I have recently been reading the mounting evidence on two fronts, which thoroughly challenges conventional wisdom.  The first is that taking calcium (either dietary intake of dairy products, or by taking calcium supplements) has little to no effect on osteoporosis.  The second is that the amount of fat that you eat has little to no effect on your cholesterol levels.

Now obviously, everyone needs to still get a certain amount of calcium in their diet.  And the cholesterol findings don't give you an excuse to eat Big Macs with every meal.  But it seems that our understanding of how these two processes works is not entirely correct.

Dietary calcium is certainly helpful, as your body needs a certain amount of calcium to survive.  Without it, your body will leach calcium from your bones, and that is a big problem.  In fact, it turns out that your body sees your bones as a storehouse of calcium, and it dips into those stores to balance out the pH of your blood whenever it gets too acidic.  In other words, your skeletal system is one big antacid.

This gets interesting when you correlate high protein diets (such as what we eat in the West) with osteoporosis.  And contrast those with the rates of osteoporosis in Asian countries, where people live longer than Americans, but eat almost no dairy products, and yet osteoporosis is a rare condition there.

Fruits and vegetables help neutralize acid, while protein and grains are metabolized into acid.  This means that a protein-heavy diet will make your blood very acidic, and cause your body to leach calcium out of your bones in order to balance that.  According to the "acid theory" researchers, you can prevent osteoporosis by following Michael Pollan's dictate to "Eat food.  Not too much.  Mostly plants."

As for the cholesterol link, we are accustomed to thinking that eating bad, fatty foods will raise your cholesterol.  It's natural to use the phrase "artery clogging" to describe delicacies like French fries and ice cream, but it may not be true.  There is mounting evidence that what you eat has very little effect on your blood cholesterol - less than chemical factors caused by genetics and stress.

Most reputable outlets are still pushing "low cholesterol" diets, of course, because they are frankly healthier.  Just because eating fatty foods won't affect your arteries, that doesn't mean that you should eat three deep-fried meals per day.  Fat is the thing we need least of in our diet, regardless of cholesterol levels!

But even the Mayo Clinic's cardiologist Thomas Behrenbeck, M.D. admits that "the extent to which dietary cholesterol raises blood cholesterol levels isn't clear."  It seems likely that the type of fat - trans fats in particular, the boogeyman of the 21st century - matters more than the amount.  

Coronary heart disease is linked to high cholesterol levels, and every year heart disease kills more Americans than cancer.  Nevertheless, it is not entirely clear that high cholesterol levels CAUSE atherosclerosis (the thickening of the artery walls, and clogging of arteries with plaques).  For example, we know that smoking increases atherosclerosis, which is interesting since cigarettes are a non-fat product.