I fell like there's an awful lot of confirmation bias in people's reports of how well low-carb diets work, just like there was back when low-fat diets were the big fad. In general, any deliberate change in your diet is likely to lead to results, at least in the short term, as you're paying that much more attention to what you're eating. This is similar to the strength of the placebo effect in medical studies; one reason it's so strong is that even the people getting the placebo in the study are getting a lot more medical attention, and are paying more attention to their health.

Now, I suspect that low-carb diets do actually work better than low-fat, merely because it's easier to keep the calories down on a low-carb diet. "Carb-loading" is a popular way for athletes to give themselves plenty of energy to perform for a reason; carbs are the easiest way to boost calorie intake. So if you have an extreme low-fat diet, you wind up replacing the fat with even more calories in carbs; I can't count how many low-fat foods I've seen that just add a bunch of sugar to make it taste better.

But that doesn't mean that low-carb is a magic wand. In fact, it's fairly dangerous in some ways. Low-carb means you wind up replacing the calories from carbs with fats and proteins; a lot of people eat more meat as a result. Eating a lot of meat can increase your chances of getting certain kinds of cancer. I've seen studies that showed that in the long run, low-carb and low-calorie diets had about the same effects for weight loss, but the low-carb dieters were at a slightly higher risk for cancer due to the extra meat they ate.

I actually think that a large amount of the value of low-carb comes from cutting out the worst form of carbs, sugars. There is an awful lot of modern food that is being loaded with more and more sugar, especially given how cheap HFCS is. It's a very cheap and easy way to make mediocre food taste better; so we wind up eating a lot more sugar than our bodies can handle. Avoiding foods that have sugar added can help a lot.

There has also been a lot of diet fearmongering over something else that has traditionally been used to make food taste better: salt. Lots of foods are sold as "low-sodium" ever since people started blaming salt for heart disease. The problem is, most of the reason for that was based on correlation, where causation had never been shown; some groups of people at higher risk of heart disease were eating more salt, but there was never any good evidence that the salt was the reason for the risk. Reducing salt in food has meant replacing it with other things to make the food taste better, like sugars and fats.

There have been an awful lot of diet fads over the years. Many of them lead to more problems than they solve, as people take them to an extreme, and wind up replacing what they're cutting out with something equally bad or worse. And many of them have lots of adherents who proclaim their advantages, due to confirmation bias, while dismissing anyone for whom the diet doesn't work as not doing it properly (the "no true Scotsman" fallacy).

In the end, "eat less, exercise more" is the best way to lose weight. Yes, exactly what you eat can make a difference, but eating less (fewer calories) is a pretty good first step on the way to losing weight, rather than focusing on one particular source and winding up eating more or eating worse by doing so.