Is intermittent fasting a key tool for weight loss?

It's not a key tool. It's just a tool, that works for some and doesn't for others, to stay in a calorie deficit and manage appetite.

If "key" means universally necessary, no. If "key" means universally helpful, also no.

IF helps some people.

It was completely unnecessary for me, and would just be an arbitrary, annoying constraint on enjoying my life. I usually eat anytime from shortly after I get up in the morning, until shortly before bed - not continuously, but meals/snacks can occur anytime in that roughly 16 hour timespan, depending on my hunger and the logistics of that day's schedule.

I'd been overweight to class 1 obese for around 30 years, the last 10 or so of which I was a regular pretty intense exerciser. Then, using calorie counting and MFP, I lost from class 1 obese to a healthy weight in less than a year, have been at a healthy weight for 6+ years since . . .

. . . without IF, low carb, paleo, Bright Line Eating, Whole 30, carnivore, keto, whole foods plant based, clean eating, . . . etc.

There's nothing wrong with most of those, if they help a person feel full and happy while getting good overall nutrition, while en route to a long-term healthy weight.

But are any of them essential for everyone? No.

Even calorie counting isn't essential for everyone.

Getting calorie intake below calorie expenditure is the way to lose fat; counting calories isn't the only way to achieve that. It just happens to be the one that worked well for me.

The only key for weight loss is a calorie deficit. How one accomplishes that is individual.

I lost from obese to very lean while always eating 3 meals a day. IF was definitely not necessary.

Then I regained a bit of that weight due to meds and illness/injury and spent 2 years trying to lose around 20lbs with absolutely no luck. I just couldn't restrict enough to lose and if I did restrict enough to lose ~0.5lbs/mo, I would gain it back the next month with just a few restaurant meals.

My metabolism was in the toilet, just getting up to use the bathroom felt like my body was heavy. I basically felt like I was hauling a wet bag of sand everywhere. I just attributed it to my illness.

My neurologist prescribed IF for my nerve damage, and within a few weeks my energy was MUCH better, I was more able to get up and move, and engage in a lot more daily activities and exercise. And I was able to lose all of the weight at a normal pace again while eating substantially more calories.

So no, IF is absolutely NOT necessary for most people to lose weight. But for me, specifically, it was crucial for repairing my damaged metabolic function. For me, specifically, ketosis is highly energizing and kills my appetite, and my body jumps into it very, very easily, that's not true for everyone, and some people really struggle trying to adjust. I've heard many stories of crazy cravings and binge eating.

So for *some* people under *some* circumstances, it might be a very important weight loss tool. For others, it might be useless or dangerous.

Human bodies are complex.