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Diets for weight loss: Different types

Diets for weight loss: Different types

Obesity is a worldwide, multifactorial disease defined as abnormal or excessive fat accumulation that presents a risk to health. The disease is associated with several chronic morbidities, such as cardiovascular diseases (CVDs), diabetes, and cancer. Prevalence of overweight and obesity has tripled since 1975, reaching 39% and 13% of the world's population, respectively . Because of its significant effects on health, medical costs, and mortality, obesity has become a public health concern.

diets for weight loss

The fundamental cause of obesity is an energy imbalance between calories consumed and calories expended; however, this involves a complex interplay of biological, genetic, and psychosocial factors. Evidence has shown that a weight loss of 5% to 10% within 6 month is necessary to reduce risk factors of comorbidities and to produce clinically relevant health improvements such as reductions in blood glucose, triacylglycerols, and blood pressure.

To achieve successful weight loss and sustain it over time, the Academy of Nutrition recommends changes in lifestyle behavior; a diet that reduces excessive energy intake and enhances dietary quality; and an increase in energy expenditure. Furthermore, the successful treatment of overweight and obesity could require adjuvant therapeutics such as cognitive-behavioral therapy, pharmacotherapy, and even bariatric surgery. These therapies are indicated for specific conditions and should be individually analyzed, which is a topic that goes beyond the scope of this review.

Regarding dietary interventions for weight loss, an individualized diet that achieves a state of negative energy balance should be rescribed.

Many dietary approaches can generate this desired reduction in  caloric intake. Diets are usually based on the inclusion or exclusion of different foods or food groups .

Historically, several diets have become popular and then faded owing to a lack of reliable scientific support. In this context, this review aimed to provide scientific evidence to support the adoption of dietary strategies to promote weight loss.

We classified these strategies into three main categories:

  1. Diets based on the manipulation of macronutrient content (i.e., low-fat [LF], high-protein [HP], and low-carbohydrate diets [LCDs]).
  2. Diets based on the restriction of specific foods or food groups (i.e., gluten-free, Paleo, vegetarian/vegan, and Mediterranean diets).
  3. Diets based on the manipulation of timing (i.e., fasting).


diets for weight loss

Diets based on the manipulation of macronutrient content

The manipulation of macronutrient content in isocaloric diets has been studied to determine which composition best promotes weight loss while including other metabolic benefits.

Increased protein and decreased carbohydrates are the most common modifications and have resulted in several popular diets created over time.

Changes in the macronutrient composition affect hormones, metabolic pathways, gene expression, and the composition and function of the gut microbiome that might effect fat storage.


Metabolically, carbohydrates elevate insulin secretion, thereby directing fat toward storage in adipose tissue, described as the carbohydrateinsulin model of obesity . In this context, LCDs ranging from 20 to 120 g of carbohydrates claim to treat obesity because they promote reduced insulin secretion and increased glucagon, which cause a metabolic shift to higher fat oxidation

LCDs can be designed to be either normal-fatHP or high-fat  HF normal-protein. However, despite the theory of the carbohydrateinsulin model, clinical trials comparing LCDs with low-fat diets (LFDs) in isoprotein diets reported similar weight loss  and even higher body fat loss when reducing fat but not carbohydrates.

Moreover, an important meta-analysis of 32 controlled studies concluded that energy expenditure and fat loss were more significant with LFDs when compared with isocaloric LCDs.

Finally, individuals with insulin resistance (IR), glucose intolerance,or both may benefit from a LCD , although this has not been confirmed in a recent study with 609 individuals.

Furthermore, observational data have demonstrated an increase in mortality associated with the long-term intake of both LCDs and high-carbohydrate diets (HCDs) with minimal risk at 50% to 55% (energy derived from carbohydrates). They also reported that animal-derived protein and fat were associated with higher mortality, whereas plant-derived protein and fat were associated with lower mortality.

Finally, high-protein diets (HPDs), in which 20% of energy is derived from protein, appear to offer advantages regarding weight loss and body composition in the short term.

