Most Europeans do not bike daily. Most drive cars where they need to go. You are not losing 5 to 10 pounds in 10 days (unless you are dehydrating yourself). 5 pounds would be a 17,500 calorie deficit or 1,750 per day. The base metabolism for a male is around 1800 calories. That means that you'd be eating 1/10th of a banana every day to get that type of loss. For me a century bike ride (100 miles with 5,000ft of climbing) consumes about 2,900 calories. Are you doing century bike rides every day while only eating 1,200 calories while in Europe?