When it comes to diets there is no one size fits all. Low fat, low carb, high protein or low calorie can all work for some people and not for others. Weight is a numbers game, and kilocalories or “calories” are the currency of weight [4]. Therefore, all effective diets include some form of calorie reduction. What’s more important than the type diet is whether or not people can stick with it in the long term. In the following we will outline the most common weight loss programmes and the supporting evidence for their effectiveness. Small manageable changes may be more realistic for most people rather than jumping in and changing the entire diet at once. This will all depend on the person’s level of nutrition knowledge and their motivation to change.

Very Low Calories Diets (VLCDs) are less than 800–900 kcal/day and are very structured typically using meal replacement bars or shakes. These diets are only considered helpful for those who have a body mass index of 30 or greater and are often used in preparation for abdominal surgery including weight loss surgery (Academy of nutrition and dietetics 2016). This diet has proven to be effective for short-term weight loss with an average weight loss of 16.1 ± 1. 6 % at 4 months and 6.3 ± 3.2 % by 1 year (Academy of nutrition and dietetics 2016). Maintenance and long-term health outcomes beyond 1 year have not been studied as this diet is not considered to be sustainable.

Low Calorie Diets (LCDs) have greater than 800 kcal/day but less than 1600 kcal/day [7]. They can be highly structured, like VLCDs, and include the use of meal replacement bars or shakes or they can be semi-structured using meal plans. Research suggests that the greater the structure of the diet the more likely one is to adhere to it [7]. A meta-analysis of six studies comparing LCDs with or without meal replacements found that the meal replacement group lost 2.43 kg more weight after 1 year than the non-meal replacement VLC dieters [7].

Macronutrients (Carbohydrates, Fat and Protein) have long been investigated for their effects on weight loss. In the 1980s the low fat diet was all the rage but was quickly followed by the low carb diets of Dr. Atkins and South Beach. When considering a macronutrient-focused diet it is important to realize that you cannot change the amount of one nutrient in the diet without inadvertently changing the amount of the other nutrients [7]. For example, if someone chooses to follow a low- fat diet then they will end up either consuming more protein or more carbohydrates. Depending on what macronutrient you are limiting or having more of you can see various health effects. However, it is important to note that no one macronutrient-focused diet has proven to be any more effective than any other for weight loss [7]. It is instead more important to determine what diet would work best given a patient’s food preference, dieting history and level of nutrition knowledge.

A diet is considered low-carbohydrate if it recommends consuming no more than 20 g of carbohydrate per day during the period of weight loss and no more than 50 g of carbohydrate per day once one’s weight loss goal is achieved [7]. Low-carbohydrate diets with no limit on fat or protein intake produce an increase in high-density lipoproteins and a reduction in triglycerides while combined low-carbohydrate, low-fat diets promote a greater reduction in low-density lipoprotein. Depending on the person’s cardiometabolic profile they may want to chose one diet over the other for this reason [7].

High-protein diets recommend consuming at least 20 % of daily calories from protein [7]. Sometimes these diets use meal replacement bars or shakes and are often combined with an energy restriction to promote weight loss [7].

Dietary pattern focused and the portfolio diet do not put restrictions on or promote particular macronutrients. Instead they focus on the diet as a whole to promote overall health [7]. Adding more fruits and vegetables to your diet by having one serving at each meal or snack is an example of this type of diet. These types of diets have not been proven to be more or less effective than any other [7].

Both the DASH and Mediterranean diet have been proven to be effective for managing cardiovascular risk factors such as high blood pressure . In terms of weight loss, neither has been shown to cause weight loss on their own; however, both can be effective when combined with a calorie restriction [7].

Research on the impact of the timing of meals, how much is consumed at various times of the day, eating frequency and breakfast consumption is limited [7].

