INTRODUCTION

According to the Global Nutrition Report¹ the world's nutritional status is severe, as two billion people lack essential micronutrients such as iron and vitamin A. Two billion adults are overweight or obese, 41 million children are overweight, 88% of countries face two or three problems related to malnutrition (overweight in adult women, anemia in women of reproductive age and child malnutrition), and one in three people is malnourished. Overweight and obesity is a worldwide epidemic and, in Brazil, it affects 53.8% of adults and has become a public health problem justified by their increasing prevalence^2,3. In this context, studies^4,5,6 and guidelines have been developed with the purpose of providing attention to problems related to food issues⁷.

In the last decades, cohort studies have been carried out in the European Union, which will be presented as follows:

European Prospective Investigation into Cancer and Nutrition (EPIC)8 is a prospective cohort study, with more than 521.000 participants, studied in 23 centers in Western Europe. From 1992 to 1999 information on diet, lifestyle characteristics, anthropometric measures and medical history was collected, as well as a biological sample of plasma, serum, leukocytes and erythrocytes⁸.

In 2005, an innovative and multicenter multidisciplinary research project developed in the European Union called Diet, Obesity and Genes (DIOGenes) was started, which sought to understand how obesity can be prevented and treated, focusing on the food perspective. It covers studies of dietary, genetic, physiological and psychological/behavioral factors, and involved 34 European partners, as well as four large food industries and five small companies, lasting for five years^9,10.

Supplementation in Vitamins and Minerals Antioxidants (SU.VI.MAX)¹¹ is a study of 13,017 adults (7,876 women between 35 and 60 years of age and 5.141 men between 45 and 60 years), using a randomized, double-blind study, placebo-controlled, primary prevention with an average duration of 7.5 years. All participants took 120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta-carotene, 100 mg of selenium and 20 mg of zinc, or placebo¹¹.

The guidelines developed by each country are important for guiding healthy eating. These guidelines are established on the basis of scientific evidence of the relationship between food, nutrition and health and data on food production, consumption, composition, cost, and accessibility. Thus, recommendations are provided regarding food groups, quantity of portions to be consumed, lifestyle messages, physical activity practice and attention to alcohol consumption^12,13.

The World Health Organization (WHO, 2015)¹⁴ advises adults that total fat consumption be less than 30%. In addition, changes in food preparation are recommended, including: the removal of the visible fat from the meat, replacing fried with baked, cooked and grilled preparations, using vegetable instead of animal oil, as well as avoiding ultra-processed foods containing trans-fat. Limiting the consumption of free sugar (added or naturally present sugar in honey, syrups, fruit juices and concentrated juices) to less than 10%, i.e. preferring fruit and vegetable snacks instead of sugary snacks. Sodium intake should not exceed 5 g/day. Thus, recommendations include not adding salt, soy sauce, industrialized sauces in food preparation, removing the salt shaker from the table, avoiding ultra-processed and paying attention to the food labels. As for fruits and vegetables, the recommendation for daily consumption is 400 g and it is important that fruits and vegetables be included in meals, favoring those of the season and valuing variety. Finally, fiber consumption of 25-30 g per day is recommended¹⁴.

Obesity has reached pandemic levels and is related to increased risk for type 2 diabetes mellitus, fatty liver disease, hypertension, stroke, dementia, osteoarthritis, apnea obstructive sleep and various types of cancer. In addition, it has been related to unemployment, social disadvantage and a reduction in economic productivity¹⁵. In view of the above, the nutritional situation of the population is of great concern. The purpose of this scoping review was to evaluate the type of diet most effective for weight loss.

METHODOLOGY

A scoping review is designed on the basis of scientific evidence that seeks to identify new situations in which no research has been previously conducted, as well as to detail findings and the range of subjects in specific areas of study. The current study was based on PRISMA¹⁶, since no checklist for a scoping review separate from a systematic review has been elaborated. For this type of review, the research question is not limited to a specific problem but addresses different topics. To better understand/organize the methods for this type of study is divided into five stages^{17,18,19,20,21}.

RESULTS

Selection of studies

The publications were selected in June 2018 and totaled 537 articles, 104 from the electronic databases, 27 from the hand search and 406 from the gray literature. After the removal of duplicate articles, the title and summary of 113 articles were read, from which 37 were selected and read in their entirety. At the end, 14 publications were included (Figure 1).

