The four innovative new routes, set among some of the most breathtaking scenery in Wales, will be signposted with weight loss information.

The signpost idea, in association with Brecon Carreg Natural Mineral Water, is aimed at promoting the Beacons as "nature's gym".

On one of the routes, 27.2 miles based around the picturesque Talybont Reservoir, a cyclist weighing 15st 8lb could lose 1,195 calories - the equivalent of eight and a half Mars Bars.

The calorie controlled routes cater for all shapes and sizes ranging from people weighing just over seven stone to those weighing 14 and 15 stone.

Carol Williams, who is the tourism growth area development officer at Brecon Beacons National Park, said, "This is the first of its kind for a national park so, whether you're looking for a relaxing ride on quiet country lanes and canal towpaths, or you're more adventurous and fancy heading for the hills for a dose of excitement, these new cycle routes have something for everyone.

"The beauty of the cycle paths is that they are suitable for teenagers and families to enjoy and cycling is a fantastic way to get fit whilst still having fun.

"We want to show the Beacons are really nature's gym and a fantastic place to blast away calories by getting on your bike."

Gill Bullock, marketing manager at Brecon Carreg, said, "Our association with the Brecon Beacons National Park Authority is essential. The rainfall here, and the geology are our raw materials, so without this wonderful landscape Brecon Carreg wouldn't exist."

Brecon Beacons National Park spokeswoman Samantha Games said, "If you can see clearly how much weight you could lose on a single cycle run it is a big incentive to head for the hills with your bike.

"Hopefully it will attract children, teenagers and their parents helping to ensure entire families keep fit, healthy and in shape."

To help celebrate the launch of the calorie counted cycle rides an inaugural sunset cycle has been organised during National Bike Week on June 19 when families are being encouraged to don their helmets, climb aboard their bikes and pedal away calories