Janis F. Swain

Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance

CONTEXT Reduced energy expenditure following weight loss is thought to contribute to weight gain. However, the effect of dietary composition on energy expenditure during weight-loss maintenance has not been studied. OBJECTIVE To examine the effects of 3 diets differing widely in macronutrient composition and glycemic load on energy expenditure following weight loss. DESIGN, SETTING, AND PARTICIPANTS A controlled 3-way crossover design involving 21 overweight and obese young adults conducted at Childrens Hospital Boston and Brigham and Womens Hospital, Boston, Massachusetts, between June 16, 2006, and June 21, 2010, with recruitment by newspaper advertisements and postings. INTERVENTION After achieving 10% to 15% weight loss while consuming a run-in diet, participants consumed an isocaloric low-fat diet (60% of energy from carbohydrate, 20% from fat, 20% from protein; high glycemic load), low-glycemic index diet (40% from carbohydrate, 40% from fat, and 20% from protein; moderate glycemic load), and very low-carbohydrate diet (10% from carbohydrate, 60% from fat, and 30% from protein; low glycemic load) in random order, each for 4 weeks. MAIN OUTCOME MEASURES Primary outcome was resting energy expenditure (REE), with secondary outcomes of total energy expenditure (TEE), hormone levels, and metabolic syndrome components. RESULTS Compared with the pre-weight-loss baseline, the decrease in REE was greatest with the low-fat diet (mean [95% CI], -205 [-265 to -144] kcal/d), intermediate with the low-glycemic index diet (-166 [-227 to -106] kcal/d), and least with the very low-carbohydrate diet (-138 [-198 to -77] kcal/d; overall P = .03; P for trend by glycemic load = .009). The decrease in TEE showed a similar pattern (mean [95% CI], -423 [-606 to -239] kcal/d; -297 [-479 to -115] kcal/d; and -97 [-281 to 86] kcal/d, respectively; overall P = .003; P for trend by glycemic load < .001). Hormone levels and metabolic syndrome components also varied during weight maintenance by diet (leptin, P < .001; 24-hour urinary cortisol, P = .005; indexes of peripheral [P = .02] and hepatic [P = .03] insulin sensitivity; high-density lipoprotein [HDL] cholesterol, P < .001; non-HDL cholesterol, P < .001; triglycerides, P < .001; plasminogen activator inhibitor 1, P for trend = .04; and C-reactive protein, P for trend = .05), but no consistent favorable pattern emerged. CONCLUSION Among overweight and obese young adults compared with pre-weight-loss energy expenditure, isocaloric feeding following 10% to 15% weight loss resulted in decreases in REE and TEE that were greatest with the low-fat diet, intermediate with the low-glycemic index diet, and least with the very low-carbohydrate diet. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00315354.

Comparison of the Effects of Oat Bran and Low-Fiber Wheat on Serum Lipoprotein Levels and Blood Pressure

Previous studies have shown that supplementation of the diet with oat bran may lower serum cholesterol levels. However, it is not known whether oat-bran diets lower serum cholesterol levels by replacing fatty foods in the diet or by a direct effect of the dietary fiber contained in oat bran. To determine which is the case, we compared the effect of isocaloric supplements of high-fiber oat bran (87 g per day) and a low-fiber refined-wheat product on the serum lipoprotein cholesterol levels of 20 healthy subjects, 23 to 49 years old. After a one-week base-line period during which they consumed their usual diets, the subjects were given each type of supplement for six-week periods in a double-blind, crossover trial. Mean serum cholesterol levels (+/- SD) were not significantly different during the high-fiber and low-fiber periods: total cholesterol, 4.44 +/- 0.73 and 4.46 +/- 0.64 mmol per liter (172 +/- 28 and 172 +/- 25 mg per deciliter); low-density lipoprotein, 2.69 +/- 0.63 and 2.77 +/- 0.59 mmol per liter (104 +/- 24 and 107 +/- 23 mg per deciliter); and high-density lipoprotein, 1.40 +/- 0.39 and 1.32 +/- 0.39 mmol per liter (54.2 +/- 15.0 and 50.9 +/- 15.2 mg per deciliter), respectively. However, both types of supplements lowered the mean base-line serum cholesterol level, 4.80 +/- 0.80 mmol per liter (186 +/- 31 mg per deciliter), by 7 to 8 percent (95 percent confidence interval for high fiber, 11 to 4 percent, and for low fiber, 11 to 3 percent). The subjects ate less saturated fat and cholesterol and more polyunsaturated fat during both periods of supplementation than at base line. Those changes in dietary fats were sufficient to explain all of the reduction in serum cholesterol levels caused by the high-fiber and low-fiber diets. The average blood pressure was 112/68 mm Hg at base line and did not change during either dietary period. We conclude that oat bran has little cholesterol-lowering effect and that high-fiber and low-fiber dietary grain supplements reduce serum cholesterol levels about equally, probably because they replace dietary fats.

