Introduction:
Arguably, obesity is the most daunting challenge among the epidemics facing the world. This is mainly due to the facts that obesity and overweight are on the rise in both high and low-income countries, no country has a record of being able to attenuate or reverse the epidemic, and they have major connections to increased risks of diabetes, cardiovascular diseases, some cancers, and arthritis (World Health Organization, 2017). Surprisingly, overweight and obesity are linked to more deaths worldwide than underweight (World Health Organization, 2017), and are actually considered to be the fifth largest cause of death around the world (Bennett & Appel, 2016). According to the World Health Organization (WHO), obesity is a condition “where a person has accumulated so much body fat that it might have a negative effect on their health” (World Health Organization, 2018) and is classified as a body-mass index (BMI) of ≥30kg/m2. Overweight classification is considered as having a BMI of ≥25kg/m2. Body Mass Index is a simple calculation using a person’s height and weight, which is then used as a quick screening tool to assess health risk.
Good nutrition, physical activity, and a healthy body weight are essential aspects of the health and well-being of a person. Among these factors, one of the most important and influential elements that affects the loss and stability of body weight is a proper diet. Despite a continued debate over the most efficient and effective way to lose weight safely, a combination of diet and exercise has been demonstrated to have the largest positive impact on attaining a healthy body weight (Claessens, Baak, Monsheimer, & Saris, 2009; Soeliman & Azadbakht, 2014). However, there has also been much research on the different effects that change in diet alone will have on weight loss, weight management or maintenance, and little to no weight regain. The purpose of this paper is to critically examine the literature, in order to analyze several diets in order to determine their efficiency, effectiveness, potential side effects, long-term health benefits, and to ultimately determine which diet is the best for sustained weight loss when used as the primary intervention method. The diets that will be studied are: a vegetarian and vegan diet; a high-protein diet; and, a low-carbohydrate diet.
Prevalence of Obesity and Overweight:
Worldwide, obesity has nearly tripled since 1975 (World Health Organization, 2017), with two thirds (39%) of American adults being overweight (Swinburn, Caterson, Seidell, & James, 2004; World Health Organization, 2018). Obesity and overweight, however, are not limited to the adult population. As of 2016, 41 million children under the age of five, and over 340 million children and adolescents aged 5-19 were overweight or obese (World Health Organization, 2017). These numbers are staggering, especially since obesity is preventable (World Health Organization, 2018), and has huge implications for our health sectors.
Effects of Obesity and Overweight on Health:
Falling under the World Health Organization’s obese or overweight BMI classifications increases the incidence of many health problems. According to the World Health Organization (2018), a raised BMI is a major risk factor for such diseases as: cardiovascular diseases (mainly heart disease and stroke), which were the leading cause of death worldwide in 2012; diabetes; musculoskeletal disorders; and some cancers (including endometrial, breast, ovarian, prostate, liver, gallbladder, kidney, and colon). Due in part to these diseases, among people with a BMI of ≥29kg/m2, 53% of all deaths could be directly related to their obesity (Swinburn, Caterson, Seidell, & James, 2004). A high BMI is also associated with higher blood pressure and risk of hypertension, higher total cholesterol, low-density lipoprotein cholesterol (LDL-cholesterol), and triglyceride levels, and lower high-density lipoprotein (HDL-protein) levels (Swinburn, Caterson, Seidell, & James, 2004). All of these put the individual at a substantially higher overall risk of coronary heart disease. According to the National Heart, Lung, and Blood Institute (2017), being obese also puts individuals at a higher risk of gout, sleep apnea, and obstetric and surgical complications (National Heart, Lung, and Blood Institute, 2017). These health-related factors place a huge strain on the healthcare industry, and increase the cost of healthcare for overweight, obese, and severely obese patients by 22%, 28%, and 41% respectively (Peitz, et al., 2014).
