Stress fractures are one of the most common and potentially serious overuse injuries reported in athletes, both elite and recreational. With this in mind, Andrew Hamilton looks at recent evidence linking stress fractures and nutritional status… MORE
Thiamin: If you rely too much on snacks and convenience foods, you may be short of B1.
Vitamin B1, or thiamin, is a crucial vitamin for athletes, as it is necessary for the process of converting carbohydrates into energy. Because of this, the requirement increases the more exercise you take, and the more food you eat. Some standardised Recommended Daily Intakes take this into account by recommending an amount of thiamin required per calories consumed – for example, the World Health Organisation recommends 0.4 mg thiamin per 1,000 calories.
So, do athletes need extra vitamin B1? The standard wisdom is that athletes burning more energy than Mr & Ms Average will eat more, and from the extra food they will get more B1. This assumption only works, however, if the extra food contains enough extra B1. Some studies have asked athletes to weigh and record all the food they eat in a week, providing them with mini scales to carry around. Results from such studies have been used to ‘prove’ that the participants of the studies were getting enough vitamin B1. However, a team of German researchers have recently pointed out that there is a snag with this type of research. People tend not to be totally honest about what they’ve eaten!
A team of sports scientists and nutritionists from Hamburg and Freiburg decided to investigate athletes’ B1 status, using a number of different methods.
Sixty-one athletes were asked to weigh and record the food they ate. They also had their blood and urine B1 levels measured. When the participants had been weighing and recording their food for two days, they were interviewed, and encouraged to remember if there was anything they had left off the record. This revealed that there was a tendency not to record high-calorie drinks (colas, juices), high-calorie snacks (eg, chocolate, chips) or food eaten in restaurants after training. This meant that the original food record would show a higher proportion of B1 per calories eaten than the true figure reached when all the ‘forgotten’ foods were added in. This is because B1 is one of the more fragile vitamins – it is easily destroyed by food processing. Therefore, it tends to be low in prepared snack foods, and much higher in foods closer to their natural state – eg, wholemeal bread, brown rice.
These results indicate that studies relying on self-recorded food intakes are unreliable for assessing B1 intakes. The researchers therefore concluded that the common assumption that athletes will eat more food thereby ensuring extra B1 intake cannot be confirmed. When assessing B1 intake from the more rigorous food records obtained in this study, over 34 per cent of the athletes did not meet recommended levels. Blood and urine levels of B1 were also found to be low, although these results were difficult to interpret
Athletes wanting to ensure adequate B1 intakes therefore need to ensure that they aren’t relying too much on heavily processed snacks and convenience foods. Pulses and wholegrain cereals are an excellent source of the vitamin, as is yeast extract. Fresh fruit and vegetables can also provide fair amounts.
(‘Vitamin B1 status in athletes of various types of sports’, Rokitzi et al, Med Exerc Nutr Health vol 3, pp240-247)