## 1 Introduction  
Metabolic syndrome (MetS) can be defined as a combination of interrelated risk factors for cardiovascular disease and diabetes, including elevated blood glucose and triglyceride levels, high blood pressure, low high-density lipoprotein cholesterol levels, and obesity, particularly central adiposity [1]. The qualifying factors are defined in the ATP III Panel as follows:  
* Waist circumference above 102 cm in men and above 88 cm in women
* Proved Type 2 Diabetes Mellitus or fasting glucose level above 5.6 mmol/L
* Treated hypertension or spontaneous blood pressure \(\geq\) 130/85 Hgmm
* Treated hypertriglyceridemia (HTG) or serum TG level above 1.7 mmol/L
* Serum HDL-C level under 1.03 mmol/L in men, under 1.3 mmol/L in womenA person is considered to have MetS if at least three of the above are satisfied [1; 2]. The relevance of MetS for public health is due to its association with several serious chronic diseases and health conditions, including cardiovascular disease, type 2 diabetes, and stroke. Due to the high social and financial burden related to MetS [3], there are comprehensive efforts worldwide to introduce new methods for its management via medication, lifestyle intervention or bariatrics [4; 5; 6]. Since the development of MetS is highly influenced by the lifestyle, a promising current method is the application of Information Technology (IT)-supported telemedicine that builds on self-management and personalized advice. Diet is one of the most important controllable factors of lifestyle, and there is also general scientific consensus on the fact that weight loss is the most important part of any dietary intervention therapy for MetS, as the other risk factors are expected to improve due to weight loss as a result. Yet weight loss is the goal that often proves the hardest to achieve. The literature and our own experience show that interventions based on just a few consultations are not effective for weight loss. Rather, a successful lifestyle change and weight loss can be supported only by comprehensive intervention schemes with at least one meeting per month [7; 8], or even more than 14 meetings over a 6-month period for best results [9]. Such schemes require a large investment of time and money by both the health care staff and the patient. However, telemedicine can help maintain a high meeting number while keeping the scheme economically viable for the general public [9]. Works related to dietary intervention for MetS include several studies performed over the last decade to test the viability of IT supported dietary intervention in a telemedical setting. Most of these studies had a 3 to 6 month observation period and a cohort ranging from 40 to several hundreds, involving patients with a body mass index (BMI) above 30. In a trial using the Fitbit mobile app, structured phone calls were used to maintain patients' motivation, which resulted in more weight loss and a significantly improved adherence to the protocol [10]. Similarly, the application of the My Meal Mate smartphone app combined with text messages helped with adherence to the calorie goals between 1200 and 1500 kcal/day in a study with more than 120 participants [11]. The effect of a mobile app vs. a wearable bite counter device was compared in the study of [12], while participants also received behavioral weight loss information via twice-weekly podcasts. The results were in favor of the mobile app method. Extensive use of wireless measurement technology was the cornerstone of another trial resulting in an impressive average weight loss of 7.8 kg over 3 months [13]. Perhaps the most similar in design to our study, [14] used detailed exercise and food diaries in a solution called the 'Mobile health behaviour change support system' in a trial of 6 months. The measured weight loss, however, somewhat falls behind the ca. 3% over 3 months reported in other studies. Some important parameters of these studies are summarized in Appendix A. The dietary databases supporting the above apps are quite diverse.