Effect Nutrition has on Obesity and Overweight:
It is generally accepted that the prevention and treatment of obesity and overweight involves some sort of manipulation of energy intake and energy expenditure. Regardless of the diets that people consume, a reduced caloric intake, paired with a higher energy expenditure (more exercise), is the foundation of behavioral weight loss interventions (Bennett & Appel, 2016). In addition to creating an energy or caloric deficit or surplus, there are some nutrition changes that affect the incidence of overweight or obesity.
Maintaining a diet that is high in dietary fibre (non-starch polysaccharide (NSP)) has been shown to decrease the risk of obesity (Swinburn, Caterson, Seidell, & James, 2004). Some examples of foods that are high in NSP are: whole grain cereals, wholemeal bread and pasta, whole grain/brown rice, bran, vegetables, and fruits/dried fruits (Scottish Qualifications Authority, 2005). The decreasing effect that dietary non-starch polysaccharides have on satiety and hunger are likely the main cause in the weight reduction, as diets high in dietary fibre/NSP have shown a decrease in energy intake of about 10%, and body weight loss of 1.9kg over 2.9 months (Howarth, Saltzman, & Roberts, 2001). On the other side, diets that involve high intake of energy dense foods has been shown to increase the risk of overweight and obesity (Swinburn, Caterson, Seidell, & James, 2004). Swinburn et al. (2004) define energy dense foods as those that are: “high in fat and/or sugar” (p. 126). The main mechanism for this appears to be that foods that are high in fat have a weak impact on satiety because of their high caloric density, which leads to a passive overconsumption of total energy, thus creating a caloric surplus.
After assessing these subtle differences, and seeing how certain foods can affect weight loss, weight management, and the prevention of weight regain, one cannot help but wonder if there is a diet out there that is more effective and efficient for weight loss in obese and overweight individuals, that does not just do so through a caloric deficit.
Vegan and Vegetarian Diets:
What is a Vegan or Vegetarian diet:
The vegan, or total vegetarian, diet involves refraining from eating animals and animal products, as well as any animal derived substances. The vegan diet includes foods mainly from plants such as: fruits, vegetables, legumes (beans and peas), grains, seeds, and nuts. The lacto-ovo-vegetarian diet takes the vegan diet and adds milk, cheese, and other dairy products, as well as eggs. Likely because of the high intake of fruits and vegetables, vegan diets are typically higher in dietary fibre, magnesium, folic acid, vitamins C and E, and phytochemicals. A vegan diet also tends to be lower in calories, saturated fat and cholesterol, long chain n-3 (omega-3) fatty acids, vitamin, D, calcium, zinc, and vitamin B-12 (Spencer, Appleby, Davey, & Key, 2003). As meat and meat products are rich in many of these important nutrients, this makes sense.
Positive Research:
According to a study done by Mishra et al. (2013), a plant based, or vegan diet will cause weight loss in obese or overweight individuals even in the absence of caloric restriction and exercise. The leading cause for this weight loss seems to stem from satiety due to the higher dietary fibre intake. This increase of fibre leads to a drop in caloric intake, and thus to weight loss. They also propose that the weight loss may be caused by the thermic effect of food, in which the vegan dieters experience a small extra energy expenditure each day, which adds up to extra weight loss (Mishra, et al., 2013). This additional thermic effect results from the vegan diet typically being extremely low in fat. This low-fat diet “increases insulin sensitivity in cells, allowing cells to metabolize glucose more quickly rather than storing it as body fat” (Mishra, et al., 2013, p. 723). Vegan diets, as a result of this, have been shown to increase calorie burning by about 16% up to three hours after consuming the meal.
When sticking to a vegan diet, individuals have been shown to have a weight reduction of 2kg more than those consuming a lacto-ovo-vegetarian diet, and even greater than those consuming a non-vegetarian diet. In addition, strict vegan diets showed a 15-kg weight reduction over a three-year trial period when compared to the control group (Bennett & Appel, 2016). Due to these findings, Bennett and Appel concluded that the adoption of a vegetarian or vegan diet, when implemented correctly, might accomplish weight loss in obese or overweight individuals.
