Rowan - Since my wife has cut her carbs down to very low amounts and increased the fats in her diet her HDL numbers have increased and triglyceride numbers have dropped.
This works for her because she is not a rodent, these are animals that have different dietary requirements than humans and anyone who has kept them should know that a high fat diet is really bad for them... our birds are the same way in that they cannot be fed a high fat diet either but are well adapted to eat more high carb foods.
Gluttony is an issue... and the sky is also blue.
Eat too much and you will experience weight gain but it is not as simple as calories in / calories out and we have covered the fact (ad nauseum) that the laws of thermodynamics do not apply to humans due to the complex nature of our metabolisms and how we process different food sources.
Evidence is mounting that the low fat / low cholesterol, low GI mantra that has been preached for decades has done nothing to improve general health and in many cases, caused declines in the the overall health of many populations.