You've probably heard this all your life, and it's difficult to imagine it not being true. However, it is the exact opposite of what many low-carb proponents maintain. They say we should be minimizing our carbohydrate consumption, favouring quality protein foods like meats instead, and that they don't have to be lean to be good for us.
Let's look at something that is not controversial: HDL or high density cholesterol, otherwise known as "good" cholesterol. Most of us are now aware that it's not so much our total cholesterol that is important, but the ratio of the total to "good" cholesterol. In other words, we want HDL to be as high as possible, and the ratio to be as low as possible.
Furthermore, it is widely recognized that low HDL is a potent predictor of coronary heart disease, even more so in women than in men. This is an even better predictor than the ratio of total to HDL.
For example, this is from the Jewish Hospital of Cincinnati:
There is considerable evidence that low levels of high-density cholesterol (HDL-C) are a contributory factor in the development of atherosclerosis and coronary heart disease (CHD). Low HDL-C is one of the most common lipid disorders in patients with premature coronary artery disease. In the Framingham study, for example, low HDL-C values were associated with increases in risk for CHD of approximately 70% in men and of more than 100% in women. (my emphasis)Edit (2014): This link is no longer working. Here is another link to the same quote.
High triglyceride levels are the other uncontroversial measurement: the higher your triglycerides, the higher your risk for cardiovascular disease.
You would think this would be an easy nut to crack. Focus on increasing HDL and lowering triglycerides, and you'll have your health under control. For some people this is genetic, and sometimes there is an underlying medical condition, but for most of us, it's determined by our diet.
So how to go about increasing HDL cholesterol and reducing triglycerides?
This is what the New England Journal of Medicine has to say:
When fat is replaced isocalorically by carbohydrate, high-density lipoprotein (HDL) cholesterol decreases in a predictable fashion.Going back to the Jewish Hospital of Cincinnati website quoted above, we read that:
Triglyceride-rich particles derived from dietary fat, chylomicrons, are not themselves associated with CHDIt goes on to list the following 6 most common causes of high triglycerides:
excessive alcohol intake, exogenous estrogens or estrogen agonists, poorly controlled diabetes, beta blocker drugs, corticosteroids, and uremia.The most common causes of low HDL:
Patients with hypertriglyceridemia usually have lower HDL cholesterol and a higher risk of heart attack and stroke. Beta blockers, poorly controlled diabetes, uremia, anabolic steroids, corticosteroids, male sex hormones (testosterone), excessive zinc intake, and severe physical inactivity lower HDL cholesterol levels.I don't see dietary fat anywhere in that list, do you? Never mind, let's continue....
The textbook, High Density Lipoproteins, Dyslipidemia, and Coronary Heart Disease, edited by Ernst J. Schaefer also has this to say:
So now we know that poorly controlled diabetes is a factor in high triglycerides and lower HDL. We also know that diabetes is a disease that results from the body's inability to properly manage carbohydrates. And we have also learned that low fat, high carbohydrate diets lower HDL.
This might leave you wondering why we are encouraged to replace fats in our diet with carbohydrate.
It's not clear to me either. I can tell you one thing for sure: while there are plenty of studies that show that people who eat lots of fat have more coronary heart disease, it's unclear how much carbohydrate they eat. Put another way, how do we know it isn't the carbs, rather than the fat, that caused their heart disease?
How many people do you know with heart disease or low HDL but who don't eat plenty of grains and sugars?