of calcium phosphate deposited in bones. Phosphate is the major anion in intracellular fluids. Phosphates combine reversibly with many coenzyme systems and with other compounds involved in the operation of metabolic processes.

Iron. Iron is essential for most of the oxidation that occurs in cells. It is also essential for transport of oxygen to the tissues.

Trace Elements in the Body. These are present in the body in very small quantities. However, their importance is great and without them, specific deficiency syndromes are likely to develop. There are many trace elements in the body, but the most important are iodine, zinc, fluorine, manganese and selenium. Certain elements are found in such small quantities, and until recently the presence of these minerals was thought to be accidental. However, these elements play important roles, such as regulating specific enzymes. It is important to emphasize that these trace elements are found in adequate quantities only in unprocessed foods. Unfortunately, today’s agricultural practices have depleted the soil of its mineral content, resulting in mineral-deficient plants.


These organic compounds are needed in very small quantities for normal body metabolism. They can not be synthesized in the cells of the body. Requirements for different vitamins vary considerably. They depend on such factors as body size, rate of growth, amount of exercise, etc. Specific metabolic deficits may occur when insufficient amounts of vitamins are present in diet. Some vitamins are stored in all cells. This is particularly true of the fat-soluble vitamins. The quantity of vitamin A stored in the liver may be sufficient for 5 to 10 months, and the quantity of vitamin D, also stored in the liver, is sufficient to maintain a person for 2 to 4 months.
Water-soluble vitamins are stored in relatively small quantities. If the diet is deficient especially in vitamin B compounds, clinical symptoms of deficiency can sometimes be seen within a few days. An exception is vitamin B12, which can last in the liver in a bound form for a year or longer.

Vitamin A. The metabolic function of this vitamin is not clear, although effects of vitamin A deficiency have been well described and documented. This vitamin has been called an "anti-infection" vitamin because deficiency leads to damaged epithelial structures, which in turn often become infected. In animal tissues this vitamin occurs as retinol. Retinol is not found in foods of vegetable origin. However, many vegetable foods are abundant in yellow and red carotenoid pigments, which can be changed into vitamin A (retinol) in the liver.

Vitamin B1 (Thiamine). Thiamine deficiency causes many debilitating conditions because this vitamin is involved, as thiamine pyrophosphate, in many metabolic systems. Thiamine is specifically needed for the final metabolism of carbohydrates and many amino acids. Since central nervous system function depends almost entirely on the metabolism of carbohydrates, in thiamine deficiency the utilization of glucose by nervous tissue may be decreased by 50 to 60 percent. This in turn can disrupt communications in many portions of the central nervous system. Deficiency of this vitamin also weakens the heart muscle, and a person with severe thiamine deficiency eventually develops cardiac failure. Indigestion, severe constipation, anorexia, gastric atony, and hypochlorhydria are gastrointestinal symptoms of thiamine deficiency. A disease that results from thiamine dietary deficiency is frequently referred to as "beriberi," especially when the cardiovascular symptoms predominate.

Niacin (Nicotinic acid). This vitamin functions in the body as coenzymes in the forms of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Many metabolic systems depend on these coenzymes and if deficiency of niacin exists, oxidative delivery of energy from the foodstuffs to the cells cannot occur at normal rate. Physiological changes such as muscle weakness and poor glandular secretion are some of the early symptoms of niacin deficiency. Severe niacin deficiency may lead to actual death of tissues. A clinical condition called pellagra is caused mainly by niacin deficiency and it is greatly exacerbated in people on corn diet because corn is deficient in the amino acid tryptophan, which can be converted by the body into limited quantities to niacin

Riboflavin (Vitamin B2). Riboflavin combines in cells with phosohoric acid to form coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These two coenzymes are involved in hydrogen transfer within mitochondria, and are important in the process of obtaining energy from food.
In humans, severe deficiency of riboflavin has not been observed. However, symptoms of mild riboflavin deficiency are common and may include headaches, digestive problems, cracking of skin at the corners of the mouth, burning sensations of eyes and skin, depression, and forgetfulness.

Vitamin B12 (Cyanocobalamin). There are several cobalamin compounds that exhibit so-called "vitamin B12" activity. This vitamin performs several metabolic functions among which the most prominent one is to act as a coenzyme for reducing ribonucleotides to deoxyribonucleotides. This step is necessary in the replication of genes and could explain the major functions of vitamin B12 which are:

1) promotion of growth and
2) promotion of red blood cell formation and maturation.

Folic Acid. Several compounds show folic acid activity. The most significant function of folic acid is its role in the synthesis of thymine. As a component of DNA, thymine is required for replication of DNA. Thus, the function of folic acid is similar to that of vitamin B12: it stimulates growth and the maturation of red blood cells. Absence of folic acid in the diet results in stunted growth and anemia.

Vitamin B6 (Pyridoxine). Vitamin B6 is involved as a coenzyme in the metabolism of amino acids and proteins. It may also transport some amino acids across cellular membranes. In rare cases, pyridoxine deficiency may case seizures, dermatitis, nausea, and vomiting.

Pantothenic Acid. This vitamin is incorporated into coenzyme A (CoA), which has an important role in the aerobic metabolism of glucose, degradation of fatty acids, and energy production. Deficiency of this vitamin is rare in humans, because it is found in many foods. The human body can also make small amounts of this vitamin. Withholding of this vitamin from experimental animals caused stunted growth, reproductive failure, fatty liver, and dermatitis.

Vitamin C (Ascorbic Acid). This vitamin is involved in the strengthening of collagen fibers, thus providing healthy skin, cartilage, bones, and teeth. One of the well-known vitamin deficiencies, scurvy occurred in sailors who had no vitamin C in their diets for over 20 weeks. The deficiency resulted in bleeding of gums, and slow healing of wounds and bone fractures. This condition gradually worsened in the absence of vitamin C, leading to vomiting of blood, bloody stools, cerebral hemorrhage, fever, and finally death.

Vitamin D. The most important role of this vitamin is to promote calcium absorption in the gastrointestinal tract, and deposit calcium in the bones. Some vitamin D is formed in the skin, after exposure to UV rays. Lack of vitamin D causes rickets in children, who develop weak bones due to inadequate calcium depositing. In adults, rickets is rare, but may occur in some cases of severe vitamin D deficiency.

Vitamin E. Several compounds have vitamin E activity, and their main role is to act as antioxidants, preventing the oxidation of unsaturated fats. Lack of vitamin E causes abnormalities in cellular organelle structure and function, and results in infertility.

Vitamin K. This vitamin is important in the formation of several blood clotting factors, which are synthesized in the liver. Humans obtain most of this vitamin from intestinal bacteria. Heavy use of antibiotics destroys beneficial intestinal bacteria, which leads to vitamin K deficiency. The main symptom of this deficiency is slow clotting of blood.


Caffeine is probably the most common and socially accepted stimulant. Its greatest benefit for an endurance athlete is not, as many may think, its stimulating effect on the central nervous system, but rather its ability to raise free fatty acids levels in blood. The level of fatty acids reaches its peak about one hour upon taking caffeine and remains high up to four hours. Though an unhealthy practice, taking caffeine might provide short term benefits to your performance. Insulin (the anti-exercise hormone) has the opposite effect. Its level rises after high carbohydrate intake, inhibiting the mobilization of fatty acids and breakdown of glycogen in the liver.

By Smiljka Kitanovic, Vladimir Rodic, and Nenad Rodic