How does exercise affect my protein requirement?
Numerous studies involving both endurance and strength exercise have shown that the current recommended protein intake of 0.75 g/kg body weight/day is inadequate for people who participate in regular exercise or sport. Additional protein is needed to compensate for the increased breakdown of protein during and immediately after exercise, and to facilitate repair and growth. Exercise triggers the activation of an enzyme that oxidises key amino acids in the muscle, which are then used as a fuel source. The greater the exercise intensity and the longer the duration of exercise, the more protein is broken down for fuel.

Your exact protein needs depends on the type, intensity and duration of your training. How these needs differ for endurance athletes and strength power athletes are discussed in detail below:

Endurance Training
Prolonged and intense endurance training increases your protein requirements for two reasons. Firstly, you will need more protein to compensate for the increased breakdown of protein during training. When your muscle glycogen stores are low which typically occurs after 60-90 minutes of endurance exercise certain amino acids, namely, the BCAAs can be used for energy. One of the BCAAs, leucine, is converted into another amino acid, alanine, which is converted in the liver into glucose. This glucose is released back into the bloodstream and transported to the exercising muscles where it is used for energy. In fact, protein may contribute up to 15% of your energy production when glycogen stores are low. This is quite a substantial increase, as protein contributes less than 5% of energy needs when muscle glycogen stores are high. Secondly, additional protein is needed for the repair and recovery of muscle tissue after intense endurance training.

Strength and Power Training
Strength and power athletes have additional needs as protein provides an enhanced stimulus for muscle growth. To build muscle, you must be in positive nitrogen balance. This means the body is retaining more dietary protein than is excreted or used as fuel. A sub-optimal intake of protein will result in slower gains in strength, size and mass, or even muscle loss, despite hard training. In practice the body is capable of adapting to slight variations in protein intake. It becomes more efficient in recycling amino acids during protein metabolism if your intake falls over a period of time. The body can also adapt to a consistently high protein intake by oxidising surplus amino acids for energy.

It is important to understand that a high protein diet alone will not result in increased strength or muscle size. These goals can only be achieved when an optimal protein intake is combined with heavy resistance (strength) training.

Do beginners need more or less protein than experienced athletes?
Contrary to popular belief, studies have shown that beginners have slightly higher requirements for protein per hg body weight. When you begin a training programme your protein needs rise due to increases in protein turnover. After about 3 weeks of training, the body adapts to the exercise and becomes more efficient at recycling protein. Broken down protein can be built up again from amino acids released into the amino acid pool. The body also becomes more efficient in conserving protein. One study has shown that the requirements per kg body weight of novice bodybuilders can be up to 40% higher than those of experienced bodybuilders.

Can I minimise protein breakdown during exercise?
Protein is broken down in increased quantities when muscle glycogen stores are low. Thus, during high-intensity exercise lasting longer than 1 hour, protein can make a substantial contribution to your energy needs (up to 15%). Clearly, it is advantageous to start your training session with high muscle-glycogen stores. This will reduce the contribution protein makes to your energy needs at any given point during training.

If you are on a weight/fat loss programme, make sure you do not reduce your carbohydrate too drastically otherwise protein will be used as energy source making it unavailable for tissue growth. Aim to maintain 60% of your calorie intake from carbohydrate by reducing your calorie intake from carbohydrate in proportion to your calorie reduction.

How much protein do I need for maximum performance?
At low-moderate exercise intensities (,50% VO2max), it appears there is no significant increase in protein requirements.

For an endurance athlete, the recommended range is about 1.2-1.4 g/kg body weight/day.

Many recent studies show that strength and power athletes have a greater daily requirement for protein than most endurance athletes. The current consensus recommendation is an intake between 1.4 and 1.8 g/kg body weight/day. The American Dietetic Association and ACSM recommend 1.6-1.7 g/kg body weight per day. So, for example, a distance runner weighing 70 kg would need 84-98 g/day. A sprinter or bodybuilder with the same body weight would need 98-126 g/day.

In practice, protein intakes generally reflect total calorie intake, which is why the International Consensus Conference on Foods, Nutrition and Performance in Lausanne stated that protein should comprise 12-15% of total energy intake. This assumes that your calorie intake matches your calorie requirements.

• Endurance athlete moderate or heavy training, 1.2-1.4 (g) protein requirement per kg body weight

• Strength and power athlete, 1.4-1.8 (g) protein requirement per kg body weight

• Athlete on fat-loss programme, 1.6-2.0 (g) protein requirements per kg body weight

• Athlete on weight-gain programme, 1.8-2.0 (g) protein requirements per kg body weight