In this telemedically guided weight reduction program both, an energy-restricted high-carbohydrate diet (DGE group) and an energy-restricted low-carbohydrate diet (LOGI group) resulted in a satisfactory weight loss and an improvement of several metabolic parameters over a period of 12 months. However, weight loss tended to be greater, and the decline in waist circumference and systolic blood pressure was more pronounced in the LOGI group than in the DGE group. With respect to HDL-cholesterol and triglycerides, beneficial effects in the LOGI group compared to the DGE group were only seen at the 6-month follow-up visit. Since mean energy intake and energy expenditure did not differ between the two groups, the differences in the aforementioned parameters are most likely due to differences in macronutrient relations.
The mean body weight loss of 7.2 kg at month 6 and 5.8 kg at month 12 in the LOGI group (Figure ) was similar compared to literature reports about efficacy of carbohydrate-restricted diets [12
]. In these earlier reports, results of carbohydrate-restricted diets were also compared with fat-restricted diets. Mean weight loss of the fat-restricted diets was only 1.6 kg – 3.9 kg at month 6 [12
] and 2.2 kg – 3.1 kg at month 12 [12
] and thus lower than the mean weight loss in the energy-restricted fat-reduced group (DGE group) in our study (6.2 kg at month 6 and 4.3 kg at month 12, respectively). It has been assumed that the better 1-year efficacy of carbohydrate-restricted diets on weight loss compared to fat-restricted diets can be explained by a greater energy deficit in subjects on a low-carbohydrate intake. Since in our study energy intake and body weight loss were similar in both groups within the first 6 month, our results are in line with the aforementioned hypothesis. However, despite similar energy intake at month 12, weight loss tended to be greater at month 12 in the LOGI group compared with the DGE group of our study. Note that differences in macronutrient composition of the diet may influence resting or postprandial energy expenditure [15
]. Since protein intake increases diet-induced thermogenesis, it can well be that the slightly higher protein intake in the LOGI group compared with the DGE group during the entire study period could also have resulted in a slightly higher metabolic rate, and thus in a slightly higher weight loss. Nevertheless, our data also demonstrate that even with an energy-restricted high-carbohydrate diet a weight loss similar to an energy-restricted carbohydrate-reduced diet can be achieved. Importantly, the regain of weight after 12 months confirms earlier assumptions [17
] that continuous intensive care and control is a more important factor for participants' compliance and, thus, for the success of a weight loss program than minor alterations in macronutrient composition in the diet. Our results are in line with a very recently published trial by Sacks et al. [30
]. They investigated four diets with different macronutrient relations and showed that weight loss is related to adherence and attendance to instructional sessions. All diets were equally successful in promoting weight loss and maintaining weight.
Despite the favourable effects of both diets on weight loss in our study, the carbohydrate-reduced diet was more beneficial with respect to some cardiovascular risk markers such as waist circumference, triglycerides, HDL-cholesterol, and systolic blood pressure compared to the fat-reduced diet. Our data show into the same direction than earlier study results [12
] but were less pronounced. This may at least in part be due to two factors: the comparably higher weight loss by carbohydrate-restricted diets in these earlier studies [12
], and/or a more pronounced carbohydrate restriction in the low-carbohydrate diets used [12
Low-carbohydrate diets may diminish triglyceride production in the liver in response to decreased carbohydrate delivery [14
]. The greater preservation of HDL-cholesterol on a low-carbohydrate diet may be the result of down-regulation by dietary fats of those hepatic receptors, which bind HDL-cholesterol [33
]. However, it remains unclear why HDL-cholesterol and triglycerides differed only at the 6-month visit between the two groups of our study. It may well be that the transient effects on triglycerides and HDL-cholesterol are related to differences in macronutrient composition in our study groups which became smaller over time (Table ). Obviously, other variables like waist circumference and systolic blood pressure were only influenced by the degree of weight loss in the two groups and not by macronutrient composition (Table ).
Our results also demonstrate the general problem of adherence to a diet with extreme nutrition relations. The use of telemedicine permits continuous contact to participants, individual support, and control of weight loss. Moreover, use of this technique resulted in a low drop-out rate of only 17% in our study participants. Nevertheless, it was not possible to achieve the target macronutrient relations in the two study groups in the long run. The target of carbohydrate content in the LOGI group (< 40% energy) was only reached within the first 3 months and the target of carbohydrate content in the DGE group (>55% energy) was not reached at any time. Note that earlier investigations have already reported relatively high attrition-rates of 30–50% in studies using very low-carbohydrate diets [12
]. Despite some additional beneficial effects of energy-restricted low-carbohydrate diets on cardiovascular risk markers it appears that poor long-term adherence to such diets limits its success in clinical practise [34
It should also be mentioned that the similar loss in body weight in both groups of our study was associated with a similar improvement in several metabolic risk markers such as fat mass, diastolic blood pressure, and glucose, fructosamine, proinsulin, and adiponectin blood concentrations (Table ). Decreasing insulin resistance and increasing adiponectin levels reduces atherosclerotic and inflammatory processes and endothelial dysfunction [35
] and may thus have decreased the cardiovascular risk in both study groups.