The dramatic increase in obesity worldwide remains challenging and underscores the urgent need to test the effectiveness and safety of several widely used weight-loss diets.1,2,3 Low-carbohydrate, high-protein, high-fat diets (referred to as low-carbohydrate diets) have been compared with low-fat, energy-restricted diets.4,5,6,7,8,9 A meta-analysis of five trials with 447 participants10 and a recent 1-year trial involving 311 obese women4 suggested that a low-carbohydrate diet is a feasible alternative to a low-fat diet for producing weight loss and may have favorable metabolic effects. However, longer-term studies are lacking.4,10 A Mediterranean diet with a moderate amount of fat and a high proportion of monounsaturated fat provides cardiovascular benefits.11 A recent review citing several trials12 included a few that suggested that the Mediterranean diet was beneficial for weight loss.13,14 However, this positive effect has not been conclusively demonstrated.
In this 2-year dietary-intervention study, we found that the Mediterranean and low-carbohydrate diets are effective alternatives to the low-fat diet for weight loss and appear to be just as safe as the low-fat diet. In addition to producing weight loss in this moderately obese group of participants, the low-carbohydrate and Mediterranean diets had some beneficial metabolic effects, a result suggesting that these dietary strategies might be considered in clinical practice and that diets might be individualized according to personal preferences and metabolic needs. The similar caloric deficit achieved in all diet groups suggests that a low-carbohydrate, non–restricted-calorie diet may be optimal for those who will not follow a restricted-calorie dietary regimen. The increasing improvement in levels of some biomarkers over time up to the 24-month point, despite the achievement of maximum weight loss by 6 months, suggests that a diet with a healthful composition has benefits beyond weight reduction.
The present study has several limitations. We enrolled few women; however, we observed a significant interaction between the effects of diet group and sex on weight loss (women tended to lose more weight on the Mediterranean diet), and this difference between men and women was also reflected in the changes in leptin levels. This possible sex-specific difference should be explored in further studies. The data from the few participants with diabetes are of interest, but we recognize that measurement of HOMA-IR is not an optimal method to assess insulin resistance among persons with diabetes. We relied on self-reported dietary intake, but we validated the dietary assessment in two different dietary-assessment tools and used electronic questionnaires to minimize the amount of missing data. Finally, one might argue that the unique nature of the workplace in this study, which permitted a closely monitored dietary intervention for a period of 2 years, makes it difficult to generalize the results to other free-living populations. However, we believe that similar strategies to maintain adherence could be applied elsewhere.
The strengths of the study include the one-phase design, in which all participants started simultaneously; the relatively long duration of the study; the large study-group size; and the high rate of adherence. The monthly measurements of weight permitted a better understanding of the weight-loss trajectory than was the case in previous studies.
We observed two phases of weight change: initial weight loss and weight maintenance. The maximum weight reduction was achieved during the first 6 months; this period was followed by the maintenance phase of partial rebound and a plateau. Among all diet groups, weight loss was greater for those who completed the 24-month study than for those who did not. Even moderate weight loss has health benefits, and our findings suggest benefits of behavioral approaches that yield weight losses similar to those obtained with pharmacotherapy.29
We distinguished between changes in levels of biomarkers (leptin, adiponectin, and high-sensitivity C-reactive protein) that are apparently related to loss of adipose tissue and changes in biomarkers (triglycerides, HDL cholesterol, glucose, and insulin) that apparently reflect, in part, the effects of specific diet composition. The changes we observed in levels of adiponectin and leptin,30 which were consistent in all groups, reflect loss of weight. Consumption of monounsaturated fats is thought to improve insulin sensitivity,14,31,32 an effect that may explain the favorable effect of the Mediterranean diet on glucose and insulin levels. The results imply that dietary composition modifies metabolic biomarkers in addition to leading to weight loss. Our results suggest that health care professionals might consider more than one dietary approach, according to individual preferences and metabolic needs, as long as the effort is sustained.
This trial also suggests a model that might be applied more broadly in the workplace. As Okie recently suggested,33 using the employer as a health coach could be a cost-effective way to improve health. The model of intervention with the use of dietary group sessions, spousal support, food labels, and monthly weighing in the workplace within the framework of a health promotion campaign might yield weight reduction and long-term health benefits.
