Sacks et al., 2009

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The new england journal of medicineThere is intense debate about whattypes of diet are most effective for treatingoverweight — those that emphasize protein,those that emphasize carbohydrates, or those thatemphasize fat. 1-3 Several trials showed that lowcarbohydrate,high-protein diets resulted in moreweight loss over the course of 3 to 6 months thanconventional high-carbohydrate, low-fat diets, 4-12but other studies did not show this effect. 13-17A smaller group of studies that extended the follow-upto 1 year did not show that low-carbohydrate,high-protein diets were superior to highcarbohydrate,low-fat diets. 6,10,16,18-21 In contrast,other researchers found that a very-high-carbohydrate,very-low-fat vegetarian diet was superior toa conventional high-carbohydrate, low-fat diet. 22‐24Among the few studies that extended beyond1 year, one showed that a very-low-fat vegetariandiet was superior to a conventional low-fat diet, 24one showed that a low-fat diet was superior to amoderate-fat diet, 25 two showed that a moderatefat,Mediterranean-style diet was superior to a lowfatdiet, 12,26 one showed that a low-carbohydratediet was superior to a low-fat diet, 12 and anothershowed no difference between high-protein andlow-protein diets. 10 Small samples, underrepresentationof men, limited generalizability, a lack ofblinded ascertainment of the outcome, a lack ofdata on adherence to assigned diets, and a largeloss to follow-up limit the interpretation of manyweight-loss trials. 27 The novelty of the diet, mediaattention, and the enthusiasm of the researcherscould affect the adherence of participants to anytype of diet. The crucial question is whether overweightpeople have a better response in the longterm to diets that emphasize a specific macronutrientcomposition. Thus, we recognized the needfor a large trial that would be designed to overcomethe limitations of previous trials and thatwould compare the effects of three principal dietarymacronutrients. We studied weight changeover the course of 2 years, since weight loss typicallyis greatest 6 to 12 months after initiationof the diet, with steady regain of weight subsequently.28MethodsStudy Design and SitesWe designed a randomized clinical trial to comparethe effects on body weight of energy-reduceddiets that differed in their targets for intake ofmacronutrients — low or high in fat, average orhigh in protein, or low or high in carbohydrates— and otherwise followed recommendations forcardiovascular health. 29 The trial was conductedfrom October 2004 through December 2007. Anexpanded description of the methods is availablein the Supplementary Appendix, available with thefull text of this article at NEJM.org. The trial wasconducted at two sites: the Harvard School of PublicHealth and Brigham and Women’s Hospital,Boston; and the Pennington Biomedical ResearchCenter of the Louisiana State University System,Baton Rouge. The data coordinating center was atBrigham and Women’s Hospital. The project staffof the National Heart, Lung, and Blood Institutealso participated in the development of the protocol,monitoring of progress, interpretation of results,and critical review of the manuscript.ParticipantsOur goal was to recruit 800 overweight and obesesubjects (400 at each site), of whom about 40%would be men. Participants had to be 30 to 70 yearsof age and have a body-mass index (the weight inkilograms divided by the square of the height inmeters) of 25 to 40. Major criteria for exclusionwere the presence of diabetes or unstable cardiovasculardisease, the use of medications that affectbody weight, and insufficient motivation as assessedby interview and questionnaire. The studywas approved by the human subjects committee ateach institution and by a data and safety monitoringboard appointed by the National Heart, Lung,and Blood Institute. All participants gave writteninformed consent. They were informed that thestudy would be comparing diets with different fat,protein, and carbohydrate contents and that theywould be assigned a diet at random. Mass mailingswere the primary means of recruitment; names wereidentified with the use of lists of registered votersor drivers. Random assignments to one of four dietgroups were generated by the data manager at thecoordinating center on request of a study dietitian,after eligibility of a participant was confirmed.Weight-Loss InterventionThe nutrient goals for the four diet groups were:20% fat, 15% protein, and 65% carbohydrates (lowfat,average-protein); 20% fat, 25% protein, and55% carbohydrates (low-fat, high-protein); 40% fat,15% protein, and 45% carbohydrates (high-fat, average-protein);and 40% fat, 25% protein, and 35%carbohydrates (high-fat, high-protein). Thus, twodiets were low-fat and two were high-fat, and two860n engl j med 360;9 nejm.org february 26, 2009Downloaded from www.nejm.org on March 14, 2009 . For personal use only. No other uses without permission.Copyright © 2009 Massachusetts Medical Society. All rights reserved.
