We don't know much about our bodies. I feel like every time a major news publication publishes an op-ed or a study, they're contradicting themselves[1]. One week eggs are bad, the next they're good. Same with dairy, carbs, and red meat. Then you mix in the whole "diet" complexity: Atkins? Paleo? Keto? Vegan? How do I choose?
When you study the longest-living peoples of the world, you also find extremely varied diets: the carbohydrate-rich Greeks rely heavily on fruits, veggies and whole grains. They also love goat's milk and wine. While natives of costa rica are primarily relying on "evil" white rice and beans, and heavy on pork and chicken. The people of Japan are also heavy on white rice, and virtually no fat in their diet, since their diet is primarily plant-based[2].
The truth is that everyone's needs are different. As an anecdotal example, I was convinced that keto was the right way, and that carbohydrates were not going to help me. Did I lose fat? Yes. Did I feel great? Sure. It turns out that even with great HDL and Triglycerides, my LDL and fasting glucose were still high. And I'm not alone in this problem from keto either [3].
After switching to a broader, less-restrictive diet, which now includes whole grains (quinoa, oatmeal, and wild rice), beans, and fermented vegetables (kimchi, sauerkraut), lots of fruits and vegetables (including starchy carbs like sweet potatoes and squash), I've lowered my LDL and fasting glucose (yes, now that carbs are back in my diet). Different things work for different people because everyone has a different metabolism. It seems that, if you study the longest-living people, the trends are as follows:
* Don't overeat.
* Eat mostly plant-based, whole or minimally-processed/refined foods.
* Leave 10-20% of your diet for indulgences. Virtually all of the longest-living peoples drink alcohol or coffee on the regular. And even then, by allowing yourself that affordance, you don't risk binge eating or rebounding for days/weeks/months on end.
* Ignore fad diets. Stick with the whole foods that you like to eat, get in some variety, but don't be dogmatic about dietary approaches, because not only will you likely not adhere to such restrictions, but you'll probably find yourself being contradicted by another study in the next 3-10 years.
[1] http://www.nytimes.com/2014/02/09/opinion/sunday/why-nutriti...
[2] http://www.nsca.com/uploadedfiles/nsca/inactive_content/prog...
[3] https://www.google.com/webhp?#safe=off&q=keto+fasting+glucos...