To clarify things a bit, just because something is low carb, it doesn't mean that it's a cutting diet. I eat fairly low carb all the time and I'm almost never cutting.
That said, most of the people who start a low carb diet do it to lose weight, not to improve health or strength/performance. So they pig out at the local all you can eat buffet before the first diet day then dive into the zero/low carb phase.
It takes a few weeks for a body that's run on carbs for 20-40 years to switch over to using fats for energy. The side effects of that switch over period vary but include tiredness, lack of mental acuity and lack of energy. Just like a fat bastard who has lived on chips and ice cream for the last 20 years may feel a little flat if they just dive into eating real food, like veggies.
The other factor is that the new low carb dieter cuts their calories via cutting quantity of food. That's always a bad move for someone who has never done low carb before or who has been mid to high carb for a year or so. You should actually increase the amount of food you eat during the first 3 weeks.
For example, one low carb diet, the Metabolic or Anabolic Diet, has the beginner bumping up their calories to 4000+ per day during the initial cross over phase. Strangely enough, you don't add fat and you have more energy to train.
Once the adaptation phase is over, then you have normal to higher energy levels.
But.
If you are on a low carb diet, or a mid to high carb diet for that matter, and are eating 2/3 or less of your normal calories, of course you are going to feel like crap.
Going to the extreme, the Velocity diet which is mostly protein shakes and a bit of fibre has a workout program that is a glorified warm up. Why? Not because it's also low carb. It's because you are on a near starvation calorie level and you feel like shit.
In all cases, I suggest that anyone struggling with a low carb diet is not struggling because of the types of food they are eating. It's either a lack of adaption (not giving it enough time) and/or calories set too low.
Remember, you can stuff yourself silly with clean protein and never put on fat, or minimal fat. Try that with rice.
https://www.t-nation.com/diet-fat-loss/protein-will-not-make-you-fat