The problem with nutritional science is that we've got as far as inventing the wheel. The infernal combustion engine it isn't, but the General We (Wee. Wheeee! Think what you will... ;-) ) thinks it is because it's the best we've got.

I've said here recently that I am not a believer that we could have evolved as we have without a significant fat / protein component in our diet. I'll go a little bit further, and say that until the "invention" of agriculture 12,000 years ago (there was no "Eureka" moment; it was a long slow process, so it was more an evolution than invention), there is no way we could have evolved to where we were on a carb diet, or even on the modern 'ideal', the balanced diet. The carbs weren't available. Our digestive system cannot deal with unprocessed cellulose - no four chambered stomach, only a vestigial appendix. Fruit wasn't available all year round, we had to come quite a long way before we sort-of mastered fire, and the wild precursors of our crops would not only have been far less productive (as wild fruit is far less sweet than the modern descendants), but sparser & harder to find. So where were all these carbs coming from?

On the other hand, there has been a good deal of stuff coming out in the last 10-15 years that suggests that evolution can make tiny but significant adjustments in an evolutionary eye-blink. It only needs one or two genes to switch on / off and suddenly e.g. the milk thing works (so I think I've read in recent past, anyway). Going back to my opening comment, we've barely scratched the surface when it comes to nutritional science. At the moment, it's all rather medieval dogma. Questioning the balanced diet is likely to get you at least metaphorically burned at the stake. The Sun orbits the Earth; no really, it does! It says so right here & you're not allowed to argue with this source...

The fact is, we don't know very much at all, so the dogma of balanced diet, of calories, of hopelessly crude tools such as BMI, is very much open to question. As for the alcohol guidelines... Don't get me started! If you have an enquiring mind, I heartily recommend a book called "How We Get Fat" by Gary Taubes. He is not everyone's cup of tea, and a lot of what he argues is open to debate. But, whatever your position on diet & nutrition, there is a lot of information in the book. Whatever you conclude, it ought to make you think.