SAN FRANCISCO, CALIFORNIA. Rapidly accumulating evidence points to postprandial lipemia (high cholesterol and triglyceride levels after the intake of a fatty meal) as a major risk factor for coronary heart disease. This has led to a recommendation to reduce the intake of fat and increase the consumption of carbohydrates. A team of medical researchers from the Stanford University School of Medicine and the Tokyo Medical and Dental University now questions this recommendation. Recent research has shown that high carbohydrate diets increase fasting plasma triglyceride concentrations and that high fasting triglyceride concentrations tend to correlate with a greater degree of postprandial lipemia. Inasmuch as triglyceride-rich lipoproteins are highly atherogenic (ie. involved in the development of atherosclerosis) it would seem prudent to question the current thinking that high carbohydrate diets help protect against heart disease.
The study involved four healthy men and four healthy women (mean age of 57 years). The participants were randomly assigned to one of two groups. Group 1 consumed a diet containing 40 per cent carbohydrates, 15 per cent protein, and 45 per cent fat while the diet for the second group contained 60 per cent carbohydrate, 15 per cent protein, and 25 per cent fat. The diets contained the same amount of calories and saturated fat was less than 10 per cent of total calories in both. The ratio of polyunsaturated fat to monounsaturated fat was 0.9 in both diets. The participants consumed one of the two diets for 14 days and then switched to the other one after a two-week wash-out period.
Cholesterol, lipoprotein, and triglyceride levels were determined
at the start of the experiment, on the morning of the 15th day of
the two diet periods, and at two-hour intervals during the 15th
day. The researchers found that a high carbohydrate diet
increases the level of triglycerides, decreases the level of HDL
("good") cholesterol, and markedly increases the level of the so-
called RLP (remnant lipoprotein) cholesterol that is believed to
be highly atherogenic. They also found that the detrimental
changes in lipid profile persisted throughout the day in response
to breakfast and lunch. They conclude that substituting
carbohydrates for saturated fat leads to lower HDL concentrations
and higher triglyceride levels and that a lowering of LDL ("bad")
cholesterol levels can be accomplished equally well by replacing
saturated fat with monounsaturated or polyunsaturated fats as by
substituting carbohydrates for saturated fat.