One RCT that examined the timing of energy intake and weight loss found that women who consumed more of their energy earlier in the day lost more weight than those who did not [7]. Jacubowicz et al. also found that eating a larger percentage of calories earlier in the day equated to a greater reduction in waist circumference and fasting glucose levels [9]. Those randomized to the breakfast group also reported higher feelings of satiety and lower levels of hunger throughout the day. For this reason, it may be beneficial to encourage those struggling with their weight to shift more of their calories to earlier in the day [9]. Breakfast, however, because it is not consistently defined as a certain amount of calories or as being eaten at a certain time, has not been adequately researched and therefore not definitely proven to assist with weight management.

Food logging is an important self-management strategy that is part of most weight loss programmes. This is because it is an effective tool for bringing one’s awareness to food and eating challenges while also providing a way to reflect on progress made.

Logging the traditional way, using pen and paper, or a food logging notebook is however very time consuming and requires a high level of commitment from the patient. In order for paper food records to be effective they should be reviewed weekly or biweekly with a RD or RDN so that she can assess the macronutrient and calorie intake of logged foods and can work collaboratively with the patient to provide education around what foods are better choices and to set up a plan for changes moving forward. Because this can often be a tedious and time-consuming process both for the patient and the RD or RDN , electronic food logging has become more prevalent. Many free websites and applications are available for most portable electronic devices. The benefit of electronic food logging is that it provides real-time feedback on the calorie and nutrient content of the food at the time the food is logged. For example, if when a patient logs their morning coffee with two cream and two sugar they instantly see that this is over 200 kcal, this alone may work as a deterrent for ordering it either in the moment or in the future. While still time consuming to initiate, most electronic food logging programmes have time saving functions including being able to save frequent meals to prevent people from having to enter all the ingredients of a meal each time, as well as an import recipe function that allows for the instant nutrient analysis of any recipe found online. Unfortunately research on stand-alone electronic weight loss programmes is still in its infancy; however, some short trials how proven that they are more effective than minimal interventions [7]. That being said, there is consensus that comprehensive weight loss programmes that include both electronic self-monitoring strategies as well as counselling by a trained clinician produce greater and longer-lasting results [7]. RDs and RDNs will often also use “food and mood” logs as a CBT tool to help patients deconstruct and problem solve strategies for overcoming emotional eating.

While physical activity alone has not been proven to be an effective weight management strategy we would be remiss if we didn’t talk about the way that it can augment any diet programme. In a recent meta-analysis it was shown that a combined programme of diet and exercise produced slightly more (1.7 kg) weight loss at 12 months than diet alone [7]. One might argue that this is a very modest difference for the amount of effort it takes to incorporate physical activity into a lifestyle; however, we cannot overlook the other health benefits that come with physical activity. These include improved cardiometabolic health, improved mood and decreased risk of certain cancers [10]. Physical activity has also been proven to play a more important role in weight maintenance after weight loss. The National Weight Control Registry reports that 90 % of participants (members have lost an average of 66 lb and maintained it for 5.5 years) report that they exercise on average 1 hour per day [11]. Currently, Health Canada and the US Department of Health and Human Services both recommend 150 minutes of moderate intensity activity per week or 30 minutes per day most days of the week. Ideally, moderate intensity is accumulated in occasions that are at least 10 minutes in length [7].

