The book talks about that study in great detail, and it is not the only study mentioned. First of all, the initial weight loss in most diets is water weight and ends up being reversed over the long run because the body prefers to store fat when possible, and it is only possible during heavy insulin response. If you restrict calories, the body will drop temperature and restrict energy usage, so your calories in will still balance calories out, you will just be miserable.
The book uses many longitudinal studies that span 5, 10, even as long as 30 years to examine the relationship between diet and weight, and goes into great detail about the differences between the first part of a diet and going out several years, why people go off diets and why different diets are easier to stick to.
Also, one major group of studies you are neglecting is discussed heavily in the book: studies of diabetes and obesity in “malnurished” areas in poverty living mostly off of high GI grains like soylent mostly ends up being. Those studies include millions of participants and come to very solid results.
The second set you are neglecting is studies of unrestricted calorie low carbohydrate diets, which show better results than caloric restriction low carbohydrate diets over time, as the hormonal balance that so quickly allows fat to absorb blood sugar and prevents it from releasing fat is no longer present.
There is an enormous difference, not just for weight loss, but for insulin resistance and all major markers of health. High HDL, low LDL, Inflammation markers, triglycerides, and insulin sensitivity all seem to be unaffected or negatively effected by soylent among those who voluntarily did blood panels before and after, just as we would expect.
I suggest you actually read the book instead of googling 5 second rebuttals to it and tossing out poorly research straw man points. Carbohydrates are best minimized for health as much as possible.
And personally, I’ve tried them all. plain caloric restriction causes extremely painful hunger pangs and puts me to sleep very rapidly, and even after persisting for 6-8 months my weight remains entirely stagnant. Low carb unrestricted diets, I’ve lost 7 pounds in the past month and have plentiful energy, my blood pressure, LDL, triglycerides, resting heart rate are all down, my HDL and insulin sensitivity have both risen, and I subjectively feel amazing, and not hungry at all.
The book really is worth a read. It’s extensive citations and review of the past 120 years of the literature on the subject is amazingly thorough and explains the physiological mechanisms in detail that match up quite closely to the details in my A&P book, and it is absolutely an enlightening perspective that has helped me, after nearly 15 years of obesity and weight gain, to get control of, and start making progress on becoming healthy. Also, if you think an analysis of 50 trials on a short coverage term beats an analysis of dozens of literature reviews and longitudinal studies, you may want to rethink your approach to scientific thinking.