Long-term effects of a low carbohydrate, low fat or high unsaturated fat diet compared to a no-intervention control

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Abstract

Background and aim

Very low carbohydrate ad libitum diets have been shown to enhance weight loss without increasing cardiometabolic risk factors but no kilojoule-controlled trials have been conducted relative to no intervention. The aim of this study was to compare the changes in weight and other cardiovascular risk factors in 3 isocaloric energy-restricted diets to no-intervention control after 1 year.

Methods and results

One hundred and thirteen subjects (age 47 ± 10 years, BMI 32 ± 6 kg/m2 with one additional cardiovascular risk factor) were randomly allocated to one of three isocaloric diets (VLC-very low carbohydrate, 60% fat, 4% carbohydrate, n = 30; VLF-very low fat, 10% fat, n = 30; HUF-high unsaturated fat, 30% fat, n = 30) with intensive support for 3 months followed by minimal support for 12 months compared to a control group (no intervention, n = 23). The estimated weight change was −3.0 ± 0.2 kg for VLC, −2.0 ± 0.1 kg for VLF, −3.7 ± 0.01 kg for HUF and 0.8 ± 0.5 kg for controls (P = 0.065). After correcting for baseline values, decreases in body weight and diastolic blood pressure in the diet groups (−2.9 ± 5.2) were significantly different to the increase in the control group (0.8 ± 5.0) (P < 0.05). No differences in cardiovascular risk factors were observed between the diet groups.

Conclusion

Significant cardiometabolic risk factor reduction was observed equally with VLC, VLF and HUF diets after 15 months, compared to an exacerbation of risk factors in the control group. At a modest level of adherence, 3 months of intensive support on these dietary patterns confer an improvement in cardiometabolic profile compared to no dietary intervention after 15 months.

Introduction

Obesity and weight gain are significant risk factors for cardiovascular disease (CVD) [1], [2]. Weight loss is associated with improvements in cardiovascular risk factors such as blood pressure and serum lipids [3], [4]. While the traditional weight loss approach advises a high carbohydrate low fat diet, in recent years very low carbohydrate (VLC) diets have been suggested to have possibly greater effectiveness in weight loss and metabolic improvements [5]. However, no energy-controlled trials have been conducted to elucidate the long-term effects of this dietary pattern in individuals with cardiovascular risks.

The safety and efficacy of a VLC diet on cardiovascular health remains controversial [6]. Population studies provided conflicting evidence on the effects of this dietary pattern on cardiovascular risks and CVD mortality [7], [8]. Several intervention studies found these dietary patterns to be more effective in weight loss without incurring adverse metabolic effects [9], [10], [11], [12], [13], [14]. A recent meta-analysis reported that at 12 months, weight loss and changes in HDL cholesterol were similar between VLC diets and low fat diets, although VLC diets remained more effective in lowering triglycerides and a low fat diet more effective in lowering total and LDL cholesterol [5].

As most studies investigating VLC employed an ad libitum approach, the sustainability of these dietary patterns based on macronutrient profiles alone, and their long-term effects on body weight and metabolic health could not be determined independent of these confounding effects. In addition, how dietary interventions affect the longitudinal changes in cardiometabolic risk factors of an at-risk population relative to a control group have not been well described.

Therefore, the primary objective of this study was to compare the long-term effects of three energy reduced, isocaloric diets, which is the very low carbohydrate (VLC) diet, very low fat (VLF) diet and high unsaturated fat (HUF) diet on weight loss and cardiovascular risk factors in a 15-month randomized controlled trial in overweight or obese individuals with elevated cardiovascular risks. The secondary purpose of this study was to determine if these diets would result in significantly different effects compared to a no-intervention control after 15 months.

Section snippets

Study population

A total of 113 volunteers aged between 20 and 65 years with at least one CVD risk factor other than obesity were recruited by public advertisement. Other inclusion criteria included having a body mass index (BMI) between 28 and 40 kg/m2. Exclusion criteria included the use of hypoglycemic medication or drugs that affect insulin sensitivity, a history of heavy alcohol consumption, a history of metabolic or coronary heart disease, type 1 or type 2 diabetes, widely fluctuating exercise patterns and

Subjects

A total of 104 subjects (17 male and 87 female, age 47 ± 10 years, BMI 32 ± 6 kg/m2) commenced the study. Of these, 69 subjects (13 male, 56 female) completed the 15 months study (Fig. 1). The attrition rate was 43%, 40%, 50% and 17% for VLC, VLF, HUF and the control group respectively (P = 0.098). Reasons cited for withdrawal included personal reasons, work commitments, travel and difficulties with the allocated diet (Fig. 1). The baseline characteristics of subjects are shown in Table 1. Baseline

Discussion

This study reports the outcomes at 1 year following a 3-month intensive intervention in a randomized controlled trial involving a comparison of three energy-restricted, isocaloric dietary patterns with a no-intervention control group. Despite receiving minimal support during the 12-month follow-up period, dietary patterns remained significantly different between the groups at 1 year. Although weight regain occurred across the three diet groups, they maintained a net weight loss at 1 year after

Conflict of interest

No conflict of interest exists for any of the authors.

Acknowledgements

We thank Anne McGuffin, Kathryn Bastiaans and Rosemary McArthur for assistance in performance of this study. Manny Noakes and Peter Clifton designed the study. Siew Seen Lim performed data analysis and wrote the manuscript. Paul Foster assisted with the dietetic counseling. Jennifer Keogh contributed to the data analysis and interpretation, critically reviewed the manuscript and was involved in the dietetic counseling of the volunteers. Kylie Lange provided statistical advice.

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    Funding source: This study was supported by a National Heart Foundation, Australia and CSIRO Health Sciences and Nutrition, Adelaide, Australia.

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