Figure 1 Prisma Diagram 

DISCUSSION

Food fiber, also called dietary fiber, consists of carbohydrate polymers, formed by three or more monomeric units, in addition to lignin, and might be soluble or insoluble. Soluble fiber dissolves in water and forms gel, which is easily fermentable, specifically in the colon, by the micro flora of the large intestine. The most common types are pectin, gums, inulin and some hemicelluloses. Unlike insoluble fiber, which is difficult to ferment in the colon, it increases the volume of the fecal matter, such as lignin, cellulose and some hemicelluloses. The benefit of fiber is related to the fermentation process in the large intestine. Fiber slows intestinal transit causing the pH to drop in the colon, making the medium more acidic. In this way, fiber prevents the formation of pathogens and facilitates the absorption of calcium interfering with bone metabolism and reducing the solubility of bile acids³³.

Fiber is composed of carbohydrates resistant to digestive enzymes, which in contact with the intestinal microbiota produce important metabolites that give rise to short-chain fatty acids in the colon, which bind to fatty acid receptors and stimulate hormones associated with reduced appetite, gastric emptying delay and improved insulin response. In this way, intestinal microbiota is modulated by increasing the availability of fibers which helps in the prevention of metabolic disorders^34,35.

A fiber intake of 25 g to 30 g/day is recommended. Its benefits are proven, especially regarding the reduction of risk of chronic non-communicable diseases, coronary artery disease, stroke, hypertension and diabetes. It is also related to improved lipid profile and some intestinal disorders, in addition to the positive relationship with the immune system and reduction in body weight. Therefore, it is associated with the treatment of obesity along with physical activity, hypocaloric diet and medications^36,37.

The high consumption of fruits and vegetables helps with weight loss and reduced waist circumference, due to an increase in satiety, a reduction in energy intake due to slow gastric emptying and absorption of macronutrients²⁸. Results corroborated by several authors^{22,24,27,29,36} included in this review, affirm the benefits of fruits and vegetables in reducing the percentage of total adiposity, in the prevention of obesity, cardiovascular disease and type 2 diabetes. A cohort study conducted at Harvard University, for 24 years (1986-2010), with men and women, obtained strong evidence that reinforces the relationship between fruit and vegetable intake and lower weight gain in the long term³⁶.

Fruits and vegetables are also included in the dietary guides that have existed since 1980, being reviewed and updated every five years to address urgent public health issues and the nutritional needs of a specific populations. They are made up of healthy guidelines for six meals, respecting regional differences and suggesting foods and beverages that are easily accessible to the population³⁸.

The American Food Guide³⁹ is based on five guidelines that address issues about the importance of maintaining healthy lifelong nutrition; focusing on variety, nutrient density, and quantity; limiting consumption of sugar, sodium and saturated fat, changing food choices, which involves food and drink and supports healthy eating patterns for everyone. The Brazilian Food Guide¹³ is based on the ten steps to healthy eating: “Always prefer natural or minimally processed foods; use oils, fats, salt and sugar in small amounts; limit the consumption of processed foods; avoid ultra-processed foods; eat regularly and with care; prefer to eat in quiet and clean places and in the company of other people; do your shopping in places that have a wide variety of natural foods, when possible, prefer organic and agroecological foods; develop your culinary skills; plan your time; distribute responsibilities with food in your home because eating well is everyone's job; when eating out, prefer places that make food on time; be critical. There are many myths and misleading advertisements around food, evaluate the information that comes to you and advise your friends and family to do the same”.

Thus, the guidelines vary according to countries, customs and religions. The dietary guidelines, studied^24,32 were developed with the purpose of verifying the efficacy of these guidelines in several populations and their relationship with the improvement in diet quality, increased levels of physical activity, as well as the reduction of percentage of body fat. The Food Guide came to be seen as a starting point for nutritional education, in which the basis is an increase in consumption of fruits, vegetables, lean meats, fish and foods with lower concentration of fat, sugars, caloric drinks and foods rich in sodium. Although they are known, these guidelines have low adherence. There are difficulties related to comprehensiveness, food grouping and nutritional needs that are insufficient for the populations^40,41.

Fish, lean, and preferably white meat, whole grains, polyunsaturated and monounsaturated fat source foods, nuts, fruits, spices, vegetables and wine are the bases of the Mediterranean diet which is old and well known, although it has been replaced by ultra-processed foods due to the industrial revolution and globalization. However, the diet has been growing in popularity again because of the noted benefits in health and the environment⁴².

