"In 1969, 48 percent of children 5 to 14 years of age usually walked or bicycled to school (The National Center for Safe Routes to School, 2011). In 2009, 13 percent of children 5 to 14 years of age usually walked or bicycled to school (National Center, 2011). In 1969, 41 percent of children in grades K–8 lived within one mile of school; 89 percent of these children usually walked or bicycled to school (U.S. Department of Transportation [USDOT], 1972). In 2009, 31 percent of children in grades K–8 lived within one mile of school; 35 percent of these children usually walked or bicycled to school (National Center, 2011)."
[Source](http://guide.saferoutesinfo.org/introduction/the_decline_of_...)
1. As another commenter posted, total calories consumed per capita has gone up considerably since 1970.
2. As you posted, we move a lot less than we used to. There are tons of studies that confirm this across a number of different metrics (e.g. average grip strength has gone down considerably since the 80s, https://www.npr.org/sections/health-shots/2016/06/13/4815909... ).
We eat a lot more, of more foods that have higher calorie-to-nutrient ratios than we used to, and we move a heck of a lot less.
Exercise does have many positive metabolic and other benefits, but not anywhere enough to be a causal explanation on its own. If people started walking 5 miles a day, every day, not only would there still almost certainly be a widespread and growing obesity epidemic, but there's even an argument that it could be worse. Increases in activity tend to drive increases in hunger which will typically surpass caloric deficits if somebody is not actively controlling their diet, in which case they would not be fat in the first place.
This is made even worse by misleading advertising which will do things like showing fit athletes drinking Gatorade, Coke, etc during their training or competition. And somebody goes and does a couple of miles on a training bike and does the same thing - which is going to send their net caloric input skyrocketing.
> Increases in activity tend to drive increases in hunger As far as I know, certain types of high intensity exercise do so but not necessarily all exercise.
If we take your numbers at face value, that'd be a delta of 684 pounds per 20 years. Again kind of an obvious indicator why these long term calorie/pound measurements are pretty dubious, but at the same time also an indicator of why diet is just so much more important than exercise for weight management.
[1] - https://www.pewresearch.org/short-reads/2016/12/13/whats-on-...
People who stop doing sports suddenly gain weight. People who get into sports habit like running or swimming slowly loose weight.
So, imo, this uber simplified model of just don't work like that.
Presuming one does not replace the burned calories, even walking 5km a day will burn the calorie equivalent of about 80 pounds of fat over the course of a year. It adds up. Conversely, not walking 5km a day adds up. After suffering a broken leg I spent a couple years largely sedentery in my late 30s, and I put on 25 pounds in that time. I snapped out of my stupor, started exercising again, and burned it off in short order.
But two decades of "fat doesn't make you fat" probably didn't help, and neither did the continued trend of increasing empty calories from cheap vegetable oils, especially soybean oil: https://thedietwars.com/why-are-americans-getting-fatter-a-f...
https://www.ers.usda.gov/webdocs/charts/59529/indicators_goa...
>Added fats and oils provide more calories per day for the average American than any other food group
"The scientists theorize relationships among the global increase of plastics production, human exposure to microplastics, and the global increase of overweight and obesity in populations." https://www.niehs.nih.gov/research/programs/geh/geh_newslett...
You can note that average male height in the US continued increasing up until the late 1980s.
That points to a general caloric deficit up until roughly 1990--which is roughly where we claim the "obesity epidemic" kicks off.
Also, a graph of sugar doesn't include calroic fillers like "soy protein" which now seems to be in everything.
Fat is estrogenic, and estrogen accelerates growth plate fusion.
I meant bodyfat specifically
So we should expect people to continue to get fatter as we get better at engineering food.
Note that I don't think that engineered food is inherently bad, just that today most food are engineered to be unhealthy because that is better for sales.
As I said, engineering food isn't bad in itself, it depends on what goals you have when you engineer it. Just because Japanese people eat a lot of engineered food doesn't mean it is bad for them if that food wasn't engineered to make them fat.
Many say they slim down as they visit Japan, so I wouldn't rule it out.
What I'd want to see is if two countries that has the same snacks available had vastly different outcomes. But as far as I know most countries has domestic snacks so it varies wildly around the world. For example, why is Czechia much fatter than Slovakia? They were the same country 30 years ago.
I'm sure Japan has a variety of unhealthy foods, I don't see how that matters. That unhealthy food exists in Japan doesn't tell us anything about how much of it people actually eat.
That's why I linked the video, its author talks about the experience of the average person, here's an exact link: https://youtu.be/lr4MmmWQtZM?t=176.
I cannot stress this enough, the only thing that matters is what is readily available to the average person. That's the determining factor of most people's diets, not what's theoretically possible to purchase.
Protein is a major appetite suppressant. I'd read this but never really realized how true it is until starting on a protein heavy diet. I now eat near 500g of chicken breast a day, and by the end of the day I'm basically having to force feed myself. Yet 500g of chicken breast is less than 800 calories! And the other stuff is just to balance out my diet.
And I love eating as much as anybody else. But you simply cannot eat that much when you're on a protein heavy diet. Finding data on protein consumption rates over time is difficult, but I'd hypothesize we were probably much higher on effective protein consumption in the past. I know absolutely nobody that regularly had something like 'steak and eggs' for breakfast, yet it seems that was indeed a thing at some point.
[1] - https://en.wikipedia.org/wiki/Digestible_Indispensable_Amino...
Meat consumption is associated with higher BMI: https://pubmed.ncbi.nlm.nih.gov/32443920/ (summarized in: https://www.news-medical.net/news/20200615/Vegetarians-have-...)
Observational studies on diet are completely irrelevant because they invariably end up comparing some group of people opting into some diet or another, versus the population at large. An apples to apples comparison would be something closer like comparing those on a long-term vegetarian diet to those on a long-term carnivore or keto diet. The idea is to just make sure you control for the "I care about my diet and have sustained dietary self control" variable.
Something you have to keep in mind in modern times is also food processing. A 10 piece set of McDonalds chicken nuggets weighs around 163 grams, but contains only 23g of protein. By contrast 163 grams of chicken breast contains just about exactly 50 grams of protein. The more processed something is, the more it tends to drift from its nominal nutritional value, and it's safe to say that a much larger chunk of people's "meat" is also coming from these sort of heavily processed meat-like foods.
As for the studies, you have a common bias they suffer from. You're comparing some group of people opting into some diet or another, versus the population at large. An apples to apples comparison would be something closer like comparing those on a long-term vegetarian diet to those on a long-term carnivore or keto diet. The idea is to just make sure you control for the "I care about my diet and have sustained dietary self control" variable. Unfortunately actually controlling studies means you'd get far fewer exciting headlines and bullet points for our CVs.
[1] - https://www.pewresearch.org/short-reads/2016/12/13/whats-on-...
The obvious answer for why portion sizes are increasing is that food keeps getting cheaper, in particular relative to other costs in the food service industry. The traditional formula for restaurant pricing is 1/3 ingredients, 1/3 labour and 1/3 overheads; if your food costs have decreased over time but your rent and labour costs continue to increase, it's natural to increase portion sizes to maintain the appearance of value-for-money. The same would apply (to a moderately lesser extent) to convenience foods sold at retail. This has a quite drastic anchoring effect - when you normalise excessively large portions, reasonable portions seem meagre.