The Lipid Hypothesis, manifested as "Eat a low-fat, low-cholesterol diet", has been the mantra for healthful eating for decades We are dutifully avoiding dietary fat and cholesterol which we believe are responsible for chronic disease, such as heart disease, type 2 diabetes etc. This hypothesis has been revered like a dogma for more than 30 years and your cardiologist will be repeating it to you whenever your cholesterol level rises or whenever you seek advice on dietary matter.
A group of scientists at the Harvard School of Public Health, led by Dr. Frank Hu, has in late 2000, published a review on “Types of Dietary Fat and Risk of Coronary Heart Disease: A Critical Review”. The scientists, one by one, have removed practically all the supports of the hypothesis that dietary fat and cholesterol cause heart disease and obesity. The authors said, in the review, that “it is now increasingly recognized that the low-fat campaign has been based on little scientific evidence and may have caused unintended health consequence”.
The Review noted only two studies have ever found “a significant positive association between saturated fat intake and risk of CHD(coronary heart disease)” and “a weak and nonsignificant positive association between dietary cholesterol and CHD” and “there is little direct evidence linking high egg consumption and increased risk of CHD”. The Review also found that “long-term clinical trials have not provided convincing evidence that reducing dietary fat can lead to substantial weight loss. On the contrary, there is some evidence that a diet containing a high amount of refined carbohydrates may increase hunger and promote overeating, which can lead to weight gain and obesity”.
Rather than simply dietary fat, the Review found that trans fat is the major culprit. “A higher intake of trans fat can contribute to increased risk of CHD through multiple mechanisms. First, trans fatty acids raise LDL cholesterol levels and lower HDL cholesterol relative to cis unsaturated fatty acids. As such, the increase in the ratio of total to HDL cholesterol for trans fat is approximately double that for saturated fat. Second, trans fat increases lipoprotein (a) levels, which are positively associated with risk of CHD. Third, trans fat raises plasma triglyceride levels, and increased triglycerides are independently associated with increased risk of CHD . Fourth, trans fatty acids can adversely affect essential fatty acid metabolism and prostaglandin balance by inhibiting the enzyme delta-6-desaturase and, as a result, may promote thrombogenesis. Finally, recent data have suggested that high intake of trans fat may promote insulin resistance in humans”.
In conclusion, what really matters is the type of fat in the diet, not the total amount of fat. Trans and saturated fats increase the risk for certain diseases. Monounsaturated and polyunsaturated fats,do just the opposite. They are good for the heart and most other parts of the body. And as far as dietary cholesterol is concerned, for most people, the mix of fats in the diet influences cholesterol in the bloodstream far more than dietary cholesterol.
Laymen are always at the mercy of the experts. But we all are laymen, though some of us are experts in certain fields, but never in all fields. Laymen (that means all of us) just have to hear from the experts with a critical mind and take the risk for listening or otherwise to the experts. Some experts are telling us now what the authorities have been advising us are wrong, what many experts are advising us are wrong: dietary fat and dietary cholesterol are not the culprits, trans fat and may be saturated fat are the culprits for CHD, over-eating refined carbohydrates is the culprit for obesity and type 2 diabetes.
Who do you want to listen to?
