In my opinion there is a dangerous spate of books and websites which don't really stand up to much scientific scrutiny advising low-carb, paleo, etc. They are simply not held up by the majority of evidence, and rely on cherry-picked results. While it is true that sugar and refined carbs are bad, it doesn't follow that whole grains are bad (unless of course you specifically have a gluten or wheat intolerance or allergy), or that fat and animal protein are good. The argument put by paelo diet and the like poses a false choice between low sugar and low fat - but the scientific consensus points to the healthiest diets being low sugar AND low fat. Maximising intake of vegetables, fruit, pulses, nuts and seeds, and eating fish, lean meats and whole grains in moderation is a sensible and balanced plan. Animal fats, oils and spreads and refined carbohydrates and sugars should be avoided as far as possible.
Just my opinion based on my own reading, and my parents' successful use of plant based low-fat, no-sugar whole foods diet to overcome serious health problems. I would use quality peer-reviewed publications such as the BMJ etc. to check nutrition information.
As I've said on another thread, despite my own health-nut tendencies, I tend to think people past a certain age and/or with dementia have the right to 'unhealthy' foods as treats, as long as it doesn't worsen conditions they have such as diabetes or mood swings. And for people experiencing unwanted weight loss, of course they should eat higher calorie foods than the rest of us.