Weight-Loss Diets with Different Compositions of Macronutrientswere average-protein and two were high-protein,constituting a two-by-two factorial design. The fourdiets also allowed for a dose–response test of carbohydrateintake that ranged from 35 to 65% ofenergy. Other goals for all groups were that thediets should include 8% or less of saturated fat,at least 20 g of dietary fiber per day, and 150 mgor less of cholesterol per 1000 kcal. Carbohydraterichfoods with a low glycemic index were recommendedin each diet. Each participant’s caloric prescriptionrepresented a deficit of 750 kcal per dayfrom baseline, as calculated from the person’s restingenergy expenditure and activity level.Blinding was maintained by the use of similarfoods for each diet. Staff and participants weretaught that each diet adhered to principles of ahealthful diet 29 and that each had been recommendedfor long-term weight loss, thereby establishingequipoise. 1,2,26 Investigators and staff whomeasured outcomes were unaware of the diet assignmentof the participants.Group sessions were held once a week, 3 ofevery 4 weeks during the first 6 months and 2 ofevery 4 weeks from 6 months to 2 years; individualsessions were held every 8 weeks for the entire2 years. Daily meal plans in 2-week blocks wereprovided (see the Supplementary Appendix). Participantswere instructed to record their food andbeverage intake in a daily food diary and in a Webbasedself-monitoring tool that provided informationon how closely their daily food intake met thegoals for macronutrients and energy. Behavioralcounseling was integrated into the group andindividual sessions to promote adherence to theassigned diets. Contact among the groups wasavoided.The goal for physical activity was 90 minutesof moderate exercise per week. Participation inexercise was monitored by questionnaire 30 and bythe online self-monitoring tool.MeasurementsBody weight and waist circumference were measuredin the morning before breakfast on 2 daysat baseline, 6 months, and 2 years, and on a singleday at 12 and 18 months. Dietary intake was assessedin a random sample of 50% of the participants,by a review of the 5-day diet record atbaseline and by 24-hour recall during a telephoneinterview on 3 nonconsecutive days at 6 monthsand at 2 years. 31 Questionnaires that asked for informationon satiety, food craving, eating behavior,and satisfaction with the diet 32,33 were administeredat baseline (except for diet satisfaction) andat 6 months and 2 years. Fasting blood samples,24-hour urine samples, and measurement of restingmetabolic rate were obtained on 1 day, andblood-pressure measurement on 2 days, at baseline,6 months, and 2 years. Levels of serum lipids,glucose, insulin, and glycated hemoglobin weremeasured at the clinical laboratory at the PenningtonBiomedical Research Center. Blood pressurewas measured with the use of an automated device(HEM-907XL, Omron). The participants wereevaluated for the presence of the metabolic syndrome,which was defined by the presence of atleast three of the following five criteria: waist circumferenceof more than 102 cm in men or morethan 88 cm in women, a triglyceride level of 150 mgper deciliter (1.69 mmol per liter) or more, a highdensitylipoprotein (HDL) cholesterol level of lessthan 40 mg per deciliter (1.03 mmol per liter) inmen or less than 50 mg per deciliter (1.29 mmol perliter) in women, a blood pressure of 130/85 mm Hgor more, and a fasting glucose level of 110 mg perdeciliter (6.1 mmol per liter) or more.Statistical AnalysisThe primary outcome of the study was the changein body weight over a period of 2 years, and thesecondary outcome was the change in waist circumference.Data were pooled from the diets forthe two factorial comparisons: low fat versus highfat and average protein versus high protein. Theanalysis also included a comparison of two of thefour diets, the diet with the lowest carbohydratecontent and the diet with the highest carbohydratecontent, and included a test for trend across thefour levels of carbohydrates. The effects of protein,fat, and carbohydrate levels were evaluated independentlywith the use of two-sample t-tests at atwo-sided significance level of 0.05. Exploratorypost hoc analyses were performed with thresholdamounts of weight loss as outcomes, with Bonferroni’sadjustment for multiple comparisons. Associationsbetween adherence to the fat and proteingoals and weight loss were also explored inpost hoc analyses (see Methods in the SupplementaryAppendix).We performed an intention-to-treat analysis inwhich long-term weight loss for persons who withdrewfrom the study early (after at least 6 monthsof participation) was imputed on the basis of a rateof 0.3 kg per month of regained weight 34 and arate of 0.3 cm per month of regained waist circumferenceafter withdrawal (see Methods in the Sup-n engl j med 360;9 nejm.org february 26, 2009 861Downloaded from www.nejm.org on March 14, 2009 . For personal use only. No other uses without permission.Copyright © 2009 Massachusetts Medical Society. All rights reserved.
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