Popular HPHF diets, such as Atkins or Zone, promoted significant weight loss for short periods . HP intake acts on relevant metabolic targets, increasing satiety and energy expenditure . Conversely, in clinical trials >1 to 2 year, evidence indicated no significant differences in weight loss. Moreover, HP-HF diets are often associated with a high intake of animal products and saturated fat, causing detrimental effects of increased low-density lipoprotein cholesterol.

In conclusion, in the short term, HP-LCDs are suggested to present benefits for weight-loss. However, owing to their major effects on metabolism and gut health, they should be considered as a jump-start weight loss tool rather than a diet for life. In the long term, current evidence indicates that a different ratio of macronutrients associated with a caloric restriction in healthy diets promotes similar weight loss.


diets for weight loss

Diets based on the restriction of specific foods or food groups

Different foods and food groups have emerged as villains and have been removed from specific diets to promote weight loss. The long list includes a vegetarian diet, which excludes all animal products; the Paleo diet, which restricts many food groups including grains, dairy, and legumes; and the popular gluten-free diet (GFD).

The Mediterranean diet is not based on the complete restriction of a specific food group, but instead is characterized by a richness of plant-based food and moderation of refined grains, red meat, and dairy.

Plant-based diet for weight-loss

Vegetarian dietary patterns are very diverse due to the different reasons for its adoption and the wide variety of available food choices.

A vegetarian plan can range from the simple exclusion of meat products to the raw vegan plan, which only includes raw vegetables, fruits, nuts, seeds, legumes, and sprouted grains . Exclusion of animal products can reduce the intake of certain nutrients, which might lead to nutritional deficiencies of protein, iron, zinc, calcium, and vitamins D and B12.

Adoption of plant-based diets is growing because evidence has shown some health benefits when compared with omnivorous diets. They can protect against chronic diseases, such as CVDs , hypertension and type 2 diabetes, and some cancers.

Further research will clarify whether these benefits are related to the reduction of animal products or the increased intake of fruits, vegetables, and fibers.

In observational studies, individuals on a plant-based diet usually present a lower body mass index (BMI) than non-vegetarians.

In interventional studies, prescription of vegetarian diets was well accepted  and was associated with weight loss.

Two meta-analyses reported a significant reduction of body weight after the adoption of vegetarian diets . Subgroup analysis observed a higher reduction in weight loss with vegan diets compared with lacto-ovo-vegetarian diets.

It is likely that this reduction is due to the typically low energy density, LF and HF intake associated with plant-based diets.

In summary, evidence has supported the therapeutic use of plant-based diets as an effective treatment of overweight and obesity. However, further long-term trials are required to confirm the relevance of results, as some studies did not report differences in weight loss . The adoption and implementation of a well-designed vegetarian diet require effective counseling and adequate nutritional supplementation.

Paleo diet for weight-loss

The Paleolithic diet, also called Paleo, is based on everyday foods that mimic the food groups of our preagricultural, hunter gatherer ancestors.

The diet claims to help optimize health, minimize risks for chronic disease, and result in weight loss. These statements are supported by the theory that the hunter gatherer diet and lifestyle sustained humanity for  2.4 million years, causing humans to be genetically adapted to it.

According to proponents of the Paleo diet, profound changes in diet and other lifestyle conditions after the introduction of agriculture and animal husbandry 10,000 years ago have been too recent on an evolutionary time scale for an adjustment of the human genome.

Only foods that were available to hunter gatherers are included in the diet. These include meat, nuts, eggs, healthy oils, and fresh fruits and vegetables. Cereal grains, legumes, dairy, and other processed/refined products are excluded.

The Paleo diet features characteristics such as a lower ratio of v-6 to v-3 fatty acids and lower sodium, along with a high content of unsaturated fatty acids, antioxidants, fiber, vitamins, and phytochemicals that operate synergistically to promote health benefits.

The diet is high in protein (20-35% of energy) and moderate in fat and carbohydrates (22-40% of energy, specifically restricting a high glycemic index).

Finally, the Paleo diet yields a healthier net alkaline load compared with the net acid load estimated for the typical Western diet.

Much has been studied about the beneficial metabolic outcomes of the Paleolithic diet. Evidence has demonstrated several improvements such as ameliorations in metabolic syndrome (MetS) , increase in insulin sensitivity , reduction of cardiovascular risk factors , increased satiety , and beneficial modulation of intestinal microbiota.

