What we think we know

I suppose it's within the realm of possibility that readers believe that dietitians/nutritionists (and by that I mean real, accredited nutritionists, not ones that get there so-called degree from a phoney organization) actually know all there is to know about nutrition. Not by a long shot. The unfortunate fact is that an awful lot that needs to be known about nutrition and health remains unknown. But that, unfortunately, is part of what separates the qualified, registered dietitian from the pretenders: we're quite willing to acknowledge when there are doubts or mysteries around a particular nutrition issue. The fakes are more than happy to supply an answer as fact, when the actual science around the question is very cloudy.Which brings me to today's topic: what are some of the questions about nutrition that we're still struggling with; still hoping that science will come up with a definitive answer? And, more to the point, what about the questions that science has clearly answered, but about which we keep hearing contradictory reports. A question that continues to plague me, for example, is how the purveyors of those pills that promise both calcium and fibre can ignore the fact that the fibre causes the calcium to be unavailable for absorption. Do these guys know something that the scientific nutrition community doesn't? And speaking of such things, how come olestra (one of many sugar substitutes) took such a beating for allegedly causing certain nutrients to be unabsorbed when a high-fibre diet (which everybody promotes) will do the same thing?Then there's the water issue. I'm sure you remember me discussing it before, but in a nutshell it's a known fact that the human body requires zero glasses of water per day. What it needs is the equivalent of eight glasses (250 mL) of fluid, but it can get that from many sources like fruit, vegetables, milk (90% water) and even (gasp) tea and coffee. But yet, you'll read and hear on an almost continuous basis (no doubt abetted by the bottled water industry) that you have to have the proverbial eight glasses on a daily basis.Then there's the whole subject of fats and heart disease. What we now seem to know beyond any reasonable doubt is that rather than your total cholesterol level or the amount of LDLs (low-density lipoproteins) in your bloodstream, among the best predictors of future heart disease is your ratio of total cholesterol to HDLs (high density lipoproteins). In that regard we know three things: the higher your HDLs the better; a diet rich in polyunsaturates will lower HDL levels; and specific saturated fatty acids will raise them. Yet what the public hears is: consume oils rich in polyunsaturates and avoid fats (mostly animal) that contain saturated fatty acids! Go figure. In a similar vein, there's the issue of trans fatty acids. We know most assuredly that they're bad: they will not only increase the LDL level, but also lower HDLs. So, without question, it's a good thing to get them out of our food supply by eliminating products made with partially hydrogenated vegetable oil (PHVO). But the PHVO has to be replaced by something, and guess what it usually is: vegetable oils rich in polyunsaturates. Not only will this do a number on your HDL levels, but there's also the issue of the ratio of omega-6 fatty acids (from polyunsaturates) to omega-3 fatty acids. Please don't let your eyes glaze over.this is important stuff. It would be great if we could get more people eating fatty fish, but so far that doesn't seem to be working very well. Common sense (based on scientific evidence) would dictate that we replace at least part of the PHVO with animal fat, but that triggers such a scare response that it's likely not going to happen. So my question is: how did we get to this sorry state of affairs where emotional response outweighs good science? As I've also mentioned previously, the animal fats, at least those from ruminant animals, along with raising HDL levels, will also contribute conjugated linoleic acid, which has been shown to help reduce cancer risk.Please don't misunderstand me: I'm not for a second suggesting that we should go whole hog on animal fats; nor should we abandon vegetable oils, some of which (olive and canola) supply important levels of monounsaturates. What I'm saying is that we should adhere to a principle that Health Canada advocated many years ago. And that is that the fat in our diet should be roughly 30%, and that should be made up of 10% polys, 10% monos, and 10% saturates. It was a sound idea then and it's a sound idea now. The question is: how did it get tossed?