Huang, Huang, Hu, and Chavarro’s (2016) meta-analysis of randomized control trials demonstrated that individuals assigned to vegetarian diets for 9-74 weeks lost an average of 2.02kg more than those assigned to a control diet, and that studies that involved a vegetarian diet and an energy restriction showed an even greater decrease in body weight loss than the same vegetarian diet without the energy restriction. They were also able to find that individuals that were randomized to vegan diets lost more than those randomized to lacto-ovo-vegetarian diets, relative to the control. Specifically, those consuming the vegan diet lost 2.52-kg, whereas the weighted mean average for the lacto-ovo-vegetarian diets was a 1.48-kg reduction (Huang, Huang, Hu, & Chavarro, 2016). This same research concluded that despite the intervention effects being attenuated by the one-year follow up, the implementation of a vegan or vegetarian diet still remained worthy for daily use.
In other studies, where diet was observed, but not altered, fish eaters, vegetarians, and especially vegans had a lower BMI than meat eaters (Spencer, Appleby, Davey, & Key, 2003). Additionally, studies of vegetarians have consistently shown that vegetarians have lower BMIs than otherwise comparable non-vegetarians, with the typical difference being 1-2kg/m2 (Appleby & Key, 2016). Other confounding lifestyle factors such as smoking, and exercise explained less than 5% of the difference in BMI between the two groups. Another factor that explained 50% of the difference in mean BMI between meat eaters and vegans was the energy and micronutrient intake. This factor making up such a large proportion of the difference may be accredited to dietary factors. Even after adjusting for all of the lifestyle and dietary differences, there remained a statistically significant gap between the two diet groups’ BMI (Spencer, Appleby, Davey, & Key, 2003).
Negative Research:
Despite the majority of the literature supporting a vegetarian or vegan diet for obese or overweight individuals seeking to lose weight, there remain some reservations for the diet intervention. Micronutrient deficiencies are of special concern for vegans and vegetarians. Common faults of the diet include a lack of sufficient protein, iron, zinc, calcium, vitamin B-12, vitamin D, and long chain n-3 (omega 3) fatty acids (Craig, 2009; Crane & Sample, 1994). Unless vegans regularly consume foods that are fortified with these nutrients, supplementation may be necessary.
Biochemistry Behind a Vegan or Vegetarian Diet:
When a soy high protein weight loss diet was compared to a meat high protein weight loss diet, Neacsu, Fyfe, Horgan, and Johnstone (2014) found that when a similar energy intake for each diet was consumed, there were similar effects on weight loss, satiety, desire to eat, and percent of fat mass lost (relative to total mass lost). Between the two high protein diets, there was also a similar average plasma concentration of metabolites. Both diets showed a decrease in LDL cholesterol, total cholesterol, and glucose triacylglycerol; however, the soy protein diet actually showed lower total cholesterol and LDL cholesterol. Additionally, after consuming the soy high protein weight loss diet, higher concentrations of leucine, tryptophan, isoleucine, and threonine were found in the blood than after consuming a meat high protein weight loss diet. They summarized that because the two diet interventions had similar impacts on subjective appetite and motivation to eat, and weight loss, that a vegetarian high protein diet “could be a healthier alternative to [a] meat based high protein weight loss diet, achieving the desired results without the potential negative health effects” (Neacsu, Fyfe, Horgan, & Johnstone, 2014, p. 557).
Diet Verdict:
In summary, vegetarian diets, and specifically vegan diets, appear to have a real, significant impact on weight loss, weight maintenance, and a prevention of weight regain, despite these benefits being attenuated over time. Tied to the decrease in BMI, vegetarians typically have a lower risk of cardiovascular disease (CVD), type 2 diabetes, and some cancers (Craig, 2009). A main cause for this weight reduction probably lies in the micronutrients that vegans typically get in abundance. By consuming large quantities of fruits, vegetables, and whole grains, which have low glycemic index (GI) values, are rich in fibre, antioxidants, phytochemicals, and minerals, vegans and vegetarians are able to achieve greater weight loss, and weight maintenance throughout their lives.
