If these people are getting "cold, tired and irritable" when cutting down on carbohydrate, what I wonder is are they compensating energy-wise by consuming more healthy fats or just moving toward a calorie-deficient semi-starvation diet? Those symptoms sound like what people doing low calorie low fat diets get, not what people consuming a healthy low-carb high-fat moderate protein diet get. I never feel cold, tired and irritable on a well-formulated ketogenic diet without some obvious non-dieting reason like I'm outside where it's freezing cold, didn't get enough hours of sleep, etc.