The analyses presented in this paper demonstrate that free living subjects are able to make significant dietary change in line with instructions provided by commercial companies regardless of whether this information is given at group classes or as written instructions. Substantial alteration in participants macro-nutrient composition were recorded and these are supported by the recorded weight losses obtained during the 'Diet Trials' study; indicating compliance with the allocated dietary regimen .
In the low CHO Atkins diet, we have shown that subjects were able to reduce their CHO intake substantially without the need for individualised dietary counselling. Furthermore, the energy deficit induced can be attributed to a reduction in overall energy intake with non-replacement of CHO energy and no substantial increase, in absolute terms, of dietary fat. The low fat diets, WW and RC both led to reductions in saturated fat intake, as both proportions of energy and in absolute terms, but it is of interest that the Atkins dieters in this study did not substantially increase their absolute intake of saturated fat which is what might have been anticipated. The effects of these diets on lipid profile are reported elsewhere  but confirm that there was no substantial adverse effect of the Atkins diet on lipid profile. This is in addition to the general benefit of reducing cardiovascular risk factors by weight body loss per se in obese adults regardless of the macronutrient diet composition [21–24].
Baseline intake of fruit and vegetables were lower than the recommended '5 a day' that is encouraged in the UK but was similar to that reported as 'usual' intake for adults in the UK . Although it is not surprising that those following a low CHO approach would not increase their fruit and vegetable intake over time, it is interesting that after two months of this diet, most people had not decreased their 'usual' level of fruit and vegetables. This is particularly notable given the timing of the data collection in this study. The Atkins diet only recommends a very low CHO intake (5–10 g/day) for the first few weeks of this approach so after two months, subjects may have chosen to use their CHO allowance for fruit and vegetables instead of bread and cereals. This is supported by the micronutrient profile of the Atkins dieters, who tended to have a reduction in iron and niacin, probably due to a fall in the intake of cereal and flour, which is fortified in the UK, on the low CHO diet. The significant reduction in the Atkins dieters of NSP and the generally low intake of dietary fibre overall may have implications for bowel health in the longer term.
All the other commercial diets encourage an increase in fruit and vegetables partly to increase the satiety of the meals and also to replace high fat, high sugar snacks. A significant increase in fruit and vegetables was only observed in those following the WW diet but this increase was less than one portion per day. These disappointing findings suggest that people remain resistant to the advice to 'eat more fruit and vegetables' even when they are advised to as part of a modified weight loss programme.
On the whole, micronutrient intake remained above the RNI for most nutrients on all the commercial diets even with the degree of mis-reporting of energy intake. Bearing in mind the degree of under-reporting established in this study, there is little evidence to suggest that subjects following self-selected weight reducing diets in the long term would be at risk of micronutrient deficiency. Some subjects following the Atkins diet may have been following advice and taking a daily multi-vitamin supplement which is recommended in the book but this was not analysed. Gender differences were apparent, with women tending to reduce their daily iron intake with energy restriction. Those with high iron requirements due to menstrual losses may be at risk of iron deficiency if they were dieting for long periods of time. This could occur on low either of the low fat approach and the low CHO diet. Meal replacement products that ensure adequate micronutrient provision appeared to offer an advantage in this respect.
This analysis aimed to compare the nutritional composition of a low CHO diet to low fat diets. We find little evidence of short-term detrimental effects on nutrient intake with a low CHO approach compared to a low fat approach. Folate intake was only just above recommended levels on all the diets tested, although it fell on the Atkins diet at 2 months but still met 93% of the RNI. Women planning a pregnancy would be well advised to take additional folate while following any of these weight reducing regimens. Health professionals should be aware that in the UK, fortified breakfast cereals and bread flour contribute substantially to iron and B complex vitamin intakes and when these foods are restricted, other sources of these nutrients need to be found. The assumption that low CHO diets become very high in protein due to increased consumption of meat is not substantiated by these data.
There is little published data on nutrient adequacy in those trying to lose weight. Ashley et al (2007)  reported nutrient profiles of two groups one following a meal replacement approach and the other more traditional structured low fat diet approach. Despite these groups receiving supervision by a dietitian, the traditional diet had lower intake of calcium and other minerals compared to the meal replacement group, leaving the authors to suggest some benefits of taking fortified food/drink while following an energy restricted diet.
This study provides some information on the usual diet of overweight people in a reasonably large sample of free living subjects from geographically diverse areas of the UK. There are a number of limitations with the methodology used that need to be considered when interpreting the results. First, nutrient intake profiles are the result of self-reported measures of diet which have a number of known limitations, the most significant of which has to be the well documented and long standing issue of mis-reporting of food intake which is common in overweight and obese populations [19, 27–29]. It was beyond the scope of this study to validate the energy expenditure estimations using the gold standard of doubly labelled water. The challenge of collection of accurate food intake data has directed the analysis presented in this paper to focus on change in nutrient profile from baseline measures rather than rely only on absolute nutrient values. When describing the relative adequacy of the diet in terms of %RNI of micronutrients, the effect of under-reporting food eaten would be likely to lead to under estimates of actual intake. We have been able to use estimated energy expenditure values to derive individual energy requirements and utilise this information to calculate cut-offs for mis-reporting rather than rely on the blunter instrument of the Goldlberg cut-offs for under reporting of energy intake . Food recording for only 7 days may also under represent some micronutrients as longer recording periods would be preferable to ascertain habitual intake. Additionally, not all subjects provided food records so combined with the attrition rate, we report on a small sample size. However, support that the nutrient profiles obtained in this study are representative comes from the general agreement with the nutrient profile of the UK population obtained from National Dietary Surveillance surveys . The decline of energy intake described on a per kg body weight basis in the 'plausible reporters' group concurs with the actual weight loss achieved in this study and supports the relative direction of accuracy of the food reporting procedures overall. Thus, regardless of dietary energy macronutrient composition, weight loss will occur on popular diets if an overall energy deficit is achieved. The final limitation is connected to the development of the RNIs themselves and their applicability at an individual level. Some nutrients such as selenium and calcium, these may actually prove to be a lot higher for 'optimal health' as opposed to their current use which are set at a population level to prevent deficiency states.
To conclude, this is a novel study which provides comprehensive dietary data on a substantial cohort of subjects following four popular diets without supervision. Health professionals generally would consider three of the diets as nutritionally acceptable (WW, RC and SF) and one diet (Atkins) being controversial. Comparisons of pre- and post-intake indicated dietary compliance. Baseline data suggested overall nutritional adequacy and none of the diets resulted in micronutrient insufficiency or an increase in absolute fat intake which has been a common criticism of low CHO diets. An inadequate intake of dietary fibre was noted in this diet. The caveats to this study are the inherent errors of dietary assessment and that findings may not be generalisable to certain subgroups within the population with specific nutritional requirements, particularly women with raised iron requirements and those with increased calcium needs. This analysis provides reassuring and important evidence for the effectiveness and nutritional adequacy of four commercial diets in weight management for the general public which are particularly pertinent for community and public health nutritionists and those working in primary care. It is suggested that commercial companies work in partnership with health professionals to identify and intervene with high risk clients, such as those planning pregnancies, to provide more individualised dietary advice.