Low-carbohydrate Diets: Do the Benefits Outweigh the Risks?
In the struggle to lose weight, a rivalry has developed between low-carbohydrate diets—which emphasize protein and fat while shunning sugar and starch—and low-fat diets, which focus on calorie control by limiting fat intake. A few, small studies have yielded mixed results on which plan is best. The bigger issue fueling this rivalry is cardiovascular disease (CVD) risk. Weight loss can decrease CVD risk; however, critics of low-carbohydrate diets worry that the potential rise in cholesterol levels from excess dietary fat will offset any benefits from weight loss. The American Heart Association recommends a low-fat diet as the safest means to reduce weight and CVD risk. The merit of low-carbohydrate diets is unclear.
A group of Swiss researchers set out to clarify the effects of low-carbohydrate diets on weight and CVD risk by analyzing the best studies to date. Their findings, published in the February 13, 2006 Archives of Internal Medicine , are mixed: over 12 months, low-fat and low-carbohydrate diets are equally effective for weight loss. In terms of CVD risk, low-fat diets show greater reductions in total and LDL cholesterol, while low-carbohydrate diets show more favorable changes in HDL cholesterol and triglycerides.
About the Study
Researchers from the University Hospital Basel in Switzerland combined and analyzed five randomized, controlled trials comparing low-carbohydrate and low-fat diets. The low-carbohydrate diets allowed 60 grams of carbohydrates (about 4 slices of bread) per day; intake of protein, fat, and calories was not restricted. The low-fat diets limited calorie intake and allowed 30% of calories from fat per day. A total of 447 people were included (222 on low-carbohydrate diets, 225 on low-fat diets). The researchers compared changes in weight and cholesterol levels.
At six months, low-carbohydrate dieters lost more weight than low-fat eaters, but by 12 months, weight loss was similar between the groups. Significant differences were seen in the effects on CVD risk factors. Volunteers eating a low-fat diet had greater drops in total and LDL (bad) cholesterol; reductions in these two factors can decrease CVD risk. In comparison, low-carbohydrate eaters had increases in total and LDL cholesterol. Low-carbohydrate diets also showed two benefits: increases in HDL (“good”) cholesterol and decreases in triglyercides. Low-fat eaters had less favorable changes in these two factors. Considering these findings, the researchers do not recommend a low-carbohydrate diet for CVD prevention.
This study is limited by the small number of trials (5) and the high rate of dropouts. In addition, the follow-up period was too short to determine if the changes in cholesterol would translate into fewer or greater incidences of CVD. In these studies, volunteers chose and prepared their food. A more stringent, blinded trial—one in which food is provided and volunteers do not know which diet they are eating—would better assess the link between diet and CVD.
How Does This Affect You?
Fewer bagels or less cream cheese? Neither; choose a whole-wheat English muffin with natural peanut butter and an orange instead. In this nutrition rivalry, both sides have some merit. However, it’s difficult for small, short-term studies to pick up the nuances in dietary choices. A healthful diet includes protein, carbohydrate, and fat, the key is to choose the best sources of these nutrients and limit the less healthful ones. The table below provides some guidance. For a healthy weight and low CVD risk, combine a balanced eating plan with regular exercise.
More of these
Less of these
Whole-wheat breads, pastas, crackers
White breads, pastas, rice, crackers
Soda, juice drinks
Cookies, cakes, candy, sweets
Legumes (black beans, lentils, hummus, etc.)
Nuts & natural peanut butter
Skinless, white-meat poultry
Lean beef (round, loin) and pork (loin, leg)
Full-fat milk, cheese, & other dairy
Pepperoni, salami, etc.
Fish (salmon, trout, etc.)
Nuts & natural peanut butter
Low-fat, fat-free, and trans-free mayonnaise, margarine, and spreads
Saturated fat and trans fat:
Commercially fried foods
Packaged baked goods and snacks
American Heart Association
American Dietetic Association
Nordmann AJ, Nordmann A, Briel M, et al. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors. Archives of Internal Medicine . 2006;166:285-293.
Last reviewed Feb 16, 2006 by ]]>Richard Glickman-Simon, MD]]>
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