Juice = sugar. The difference between fruit and juice is just the lack of fiber, which fasttracks the sugar absorption in the gut.
We ate bread even 100 years ago, and that’s the reason why there was a spike in artherosclerosis and diabetes. Processed food and vegetable oils just accelerated the process, we used to stand the carb beating for a few decades, nowadays even children are sick. Years of hunger during the war however did a lot to offset that damage.
But we didn’t eat bread when we were hunter and gatherers, and we didn’t have t2d, artherosclerosis and other crap back then. Watch Mike Eades talk, it’s great. Bread is enough to cause severe damage, even in the absence of sugar.
Well, 25g of carbs a day for most of us. Fasting will help. If I eat a plate of pasta I’m out of ketosis for 24-48 hours.
There is a big difference between willpower and willpower. Hardly anyone is able to stick to a diet where hunger is a constant compagnion, while most people are able to walk past a shop without shoplifting. I’m sure we agree that these are two very different things. But so are sticking to a diet where you have restricted food choices but can eat as much as you like vs. a diet where you have restricted food choices and not only have to stay hungry, but the reward systems of your brain are activated just as they are from heavy drugs, and you aren’t allowed to satisfy them.
In Keys starvation experiments, those healthy young men, selected for willpower because the scientists expected trouble, literally broke down after a couple of months of a diet that had 1600 calories, more than we recommend today for losing weight. They got serious psychiatric issues, a lot of them dropped out, the rest fantasized over food and recipes for most of the time.
Evolution just didn’t equip us for a situation where our hormones say “plenty of food, now fatten up” (high insulin) but we eat a starvation diet. You can put diesel in a gasoline car, you might be able to drive it for a while, but you should expect problems fairly soon. Exactly the same happens if there is a mismatch between our hormones and the food we get. It may not be noticable right away, but problems will creep up with time.