Descriptive Characteristics of the Dietary Patterns Used in the Dietary Approaches to Stop Hypertension Trial

The Dietary Approaches to Stop Hypertension trial was a randomized, multicenter, controlled feeding study to compare the effect on blood pressure of 3 dietary patterns: control, fruits and vegetables, and combination diets. The patterns differed in selected nutrients hypothesized to alter blood pressure. This article examines the food-group structure and nutrient composition of the study diets and reports participant nutrient consumption during intervention. Participants consumed the control dietary pattern during a 3-week run-in period. They were then randomized either to continue on the control diet or to change to the fruits and vegetables or the combination diet for 8 weeks. Sodium intake and body weight were constant during the entire feeding period. Analysis of variance models compared the nutrient content of the 3 diets. Targeting a few nutrients thought to influence blood pressure resulted in diets that were profoundly different in their food-group and nutrient composition. The control and fruits and vegetables diets contained more oils, table fats, salad dressings, and red meats and were higher in saturated fat, total fat, and cholesterol than was the combination diet. The fruits and vegetables and combination diets contained relatively more servings of fruits, juices, vegetables, and nuts/seeds, and were higher in magnesium, potassium, and fiber than was the control diet. Both the fruits and vegetables and combination diets were low in sweets and sugar-containing drinks. The combination diet contained a greater variety of fruits, and its high calcium content was obtained by increasing low-fat dairy products. In addition, the distinct food grouping pattern across the 3 diets resulted in substantial differences in the levels of vitamins A, C, E, folate, B-6, and zinc.

The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium): Rationale and Design

The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium) is a multicenter, randomized trial comparing the effects of 3 levels of sodium intake and 2 dietary patterns on blood pressure among adults with higher than optimal blood pressure or with stage 1 hypertension (120-159/80-95 mm Hg). The 2 dietary patterns are a control diet typical of what many Americans eat, and the DASH diet, which, by comparison, emphasizes fruits, vegetables, and low-fat dairy foods, includes whole grains, poultry, fish, and nuts, and is reduced in fats, red meat, sweets, and sugar-containing beverages. The 3 sodium levels are defined as higher (typical of current US consumption), intermediate (reflecting the upper limit of current US recommendations), and lower (reflecting potentially optimal levels). Participants are randomly assigned to 1 of the 2 dietary patterns using a parallel group design and are fed each of the 3 sodium levels using a randomized crossover design. The study provides participants with all of their food during a 2-week run-in feeding period and three 30-day intervention feeding periods. Participants attend the clinic for 1 meal per day, 5 days per week, and take home food for other meals. Weight is monitored and individual energy intake adjusted to maintain baseline weight. The primary outcome is systolic blood pressure measured at the end of each intervention feeding period. Systolic blood pressure is compared across the 3 sodium levels within each diet and across the 2 diets within each sodium level. If effects previously observed in clinical trials are additive, sodium reduction and the DASH diet together may lower blood pressure to an extent not as yet demonstrated for nonpharmacologic treatment. The DASH-Sodium results will have important implications for the prevention and treatment of high blood pressure.

Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity: The OmniCarb Randomized Clinical Trial

IMPORTANCE Foods that have similar carbohydrate content can differ in the amount they raise blood glucose. The effects of this property, called the glycemic index, on risk factors for cardiovascular disease and diabetes are not well understood. OBJECTIVE To determine the effect of glycemic index and amount of total dietary carbohydrate on risk factors for cardiovascular disease and diabetes. DESIGN, SETTING, AND PARTICIPANTS Randomized crossover-controlled feeding trial conducted in research units in academic medical centers, in which 163 overweight adults (systolic blood pressure, 120-159 mm Hg) were given 4 complete diets that contained all of their meals, snacks, and calorie-containing beverages, each for 5 weeks, and completed at least 2 study diets. The first participant was enrolled April 1, 2008; the last participant finished December 22, 2010. For any pair of the 4 diets, there were 135 to 150 participants contributing at least 1 primary outcome measure. INTERVENTIONS (1) A high-glycemic index (65% on the glucose scale), high-carbohydrate diet (58% energy); (2) a low-glycemic index (40%), high-carbohydrate diet; (3) a high-glycemic index, low-carbohydrate diet (40% energy); and (4) a low-glycemic index, low-carbohydrate diet. Each diet was based on a healthful DASH-type diet. MAIN OUTCOMES AND MEASURES The 5 primary outcomes were insulin sensitivity, determined from the areas under the curves of glucose and insulin levels during an oral glucose tolerance test; levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides; and systolic blood pressure. RESULTS At high dietary carbohydrate content, the low- compared with high-glycemic index level decreased insulin sensitivity from 8.9 to 7.1 units (-20%, P = .002); increased LDL cholesterol from 139 to 147 mg/dL (6%, P ≤ .001); and did not affect levels of HDL cholesterol, triglycerides, or blood pressure. At low carbohydrate content, the low- compared with high-glycemic index level did not affect the outcomes except for decreasing triglycerides from 91 to 86 mg/dL (-5%, P = .02). In the primary diet contrast, the low-glycemic index, low-carbohydrate diet, compared with the high-glycemic index, high-carbohydrate diet, did not affect insulin sensitivity, systolic blood pressure, LDL cholesterol, or HDL cholesterol but did lower triglycerides from 111 to 86 mg/dL (-23%, P ≤ .001). CONCLUSIONS AND RELEVANCE In this 5-week controlled feeding study, diets with low glycemic index of dietary carbohydrate, compared with high glycemic index of dietary carbohydrate, did not result in improvements in insulin sensitivity, lipid levels, or systolic blood pressure. In the context of an overall DASH-type diet, using glycemic index to select specific foods may not improve cardiovascular risk factors or insulin resistance. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00608049.

