Dietary intake in the diabetes prevention program cohort: baseline and 1-year post randomization

The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus

OBJECTIVE

Dietary carbohydrate is the major determinant of postprandial glucose levels, and several clinical studies have shown that low-carbohydrate diets improve glycemic control. In this study, we tested the hypothesis that a diet lower in carbohydrate would lead to greater improvement in glycemic control over a 24-week period in patients with obesity and type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

Eighty-four community volunteers with obesity and type 2 diabetes were randomized to either a low-carbohydrate, ketogenic diet (<20 g of carbohydrate daily; LCKD) or a low-glycemic, reduced-calorie diet (500 kcal/day deficit from weight maintenance diet; LGID). Both groups received group meetings, nutritional supplementation, and an exercise recommendation. The main outcome was glycemic control, measured by hemoglobin A1c.

RESULTS

Forty-nine (58.3%) participants completed the study. Both interventions led to improvements in hemoglobin A1c, fasting glucose, fasting insulin, and weight loss. The LCKD group had greater improvements in hemoglobin A1c (-1.5% vs. -0.5%, p = 0.03), body weight (-11.1 kg vs. -6.9 kg, p = 0.008), and high density lipoprotein cholesterol (+5.6 mg/dL vs. 0 mg/dL, p < 0.001) compared to the LGID group. Diabetes medications were reduced or eliminated in 95.2% of LCKD vs. 62% of LGID participants (p < 0.01).

CONCLUSION

Dietary modification led to improvements in glycemic control and medication reduction/elimination in motivated volunteers with type 2 diabetes. The diet lower in carbohydrate led to greater improvements in glycemic control, and more frequent medication reduction/elimination than the low glycemic index diet. Lifestyle modification using low carbohydrate interventions is effective for improving and reversing type 2 diabetes.

Assessing gene-treatment interactions at the FTO and INSIG2 loci on obesity-related traits in the Diabetes Prevention Program

AIMS/HYPOTHESIS

The single nucleotide polymorphism (SNP) rs9939609 in the fat mass and obesity associated gene (FTO) and the rs7566605 SNP located 10 kb upstream of the insulin-induced gene 2 gene (INSIG2) have been proposed as risk factors for common obesity.

METHODS

We tested for genotype-treatment interactions on changes in obesity-related traits in the Diabetes Prevention Program (DPP). The DPP is a randomised controlled trial of 3,548 high-risk individuals from 27 participating centres throughout the USA who were originally randomised to receive metformin, troglitazone, intensive lifestyle modification or placebo to prevent the development of type 2 diabetes. Measures of adiposity from computed tomography were available in a subsample (n = 908). This report focuses on the baseline and 1 year results.

RESULTS

The minor A allele at FTO rs9939609 was positively associated with baseline BMI (p = 0.003), but not with baseline adiposity or the change at 1 year in any anthropometric trait. For the INSIG2 rs7566605 genotype, the minor C allele was associated with more subcutaneous adiposity (second and third lumbar vertebrae [L2/3]) at baseline (p = 0.04). During follow-up, CC homozygotes lost more weight than G allele carriers (p = 0.009). In an additive model, we observed nominally significant gene-lifestyle interactions on weight change (p = 0.02) and subcutaneous (L2/3 [p = 0.01] and L4/5 [p = 0.03]) and visceral (L2/3 [p = 0.02]) adipose areas. No statistical evidence of association with physical activity energy expenditure or energy intake was observed for either genotype.

CONCLUSIONS/INTERPRETATION

Within the DPP study population, common variants in FTO and INSIG2 are nominally associated with quantitative measures of obesity, directly and possibly by interacting with metformin or lifestyle intervention.

Intakes of long-chain n-3 polyunsaturated fatty acids and fish in relation to measurements of subclinical atherosclerosis

BACKGROUND

Data on the relations of different types of fish meals and long-chain n-3 polyunsaturated fatty acids (PUFAs) to measures of atherosclerosis are sparse.

OBJECTIVE

We examined intakes of long-chain n-3 PUFAs and fish in relation to clinical measures of subclinical atherosclerosis.