High Protein:
What is a High Protein Diet:
A high protein diet is a weight loss plan that places emphasis on the consumption of foods that are high in protein. This intervention method may be paired with a low carbohydrate diet but is typically only put together with an energy restrictive program (Falcone, et al., 2015). High protein diets have become increasingly popular as a means of controlling weight in overweight and obese individuals (Devassy, et al., 2015), however, the results of the research seems to be quite controversial.
Positive Research:
In a study done by Falcone et al. (2015), women completed one of three three-week programs in order to investigate how a high protein diet, with and without supplementation, would affect body composition. The three groups were: no change in diet; the addition of a conjugated linoleic acid (CLA), a protein gel, and a multi-vitamin; and, a high protein diet with isocaloric placebo supplements. Essentially, the groups were a control (CON), a placebo (PLA), or a diet with supplementation (SUP). After the three-week intervention, the control group lost 0.01kg ± 1.25, the placebo group lost 1.5kg ± 1.62, and the supplemented group lost 2.98kg ± 1.66. The SUP also demonstrated the largest drop in percent body fat, lean mass, arms fat mass, legs fat mass, and truck fat mass, and despite the weight loss of each group being relatively small, the supplements induced 97% more weight loss compared to diet alone. There was a change in body weight for both the SUP and PLA groups compared to the CON, which demonstrates that the high protein diet alone did have a significant impact on the weight loss. This study showed that the addition of a thermogenic (Burn™, from MusclePharm Inc. which includes caffeine and green tea catechins), CLA, protein gel, and a multi-vitamin to a high protein, low calorie diet improved weight loss, total fat loss, and subcutaneous fat loss (Falcone, et al., 2015).
In another study, Claessens, et al (2009) found that a high protein (whey or casein), low fat diet is more effective for weight control in obese subjects than a high carbohydrate, low fat diet, and also has no adverse effect on metabolic and cardiovascular risk factors in obese individuals that do not have metabolic or cardiovascular complications. In this study, after an initial significant weight loss, the high protein, low fat diet not only prevented weight regain, but also initiated further weight and body loss compared to the high carbohydrate, low fat diet (Claessens, Baak, Monsheimer, & Saris, 2009). These findings are further supported by Noakes, et al (2005) when they found that the high protein diet subjects lost more fat than the high carbohydrate group, when implemented on an energy restrictive diet. They surmised that this greater weight loss was due to the higher thermic effect of high protein foods, and that a high protein diet helps you feel fuller for longer, which makes you eat less and therefore further reduces caloric intake (Noakes, Keogh, Foster, & Clifton, 2005).
Negative Research:
In contrast to the research supporting the efficiency of the high protein diet, there are plenty of studies that found different results, and propose that the long term negative effects of a high protein diet far outweigh the short-term weight loss. A study completed by Moran, et al (2016) found that there were no significant differences between the high protein and high carbohydrate intervention groups in term of weight loss, with both groups losing 9.1kg ± 0.6 and 8.8kg ± 0.6 from 0-12 weeks, respectively, and 10.8kg ± 1.2, and 10.3kg ± 1.2 from 0-52 weeks. In addition to this, they found no difference between the effect that the diets had on anthropometric (such as BMI, waist circumference, fat percentage, abdominal fat, and weight), metabolic (testosterone levels, and erectile dysfunction), or psychological (sexual desire) outcomes throughout the study (Moran, et al., 2016). This research is supported by Noakes, et al (2005) when they showed that both a high protein, and an isoenergetic standard protein diet had similar effects on weight loss, change in fat-free mass (FFM), and strength and aerobic capacity in overweight and obese men (Noakes, Keogh, Foster, & Clifton, 2005).
In a study completed in 2015, study participants that were free of heart disease at the beginning of the study, but who had type 2 diabetes, or high blood pressure (HBP), poor cholesterol levels, and obesity (which are type 2 diabetes risk factors), were recruited. These participants replaced carbohydrates in their diets with protein, and found that there was a 90% greater risk of gaining more than 10% body weight, and a 59% higher risk of death from any cause, which was linked to the diet change (High-Protein Diets May Pose Long-term Health Risks (Cover Story), 2015). This study further concluded that while a high protein diet may be an attractive option for obese or overweight individuals who seek to lose weight quickly, the long-term health risks may offset the immediate gratification.
