This pertains to your comment about how people used to eat and didn't get fat.

There are probably quite a few nuances to that subject but I will bring up a few that I think are particularly important.

Insulin resistance is the key so let me start out by saying what causes it. In a nut shell, having insulin stay too high too long over an extended period of months or years. Once you understand what causes it and look at the difference in eating patterns I think you will see why more people "got by" with higher carb consumption in earlier generations.

First I will get exercise out of the way. Exercise is a rather poor way to lose weight simply because it takes a LOT of it to burn any significant calories. You can't outrun your fork and if you try LOTS of exercise will make you very hungry. Exercise is great for health. Loosing weight it is only a minor help. So what does this have to do with insulin and previous generations. Exercise DOES help tremendously with insulin sensitivity. It will make insulin "work better". That is a good thing for a diabetic. What does insulin do? It is a fat storage hormone (among many, many, many other things it is responsible for). Having insulin sensitivity is a double edge sword. It not only puts excess energy to fat, but if a person is metabolically flexible as they should be when normal and insulin sensitive they can also switch to fat burning easily when insulin is low. This is a long explanation and you are probably getting bored. But having that flexibility is one key why our forbearers may not have had the problem we do today. They ate big meals but turned around and could burn that fat right off. Once a person becomes insulin resistant and metabolically inflexible, the fat burning almost never turns on.

So why are we as a generation so metabolically inflexible and insulin resistant and they weren't?

There are at least two main keys to becoming insulin resistant. If you think about how weeds become roundup resistant it will help. Not exactly the same but along the same line of thinking. The two keys are 1. the total amount of insulin in the bloodstream with higher giving more opportunity for resistance and 2. frequency of the insulin spikes. I encourage you to listen to a bunch of Bikman's presentations. He covers it well. Number 2. is as important if not more important than number 1.

Previous generations ate basically three meals a day. I don't ever remember my parents "snacking" in between meals unless it was a holiday and going back for that second piece of pie. Dad had ate and was out of the house at sunrise. He packed a sack lunch which was enough but not a big meal. He was in by the time the sun went down and supper was when he got in. They ate three distinct meals. They drank mostly water with some tea (with sugar). Soda pop was a treat that they had once in a while or when going to "town".

Their insulin would have spiked at breakfast and being healthy went back down within a couple hours. So they had a low insulin period of at least a couple hours if not more before lunch. Bread on a sandwich so another insulin spike but again, a couple hours later it was back down to low levels and any fat they had gained could now be burned off because of low insulin. High insulin stores groceries. Low insulin burns them. Supper again bread, cream gravy with flour, maybe a piece of pie. Another insulin spike to handle the carbohydrates but by 10pm bed time or at least by 11 insulin was back low and for the next 5 or 6 hours body could burn fat and the liver could turn fat into glucose as needed during the night time "fast". Then break"fast" and the cycle starts all over. Three distinct periods, even on a high carb diet, where their bodies had a chance to burn off any fat they accumulated.

Contrast that to todays eating habits (encouraged by officialdom - I can remember when they tried to tell us many small meals a day was more healthy than three big ones - that is complete BS when it comes to metabolic health). Lets say they eat the exact same breakfast two generations ago did. Doesn't matter what it is. Eggs, bacon. pancakes, toast, whatever. But the same breakfast as above whatever it was. Same insulin spike. Ok so far (assuming they are metabolically healthy and not already insulin resistant like 3/4 of the US population is). Insulin spikes at breakfast. Ten o'clock rolls around and about the time insulin starts dropping we have a bag of chips and a Pepsi. Nope, no low insulin. It spikes again never going low so no fat burning possible. Lunch another sandwich and insulin goes up but has never got all the way down from the Pepsi and chips. Insulin up again till two or three o'clock and we are feeling peckish. Somebody brought some doughnuts over. No soda pop but sugar in the coffee. Up insulin goes again without ever getting low from lunch. Supper comes around with an other insulin spiking meal with it never having come down from mid afternoon snack. Then a bowl of cereal or ice cream while watching TV at 9 and that puts insulin high for the next three hours at least. Might get two or three hours while sleeping with insulin low. But that is for a metabolically healthy person. A person who is insulin resistant WILL NEVER HAVE INSULIN LOW ANY TIME DURING THE 24 HOURS. 

How do you become metabolically unhealthy? By eating or drinking 6 or more times a day and never letting insulin go low. THIS WAY OF EATING CREATES INSULIN RESISTANCE. Once you have insulin resistance, it may take several DAYS of low carb eating for insulin to ever get low. It is a merry go round. It never stops. It may take the first several years of eating poorly and creating 1. very high levels of insulin and 2. high levels in the blood stream nearly 24 hours a day for a person to become metabolically unhealthy and insulin resistant. But when they finally get that way they may have insulin levels of 25 for most of the time to get insulin to do the job it needs to keep blood sugar under control instead of the 5-9 level it should be during times between meals. At those high levels it may take several days of either 1. fasting by not eating or 2. eating a severely low calorie diet or 3. avoiding foods in the diet that raise insulin (a low carb ketogenic diet). It doesn't happen over night.

Once you understand all of the above, it is no longer a mystery why our forefathers could eat so much bread and pasta and get by with it. Hard work helped. But the main thing was they did not eat 6 or 10 times a day or some peoples cases nearly constantly, nibbling on stuff all day long. And a high fructose soda pop in hand with a sip every half hour is a guaranteed way to have a high insulin level all day long. That describes me from early adulthood till I was diagnosed diabetic at about 30. That is what did it to me. Our forefathers didn't have a Pepsi in hand all day long. 

Insulin is the key to fat burning. If insulin is high you DO NOT BURN BODY FAT. You store excess energy intake as fat. If you are already insulin resistant your insulin levels essentially never go low no matter what you eat unless you 1. fast for a period of time without eating or 2. eat extremely low calorie meals low enough so eventually insulin will lower or 3. eat only food that does not raise insulin. But being insulin resistant even doing number 2 or 3 it may take several days to get insulin low.

We are eating too often foods that raise insulin. One big help would be just going back to three distinct meals a day. For a person that is already insulin resistant it would be a very slow process but would eventually help. The other option is to not eat food that raise insulin and what of those foods we do eat do it only 3 or preferable only 2 times a day. There is another way and that is to drop calories to a much lower level. But about 300 of those calories will not be of benefit because that is how much the average persons metabolism drops under calorie restriction. So maybe need at least 600 calorie drop before even thinking about helping. And if eating carbs 6 times a day forget about it even then because insulin is not going to drop. Just be extremely tired and in the winter cold instead. Oh, and be hungry as hell all the time.

All of the above is just a wild guess. I am not a doctor. I am not a nutritionists. I know not what I am talking about. I'm just a dumb dirt farmer (retired even) without the ability to learn such stuff. Move along. I just made it all up.