DESIGN

A cross-sectional study was conducted in a multiethnic group of 5,488 adults aged 45-84 y and free of clinical cardiovascular disease. Diet was assessed by using self-administered food-frequency questionnaires. Subclinical atherosclerosis was determined by measurements of common carotid intima-media thickness (cCIMT, >80th percentile), internal CIMT (iCIMT, >80th percentile), coronary artery calcium score (CAC score, >0), or ankle-brachial index (ABI, <0.90).

RESULTS

After adjustment for potential confounders, intakes of long-chain n-3 PUFAs and nonfried (broiled, steamed, baked, or raw) fish were inversely related to subclinical atherosclerosis determined by cCIMT but not by iCIMT, CAC score, or ABI. The multivariate odds ratio comparing the highest to the lowest quartile of dietary exposures in relation to subclinical atherosclerosis determined by cCIMT was 0.69 (95% CI: 0.55, 0.86; P for trend < 0.01) for n-3 PUFA intake; 0.80 (95% CI: 0.64, 1.01; P = 0.054) for nonfried fish consumption; and 0.90 (95% CI: 0.73, 1.11; P = 0.38) for fried fish consumption.

CONCLUSIONS

This study indicates that the dietary intake of long-chain n-3 PUFAs or nonfried fish is associated with a lower prevalence of subclinical atherosclerosis classified by cCIMT, although significant changes in iCIMT, CAC score, and ABI were not observed. Our findings also suggest that the association of fish and atherosclerosis may vary depending on the type of fish meal consumed and the measures of atherosclerosis.

Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet

BACKGROUND

Trials comparing the effectiveness and safety of weight-loss diets are frequently limited by short follow-up times and high dropout rates.

METHODS

In this 2-year trial, we randomly assigned 322 moderately obese subjects (mean age, 52 years; mean body-mass index [the weight in kilograms divided by the square of the height in meters], 31; male sex, 86%) to one of three diets: low-fat, restricted-calorie; Mediterranean, restricted-calorie; or low-carbohydrate, non-restricted-calorie.

RESULTS

The rate of adherence to a study diet was 95.4% at 1 year and 84.6% at 2 years. The Mediterranean-diet group consumed the largest amounts of dietary fiber and had the highest ratio of monounsaturated to saturated fat (P<0.05 for all comparisons among treatment groups). The low-carbohydrate group consumed the smallest amount of carbohydrates and the largest amounts of fat, protein, and cholesterol and had the highest percentage of participants with detectable urinary ketones (P<0.05 for all comparisons among treatment groups). The mean weight loss was 2.9 kg for the low-fat group, 4.4 kg for the Mediterranean-diet group, and 4.7 kg for the low-carbohydrate group (P<0.001 for the interaction between diet group and time); among the 272 participants who completed the intervention, the mean weight losses were 3.3 kg, 4.6 kg, and 5.5 kg, respectively. The relative reduction in the ratio of total cholesterol to high-density lipoprotein cholesterol was 20% in the low-carbohydrate group and 12% in the low-fat group (P=0.01). Among the 36 subjects with diabetes, changes in fasting plasma glucose and insulin levels were more favorable among those assigned to the Mediterranean diet than among those assigned to the low-fat diet (P<0.001 for the interaction among diabetes and Mediterranean diet and time with respect to fasting glucose levels).

CONCLUSIONS

Mediterranean and low-carbohydrate diets may be effective alternatives to low-fat diets. The more favorable effects on lipids (with the low-carbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions. (ClinicalTrials.gov number, NCT00160108.)

Carbohydrate intake and obesity

The prevalence of obesity has increased rapidly worldwide and the importance of considering the role of diet in the prevention and treatment of obesity is widely acknowledged. This paper reviews data on the effects of dietary carbohydrates on body fatness. Does the composition of the diet as related to carbohydrates affect the likelihood of passive over-consumption and long-term weight change? In addition, methodological limitations of both observational and experimental studies of dietary composition and body weight are discussed. Carbohydrates are among the macronutrients that provide energy and can thus contribute to excess energy intake and subsequent weight gain. There is no clear evidence that altering the proportion of total carbohydrate in the diet is an important determinant of energy intake. However, there is evidence that sugar-sweetened beverages do not induce satiety to the same extent as solid forms of carbohydrate, and that increases in sugar-sweetened soft drink consumption are associated with weight gain. Findings from studies on the effect of the dietary glycemic index on body weight have not been consistent. Dietary fiber is associated with a lesser degree of weight gain in observational studies. Although it is difficult to establish with certainty that fiber rather than other dietary attributes are responsible, whole-grain cereals, vegetables, legumes and fruits seem to be the most appropriate sources of dietary carbohydrate.

