> 121 eligible trials with 21 942 patients were included and reported on 14 named diets and three control diets ... At 12 months the effects on weight reduction and improvements in cardiovascular risk factors largely disappear.
You cut out the part that said the diets improved people’s health at 6 mo. But they were hard to maintain for 12 months. I think a lack of consistency is the issue. From your link:
>What if they'd lasted 12 months, or two years, or a lifetime? The benefit would likely have been greater and more long-lasting. The trick is to pick a diet with foods you actually like so that it's not so hard to stick with it.
Meaningful behavioral change is hard, especially in a modern food environment.
I think metabolic adaptation plays a larger role. In this Biggest Loser followup study, even after six years (!), participants' resting metabolism burned 20% fewer calories than a "typical person of their current weight":
> In contrast, a matched group of Roux-en-Y gastric bypass surgery patients who experienced significant metabolic adaptation 6 months after the surgery had no detectable metabolic adaptation after 1 year despite continued weight loss (17). It is intriguing to speculate that the lack of long-term metabolic adaptation following bariatric surgery may reflect a permanent resetting of the body weight set-point (18).
Simple, it's called a selection bias. The people able to long-term control what they eat aren't obese, so by running a study on obese people, you're essentially biasing the study towards subjects who have difficulty controlling what they eat. This means most of the subjects will struggle to stick to the diet long term.
I think these studies controlled the diets entirely? The notion is that they did not deviate from the diet, yet their body adjusted to return to the original weight. Presumably by slowing the metabolism and decreasing energy for activity. If activity was controlled as well that would be truly fascinating. There is quite a bit of room for optimisation apparently. Through hikers often have trouble maintaining weight after stopping because their metabolism becomes very efficient.
You might find this NYT piece on the winners of the Biggest Loser TV show interesting. Basically, "dieting" as a reduction in calories is a lose-lose game because your basal metabolic rate goes down so you have to keep eating less and less to keep it up.
Keeping up the basal metabolic rate is part of the rationale behind intermittent/extended fasting instead of pure calories-in-calories-out weightloss advice.
I fixed your question. If obesity is caused by poor [nutrition], why doesn't [weight loss programs] work long-term?
You answered your own question. Weight loss programs do not work long term because only healthy nutrition does. I have been downvoted here before, but I would argue that healthy nutrition is expensive. It is cheaper in terms of time and cost to consume quick meals full of carbs, sugars, chemical additives that wrecks our bodies. It not only takes money but also time to cook meals that are heart healthy, prevent diabetes, and provides healthy fats/proteins/carbs.
> Weight loss programs do not work long term because only healthy nutrition does
That's not entirely true, although it is a big factor. As an anecdotal example, there was a period of my life where nearly 100% of my diet was fast food: there was a McD's, BK, and Wendy's in my neighborhood. I did this part out of laziness, and part because Supersize Me annoyed me. In contrast to Supersize Me I dilligently tracked my caloric intake from those meals and intentionally limited things to be affect the changes I wanted to see in my weight.
Net result? I lost weight until I achieved my target, and then I was able to stay steady.
Would I recommend this plan? No. I was focusing purely on weight and I'm sure there were many other suboptimal knock on effects for my body. But people act like it is physically impossible to lose weight via pure caloric deficit and/or by consuming fast food. That's not true.
Yeah, there is definitely something we are missing. Some of the stuff about portion sizes and processed foods may actually be a symptom rather than a cause. I.E. those foods sell well because something else is wrong. GLP 1 inhibitors are expected to shrink the sales of snack foods and alcohol by at least 5% in the next couple years based on shifting preferences. So the idea that some chemical or pathogen we are exposed to has contributed to it isn't farfetched at all. Especially when we view the spread of obesity across the globe even to countries with very little discretionary income on average.
https://www.health.harvard.edu/blog/when-dieting-doesnt-work...
> 121 eligible trials with 21 942 patients were included and reported on 14 named diets and three control diets ... At 12 months the effects on weight reduction and improvements in cardiovascular risk factors largely disappear.