Characteristics of the Diet Patterns Tested in the Optimal Macronutrient Intake Trial to Prevent Heart Disease (OmniHeart): Options for a Heart-Healthy Diet

OBJECTIVE To describe the nutrient and food composition of the diets tested in the Optimal Macronutrient Intake Trial to Prevent Heart Disease (OmniHeart). DESIGN Two center, randomized, three-period crossover, controlled feeding trial that tested the effects of three healthful diet patterns on blood pressure, serum lipid levels, and estimated cardiovascular risk. SUBJECTS/SETTING One hundred sixty-four participants with prehypertension and hypertension. During the 19 weeks of feeding, participants were required to consume only food prepared as part of the trial. INTERVENTION The OmniHeart trial studied three diet patterns that differed in macronutrient composition: a carbohydrate-rich diet similar to the Dietary Approaches to Stop Hypertension diet (58% carbohydrate, 15% protein, and 27% fat), a higher protein diet that had 10% more protein and 10% less carbohydrate (48% carbohydrate, 25% protein, and 27% fat), and a higher unsaturated fat diet that had 10% more unsaturated fat and 10% less carbohydrate (48% carbohydrate, 15% protein, and 37% fat). Each diet contained 6% saturated fat and 100 to 200 mg cholesterol. Sodium was 2,300 mg at the 2,100 kcal energy level and was indexed across energy levels. Calcium, magnesium, and potassium were consistent with recommendations for the Dietary Approaches to Stop Hypertension diet and also indexed to energy levels. Each diet pattern met the major nutrient recommendations set by the Dietary Guidelines for Americans 2005. The 10% protein increase in the higher protein diet emphasized plant protein; however, meat and dairy food sources were also increased somewhat. Olive oil, canola oil, and olive oil spread were used liberally to achieve the unsaturated fat content of the higher unsaturated fat diet. The 10% reduction in carbohydrate in the higher protein diet and the higher unsaturated fat diet was achieved by replacing some fruits with vegetables, reducing sweets, and using smaller portions of grain products. All three diets reduced blood pressure, total and low-density lipoprotein cholesterol levels, and estimated coronary heart disease risk. CONCLUSIONS The OmniHeart diet patterns offer substantial flexibility in macronutrient intake that should make it easier to eat a heart-healthy diet and reduce cardiovascular disease risk.

Acute effects of dietary glycemic index on antioxidant capacity in a nutrient-controlled feeding study.

Oxidative stress, caused by an imbalance between antioxidant capacity and reactive oxygen species, may be an early event in a metabolic cascade elicited by a high glycemic index (GI) diet, ultimately increasing the risk for cardiovascular disease and diabetes. We conducted a feeding study to evaluate the acute effects of low‐GI compared with high‐GI diets on oxidative stress and cardiovascular disease risk factors. The crossover study comprised two 10‐day in‐patient admissions to a clinical research center. For the admissions, 12 overweight or obese (BMI: 27–45 kg/m2) male subjects aged 18–35 years consumed low‐GI or high‐GI diets controlled for potentially confounding nutrients. On day 7, after an overnight fast and then during a 5‐h postprandial period, we assessed total antioxidant capacity (total and perchloric acid (PCA) protein‐precipitated plasma oxygen radical absorbance capacity (ORAC) assay) and oxidative stress status (urinary F2α‐isoprostanes (F2IP)). On day 10, we measured cardiovascular disease risk factors. Under fasting conditions, total antioxidant capacity was significantly higher during the low‐GI vs. high‐GI diet based on total ORAC (11,736 ± 668 vs. 10,381 ± 612 µmol Trolox equivalents/l, P = 0.002) and PCA‐ORAC (1,276 ± 96 vs. 1,210 ± 96 µmol Trolox equivalents/l, P = 0.02). Area under the postprandial response curve also differed significantly between the two diets for total ORAC and PCA‐ORAC. No diet effects were observed for the other variables. Enhancement in plasma total antioxidant capacity occurs within 1 week on a low‐GI diet, before changes in other risk factors, raising the possibility that this phenomenon may mediate, at least in part, the previously reported effects of GI on health.