The Pro12Ala variant at the peroxisome proliferator-activated receptor gamma gene and change in obesity-related traits in the Diabetes Prevention Program

AIMS/HYPOTHESIS

Peroxisome proliferator-activated receptor gamma (PPARgamma), encoded by the PPARG gene, regulates insulin sensitivity and adipogenesis, and may bind polyunsaturated fatty acids (PUFA) and thiazolidinediones in a ligand-dependent manner. The PPARG proline for alanine substitution at position 12 (Pro12Ala polymorphism) has been related with obesity directly and via interaction with PUFA.

METHODS

We tested the effect-modifying role of Pro12Ala on the 1 year change in obesity-related traits in a randomised clinical trial of treatment with metformin (n = 989), troglitazone (n = 363) or lifestyle modification (n = 1,004) vs placebo (n = 1,000) for diabetes prevention in high-risk individuals.

RESULTS

At baseline, Ala12 carriers had larger waists (p < 0.001) and, in a subset, more subcutaneous adipose tissue (SAT; lumbar 2/3; p = 0.04) than Pro12 homozygotes. There was a genotype-by-intervention interaction on 1-year weight change (p = 0.01); in the placebo arm, Pro12 homozygotes gained weight and Ala12 carriers lost weight (p = 0.001). In the metformin and lifestyle arms, weight loss occurred across genotypes, but was greatest in Ala12 carriers (p < 0.05). Troglitazone treatment induced weight gain, which tended to be greater in Ala12 carriers (p = 0.08). In the placebo group, SAT (lumbar 2/3, lumbar 4/5) decreased in Ala12 allele carriers, but was unchanged in Pro12 homozygotes (p < or = 0.005). With metformin treatment, SAT decreased independently of genotype. In the lifestyle arm, SAT (lumbar 2/3) reductions occurred across genotypes, but were greater in Ala12 carriers (p = 0.03). A genotype-by-PUFA intake interaction on reduction in visceral fat (lumbar 4/5; p = 0.04) was also observed, which was most evident with metformin treatment (p < 0.001).

CONCLUSIONS/INTERPRETATION

Within the Diabetes Prevention Program, the Ala12 allele influences central obesity, an effect which may differ by treatment group and dietary PUFA intake (ClinicalTrials.gov ID no: NCT00004992).

Factors associated with diabetes onset during metformin versus placebo therapy in the diabetes prevention program

In the Diabetes Prevention Program, treatment of subjects with impaired glucose tolerance with metformin >3.2 years reduced the risk of developing type 2 diabetes by 30% compared with placebo. This study describes the mechanisms of this effect. In proportional hazards regression models with 2,155 subjects, changes in weight, the insulinogenic index (IGR), fasting insulin, and proinsulin were predictive of diabetes, though to different degrees within each group. The mean change in weight, fasting insulin, and proinsulin, but not IGR, differed between groups during the study. The 1.7-kg weight loss with metformin versus a 0.3-kg gain with placebo alone explained 64% of the beneficial metformin effect on diabetes risk. Adjustment for weight, fasting insulin, proinsulin, and other metabolic factors combined explained 81% of the beneficial metformin effect, but it remained nominally significant (P = 0.034). After the addition of changes in fasting glucose, 99% of the group effect was explained and is no longer significant. Treatment of high-risk subjects with metformin results in modest weight loss and favorable changes in insulin sensitivity and proinsulin, which contribute to a reduction in the risk of diabetes apart from the associated reductions in fasting glucose.

Effect of weight loss with lifestyle intervention on risk of diabetes

OBJECTIVE

Diabetes Prevention Program (DPP) participants randomized to the intensive lifestyle intervention (ILS) had significantly reduced risk of diabetes compared with placebo participants. We explored the contribution of changes in weight, diet, and physical activity on the risk of developing diabetes among ILS participants.