Some of the long-term health risks associated with a high protein diet have been found to be an increase in kidney size, proteinuria, larger livers, higher alanine transaminase (ALT) concentrations, and an elevated BMI (Devassy, et al., 2015).
Biochemistry behind High Protein Diet:
For a high protein diet with protein levels near the upper level of the Dietary References Intake (DRI), the diet was able to improve some of the effects of obesity as it resulted in less weight gain, improved glucose handling, and lowered serum haptoglobin levels than the control (Moran, et al., 2016). Abete, et al (2009) also found that serum vitamin B-12, which is necessary for hematopoiesis and normal neuronal function (Babior, 1995), increased by 9% with the high protein diet, and decreased 13% with the high carbohydrate diet. They also determined that high protein, low carbohydrate diets could involve specific changes in mitochondrial oxidation that may be one of the causes of higher weight loss (Abete, Parra, De Morentin, & Alfredo Martínez, 2009).
A high protein, low glycemic-index (LGI) diet has been shown to be superior to the conventional low fat, high carbohydrate diet. However, the genetic analysis done by Astrup, et al (2015) suggests that the effect is only prevalent among 2/3 of the population that have a genetic variant in the rs987237 gene that seems to determine the effectiveness of the higher protein diet on their weight loss. However, the protein to carbohydrate ration is immaterial for weight control for the remaining 1/3 of the population (Astrup, Raben, & Geiker, 2015).
Diet Verdict:
In short term studies, the ability of a high protein diet to promote a reduction of body fat stores and a negative fat loss is well established. However, the theme of the diet seems to be that the majority of the weight loss occurs in the first six months. For obese and overweight individuals who need to lose weight, maintain the weight loss, and prevent weight regain throughout their life, the long-term health issues of this diet intervention will probably outweigh any pros. Also, the research finding that suggests that the short-term weight loss will only occur for 2/3 of the population makes this diet choice seem even riskier for people who will typically already have enough medical issues.
Low Carbohydrate:
What is a Low Carbohydrate Diet:
A low carbohydrate diet is one that limits the intake of carbohydrates, and instead emphasizes higher quantities of protein and fat. Examples of foods that are high in carbohydrates are: breads, pasta, oatmeal, rice, and potatoes. Foods that are the foundation of the low carb diet are: eggs and dairy, fish, meat, chicken, nuts and seeds, oils and fats, and low carb vegetables such as bell peppers, broccoli, and asparagus (Axe, 2018). Because of the restriction on carbohydrate intake, this diet can be seen as the result of a high protein diet, but this is not always the case.
Positive Research:
Some sources of research suggest that the success of the low carbohydrate diet, and especially the very low carb diet (Ketogenic diet) is due to the induction of ketosis. Ketosis is where the body produces ketone bodies out of fat, and uses them for energy instead of carbohydrates, which is the typical source of energy for many of the cells in the body. Because there is limited access to glucose, stored fat is providing the majority of the energy for the body, and thus people will end up losing weight (Manninen, 2004). In addition, being in a state of nutritional ketosis will suppress appetite, thus causing individuals to eat fewer calories, and create an energy deficit. The inhibition of appetite is due to the ketone β-hydroxybutyrate which has been shown to directly hinder food cravings and is the main circulating ketone body on a very low carbohydrate, ketogenic diet (Volek, et al., 2004).
Other studies found that subjects on low carbohydrate diet lost more weight than subjects on the conventional, high carbohydrate diet at three months and at six months, where they each lost 6.8% ± 5.0 vs 2.7% ± 3.7, and 7.0% ± 6.5 vs 3.2% ± 5.6 of body weight respectively (Foster, et al., 2003). In addition to producing greater weight loss for the first six months of the trial, the low carbohydrate diet was also associated with greater improvements on some risk factors for coronary heart disease (CHD). The decreases in serum triglycerides and increases in high density lipoprotein (HDL) cholesterol were the main CHD risk factors that were affected by the low carb diet. However, the diet intervention also displayed a decrease in diastolic blood pressure and the insulin response to an oral glucose load (Foster, et al., 2003).
