ABSTRACT & COMMENTARY
Bring on the Butter and the Eggs
By Barbara A. Phillips, MD, MSPH
Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington
Dr. Phillips serves on the speakers bureau for PotomaCME.
SYNOPSIS: People who were randomized to a low-carbohydrate diet lost more weight than those who were randomized to a low-fat diet over a year. They also had greater improvements in risk factors for cardiovascular disease.
SOURCE: Bazzano LA, et al. Effects of low-carbohydrate and low-fat diets: A randomized trial. Ann Intern Med 2014;161:309-318.
These Louisiana investigators recruited 148 people from the general population for this study. To be included, participants had to be obese (body mass index [BMI] > 30 kg/m2) and could not have cardiovascular disease, type 2 diabetes, or kidney disease, or be using prescription weight-loss medications. On average, the participants were about 49 years old and their mean BMI was about 35 kg/m2. A large majority (88%) were women, and 51% were black.
People in the low-carbohydrate diet group were asked to maintain an intake of digestible carbohydrates (total carbohydrate minus total fiber) of < 40 g/day. Those on the low-fat diet were told to get < 30% of their daily energy intake from total fat (with < 7% from saturated fat) and 55% from carbohydrates, based on National Cholesterol Education Program guidelines. Importantly, neither diet included a specific calorie goal. Participants were told not to change their physical activity levels during the intervention. All participants got nutritional counseling with a dietician, as well as a handbook that included recipes, sample menus, food lists, shopping lists, meal planners, and guides on reading nutrition labels. They also got one low-carbohydrate or low-fat meal replacement (bar or shake) per day for the entire study.
Data collection included a detailed medical history. Anthropometric measures and blood and urine samples were collected at the screening visit and each follow-up visit. Follow-up visits were at 3, 6, and 12 months, and retention rates were high. Body weight, height, body composition, and blood pressure were precisely measured.
Dietary logs demonstrated that although baseline reported dietary composition in the two groups was similar, the reported intake of total carbohydrates was indeed significantly higher and fat intakes were significantly lower in the low-fat group at 12 months. Physical activity and total calorie intake levels were similar throughout the study for both groups.
The low-carbohydrate group lost more weight than the low-fat group at 3, 6, and 12 months. At 12 months, those in the low-carbohydrate group lost 3.5 kg (about 7 pounds) more than those in the low-fat group. They also had larger reductions in fat mass and greater proportional increases in lean mass. Although all participants had significantly reduced waist circumference, reductions were greater in the low-carbohydrate group at 3 and 6 months.
At 12 months, high-density lipoprotein (HDL) cholesterol increased significantly more in the low-carbohydrate group than in the low-fat group and ratios of total/HDL cholesterol decreased significantly only among participants in the low-carbohydrate group. Serum levels of triglycerides also decreased significantly in both groups, but the decrease was greater in the low-carbohydrate group. Similarly, participants in the low-carbohydrate group had significantly greater decreases in C-reactive protein levels than those in the low-fat group. Participants in the low-carbohydrate group had significant decreases in estimated 10-year Framingham risk score for coronary heart disease at 6 and 12 months, whereas those in the low-fat group did not.
Serum levels of insulin and creatinine decreased significantly and approximately equally in each group. There were no significant changes in either group for blood pressures, glucose, total cholesterol, and LDL cholesterol. There were no significant adverse events, and very little difference in reported adverse events between the groups, except more people on the low-fat diet reported headaches at 3 months.
COMMENTARY
The big news here is that the low-carbohydrate diet trumped the low-fat diet, not just in the amount of weight lost over a year’s time, but also in most measures of risk factors for cardiovascular disease. Is it possible that the days of blood-letting and leaches are still with us? For years, venerable organizations within the medical establishment have been promulgating low-carbohydrate diets for weight loss and presumable reduction in cardiovascular risk.1-3 (And over that same period of time, rates of overweight and obesity in this country have soared).
Nearly coincident with the publication of this paper, a meta-analysis appeared in JAMA of 48 trials including more than 7000 people.4 This analysis found that low-carbohydrate diets were associated with greater weight loss than low-fat diets, but the difference in weight loss between proprietary low-carbohydrate diets was small.
This study from Bazzano et al is consistent with several other trials.4,5 What accounts for differences in weight loss by diet is not understood, but a recent study showed that low-carbohydrate diets may have a more favorable effect on resting energy expenditure and total energy expenditure (i.e., calorie burning) than low-fat diets.6 The current study supports this notion, since dietary recall between the two groups found no difference in overall caloric intake between the two groups.
The current study is particularly important because of the inclusion of a large number of black participants, who have a higher prevalence of both obesity and cardiovascular disease than whites.7 There were no important differences in the responses to the diets in blacks and whites in this study.
This paper also helped to debunk the prevalent concern that low-carbohydrate diets have the potential to elevate LDL cholesterol levels. This study also found no change in LDL cholesterol level among participants in either group, with no significant difference between the groups.
In contrast to many previous studies of this issue, this trial included people without diabetes or cardiovascular disease at baseline. While it is possible that the two different dietary approaches might have different effects or outcomes than were found here in sicker patients (i.e., when the horse is already out of the barn), it is unlikely. And prevention is preferable to palliation.
Because cardiovascular disease is the leading cause of death in the United States, this study has important public health implications. Perhaps first among them is to stop recommending a low-fat diet. The authors of the recent meta-analysis in JAMA concluded, "This supports the practice of recommending any diet that a patient will adhere to in order to lose weight."4 Indeed.
REFERENCES
- Krauss RM, et al. AHA Dietary Guidelines: revision 2000: A statement for healthcare professionals from the Nutrition Committee of the American Heart Association. Circulation 2000; 102:2284-2299.
- National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) final report. Circulation 2002;106:3143-3421.
- Stone NJ, Van Horn L. Therapeutic lifestyle change and Adult Treatment Panel III: Evidence then and now. Curr Atheroscler Rep 2002;4:433-443.
- Johnston BC, et al. Comparison of weight loss among named diet programs in overweight and obese adults: A meta-analysis.JAMA 2014;312:923-933.
- Hu T, et al. Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: A meta-analysis of randomized controlled clinical trials. Am J Epidemiol 2012;176 Suppl 7:S44-54.
- Ebbeling CB, et al. Effects of dietary composition on energy expenditure during weight-loss maintenance. JAMA 2012;307: 2627-2634.
- http://www.cdc.gov/obesity/data/adult.html. Accessed Sept. 7, 2014.
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