Since obesity is often considered to be a disease of overconsumption, nutritional deficiencies may not be expected. They are however shockingly prevalent. Those who eat an abundance of highly processed convenience foods of low nutritional quality are particularly at risk of nutrient deficiencies. There are also underlying mechanisms associated with obesity such as chronic inflammation that can impact the transportation of certain micronutrients e.g. iron, and changes in intestinal microflora which can impact vitamin absorption [12]. Micronutrient deficiencies are often diagnosed when patients are being assessed for bariatric surgery . A Spanish study performed in 2011 by Moize et al. revealed that of 231 patients studied prior to bariatric surgery , only 25 % did not present with nutritional deficiencies. 38.2 % presented with at least one, 22 % presented with two and 11.4 % presented with three nutritional deficiencies [13]. Deficiencies included vitamin D (67 %) iron deficiency anaemia (22.2 %); and deficiencies of vitamin A, B1 and B6 were present in 10.2 %, 7.2 % and 15.9 %, respectively. Vitamin and mineral deficiencies can not only cause long-term health issues such as blindness and osteoarthritis but can also have a significant impact on a person’s current quality of life. Iron deficiency, for example, can have an impact on mood, energy levels and sleep (related to restless leg syndrome). If these underlying deficiencies are not treated as part of a comprehensive weight management programme then they could potentially impact a person’s chance of successfully losing weight . Therefore, it is recommended that screening for micronutrient deficiencies and treatment of said deficiencies should be an integral part of any weight management programme.

Registered Dietician (RD) in Canada and Registered Dietician Nutritionist RDN in the United States are regulated professional designations that are only used for those who have completed an appropriate undergraduate degree in science majoring in dietetics followed by a accredited Dietetic Internship or Masters Degree. Anyone can call themselves a “nutritionist”, but you have to have completed the above-mentioned education and belong to a regulatory college of dietetics to call yourself an RD or an RDN. The reason why the RD or RDN is your greatest ally when it comes to helping your patients achieve weight management is because they are not only experts in food and nutrition but they are governed by a regulatory college that ensures that the advice they give is evidence based. RDs and RDNs will never promote products or diets that are based on anecdotal evidence. They will however help clients to determine what type of programme would be a good fit for them. Many RDs and RDNs have done extensive additional training in Motivational Interviewing, Cognitive Behavioural Therapy (CBT) , Acceptance and Commitment Therapy and Mindfulness-based meditation. CBT has been shown in both the Look AHEAD study and the Diabetes Prevention Program to assist patients to achieve significant sustainable weight loss as compared to education alone [7].

Bariatric surgery is a proven option for successful weight loss and resolution of obesity-related co-morbidities. The Roux-en-Y gastric bypass (RYGB) and the sleeve gastrectomy (SG) are the most common weight loss surgery procedures performed in North America [14, 15]. RYGB is a restrictive and metabolic procedure and the SG is a restrictive procedure where 80 % of the stomach is removed providing early satiety and resulting in smaller food portions. Both procedures require significant lifestyle changes including dietary modifications and lifelong commitment to taking vitamin and mineral supplements. Nutrition concerns following other less common procedures such as laparoscopic gastric banding, vertical banded gastroplasty and bilopancreatic diversion, with or without duodenal switch, will not be discussed in this chapter and are summarized in other reviews [16].

Expected weight loss after bariatric surgery is dependent upon the type of surgical procedure. A meta-analysis by Buchwald et al. [17] showed that the overall percentage of excess weight loss (%EWL) for all surgery types was 61.2 % (95 % CI, 58.1–64.4 %). There is considerable inter-individual variation in weight loss response to the RYGB and SG as described by de Hollanda et al. [18]. They found that older age, male gender, presence of pre-surgery T2DM and higher pre-surgery BMI were characteristics of poor weight loss outcomes. Li et al. [19] conducted a recent review of 62 studies published after 2008 that included 18,449 patients in which %EWL was reported in 20 studies. They reported significantly higher excess weight loss in patients undergoing a RYGB compared to those receiving a SG.

The success of bariatric surgery is also dependent upon many non-surgical factors; patient education and willingness to make permanent lifestyle changes are critical. Patients must be prepared from a physical, psychological and knowledge perspective. They should be able to demonstrate their readiness by making changes to their diet before surgery. These changes involve following a regular meal pattern and making nutritious food choices. Recommended dietary changes prior to surgery are shown in Fig. 14.1.

There is debate as to the need to demonstrate weight loss prior to surgery [20]. In some bariatric programmes this is mandatory in order to qualify for surgery, to prevent post-op complications or to optimize post-op weight loss.