Specifically, regarding Paleo diet for weightloss, scientific evidence points toward consistent reduction of body weight and body fat mass either in short-  or long-term studies. Low adherence, poor palatability, and high costs are common issues reported by those who follow the Paleo diet.

In summary, although evidence suggests general health benefits and weight loss, further research is needed to support the popular claims of the Paleo diet. As an important limitation, the Paleo diet presents a potential deficiency risk that includes vitamin D, calcium , and iodine.

diets for weight loss

Gluten-free diet for weight-loss

Gluten is a protein complex found in cereals such as wheat, rye, barley, and oats . Studies have shown that the main fraction of gluten, namely gliadin, cannot be completely digested by the gastrointestinal (GI) tract, triggering an intestinal inflammatory response in susceptible individuals.

Celiac disease, wheat allergy, and non-celiac gluten sensitivity represent the main gluten reactions mediated by the immune system. The treatment for these disorders is based on the complete dietary exclusion of all gluten-containing food, which is well established by the scientific literature . However, the market for gluten-free products has been growing for the past 15 year, mainly due to individuals who adhere to a GFD to reduce body weight or improve diet quality . Despite the popular association of gluten and weight loss, controlled studies are scarce in the scientific literature.

Evidence supports a possible obesogenic effect of gluten. First, a cereal-based diet impaired insulin sensitivity and blood pressure control and increased the levels of C-reactive protein in pigs.

In rodents, two pioneer studies reported obesogenic effects of gluten using the nutritional model of obesity: An HFD added with gluten induced higher weight gain, adiposity, blood glucose, inflammation, and IR, partly by reducing the thermogenic capacity of adipose tissues.

In summary, to date, little has been studied about gluten and body weight evolution. It is well known that gluten intake can increase inflammatory status, cause intestinal dysbiosis , and increase intestinal permeability . However, it is not known whether gluten presents obesogenic properties and, if it does, the metabolic mechanism involved is unknown.

Mediterranean diet for weight-loss

The Mediterranean diet is a balanced diet characterized by high consumption of vegetables, fruits, legumes, whole-grain cereals, seafood, olive oil, and nuts. Red meat, dairy and alcohol are recommended in moderation . The Mediterranean diet is rich in plant-based foods, having high levels of antioxidants and dietary fiber, and low glycemic load compared with other diets . It also has an adequate ratio of monounsaturated to saturated fatty acids.

Nevertheless, the main relevance of the Mediterranean diet has been related to its strong evidence-based health and metabolic benefits. Due to the high nutrition quality of its food composition, the Mediterranean diet has been considered a healthy eating pattern for many conditions.

Studies have demonstrated that the Mediterranean diet improves outcomes for glycemic control in patients with type 2 diabetes. Hence it is one of the diets recommended by the American Diabetes Association. The Mediterranean diet has been associated with a reduction of inflammatory markers, and important reduction of cardiovascular risk factors and mortality.

Moreover, this diet was efficient in decreasing inflammation  and cardiovascular risk even in the absence of meaningful weight loss . More recently, the association with amelioration of non-alcoholic liver disease  and cancers has been promising but requires further investigation.

diets for weight loss

Diets based on the manipulation of timing (fasting)

To achieve the negative energy balance required for weight loss, most weight control programs use a 20% to 40% continuous (daily) calorie restriction. However, more recently the manipulation of timing, namely intermittent calorie restriction or intermittent fasting (IF), has received considerable interest as an alternative strategy.

Intermittent fasting consists of abstaining from food and caloric beverages for a certain period of time alternated with normal eating.

Several variations of IF differ in length and frequency of the fast cycles. Moreover, modified IF allows a small amount of intake to avoid persistent hunger . IF is often combined with regular  exercise and even other diets. The most common types of IF include periodic fasting or 5:2 diet, alternate-day fasting, time restricted feeding, and religious fasting.

The basic premise of fasting is to promote changes in metabolic pathways, cellular processes, and hormonal secretions . Major physiologic responses of fasting on health indicators include greater insulin sensitivity  and reduced levels of blood pressure , body fat , glucose, atherogenic lipids, and inflammation . In  animals, fasting ameliorated functional outcomes of diseases including cancer , type 2 diabetes , and CVD.