Krebs, et al (2012) also found that insulin resistance was positively affected by a high protein, low carbohydrate diet, as well as markers of cardiovascular risk. On top of that, they found that there was a significant decrease in short term BMI and weight loss in those who adhered to the diet throughout the 13-week trial period intervention, and therefore came to the conclusion that a “high protein, carbohydrate restricted diet should be considered a safe and effective option for medically supervised treatment of severe obesity in adolescents” (Krebs, Gao, Gralla, Collins, & Johnson, 2012, p. 258).
In further research, when comparing a low-fat diet to a low carbohydrate diet, results showed that the low carb diet outperformed the low-fat diet in terms of weight loss and fat loss, and did so despite similar energy deficits between the diets. In this study, the reductions in body mass, total fat mass, and trunk fat mass were observed to be significantly greater in men than in women, although 12 out of 13 women still experienced greater fat loss in the trunk region during the low carbohydrate diet intervention (Volek, et al., 2004).
Negative Research:
Although low carbohydrate diets are becoming more and more common among the obese and overweight population (Noto, Goto, Tsujimoto, & Noda, 2013) due to the rapid weight loss, improved blood glucose levels, reduced LDL cholesterol, increased HDL cholesterol, and reduced blood pressure, long-term research suggests that low carbohydrate diets were associated with worsened diabetes health, increased cancer risk, increased cholesterol, increased atherosclerosis, harder blood vessels, and a significantly higher risk of all-cause mortality (Noto, Goto, Tsujimoto, & Noda, 2013). These effects were especially true for those who followed an animal-based low carbohydrate diet (Fung, et al., 2010).
Diet Verdict:
The low carbohydrate diet is very promising, especially for short term results, but it is a hard diet to sustain, and has some very negative potential long-term health effects. A low carb diet has been shown to create faster weight loss, normalized blood sugar levels, but depending on ones’ overall health and goals, it is not necessary to completely avoid healthy sources of carbohydrates in moderation. By limiting your carb intake, you typically increase your intake of meat, dairy products, eggs, fish, and oil. An increase in the consumption of meat has a positive association to increased mortality, particularly due to cardiovascular diseases, but also to cancer (Rohrmann, et al., 2013). Although there are risk factors involved, I am not suggesting that everyone should stay away from meat. However, the research suggests that an increase in meat consumption, particularly red meat consumption, increases mortality, which suggests that a low carbohydrate diet that prompts an increase in meat consumption is not conducive to good long-term health.
Conclusion:
Due to the obesity and overweight epidemic that is occurring around the world, dieting has become a necessity for some people. Research showed that Americans spend more than $60 billion each year on weight loss strategies such as supplements, gym memberships, and diet soda (Williams, 2013) in order to improve their health. The determinants for the ability to manage weight are genetic, behavioral, and environmental, but the most influential factor that influences the stability of body weight is nutrition (Soeliman & Azadbakht, 2014). Instead of focusing on the shortcuts and tricks, people need to pay more attention to their nutrition and eating habits if they want to lose weight, manage their weight, and prevent or reduce their weight regain. Creating a caloric deficit, or a reduced calorie diet, results in clinically significant weight loss regardless of which micronutrients they emphasize (Sacks, et al., 2009).
Finding a diet that is suitable to your lifestyle, is sustainable, and that you enjoy is the key to creating meaningful weight loss. Research has shown that vegan and vegetarian diets, high protein diets, and low carbohydrate diets all have their pros and cons. In conclusion, diets that are successful in creating weight loss in obese and overweight individuals can emphasize a range of fat, protein, and carbohydrate compositions, and can be focused on animal-based products or on non-animal products (Sacks, et al., 2009). Each diet needs to be tailored to the specific cultural, personal, and dietary preferences of the individual in order to have the best chance for long-term success. Ultimately, if you are going to successful in losing weight, and keeping it off, the diet you choose must be one that is no longer a diet, but a lifestyle choice.