This 12 week clinical trial found comparable benefits from three dietary approaches to weight loss on outcomes related to body weight and composition, components of MetS, and dietary composition in overweight and obese sedentary adults. . Diet composition changed significantly in similar ways among the three groups. Of interest, the weighted GI, GL, or energy density were not significantly different among the groups. Thus, instruction on these three dietary approaches resulted in different means to similar ends.
In assessing weight loss diets, considerations must be given to changes in body composition, chronic disease risk factors, diet composition, and appetite . Additionally, individuals must determine what will suit their lifestyle and personal preferences so that they can sustain the diet for long periods . Results of this trial indicate that over 12 weeks, PC, LED, and LGI approaches produce analogous changes in measured outcomes within a comprehensive weight loss program.
Weight loss was achieved using PC, LED, and LGI. These findings support those of some previous studies, which also found that low GI dietary plans do not result in weight reduction beyond that of traditional dietary plans [23, 27–30]. In a similar 12-week study with 129 women on four diets differing in GI and protein, weight loss did not differ among the groups, and was comparable to the current study . A study that compared a reduced GL diet to a portion-controlled plan showed significantly greater weight loss at 12 weeks in the reduced GL group, but these between-group differences were not sustained thereafter . Other studies have demonstrated better body composition improvements on low GI or low GL diets compared to other approaches [24, 37]. Lack of consistency among studies might be related to the actual GL of the diets consumed, and/or to the additional components of the weight loss program in the current study.
Both weight loss [3, 4] and lowered dietary GL  have been associated with reduced MetS risk factors. The overweight and obese subjects in this study were not clinically hyperglycemic or hyperinsulinemic, but improvements were seen in all three groups. Furthermore, C-reactive protein, a marker of inflammation and cardiovascular disease risk , was lowered regardless of dietary approach. Even modest weight reduction can profoundly reduce MetS risk , as shown in this study, and it was achieved in three different ways. All three interventions produced a similarly reduced dietary GL, which might help explain the similar reductions in risk factors. Total and LDL cholesterol did not decrease significantly in this trial, which might be due to the fact that the subjects were not hypercholesterolemic at the outset. HDL cholesterol decreased slightly in all groups, which is sometimes seen in studies that replace much of the dietary fat with carbohydrate, particularly in insulin-resistant individuals [39, 40]. However, at week 12, the LED, LGI, and PC groups consumed dietary carbohydrate at 49%, 46%, and 49% of energy intake, which is within the 45-60% range recommended for diets to reduce MetS risk [3, 4]. Weight loss studies with reduced GL diets similar to the present study have observed increased HDL cholesterol over longer time periods , so it is possible that the trend seen here in HDL cholesterol would have become more favorable with time.
The dietary plans in this trial were followed within the context of a comprehensive weight-loss program. Thus, the results cannot be ascribed solely to the diets alone [41, 42]. All groups attended weekly meetings of similar structure, which should minimize independent effects of intervention sessions. All aspects of the protocol were identical except for the dietary approaches.
After 12 weeks, the PC group reported a significantly higher GI than the other groups, but weighted GI or GL did not differ. The PC intervention emphasized portions more than food types, so participants likely incorporated foods with higher GI values . Conversely, both the LGI and LED plans emphasized foods that are rich in fiber and low in added sugars and refined starches, because these tend to be low in GI and low in ED. GL is calculated using both the quantity and quality of foods , which may help explain the similar GL among the three groups [25, 37]. The PC group focused on decreasing overall food quantity, so that would help reduce the GL. Instructions for the LED group did not address GI at all, but some overlap may exist in the food choices, particularly due to fiber-rich foods having low ED. At 12 weeks, reductions of fiber intake in the PC group are likely due to high values reported at baseline, followed by reduced total food intake over the intervention. At baseline, the LED and LGI groups reported lower fiber intakes, which increased over the intervention due to the instructions related to high fiber foods. Similar fiber intakes might have contributed, at least in part, to the similar energy density of the diets among the three groups.
LGI and LED diets have been promoted for weight loss due to effects on increased satiety [30, 33]. A previous 12-week study examined a dietary plan similar to the PC group in the current study, with and without reductions in GI . Although weight loss did not differ according to the GI manipulation, the lower GI version of the diet was associated with reduced hunger and heightened satiety ratings. In the current study, similar 6-week hunger and satiety ratings between the LGI and LED groups suggest that these diet plans did not produce different satiety effects.. Similar appetite ratings may be attributed to the comparable calculated GL, ED, and fiber intakes between the two dietary plans. Both groups received the same counseling on recognizing and responding to internal cues and hunger signals .
This study only examined a 12-week period, so longer-term studies are needed to ascertain whether the results would continue to follow the same trends. Unequal gender distribution among the subjects also indicates that future studies should include recruitment efforts targeted more towards males. Another limitation of the current study is the dropout rate, although the rates are lower than many other studies, and dropouts are common, due to challenges of following prescriptive diets over long periods, and the demands of subjects’ time for laboratory visits [20, 27]. Power calculations had taken anticipated dropout rates into account. As with most free-living human nutrition research, food intake was self-reported. However, the registered dietitians instructed subjects carefully on accurate dietary recording, and reviewed the 3-day food diaries in detail with subjects. Additionally, only the LED and LGI groups were randomized, and the PC group served as an extra comparison group who enrolled in the program. This may explain their full completion of the study. However, their data provide insight into results that may occur in the ‘real world’ situation of people choosing such a program. It is interesting to note that their dietary and other changes were similar to the other two groups.
Strengths of this study include the similar multi-disciplinary approach taken in all groups, including diet, physical activity, behavior modification, and regular social support [6, 7]. These, which follow national and international guidelines [1–3, 31], produced recommended rates of weight loss of almost 5% , which have been associated with significant reductions in risk for several chronic diseases [1, 4]. Further, multiple health-related outcomes were measured.