Emerging findings in rodents also observed the potential of fasting to delay aging, although the magnitude of the effects remains controversial. Depending on the species, the age at regimen initiation and the fasting cycle, the results ranged from a negative effect to as much as 30% life span extension.

In humans, 12 to 24 hours of fasting typically results in a 20% significant decrease in serum glucose and depletion of the hepatic glycogen. Under these circumstances, the body switches to a ketogenic metabolic mode using non-hepatic glucose, fat-derived ketone bodies, and free fatty acids as energy sources . The restriction of carbohydrates also triggers these metabolic changes.

Regarding the effects of IF on weight loss, the average reported weight loss in cohorts with overweight and obesity has ranged between »4% and 10% over dieting periods of 4 to 24 week . Nevertheless, some contradictory effects of IF were observed. In rats, alternate-day fasting (a type of IF) was unable to eliminate HF, diet-induced, muscle IR  and did not promote changes in body weight . In several clinical studies, the lack of an appropriate control group might suggest that the beneficial improvements of IF could be comparable to other types of calorie restriction.

Fasting is also adopted in several religious and spiritual traditions, and thus is intensely studied in this population. Ramadan is a month during which healthy adult Muslims fast for an average of 12 to 16 hours/day . Results describing the effects of Ramadan on body weight have been inconclusive. Several studies reported a weight loss, whereas many others showed no significant changes. Very often, a weight regain is observed a few weeks after the fasting period.

In summary, there is growing evidence demonstrating the metabolic health benefits of IF. In rodents, these appear quite profound, whereas in humans they are sparse and need further investigation, especially in long-term studies. 

It has been suggested that IF does not produce superior weight loss in comparison with continuous calorie restriction plans , and there are limited data regarding other clinical outcomes such as diabetes, CVD, and cancer. IF diets seem safe and tolerable for adults, but it is unclear if periods of fasting and hunger lead to overeating . Adverse effects of fasting, which are similar to the KD, are often moderate and include halitosis, fatigue, weakness, and headaches . It is also important to emphasize that fasting diets might be harmful to specific populations such as children, the elderly, and underweight individuals.

Alternative dietary approaches

There are several alternative dietary approaches with promising favorable outcomes in patients with overweight and obesity. For instance, the replacement of two to three meals a day with “meal replacements” that contain all recommended nutrients has been described as an approach that promotes significant weight loss . Studies also reported reductions in cardiovascular risk factors  and improvement in metabolic parameters associated with meal replacements. However, use of meal replacement products is not sustainable in the long term due to severe energy restriction.

Furthermore, the benefits and disadvantages of a long list of other weight loss diets, including the Whole30 diet, the Dukan diet, the South Beach diet, the HCG diet, and the Detox Diet, and commercial weight loss programs such as Weight Watchers require deeper scientific investigation. A complete review of all weight loss dietary approaches would not be feasible, giving the plethora of studies and trials. Hence, a few diets of primary importance were selected and discussed in this review.


Adherence to a diet is defined as the degree to which participants meet diet requirements . Many factors influence adherence to a dietary program including food preferences, cultural or regional traditions, food availability, food intolerances, and motivation. furthermore, diet cannot be addressed only as a biochemical process, since it is strongly influenced by human behavior and environmental factors.

Advancing the search for an optimal dietary weight loss approach suggests that a higher level of adherence, regardless of the type of diet, is a determinant factor in predicting success. Dansinger et al.  reported that amount of weight loss was associated with self-reported dietary adherence, but not with diet type.

Alhassan et al.  showed that adherence was significantly correlated with weight loss within each diet group after 1 year. Corral et al.  observed lower weight regain with higher adherence during the previous weight loss diet. Heymsfield et al.  also attributed the small weight loss observed in some individuals to difficulties in adherence. Conversely, Borradaile et al. reported no differences in weight loss between groups when the participants were assigned to their preferred diet.

Finally, strategies to improve adherence to diets promise to be powerful tools to improve success with weight loss dietary therapies .

Source: Scientific evidence of diets for weight loss: Different macronutrient composition, intermittent fasting, and popular diets

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