since you brought up 'low fat' -- many people are often under the misconception that if something is labeled 'low fat' or 'fat free' it must be healthy.
there are many things that have no fat, but are pure calories. soft drinks, jam, candies, etc. sugar is even worse for you than fat.

some fat is necessary in your diet. i actually disagree with all of these health fads... like with the 90s it was completely eliminating fat from your diet and going overboard on the protein, now its avoiding carbohydrates, etc.
i think that completely eliminating something from your diet can be just as harmful as overindulging in it. as for what is good for you? humans are omnivores. millions of years of evolution put us here like this. vegans? pfft..... eat your meats, grains, fruits, vegetables, and dont overdo it on the unnatural crap like sugars, synthetics, additives, preservatives, caffeines, nicotines, etc and youll be fine :)