RESEARCH DESIGN AND METHODS

For this study, we analyzed one arm of a randomized trial using Cox proportional hazards regression over 3.2 years of follow-up.

RESULTS

A total of 1,079 participants were aged 25-84 years (mean 50.6 years, BMI 33.9 kg/m(2)). Weight loss was the dominant predictor of reduced diabetes incidence (hazard ratio per 5-kg weight loss 0.42 [95% CI 0.35-0.51]; P < 0.0001). For every kilogram of weight loss, there was a 16% reduction in risk, adjusted for changes in diet and activity. Lower percent of calories from fat and increased physical activity predicted weight loss. Increased physical activity was important to help sustain weight loss. Among 495 participants not meeting the weight loss goal at year 1, those who achieved the physical activity goal had 44% lower diabetes incidence.

CONCLUSIONS

Interventions to reduce diabetes risk should primarily target weight reduction.

Dietary intake among youth with diabetes: the SEARCH for Diabetes in Youth Study

OBJECTIVE

To describe dietary intake among a large cohort of youth with type 1 or type 2 diabetes and to compare their intake with current nutrition recommendations.

DESIGN

SEARCH for Diabetes in Youth is a multicenter study of diabetes in youth. Diet was assessed among youth aged 10 to 22 years who attended a SEARCH research clinic visit and completed a previous-week food frequency questionnaire that included foods to reflect the ethnic and regional diversity represented by the cohort.

SUBJECTS/SETTING

Included were 1,697 youth with physician-diagnosed diabetes mellitus (89% type 1 diabetes, 11% type 2 diabetes), with diabetes mellitus duration of at least 12 months.

STATISTICAL ANALYSES

Descriptive data and comparisons with nutrition recommendations were unadjusted. Analyses of covariance with adjustment for total energy, clinic site, sex, race/ethnicity, age, and parental education were used to compare intake according to diabetes type.

RESULTS

Percent of energy from total fat was consistent at 37% to 38% across subgroups of age (10 to 14 years, >15 years) and diabetes type (ie, type 1 or type 2). Youth with type 2 diabetes consumed less calcium, magnesium, and vitamin E than youth with type 1 diabetes (P<0.01 for each). Intake of sweetened carbonated beverages among older (aged >15 years) youth with type 2 diabetes was twice that of older youth with type 1 diabetes (P<0.01). Only 6.5% of the cohort met American Diabetes Association recommendations of <10% of energy from saturated fat. Less than 50% met recommendations for total fat, vitamin E, fiber, fruits, vegetables, and grains, although a majority met recommendations for vitamin C, calcium, and iron.

CONCLUSIONS

Overall, dietary intake in this large cohort of youth with diabetes substantially failed to meet current recommendations. There is a critical need for improvement in dietary intake in youth with diabetes.

Nut and seed consumption and inflammatory markers in the multi-ethnic study of atherosclerosis

Nuts and seeds are rich in unsaturated fat and other nutrients that may reduce inflammation. Frequent nut consumption is associated with lower risk of cardiovascular disease and type 2 diabetes. The authors examined associations between nut and seed consumption and C-reactive protein, interleukin-6, and fibrinogen in the Multi-Ethnic Study of Atherosclerosis. This 2000 cross-sectional analysis included 6,080 US participants aged 45-84 years with adequate information on diet and biomarkers. Nut and seed consumption was categorized as never/rare, less than once/week, 1-4 times/week, and five or more times/week. After adjustment for age, gender, race/ethnicity, site, education, income, smoking, physical activity, use of fish oil supplements, and other dietary factors, mean biomarker levels in categories of increasing consumption were as follows: C-reactive protein-1.98, 1.97, 1.80, and 1.72 mg/liter; interleukin-6-1.25, 1.24, 1.21, and 1.15 pg/ml; and fibrinogen-343, 338, 338, and 331 mg/dl (all p's for trend < 0.01). Further adjustment for hypertension, diabetes, medication use, and lipid levels yielded similar results. Additional adjustment for body mass index moderately attenuated the magnitude of the associations, yielding borderline statistical significance. Associations of nut and seed consumption with these biomarkers were not modified by body mass index, waist:hip ratio, or race/ethnicity. Frequent nut and seed consumption was associated with lower levels of inflammatory markers, which may partially explain the inverse association of nut consumption with cardiovascular disease and diabetes risk.

