Well, as someone who subscribed to that for years without seeing any added benefit, and in fact actually saw less results, I can tell you it's a sham. But don't just take my word for it. Do some Googling and you'll find a number of medical journals have conducted extensive studies on the 3 large meals vs. 6 small meals theory and found that there is practically zero difference between the 2 when it comes to your metabolism.
In fact, those studies also went on to find that you could literally eat all your daily calories in one sitting, or even more than 6, and the subjects had the same metabolic reactions. Furthermore, and if you only read this, I want you to let it absorb. Over time, the people who consumed multiple small meals throughout the day actually lowered their metabolism make it harder to achieve their goals.
One last thing of note. These studies found that the person who ate less meals in larger portions experienced much less frequent hunger and urge to eat throughout the day. As I've said, I have real world experience in telling you I have seen better results eating 2 to 3 large meals a day. I was ravenous all the time when I ate 6 to 8 meals a day like I did for years. When I eat 3, I'm more than fine with controlling my hunger throughout the day, and in fact I'm starting to see added physical results because I made the switch.
So what does this mean for you? Well, for one, it makes eating much more convenient. As someone who used to take literally a grocery bag full of food to work with me every day, it's incredibly inconvenient to prepare so much food on a daily basis. It's also very stressful when you are running late and forgot to prepare your meals, so you're having to run somewhere on your lunch break to get more food or worse, getting processed junk out of the vending machines.
So relax. Have a simple breakfast, lunch and dinner. 3 larger meals a day. Heck, 2 if you really want to make it easy on yourself. I can almost assure you you'll see better results and less hunger, as long as you're eating the proper balance of fat, protein and carbs. If you don't believe me, keep on eating those 6 inconvenient meals a day and risk slowing your metabolism and being hungry all the time. The choice is yours, my friends!