New ideas have emerged as to the orientation of the use of the Mediterranean diet. The Mediterranean Diet Foundation⁴³ has created a pyramid for the Mediterranean Diet that besides bringing the foods to be consumed, also provides information on portions, frequency of consumption, as well as importance of consuming, in moderation, a diet rich in olive oil, legumes, unrefined cereals, fruit, and vegetables, the act of cooking and its relationship with the moment of leisure with family and friends. The pyramid also includes strengthening culture, the importance of living in a community and preferring foods that are season, as they are richer nutritionally, of lower price, require less pesticides to grow and contribute to the environment. Frequent physical activity of at least 30 minutes a day is also recommended, which is essential to aid in weight loss/maintenance among other health benefits and, while done in company, becomes more enjoyable. Finally, the importance of rest is also mentioned, as it is critical to living in balance and having a healthy lifestyle⁴⁴.

The Mediterranean diet is essential for weight loss and prevention of obesity, and is rich in monounsaturated fat, helps glucose metabolism, increases the oxidation of postprandial fat and potentiates thermogenesis, which helps increase daily caloric expenditure, besides reducing the number of adipocytes in the adipose tissue and is able to limit the hyperplasia in obese people⁴⁵. This positive relationship between diet and weight control was also observed in a randomized clinical trial, which showed the association between the Mediterranean diet, diet quality and weight loss in overweight or obese individuals⁴⁶.

In addition to obesity, the Mediterranean diet helps prevent cardiovascular disease, cancer and neurological diseases⁴⁷. Studies such as Prevention with Mediterranean Diet (PREDIMED) conducted in Spain showed a protective effect for cardiovascular disease of the diet and a 30% reduction in cases. The EPIC study conducted in European countries showed a relationship between the Mediterranean diet adherence and a reduction of mortality in approximately 24%^48,49. A study of 1,865 elderly persons showed that the Mediterranean diet reduces the chance of developing dementia by 10% and has positive effects on memory performance, language, perception and spatial vision⁵⁰.

Nuts are an important element of the Mediterranean diet, with high nutritional density, essential lipid profile, monounsaturated and polyunsaturated fatty acids, and antioxidant, anti-inflammatory and anticarcinogenic properties are some of its main properties. It is a healthy food increasingly consumed by people who seek healthy eating patterns and/or aim to lose weight^51,52. A study⁵³ conducted in Australia shows that the consumption of 30 g/day of oleaginous associated with healthy dietary patterns and increased consumption of fish reflected positively on the weight of the individuals. Nut consumers gained an average of 700g in five years, compared to non-consumers, who gained 2.1 kg. Therefore, it is important to emphasize that high nut consumption and weight loss are always associated with a healthy diet.

The hyperproteic diet is responsible for increasing thermogenesis and providing satiety, helping to reduce weight. The thermogenic effect is related to the body's lack of protein storage capacity, which metabolizes this macronutrient automatically. The protein is transformed into peptides that stimulate anorectic hormones such as peptide 1, very similar to glucagon (GLP-1), cholecystokinin (CCK), peptide YY, as well as inhibition of the hormone “orexigenic” ghrelin (Ghr) (Diepvens et al 2008). The ideal amount is more than 20% relative to the total macronutrients and the most appropriate sources are lean red meat, chicken, fish, dairy and vegetable protein. According to the findings of this review the hyperproteic diet alone is not enough for weight reduction and therefore needs to be implemented along with physical activity and healthy eating habits^{23,30,54,55,56,57}.

According to the findings of this review, we observed that the articles selected aimed to reduce weight, but a quality feed for different purposes, as well as different methodologies. Although studies demonstrated statistically significant values for weight change and waist circumference, when analyzed clinically, differences do not present satisfactory values.

The findings of the present study showed that weight loss or maintenance is based on foods with high nutritional density. In this perspective, it is important to prioritize the insertion of healthy foods. Thus, analyzing the above, it was possible to observe that no single food type is effective. Furthermore, to obtain the desired benefits, it is necessary to associate several foods, since only the adoption of healthy lifestyle habits can contribute to improvements in the health of individuals.

CONCLUSION

From the findings of the present study it is noted that the most effective diet for weight loss is the high fiber diet, although it contributes with small percentage values. However, in addition to diet, lifestyle change is fundamental, since this process of weight loss and maintenance is multifactorial. Along with diet, physical activity, sleep quality, and psychological control must be considered, among other factors, in the living of a balanced life.

Limitations of the study. A scoping review does not evaluate the quality of the evidence of the findings, which may reflect on the veracity of the results and the amount of data obtained is substantial, generating difficult decisions on amplitude versus depth.