A slight fall in blood levels of HDL (“good”) cholesterol in men due to a low-fat, high-carbohydrate eating plan may not be a problem, researchers reported today at the American Heart Association’s 5th
Annual Conference on Arteriosclerosis, Thrombosis and Vascular Biology.
Instead, researchers said that the lower levels of high-density lipoprotein (HDL) cholesterol may be a result of lower levels of low-density lipoprotein (LDL or “bad” cholesterol).
“Even if a low-fat/high-carbohydrate eating plan leads to a slight reduction in the level of HDL in the blood, overall this may not reflect undesirable changes from a cardiovascular risk standpoint,” said Sophie Desroches, M.Sc., R.D., doctoral candidate in Nutrition at the Institute on Nutraceuticals and Functional Foods at Laval University in Quebec City, Canada.
HDL levels normally fall in response to a high carbohydrate, low saturated fat/total fat eating plan even when body weight stays the same or is reduced.
“This created a controversy among scientists, because HDL cholesterol has a beneficial effect on coronary heart disease risk,” Desroches said. “However, body weight is also an important determinant of plasma HDL cholesterol concentrations, and low-fat/high-carbohydrate diets are associated with weight loss.”
To provide information on the effects of eating plans that can help manage weight and cardiovascular risk, the study examined HDL metabolism under realistic conditions in which participants chose how much they ate and weren’t prevented from losing or gaining weight.
Researchers studied 65 men, average age 37.5, who ate according to one of two randomly assigned eating plans for six to seven weeks.
Half the men ate a food low in saturated fat and total fat and high in carbohydrates similar to the plan the American Heart Association and National Cholesterol Education Program (AHA/NCEP) recommend for reducing cholesterol and preventing coronary heart disease. This plan had 58 percent of its calories from carbohydrates, 26 percent from fat (less than 7 percent from saturated fat), and 16 percent from protein.
The other plan was high in mono-unsaturated fatty acids (MUFA) and resembled a Mediterranean-style diet. In the MUFA plan, 40 percent of calories came from fat (with more than half of the fat from olive oil and other MUFAs), 45 percent from carbohydrates and 15 percent from protein.
At the start and end of the study, researchers measured the men’s weight, LDL, HDL, and total cholesterol, and levels of apolipoprotein A-I (apoA-I), one of the protein components of HDL. ApoA-I production and breakdown are key elements of HDL metabolism.
Both eating plans reduced the men’s LDL cholesterol and ratio of total/HDL cholesterol. HDL cholesterol levels fell 10 percent in the AHA/NCEP plan and 3 percent in the MUFA plan.
To examine how the eating plans influenced the metabolism of HDL cholesterol, 18 of the men underwent detailed studies of the production and breakdown of apoA-I. Men on the AHA/NCEP plan had decreased production of apoA-I, which was linked to lower levels of LDL. Men on the high MUFA diet had no changes in apoA-I production or breakdown.
“With this information on HDL metabolism, we believe that the reduction in plasma HDL-C should not raise concerns about cardiovascular health,” Desroches said. “We believe that lower HDL probably means less HDL is needed to remove cholesterol from peripheral tissues.
“At this point, people may be confused because of the wide array of diets that are being proposed. But there is a wealth of evidence to support a low intake of saturated and trans-fats, a moderate intake of the good fats (mono- and polyunsaturated fats from vegetables, fish, legumes and nuts), and a high intake of fiber from fruits, vegetables and grains.”