Wow, I haven't been that small since probably around the 4th Grade!
When I was 100 pounds I was at the mid school and had to go to school nurse once a month to weight checks for half a year up because they worried I could had been developing eating disorder instead of just not being able to keep up with my eating. They only let me be when it became evident that my weight was catching up my height, though slowly.
While we Europeans certainly do have our weight problems, situation is little better than in USA. And while for example in my country statistically many are overweight (especially men), the obesity rates are much lower than in USA. And because we generally are not petite people, many who fall to 'overweight' category are not that chubby nor in bad shape. For example Joy, my younger son, is statistically overweight. His BMI is bit on the over weight side, his body fat percentage is around 7-9 % depending the time of the season, he is over 6'1 tall and wears size M clothing. Ache is not officially overweight (and his BMI is very average 23), but the more generous description of him is 'lanky' and more likely descriptions are 'build like a baby squirrel in very bad year' or 'clothesline raised upwards' or the most insulting 'looks like a ski jumper.' So many people with BMI on the overweight side are not actually in any danger health wise.
Europe of course is very diverse place culturally and especially when it comes to food. I live on the Northest corner of the place and our diet is (especially traditionally) very different from Mediterranean and so is our culture. The most stables in our diet are bread (basically always whole grain, some wheat but for the big part other grains, especially rye and all kinds of mixed grain breads), potato and other root vegetables (beets, rutabagas, carrots etc.), wild berries, pork (and nowadays chicken) instead of beef mostly, fish and game. (And yes, we eat 'Rudolphs', which especially people in UK tend to find awful
) We have lots of room and few people and personal relation to nature is still important to many. Hunting is one of the most popular hobbies and we have very vast rights to roam also in privately owned forests and for example pick wild berries from other people's land. And many do.
Our government also uses taxation to strongly herd us to the directions they want to. Partly for environmental reasons, partly for infrastructural reasons private motoring is discourages, both car and gas taxes are very high and public transportation is subsidised and infrastructure is build to favour walking and cycling. Also food taxes are used to change our choices. Sugary products such as sodas are more highly taxed (and so more expensive) than more healthy options. We have also been lucky to escape some of the more unhealthy ways to prepare food. Traditionally oven and boiling have been ways to go and I have for example never seen a deep fryer in private residence in this country nor do I know anyone who would have such a thing. Only thing we fry in our home kitchens are Berliners and those we usually only make once a year for Walpurgis. Eating out tends to be expensive (and we have way less fast food options and for example McDonald's have never really made decent profit during the decades they have been in our market) so we mostly cook at home and also teach our kids to cook from early age.
And because we have public health care and so municipalities and state end up footing our health bills, they do have vested interest to keep us healthy. Not on taxing things that are bad for us highly (not only sugar but more so tobacco and alcohol) but we are offered lots of free or subsided exercise options. Not only bike ways and side walks everywhere, but cheap swimming halls, free outdoor ices in winter and tennis and basketball courts in summer, free cross country skiing routes with lights at winter and running routes at summer and so on. School lunches are also free for all and for example I never ate even one french fry or pizza slice at school nor does university cafeterias offer those kinds of options. My kids had pizza once a year when during the last month of school they got to vote the school lunch for Wednesdays and pizza often made it to top 4. Typical school lunch, or what they had in Joy's school today, is for example roasted herrings, mashed potato, salad (was grated carrot, cole and orange slices today according to Joy). Tomorrow they will have chicken-vegetable risotto.
We also take a different stand to everyday activity than what I think is typical in USA. For example when my kids were young and I was at home with them and Ache had started school and was still too young to walk alone (and around here we do consider our kids to be old enough to walk or ride their bikes to school alone when they are 7 or 8 but Ache was immature for his age), I everyday, rain or shine, 80 F or -20 F dressed both boys every morning to suitable outwear for the weather and walked with them to school (about 1 mile from our house), walked back home with Joy and then, few hours later walked the same trip again with them. If for whatever reason I drove Ache to school (yes, I did have my own car and money for gas), I felt compelled to explain everyone I met and who saw I was with the car, why it was absolutely necessary to take a car that day. I assume that in US it would be considered just efficient to take a car and make that five minute drive instead of having a almost half an hour walk in one direction with the kids who want to stop and play or explore every 100 yards. Around here taking the car would be considered laziness.
We may not hit the gym more frequently than you, but we are expected to do much more daily chores on our selves. For example it would raise eyebrows if able-bodied people hire someone to clean at their house, do their yard work for them (your own children living at home are the exception) or anything like that. If you are able, you are expected to do your own manual labour and that means quite a lot everyday activity. For example just shovelling snow tends to give you at least few 'gym hours' a week through winter. Then comes raking your lawn, turning flower and veggie beds, weeding, mowing your lawn (and you have to have a real big lawn or have a disability to justice the ride-on mower and not be considered lazy) and so on. And then there are dogs. Due to weather we basically can only keep indoor dogs, and also the outdoor dogs are expected to be taken to walks daily, and animal welfare act states dogs should be walked daily and given suitable exercise. So again, rain or shine, cold or hot, everyone is out walking with their dogs three times a day, all-together an hour at least, most often more. That kind of daily activity does a big difference especially for those people who do not consider themselves sporty.
But also when it comes to sports, there is a difference. I think the best way to explain it, is one conversation me and my husband had in the event with the US couple we had just met. We started small talk about weather and after that was exhausted, we moved to next safe topic; sports. We talked about our favourite sports and I talked about handball and skiing, husband about golf and tennis and they talked about (American) football. I innocently asked if they have lots of recreational football leagues also for ladies when the lady told she too was big on football. Turned out neither of them had ever played. They were talking about the sports they enjoyed watching, we were talking about sports we enjoy playing. Innocent communication mishap, but also very telling about the culture.