Drinks, trainers and protein shakes which purport to be performance enhancing have a "striking lack of evidence" to back up their claims, a study suggests.
Researchers said that it was "virtually impossible" for the public to make informed choice about the benefits and harms of advertised sports products.
The study's authors examined the science behind the marketing and found that more than half of 104 performance enhancing products made claims which were not substantiated by any evidence.
The researchers from the Oxford Centre for Evidence Based Medicine judged that of those that do, half of the evidence is not suitable for critical appraisal.
The vast majority of the critically appraised studies (84%) were judged to be at high risk of bias, according to the research which is published in the online journal BMJ Open.
The absence of high-quality evidence is "worrying", the authors conclude.
"There is a striking lack of evidence to support the vast majority of sports-related products that make claims related to enhanced performance or recovery, including drinks, supplements and footwear," they write.
"Half of all websites for these products provided no evidence for their claims, and of those that do, half of the evidence is not suitable for critical appraisal.
"No systematic reviews were found, and overall, the evidence base was judged to be at high risk of bias."
Deborah Cohen, BMJ investigations editor, said: "These misleading messages filter down to everyday health advice by company-sponsored scientists who advise high-profile sports bodies.
"For instance, fear about the dangers of dehydration has become gospel and now influences what and how we drink when we exercise. It's a triumph of marketing over science."
A BMJ and BBC Panorama investigation, which examines the research, also looks at claims that found that while sports drinks may be helpful for elite athletes, the drinks companies rarely study ordinary gym goers.
The Panorama investigation also suggests that the European Food Safety Authority should do more to regulate these marketing claims.
Dr Matthew Thompson, senior clinical scientist at Oxford University's department of primary health care sciences, told the programme he would like to see "a more scientific and rigorous approach" to assessing the basis of food claims in Europe.
Professor John Brewer, head of sport science at the University of Bedfordshire, said: "There is a wealth of high-quality scientific evidence supporting the sensible use of sports drinks and nutritional supplements in appropriate environments.
"Whilst those who exercise as a means of keeping fit and losing weight may find that water is a useful and simple means of staying hydrated and do not therefore require sports drinks, those who compete intensively for long durations have been shown by numerous studies to improve their performance through the sensible consumption of sports drinks.
"It is essential that athletes who use sports supplements chose reputable manufacturers who can justify their claims with scientific evidence, and have their products screened to ensure they do not contain WADA (World Anti-Doping Agency) banned substances."
A spokesman for the British Soft Drinks Association said: "It is well established that one of the factors that can help sporting performance is drinking the right amount of the right kind of drink, and there is a range of sports drinks available which are designed to meet the varying requirements of different kinds of exercise.
"Their formulation is based on the latest scientific evidence and medical knowledge, and sports drinks carry nutritional information on the label, including the calorie content.
"By helping people participating in sport to perform better and to recover more quickly, sports drinks can encourage people to exercise more."
Panorama - The Truth About Sports Products airs tonight at 8pm on BBC One.
Health Benefits Of Running
Helps You Sleep
Having trouble nodding off? It stands to reason the more energy you expend during the day the more likely you are to be able to fall asleep easily without feeling restless. Beware of exercising too close to bedtime though as this can leave you feeling over-stimulated and wide awake.
Running boosts blood flow and oxygen to the brain. It also promotes the growth of new brain cells. Studies suggest the effects are strongest in the hippocampus, the region of the brain associated with learning and memory.
Good For Your Bones
As a weight-bearing exercise, running helps to build strength in your bones and can reduce the risk of bone disease, osteoporosis.
Running makes the skin appear plumper and smoother by boosting the production of collagen in the skin cells and promotes a clearer complexion by transporting nutrients and flushing out waste. By stimulating circulation and drawing blood to the surface of the skin it promotes a rosy glow while toning the muscles in the face to counteract sagging.
Makes You Happy
Forget reaching for the chocolate to cheer yourself up. Instead, get your running shoes on. A natural anti-depressant, running stimulates the brain's pituitary gland to release endorphins, the body's natural feel-good chemicals. Plus you won't get any of those post-chocolate guilt pangs - just a feeling of achievement.
As well as boosting your mood, running increases your ability to cope with everyday stress. Go for a run in the morning before work and you'll be in a much better frame of mind to cope with the day's ups and downs.
Running changes the speed with which your body is able to burn fat by altering your metabolism. The average person burns approximately 300 calories per half hour of 10-minute-mile running, making it one of the best energy and fat burning exercises there is.
Improves Muscle Tone
Not only will running help you lose inches, it will help you convert excess fat to muscle, leaving you with a leaner and more defined silhouette - including the upper body as well as your calves, thighs and bottom.
Boosts Immune System
A 2010 study of 1,000 people, published in the British Journal of Sports Medicine, found that regular exercise nearly halved the chances of catching cold viruses, or at the least, made the infection less severe.