I started eating like this about 3 months ago, for the following reasons: wanting to lose a little weight (half-1 stone), because BIL had recently been diagnosed as diabetic and I'd been reading up on it, and then out of curiosity - would I lose the weight? Would I have this boundless energy of which people spoke? What exactly would happen if I cut out what to me appeared to be a major food group?
I couldn't be bothered to buy a book and follow an actual plan, which all sounded a bit severe, so I just stopped pasta/rice/potatoes/bread/sugar. And, for the first month, fruit, which from your body's point of view is only a baby step from a tablespoon of Tate and Lyle anyway.
I have lost the weight, about half a stone over 3 months (it's not a quick fix, which should hopefully be better for the future. I'm now a smidge over 10 stone and a size 12/14, which feels about right). And the energy lift was startling - it's the feeling of 'THIS is the fuel that my body's supposed to run on' that's kept me going beyond the initial 'I wonder what...' stage.
For the first couple of months, I was eating about 40-60g of carbs a day; now I would say I'm in the 60-100g range as I've added back in beans, lentils, the odd slice of wholegrain bread with my scrambled eggs, the occasional tablespoon or two of rice with a curry. And yes, even a slice of cake now and then - if I've gone to someone's for coffee, it's churlish to refuse on the grounds of my 'faddy' eating. For most carbing enthusiasts, this wouldn't even register as a low carb regime.
My daily menus look a bit like this:
Breakfast: about 2 large tablespoons of Total Greek yog with dusting of Splenda and chopped nuts or berries/ 2 eggs (scrambled or fried) with 4 rashers of streaky bacon. Porridge or a thin slice of wholegrain toast with the eggs is a semi-low carb option here.
Lunch: bowl of salady things with a protein like feta, chicken, prawns, etc. Semi-low carb option would be a large bowl of bacon and lentil soup.
Dinner: panfried meat with salad or veggies, courgette 'pasta' with sauce, curry on a bed of spinach. Semi-low carbing would include a small amount of wholewheat pasta, a couple of spoons of rice just to soak up the curry sauce or a generous portion of chilli which included kidney beans.
The semi-low carbing options I'm giving here mean that you pick one of these meals per day, not all three! I don't normally need snacks, but might have the odd handful of nuts, a Babybel or an apple. I personally haven't had any problems with constipation, probably because I drink tons of water and am eating large amounts of salad and veg.
To offset the missing carb calories, you need to ensure you're eating protein at virtually every meal and adding enough fats in the form of sauces like butter, cream, creme fraiche, etc. This is the really delicious part of it, but feels very contra everything you've ever done at first. If you're hungry, you're probably not eating enough fats. There's no need to go mad with them - it's not a carte blanche to eat your body weight in cheese - but a liberal hand with the olive oil or chucking in a tablespoon of sour cream, mustard and wine with the steak is necessary.
The downsides are that yes, it's more expensive than padding out the calories with what's effectively fluff, and yes, you have to prepare all your meals from scratch (because the ready meal manufacturers are padding their meals as much as poss with the cheap stuff).
The upsides are a calm and steady return to what should be your body's natural weight (this can take months, but there's no hurry), a general sense of physical wellbeing and a vastly increased energy level with no blood sugar lows. Equilibrium is the word here - never hungry, never sluggish, never feeling like food is in any way controlling your life, telling you to eat, not eat, etc. I'm a huge fan.