American Journal of Clinical Nutrition, Vol 67, 573S-576S, Copyright © 1998 by The American Society for Clinical Nutrition, Inc


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REVIEW ARTICLES


Effect of low-fat diets on plasma high-density lipoprotein concentrations
MB Katan
Department of Human Nutrition, Wageningen Agricultural University, The Netherlands.

Low concentrations of HDLs in plasma are a strong predictor of risk for coronary as well as other cardiovascular diseases. There is increasing evidence that this relation is causal and that interventions that change HDL concentrations also change risk. One such intervention is exchanging fat and carbohydrate. In controlled trials, low-fat, high- carbohydrate diets decrease HDL concentrations. The effect is strongest when carbohydrates replace saturated fatty acids, but is also seen when carbohydrates replace mono- and polyunsaturated fatty acids carbohydrates. The effect is seen in both short- and long-term trials and therefore appears to be permanent. This finding is supported by epidemiologic studies in which populations eating low-fat, high- carbohydrate diets were shown to have low HDL concentrations. Weight losses with consumption of low-fat diets could theoretically counter effects on HDL, but in published trials weight losses have been modest and insufficient to offset the decrease in HDL concentrations induced by carbohydrates. Thus, replacement of saturated fat by carbohydrates adversely affects plasma HDL concentrations; replacement of saturated fat by unsaturated fatty acids deserves consideration as an alternative.

The Journal of Nutrition, Health & Aging
Volume 5, Number 3, 2001

Diet and Coronary Heart Disease: Findings from the Nurses' Health Study and Health Professionals' Follow-Up Study

F.B. Hu, W.C. Willett

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Carbohydrates

Prevailing dietary guidelines recommend a low-fat high-carbohydrate diet to lower blood cholesterol and prevent Coronary Heart Disease (CHD). However, low-fat, high-carbohydrate diets reduce HDL levels and raise fasting triglycerides. The adverse metabolic effects are exacerbated in the presence of underlying insulin resistance. Because low HDL and high triglyceride levels independently increase risk of CHD, the value of replacing overall fat with carbohydrates has been questioned. Indeed, in both NHS and HPFS, exchange of carbohydrates for total fat has no apparent benefit. More disturbingly, and as predicted by metablic studies of blood lipids, exchange of carbohydrate for mono- and polyunsaturated fats was associated with significantly increased risk of CHD.
Traditionally, carbohydrates are classified into simple or complex carbohydrates based on chemical structures. Most of dietary recommendations have emphasized the use of complex carbohydrates or starches and avoidance of simple carbohydrates or sugars. This was based on the belief that simple sugars would be digested and absorbed more quickly, which would induce more rapid postprandial glucose response. Numerous metabolic studies have challenged this view and it is now recognized that many starchy foods such as baked potatoes and white bread produce even higher glycemic responses than sucrose. That different carbohydrate-containing foods lead to different glycemic responses has led to the development of the concept glycemic index, a term first coined by Jenkins and Coworkers....
...To examine the influence of quality and quantity of carbohydrate, we examined the dietary GL in relation to incidence of type 2 diabetes in the HPFS and the NHS. In both studies, risk increased with higher GL [glycemic carbohydrate load i.e. bread and potatoes], especially in combination of low intake of cereal fiber.

[translation: cereal fiber does not mean "breakfast cereal" which may be mostly sugar and very little fiber. Psyllium husk is "cereal fiber".]