1 COMPARISON OF WEIGHT-LOSS DIETS Wednesday Ambulatory Conference Liz Thomas, MD March 11, 2009
2 Case Scenario You are seeing gyour patient as a routine follow up visit in your clinic. She is a 45 yo female with a history of hypertension and obesity. Her BMI is 33, her blood pressure is 125/70, and her only medication is HCTZ 25mg daily. Her exam is unremarkable. Her father, who is also obese, recently suffered an MI. Now she is quite motivated to lose weight and asks you which diet she should follow. What will you tell her?
3 Background 32% of Americans are obese this translates to more than 60 million adults The obesity epidemic imposes a great cost on the nation s health and economy As primary care physicians, we need to be As primary care physicians, we need to be counseling our patients on weight loss
4 Recommendations According to the NHLBI Practical Guide Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, weight loss therapy is recommended for patients with a BMI greater than 30 or BMI between 25 and 29.9 (or high risk waist circumference) and two or more risk factors Recommendations for dietary therapy indicate that caloric intake should be reduced by 500 to 1000 calories per day below the baseline There is no specific recommendation regarding macronutrient content of diets
5 Previous trials There are very few well-designed trials comparing different types of diets for weight loss Specifically, there is debate about whether diets that emphasize protein, carbohydrates, or fat are most effective for treating overweight patients Other studies have been limited by small samples, underrepresentation of men, limited generalizability, lack of blinding, lack of data on adherence to assigned diets, and a large loss to follow-up
6 Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates Sacks FM, Bray GA, Carey VJ, Smith SR, Ryan DH, Anton SD, McManus K, Champagne CM, Bishop LM, Laranjo N, Leboff MS, Rood JC, de Jonge L, Greenway FL, Loria CM, Obarzanek E, Williamson DA. N Engl J Med Feb 26;360(9):923-5.
7 Study design Randomized controlled trial comparing effects on body weight of energy-reduced diets that differed in their targets for intake of macronutrients (protein, fat and carbohydrates) Conducted from October 2004 through December 2007 at Brigham and Women s Hospital in Boston and the Pennington Biomedical Research Center of the Louisiana State University System in Baton Rouge Primary outcome was change in body weight over a period of 2 years, and secondary outcome was change in waist circumference
8 Study Participants Goal recruitment of 800 overwieght and obese subjects of whom 40% would be men Participants had to be 30 to 70 years old and have a BMI of 25 to 40 Exclusion criteria included presence of diabetes, unstable cardiovascular disease, the use of medications that affect body weight, and insufficient motivation as assessed by interview
9 Weight loss intervention Subjects were randomly assigned to one of four diet groups Nutrient goals were as follows Low-fat, average-protein (20% fat, 15% protein, 65% carbohydrates) Low-fat, high-protein (20% fat, 25% protein, 55% carbohydrates High-fat, average-protein (40% fat, 15% protein, 45% carbohydrates High-fat, high-protein (40% fat, 25% protein, 35% carbohydrates)
10 The Diets All groups were also given the goals that the diets should include 8% or less of saturated fat, at least 20g of dietary fiber per day, and 150mg or less of cholesterol per 1000kcal Each participant s caloric prescription represented a deficit of 750kcal per day from baseline, as calculated from the person s resting energy expenditure and activity it levell
11 Blinding Blinding was achieved by use of similar foods for each diet, as well as by teaching all staff and participants that each diet adhered to principals of a healthful hf l diet and that each had been recommended for long-term weight loss. Investigators and staff who measured outcomes were not aware of the diet assignments of the participants.
