The low carb eating system is about lowering your sugar intake. How does a low carb diet affect your vascular system - your arteries and veins?
First, some quick info about your vascular system. This is how the blood moves around your body. It starts at your heart and goes out through your arteries. It gets through smaller and smaller vessels to the tiny capillaries. At the capillaries nutrients are able to get through the walls and into your body! The blood takes up the waste materials at that point. Then the blood goes back up to your heart through veins and starts all over again. Since the blood circulates through all of this, the system is also called the "circulatory system".
So, how does this factor in with low carb?
There was a really odd study done in 2009 on mice which seemed to indicate that low carb diets hurt this blood system. Because mice normally don't get clogged arteries, they had to genetically engineer mice so they could have sensitive arteries. Then they apparently fed them a ton of fatty food and protein. The mice did in fact lose weight when compared with "normal menu" mice. However, they also got atherosclerosis (hardened artery walls).
When you read the Wikipedia Page on Atherosclerosis you realize that they say one of the causes in humans is High carbohydrate intake which means a low carb diet HELPS with this issue. On the other hand, animals and people eating trans fats definitely have issues. Fats like monounsaturated fats, on the other hand, are good for you (so fats like Omega-3 and Omega-6, found in fish).
So what it appears they must have done is been feeding the rats a trans fat acid rich diet. They assumed that people eating low carb must be eating a ton of trans fats. However, low carb is about eating healthy. It is about eliminating sugar from your diet stream - not about loading up on junk food. So low carb is about eating healthy, fresh veggies - and about eating healthy meats as well. It's about trading Ring Dings for broccoli, and also about trading high trans fat foods for lean turkey.
In short, I doubt they really fed the mice a healthy low carb diet - and the mice they used had to be genetically changed to even be part of the study in the first place. With humans, I know thousands of people on low carb diets who have stellar blood work and cholesterol levels. Again, the purpose of this diet is not about loading up on healthy fats. Its primary aim is to switch from sugar-laden products to fresh vegetables and healthy foods.