Lifestyle intervention to prevent diabetes: intensive and cost effective

PURPOSE OF REVIEW

Type 2 diabetes is a major cause of morbidity and mortality, and despite treatment advances appears to be increasing in incidence. Since individuals at risk for the disease are usually identifiable in the prediabetic phase of impaired glucose tolerance, early intervention might prevent diabetes and hence its complications from developing. Obesity and sedentary living are powerful determinants of diabetes, and thus lifestyle change is a logical approach to prevention of this disease. Recent clinical trials have now tested the effectiveness of this intervention and form the basis for this review.

RECENT FINDINGS

Three clinical trials have demonstrated that, compared with usual care, lifestyle intervention significantly reduced progression rates to diabetes in prediabetic individuals. Each trial incorporated individualization and repeated long-term contacts with facilitators, in which dietary and physical activity goal setting and behavior modification were central themes. Progression to diabetes was reduced in the Da Qing study by approximately 40%, in the Finnish Diabetes Prevention Study by 58% and in the Diabetes Prevention Program by 58%. The Diabetes Prevention Program included a cost-benefit unit that estimated the per capita costs of the lifestyle intervention to exceed that of the usual care group by Dollars 3540, which translated to a cost of Dollars 15,700 per case of diabetes prevented. Lifetime cost-utility analysis demonstrated an overall cost of Dollars 1100 per quality-adjusted life year.

SUMMARY

These findings make the case for translation of research findings to healthcare systems. Although there is more to be learned about effective strategies in clinical practice, it seems clear that the intervention needs to incorporate individualization and long-term interaction with trained facilitators.

Dietary Intakes of Nutrients Thought to Modify Cardiovascular Risk from Three Groups of American Indians: The Strong Heart Dietary Study, Phase II

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality among American Indians. Rates of CVD appear to be increasing among American Indians while they are decreasing among other racial and ethnic groups in the United States. Rates of comorbid conditions associated with CVD, such as obesity, impaired glucose tolerance, and hypertension, are also higher among American Indians than among other racial and ethnic groups in the United States. Dietary factors play a role in the development of CVD and associated comorbid conditions, yet surprisingly few data exist to describe the dietary intakes and nutritional adequacy of American Indian adults at risk for CVD.

OBJECTIVE

To describe intakes of nutrients that may affect CVD risk consumed by members of 13 nations of American Indian adults, aged 45 to 70 years, who reside in tribal communities in Arizona, North Dakota, South Dakota, and Oklahoma. A secondary objective was to compare dietary intake estimates to nationally representative data from adults of similar age to determine potential dietary differences that may account for the disparities seen in rates of CVD and related conditions. Finally, dietary intake estimates were compared with national dietary guidance to determine areas for improvement.

METHODS

Data from a 24-hour dietary recall provided by 3,482 adults who participated in the Strong Heart Dietary Study, Phase II, were analyzed to describe dietary intakes of nutrients that may alter CVD risk. Nonparametric analyses of variance were used to compare data by center, age, and sex. Dietary intake data for each sex/center group were compared with data from the Third National Health and Nutrition Examination Survey (NHANES III), Phase I, dietary estimates, and to national dietary guidelines.

RESULTS

Nutrient intakes varied little between centers. Sex differences were noted in energy and nutrient intakes across all centers. Age-related decreases in energy and total and saturated fat intakes were noted among all sex/center groups. Median intakes of vitamins A and C and folate were low among all sex/center groups. Remarkably few differences in dietary intake were noted between NHANES III and Strong Heart Dietary Study, Phase II, participants. Carbohydrate and sodium intakes were higher among participants compared with NHANES III estimates, whereas intakes of several vitamins were lower.

CONCLUSIONS

Dietary intakes of American Indians vary by age, sex, and geographic location, but do not differ substantially from national estimates of dietary intake. The dietary differences noted between NHANES III and Strong Heart Dietary Study, Phase II, participants are not consistent with the remarkably different rates of CVD and associated comorbidities that currently exist.