To lose 1 kg/week of BF, it is necessary a daily negative energy balance of about 1,000 kcal, and the guidelines usually suggest a moderate reduction of the TDEI, around 500–1,000 kcal/die cut down from the estimated 24 h–EE or from the usual TDEI, whether the subject’s BW is steady and anyway never going below the BMR more than 10 %; this is aimed to a gradual and long-lasting weight loss: losing 3–5 kg of BW is an excellent achievement, allowing to preserve the LBM and prevent the dehydration, without raising the risk of eating disorders. Cognitive-behavioral therapy together with physical activity program gives the best and long-lasting results [14, 65].

To define an adequate dietary energy intake, it is also necessary to take into account the patient’s eating habit (quality and quantity of food consumption, meals planning, and eating disorders suspected by psychodynamic tests). Food surveys could be retrospective, with the use of memory such as the 24/48 h recall, food frequency, dietary history, or perspective by recording the weight or the estimated quantity of the foods consumed.

Usually, food frequency questionnaire, dietary history, and food diary allow to collect all the data required. Then, the calculated 24 h-EE can be compared to the actual TDEI taking into account the BW changes. Energy balance is the difference between food intake and energy expenditure [24 h–EE = BMR + DIT (diet-induced thermogenesis) + PA (physical activity)]. This balance is positive in obese subjects actively gaining BW; instead, if the BW is steady, the TDEI is equivalent to 24 h-EE and the subject is in energetic balance with a TDEI not necessarily too high.

Established the most adequate energy intake to obtain a healthy BW loss, it should be set the protein intake level as above stated (1–1.2 g/kg “desirable BW”) and the protein-kcal must be apart from the NP-kcal which, in the end, have to be split between CHOs and lipids, pointing out that proteins and CHOs provide 4 kcal/g while lipids 9 kcal/g. Fifty percent of protein intake should come from animal source and the other 50 % from plant to avoid a high intake of animal lipids and meanwhile providing an adequate intake of vegetable protective factors (phytochemicals). Assuming the nitrogen (N) content of the proteins to be on average 16 %, it is easy to state that 6.25 g of proteins are equivalent to 1 g of N. It must be emphasized that in order to achieve an efficient protein synthesis, 100–150 nonprotein kcal (NP-kcal) are needed for every intake of 1 g N or 6.25 g proteins. In a dietary plan providing for the actual energy expenditure, protein amount could not be higher than 13–15 % of the TDEI, but in formulating a low-calorie diet, protein requirements must be counted in grams/kg of “desirable BW” to meet the proteins need [66].

Once satisfied the protein requirement, NP-kcal should be split as CHOs, 65–70 E%, and lipids, 30–35 E%. The distribution of NP-kcal requires a careful screening of comorbidities: this is a critical issue for the metabolic effects of the dietary models described above, to avoid the possible adverse effects or in order to exploit their metabolic properties. Total CHOs should be composed between complex, 80 %, and simple, 20 %. The amount of fats should consist of SFAs (1/3), MUFAs (1/2), n PUFAs (1/6), and the RI of EFAs (essential fatty acids) and of the liposoluble vitamins (α-tocopherol, β-carotene, vitamin D) have to be assured; to respect this proportion, it is sufficient to have an intake of 30 % as animal fats and 70 % as vegetable fats. Animal fats, indeed, consist of 2/3 SFAs and 1/3 MUFA with a low PUFA content, and instead plant source are made up of 1/3 SFA and 2/3 MUFA and PUFA [67] (Fig. 21.2). With respect to the TDEI, total CHOs intake should provide 45–60 % of TDEI, with maximum 15 % of simple sugar, while fats should provide 20–35 % of TDEI [67]. The highest values of the range (RI) should be considered only in the low-carbohydrate diets, when required. In other cases, the intake of total lipids must be ≤30 %, SFAs 7–10 %, and trans-fatty acids ≤1 % of TDEI [26, 67]. On the other hand, a too-low-fat diet has poor organoleptic properties, resulting bland and tasteless. Olive oil should not be removed since its composition in MUFA helps to keep an adequate HDL cholesterol level. To achieve a good level of ω-3-fatty acids, 150 g of any kind of fish twice a week are enough, better if chosen among anchovy, sardine, mackerel, or similar. In the end, an eating plan well balanced and consistent with dietary guidelines endorses to consume at least five servings of fruits and vegetables per day, emphasizing the use of whole grains, with a daily fiber intake of 35 g or more. BW-loss diet that excludes one or more foods or food groups and/or substantially restrict macronutrients intake below the PRI could produce nutrient deficiencies and increase health risks. The micronutrient intake level should be evaluated on a weekly basis or on a longer term for liposoluble vitamins and β-carotene; in a moderate low-calorie diet, it is possible to meet PRI by the weekly consumption of the different food groups as suggested by the guidelines for a healthy diet [67]. The supply of essential fatty acids, minerals, vitamins, and fiber has to be checked in relation to the DRVs (Table 21.2).