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Fat will provide the greatest contribution to his daily activity due to the length of time he is exercising. Carbohydrate (sugary foods and starch foods such bread, rice and pasta) will also provide Mark with some of his energy however carbohydrates can only been stored in limited amounts in our bodies. For example, in very intense exercise carbohydrate stores would only last 90-120 minutes or up to around 2000kcal worth of energy and only if you can rest a few days before an event to ensure these stores are well topped up, not possible for Mark!

When you exhaust these limited stores of carbohydrates this is called or in the world of cycling they call this and your working muscles start to feel like lead, you may feel a little light headed and crave large amounts of food. It is not a nice feeling you may even get off your bike to see if the brakes have stuck to your wheels!! When this happens you have no choice but to slow your pace considerably and at this lower intensity fat is the preferred fuel (although at any speed you use a mix of both carbohydrates, fat and a smaller amount of protein). Therefore Mark will have to do most of his daily effort at a level that is predominately using fat as fuel.

For Mark to consume 6000kcal per day, he will aim to eat a high fat diet (as much as 45-50% of what he eats) this is because eating one gram of fat equals 9kcal compared to eating one gram of carbohydrate or protein providing around 4kcal. In addition research suggests that very low fat diets are not suitable for prolonged endurance athletes (but I am not suggesting all endurance athletes eat as much as 45% of their daily calories from fat! more like 25-30%) although he still needs adequate carbohydrate to maintain his blood sugar levels and also to contribute to fueling his exercise alongside fat.

When it comes to protein the body does not have any 'official' stores like fat and carbohydrate for use as energy. Protein is used to build, maintain and repair body tissues and other hormonal functions. In "normal exercise" protein only gives a small percentage (around 5%) towards calorie requirement, but when you do not eat sufficient carbohydrate or eat enough overall calories to cover daily needs then protein is broken down from your skeletal muscle in much greater amounts and converted to sugar to maintain fuel for working muscles. This breakdown of protein is not ideal as you lose power and strength.

Overall I suggest that getting enough overall calories is the most important nutrition goal so as to maintain body reserves of protein, reduce fatigue and illness. One kilogram (weight of a regular bag of sugar) of body fat equals around 7200kcal therefore if Mark does not match his calorie needs of around 6000kcal you can start to appreciate the amount of body fat and muscle protein he could loose over quite a short time period.

Vitamin needs

There are two groups of : soluble and insoluble. Those that are soluble vitamins (B and C vitamins) cannot be stored in the body so should be consumed daily. Those that are soluble (vitamins A, D, E and K) do not need to be eaten daily. Certainly Mark will get all the vitamin D he requires from the Sun (not likely the case had he spent the summer in Scotland!) and the other soluble vitamins are unlikely to be a problem for Mark as he will have stores in his body of these vitamins. However, if Mark relies heavily on processed foods then vitamin C and other nutrients will be compromised, therefore a variety of food is still important and a multi-vitamin and mineral supplement as an insurance policy would be advisable.

Mineral needs

The main minerals Mark would need to consciously consider are ) and . Iron is needed to carry oxygen round his body and more is used when at altitude and prolonged exercise.

Sodium is very important for Mark when exercising for hours day after day and this is amplified in hot and humid climates when his sweat rate is high, as sodium is a major component lost in sweat. You can often tell you are losing a lot of salt by tasting it on your skin and/or seeing white patches of salt on clothing (especially if wearing a dark colour such as black). It is vital Mark salts his food in the evening and eats salty foods regularly throughout the day. A consequence of not enough salt and dehydration can be cramps.

Another major factor effecting sodium levels comes from taking on too much water and not enough salt. This is potentially a life threatening condition called . In milder cases you may feel dizzy, vomit and become disorientated. This only occurs in extreme cases but has sadly led to some fatalities in endurance events. Therefore educating Mark on this condition and being able to self monitor his hydration status by using his urine color and volume as a practical index is essential. Very dark smelly urine indicates dehydration but equally large volumes of clear urine may indicate over hydration. When available an isotonic sports drink which contains electrolytes (sodium/salt) is a good choice whilst cycling in very humid and hot climates alongside salty foods and not taking excessive fluid (the guidelines currently suggest no more than 800ml hour, if drinking this amount hour upon hour but less for women/slighter builds).

Special Nutritional problems linked to extreme environments

We all have our own personal thermostat situated in the brain called the which can sense a change in temperature in your blood. When the air surrounding us is hot the hypothalamus tells the sweat glands to produce more sweat and tells the blood vessels to open wider to allow more blood to pass nearer to the skin to get it cool (in cold temperatures the opposite happens and you shiver which produces heat).

In hot environments it is essential to sweat to cool down. The more you acclimatised the more effective at sweating you become and the more fluid and salt you lose, not less as people often think, as sweat is loss of salt and fluid from your body. If you stop sweating your core temperature will rise leading to heat stoke, serious if not addressed.

Not only do you need to drink more you need to eat more carbohydrates in hot weather to maintain a certain exercise intensity compared to more temperate climates. Your muscles will receive less blood flow and less oxygen, a further possible cause of cramps, in hot climates as the blood is moved to the skin to cool.

For information on the effects of altitude on nutritional needs I have an article at:

Extreme exercise and common gut problems

Exhaustive endurance exercise such as Mark's may also lead to stomach problems such as a feeling that your stomach has shut down and it becomes a real struggle to take on fluid or solids and often with other symptoms such as heartburn, burping, nausea and/or vomiting, cramps and diarrhoea. Not nice but having an understanding of why this happens can help understand the strategies to reduce the severity of symptoms. During exercise there is a reduced efficiency of the stomach:

1. The rate at which your stomach empties is delayed.
2. The contents of your stomach can much more easily come back up your oesophagus hence the vomiting.
3. Secretion of acid which helps digest your food is decreased.
4. Blood flow to your digestive system is slowed as blood is diverted to the working muscles.

If it is very hot and humid the body needs to move even more blood to the skin to help cool you down, also decreasing blood supply going to the gut to help digestion. The blood supply can decrease so much to your digestive system it can cause bleeding of the bowel in some cases.

What makes the above symptoms worse is dehydration (which can also cause cramps in the stomach and other areas of the body). If you are dehydrated you have less blood volume for your digestive system to spare and the harder it is to absorb fluids. The less fluid you have in your stomach the less well the stomach empties - a vicious cycle when you need fluid most. Another example of stomach problems can be very concentrated sugary foods when you are already very dehydrated this is because water has to move into your digestive system to help neutralise the sugar before it can be absorbed. Therefore it is important to achieve a hydration balance.

Due to the nature of eating what is available on the road the recommend nutrition will often not be possible but on days when the going is easy (easier!) and plenty of food is available Mark should attempt to consume as much as possible. However Mark is likely at various times to contend with a suppressed appetite, lack of food and fluid and gut discomfort. When you consider these challenges alone Mark has undoubtedly got remarkable mental and physical strength for cycling the Americans!