12 Weight loss intervention Group sessions providing dietary and behavioral counseling were held once a week for 3 of every 4 weeks during the first 6 months, then 2 of every 4 weeks from 6 months to 2 years Individual sessions were held every 8 weeks for the entire 2 years Daily meal plans were provided in 2 week blocks Participants recorded their food and beverage intake in a food diary and a web-based self-monitoring tool Goal physical py activity was 90 minutes of moderate exercise per week
13 Statistical analysis Data were pooled for the two factorial comparisons: low fat versus high fat and average protein versus high protein Analysis included a comparison of the lowest carbohydrate and highest carbohydrate diets Effects of the macronutrients were evaluated independently using two-sample t-tests Intention-to-treat analysis was performed for patients who withdrew early (after at least 6 months of participation). Long term weight loss was imputed on the basis of a rate of 0.3 kg per month of regained weight and 0.3 cm per month of regained waist circumference after withdrawal
14 Results 1638 patients screened 811 (50%) randomly assigned to a diet 645 (80%) completed study Baseline characteristics were similar among participants assigned to the four diets and between those assigned to a diet and those who completed the study
16 Results Weight loss after 2 years was similar in participants assigned to a diet with 25% protein and those assigned to a diet with 15% protein (3.6 and 3.0 kg; P = 0.22) and among those who completed each of those diets (4.5 and 3.6 kg; P = 0.11) Weight loss was the same in those assigned to 40% fat and 20% fat (3.3 kg; P = 0.94) and was similar among those who completed each of those diets (3.9 and 4.1 kg; P = 0.76) Carbohydrate level had no effect on weight loss Carbohydrate level had no effect on weight loss There was no significant difference in waist circumference among the diet groups
17 Mean change in body weight and waist circumference from baseline to 2 years
18 Weight loss At two years, 31 to 37% of participants had lost at least 5% of their initial body weight 14-15% 15% had lost at least 10% of initial weight 2-4%had lost 20kg or more
19 Risk factors for cardiovascular disease All diets reduced risk factors for cardiovascular disease and diabetes at 6 months and two years The two low-fat diets reduced LDL more than the high-fat or lowestcarb diets The lowest-carb diet increased HDL levels l more than the highest h carb diet All diets decreased triglyceride levels similarly (12 to 17%) All diets except the one with the highest h carbohydrates decreased d fasting serum insulin levels by 6 to 12% Blood pressure decreased from baseline by 1-2mm Hg with no significant differences among the groups The metabolic syndrome was present in 32% of the participants at baseline and was lower at 2 years (from 19 to 22% in the four diet groups)
20 Adherence Mean reported intakes at 6 months and 2 years did not reach the target levels for macronutrients However, changes in biomarkers (HDL, urinary nitrogen excretion, and respiratory quotient) suggest that participants modified their intake of macronutrients in the direction of the goals Craving, fullness, and hunger and diet-satisfaction scores were similar at 6 months and 2 years among the diets
21 Group sessions Attendance at group sessions strongly predicted weight loss at 2 years (0.2 kg for every session attended) and was similar among the diet groups
22 Post-hoc analysis Protein and fat intake overlapped among the groups A high-protein intake was associated with weight loss only in the high-protein groups, and a low-fat intake was associated with weight loss only in the low-fat groups
23 Discussion Principal finding is that the diets were equally successful in promoting clinically meaningful weight loss and maintenance of weight loss over the course of 2 years Attendance at group sessions had a strong association with weight loss, suggesting behavioral factors rather than macronutrient metabolism as the main influences on weight loss
24 Study limitations Patient population: Exclusion of diabetics, low percentage of smokers, high educational level, relatively high income. Unclear whether these results can be applied to our patient population Lack of achievement of goal macronutrient levels is this truly a comparison of different diets?
25 Conclusions This is one of very few randomized controlled trials comparing diets emphasizing different macronutrients. It has a large sample size and high rate of retention Taken along with results of prior studies showing weight loss achievement with other diets, findings suggest that any diet, when taught with enthusiasm to motivated patients, can be successful in achieving weight loss This should encourage us as providers to teach reduced calorie diets to our patients regardless of the macronutrients emphasized
26 References Underdiagnosis of Obesity in Adults in US Outpatient Settings. Jun Ma, MD, PhD; Lan Xiao, PhD; Randall S. Stafford, MD, PhD. Arch Intern Med. 2009;169(3): Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. Sacks FM, Bray GA, Carey VJ, Smith SR, Ryan DH, Anton SD, McManus K, Champagne CM, Bishop LM, Laranjo N, Leboff MS, Rood JC, de Jonge L, Greenway FL, Loria CM, Obarzanek E, Williamson DA. N Engl J Med Feb 26;360(9): The Practical Guide Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. National Institutes of Health, National Heart, Lung and Blood Institute. NIH Publication Number October 2000.