Couple of obvious points to make:-
It is generally the case that the fatter a person is, the better looking their skin is when they are older, because extra fat in the skin means having fewer wrinkles. Why do you think there is a fad among some men for BBWs, for example? So, whether Nigella is fatter than someone else is relevant. The extra fat on her could well be extremely unhealthy, but she might look better on a superficial level than someone a lot skinnier or emaciated who happens to be healthier.
Here is a photo of "ugly" Nigella Lawson:-
http://www.magxone.com/uploads/2010/10/Nigella-Lawson-Magazine-2.jpg It just goes to show that if one takes a photo in a different lighting etc. , one can get an entirely different appearance in the photo. Most other photos show her to be more gamine and pretty. I think it's a certainty that she has used plastic surgery. A 51(?) year old woman that high-profile on TV who depended far more on her appearance to get her TV audience than any other "attribute", just has to have had some botox, nose job etc. etc. Simply put, a woman on an unhealthy SAD diet is extremely unlikely not to show some signs of serious aging past 40. Men can often get away with not looking aged for longer, due to their having thicker skin, regardless of diet, but that's rarer for women - by contrast, I've heard reports of middle-aged RVAFer women looking at least 10 years younger than their SAD-eating contemporaries.
Secondly, the photos that Paleophil showed of me actually harm his points. First of all, the photo of me with a shirt on shows me to have seriously bloodshot eyes and looking supposedly haggard and sickly. I think it was taken after c.6 months or so of doing the raw, palaeolithic diet. By contrast, photos of me a few months before going in for RVAF diets showed me looking very fat but jolly. The truth was, though, that before RVAF diets I was suffering from appalling ill-health and a lot of extreme pain, and, while I looked rather grim, in that photo on the left taken 6 months into this diet, I was far happier and in far better health than in previous years, with no constant, awful stomach-pains, no dizziness, no chronic fatigue etc. etc.
The photo of me on the right, provided by Paleophil from rawpaleodiet.com, is also highly deceptive. If you look at the whole photo, you would see that I was, at the time, actually extremely thin and had very skinny arms. Indeed, in the photo I made a humorous self-mocking-pose a la Schwarzenegger, with arms upraised, precisely because I was well aware of my own skeletal appearance. I should add that, at the time, I had been experimenting for many months with the concept of caloric restriction/fasting diets, which was why I was so emaciated-looking. Granted, though, I looked healthier than in the other photo, as this one was made c. a year or so later into this diet.