Rationale and design of the Optimal Macro-Nutrient Intake Heart Trial to Prevent Heart Disease (OMNI-Heart)

Background The DASH (Dietary Approaches to Stop Hypertension) diet is a carbohydrate-rich, reduced-fat diet that lowers blood pressure (BP) and LDL-cholesterol. Whether partial replacement of some carbohydrate (C) with either protein (P) or unsaturated fat (U) can further improve these and other cardiovascular (CVD) risk factors is unknown. Methods OmniHeart is a randomized, three-period, crossover feeding study designed to compare the effects on BP and blood lipids of a carbohydrate-rich diet (CARB, similar to the DASH diet) with a diet rich in protein (PROT, predominantly from nonmeat sources) and a diet rich in unsaturated fat (UNSAT, predominantly monounsaturated). Throughout feeding (run in and the three intervention periods), participants are provided with all of their meals that meet the nutrient profile of their assigned diet. Calorie intake is adjusted to maintain weight. The target sample size is 160 (50% African-American). Participants are adults, aged 30 or older, with prehypertension or Stage 1 hypertension (systolic BP 120–159 or diastolic BP 80–99 mmHg). The primary outcome variables are systolic BP and LDL-cholesterol. Secondary outcomes are diastolic BP, HDL-cholesterol, and triglycerides. Other outcome variables are total cholesterol, apolipoproteins VLDL-apoB, VLDL-apoCIII, apolipoprotein B, non-HDL cholesterol, and lipoprotein(a), and insulin resistance, as measured by Homeostasis Model Assessment (HOMA). Conclusions OMNI-Heart should advance our fundamental knowledge of the effects of diet on both traditional and emerging risk factors, and, in the process, guide policy makers, health care providers and the general public on the relative benefits of carbohydrate, protein, and unsaturated fat as a means to reduce CVD risk.

Dietary Adherence in the Dietary Approaches to Stop Hypertension Trial

Participants in controlled feeding studies must consume all study foods and abstain from all other foods. In outpatient studies in which adherence may be compromised by free-living conditions, promoting, documenting, and monitoring dietary adherence are necessary. In the Dietary Approaches to Stop Hypertension (DASH) trial, a thorough participant screening process, an orientation session, and a run-in feeding period before randomization aided in the selection of participants who would most likely adhere to the demands of the study protocol. Throughout the feeding period, various educational and motivational techniques were used to encourage DASH participants to adhere to the dietary protocol. Both objective and subjective methods documented excellent participant adherence. Daily monitoring of individual adherence was based on meal attendance, body weight measurements, and daily diaries. Urinary sodium, potassium, phosphorus, and urea nitrogen values and an anonymous poststudy survey were used to evaluate adherence at the end of the study. Most DASH participants adhered to the feeding regimen by consuming only study foods and no other foods. When adherence lapsed, participants generally cited the lack of menu variety as a reason. Successful participant adherence to the constraints of an outpatient controlled feeding study is possible with carefully selected participants and a variety of adherence-promoting strategies incorporated into the study protocol.

Validation of diet composition for the Dietary Approaches to Stop Hypertension trial

The Dietary Approaches to Stop Hypertension trial involved 4 clinical sites at which 459 participants (in 5 cohorts) were fed 3 dietary patterns over 11 weeks per cohort. The 3 patterns were a control diet, a fruits and vegetables diet, and a combination diet. Before the intervention, key nutrient levels in each diet were validated at 2 energy levels (2,100 and 3,100 kcal) by chemical analysis of the prepared menus. During intervention, diets were sampled across all cohorts, sites, and energy levels, and 7-day menu cycle composites were assayed. In general, sodium, potassium, calcium, and magnesium in the validated menus for each diet/energy level met the nutrient targets, though moderate variability was evident among individual menus, particularly for potassium, calcium, and magnesium. However, as intended, there was clear separation and no overlap in mineral levels in individual menus of diets that were designed to differ. During intervention, macronutrient contents met nutrient goals. Sodium, potassium, calcium, and magnesium in the diets generally met target levels, though potassium in the fruits and vegetables diet was 11% to 23% below target. There were no consistent differences in nutrient levels between sites. The mean nutrient levels in the validated menus and diets sampled during intervention were in excellent agreement with each other, though sodium was somewhat higher (approximately 6%) in the diets from intervention vs validation. These results indicate the success of the quality control measures implemented and suggested consistent overall diet composition throughout the 28 months during which the study was conducted.