Pursuing a career directly related to your degree is not your only option. There are many roles in a range of sectors that could make use of the skills and knowledge you have gained on your course particularly with your interest and study in Science, your ability to handle data research and your problem solving skills. One option could be to work in engineering developing or improving sports equipment for example. With further study you could consider training to be a teacher or a lecturer in a Further Education College or University. Another option requiring further study would be a Masters conversion course to become a Physiotherapist or gain a post graduate diploma to become a radiotherapist. You could also continue your interest in nutrition by going on to a post graduate diploma or Masters to work as a Dietician. Another career area to consider would be to specialise as either a Sports or Exercise Psychologist. All of these occupations will require further study and details of where to find relevant courses can be found on the UCAS site or Find a Masters.
You could also consider applying for a Graduate Scheme which would be open to a graduate of any discipline. Some Graduate Schemes are particularly looking for Graduates with an interest in Science or Research.
You may also want to consider applying for other jobs in Sport which although not directly related to your degree studies maybe sports/activities that you would like to become involved in such as Sports Coaching or Sports Development.