John has a BMI of 35 and is desperate to get it down to at least 25. He is trying a low-sugar, low-carbohydrate diet. John is likely to have difficulty losing weight while dieting because:

Because fat tissue require lower energy for maintaining them than body muscles.

Explanation:

In the Question it can be seen that john is highly obese as his body mass index (BMI) indicates. So most of his body mass is composed of fats and fats require smaller energy for their maintenance.

Many researches on obesity indicates that people don't lose fat cells by carefully eating. Acording to Kirsty Spalding our body has same number of fat cell which it is programmed to and only the size of fat cells changes. So we can either shrink the fat cells or increase their size. So by cahnging diet plan we could not destroy them.

So, John is facing difficulty in losing weight while consuming the low-sugar diet because most of his body mass is composed of fats and fats require lower energy for their maintenance.

to increase speed you need to decrease frictiona dn drag hense why sprinters wear tight track suits to keep tight against there skin to keep away from wind and decrease the amount of drag you are carrying.a swimmer will wear the tightest swim suit they can possibly fit into (i was a size 28 swim suit at meets i wore a   size 23) why? because the tighter your clothing is the less drag and negative force you have. the heavier the clothe the slower and more wind gets caught. cotton tends to hold onto alot of sweat and water making it slower then say a track suit (no idea what they are made of but they are really comfy around your answer )