As someone who recently lost 40 lbs, I should say that it is generally true. A hard ergometer exercise can have a net effect of 240 kcal for one hour and gross

As someone who recently lost 40 lbs, I should say that it is generally true. A hard ergometer exercise can have a net effect of 240 kcal for one hour and gross effect of 320 assuming 80 kcal per hour body burn. 240 kcal is not much at all, provided that my body generally burns 2800 kcal a day. Not even 10% However limiting food intake reduces not only the calories, but vitamins and micronutrients plus minerals. Also not exercising at all means muscle loss and not so much fat loss, which can have severe effects in 3-6 months. So regular exercises are must, swimming for example 3 times a week plus some brisk walk in the park twice a week will do miracles. Not to forget proper feeding is it is as much important as reducing calories intake and creating calories deficiency. If one can't balance his food to have proper vitamins and minerals, one should resort to food supplements at least for calcium, potassium, magnesium, vitamins C, B6, B12 and E if you want to keep you heart and liver healthy during the process. Know what you eat and do the numbers. I started with 39% body fat and 33% muscle.. Now I am 30% body fat and 35% muscle with a lot of cardio. A close friend of mine reduced his food intake and albeit he achieved serious weigh loss, that was on the expense of muscle and tissue, rather then fat loss.. Personally I achieved my loss with the help of numbers and constant measures - get a proper scale that can report body fat/muscle/tissue, cross check with calipers, get a fitness tracker to track daily steps and calories, track you food, exercise, calories and progress.. There are so many sites and applications to do so.. And really important - do a blood work each 3 months for you heart and liver. A few drops of blood can give you so much intel Hope that helps