Pros And Cons of Top Weight Loss Diets

The start of a new year tends to bring with it new health goals or resolutions. According to a December 2019 survey, approximately 37% of adults in the U.S. intended to lose weight as a New Year’s resolution. (6)

To accomplish this goal, individuals often turn to certain dietary patterns. Another publication in Obesity Facts reports that approximately 40% of women normally start a weight loss diet in January. (34) The success of a diet plan for weight loss depends on several factors, including the content of the diet itself and an individual’s adherence to the diet plan.

Learn about the pros and cons of the top ten diets commonly followed to promote weight loss. The diets explored in this article include:

• DASH diet
• Gluten-free diet
• High-protein diet
• Keto diet
• Low-carb diet
• Low-fat diet
• Mediterranean diet
• Paleo diet
• Vegan diet
• Vegetarian diet

What is weight loss?

Weight loss is defined as a reduction in body mass. (11) Intentional weight loss is commonly sought in order to achieve a healthy weight range and improve an individual’s health status and/or reduce the risk of disease.

Body mass index (BMI) is a tool that is used to assess an individual’s body composition. Individuals with BMI values between 18.5 to 24.9 are considered to be at a healthy weight. Those with a BMI 25.0 and over are considered overweight or obese, but note that BMI does not specify the distribution of tissue, meaning that higher BMI does not always indicate excess body fat. As an adjunct to BMI, waist circumference is also used as a measure of weight status in relation to disease risk. A waist circumference of over 35 inches in females and over 40 inches in males is associated with an increased risk of developing obesity-related health concerns. (12)

Health benefits of weight loss

In overweight or obese individuals, weight loss is associated with certain health benefits, including:

• Improved metabolic risk factors (e.g., abnormal blood lipid levels, elevated blood pressure, insulin resistance) (11)
• Decreased risk of chronic diseases (e.g., type 2 diabetes, coronary artery disease, (13) obesity-associated cancers) (11)
• Increased health-related quality of life (e.g., self-image, individual perception of well-being, and physical, emotional, and social functioning) (3)

It’s important to note that weight loss may not be desired or beneficial for individuals who are already at a healthy weight or those with special health considerations such as pregnancy. (12)

Pros and cons of the top weight loss diets

For overweight or obese individuals, health benefits may be seen with weight loss of as little as 5% to 10% of body weight. (40) Weight loss may be achieved by engaging in physical activity and/or by adhering to certain dietary patterns. The pros and cons of several weight loss diets are outlined below.

DASH diet for weight loss

The Dietary Approaches to Stop Hypertension (DASH) diet is a dietary approach designed to manage hypertension (high blood pressure) and improve cardiovascular health. The DASH diet  limits the intake of foods that may contribute to hypertension (14) and emphasizes the intake of complex carbohydrates, lean protein, low-fat dairy, vegetables, and fruit. (4)

Pros: A four-month randomized controlled trial in 46 overweight and obese adults assessed the effects of the DASH diet alone versus the DASH diet with aerobic exercise and caloric restriction. The study found that individuals in the DASH diet alone group maintained their weight, while the DASH diet with exercise and caloric restriction group lost a mean weight of 19 lbs (8.7 kg). Further, compared to the DASH diet alone and control groups, the second intervention group had improved insulin sensitivity, as well as lowered total cholesterol and triglyceride levels. (8)

In addition to addressing hypertension, the DASH diet has been associated with a reduced risk of conditions including cardiovascular disease, stroke, (21) colorectal cancer, insulin resistance, and all-cause mortality. (14)

Cons: Physical activity and caloric restriction may be required to complement the diet in order to achieve weight loss results and improve markers of cardiovascular health. (8) Research suggests that adherence to the DASH diet remains low due to the accessibility of nutrient-deficient foods (e.g., fast foods), clinician unfamiliarity with the diet, as well as the challenges individuals face with sustaining behavior change. Support such as digital health tools may be relied upon to improve individual engagement and maintain adherence to the diet. (37)

Gluten-free diet for weight loss

The gluten-free diet (GFD) restricts the intake of foods containing gluten, a protein found in certain grains, such as barley, rye, and wheat. The GFD is a first line treatment for individuals with celiac disease, and has been increasingly adopted by other individuals for various health reasons. (31)

Pros: In addition to celiac disease treatment, the GFD may improve symptoms in individuals with non-celiac gluten sensitivity and irritable bowel syndrome (IBS). (31) In individuals without celiac disease, the GFD has been associated with a lower BMI and significant self-reported weight loss over one year. (23)

Cons: Data from the National Health and Nutrition Examination Survey (NHANES) 2009-2014 suggests that in individuals without celiac disease, the GFD may not reduce the risk of cardiovascular disease or metabolic syndrome. (23) Negative impacts of a GFD may include increased financial costs, nutrient deficiencies (e.g., dietary fiber, folate, iron), and negative psychosocial implications. (31)

High-protein diet for weight loss

A diet that contains over 0.8 g of protein per kg of body weight (the recommended dietary allowance (RDA)) or above 15 to 16% of caloric intake from protein is considered to be a high-protein diet. Examples of high-protein diets include the Atkins diet, the South Beach diet, and the Zone diet. (33)

Pros: High protein diets may support weight loss by improving satiety and preserving lean body mass during weight loss. (33) A systematic review of dietary approaches for obesity found that adherence to a low-carbohydrate high-protein diet (LCHP) was greater compared to adherence to the public health-recommended low-fat high-carbohydrate diet (LFHC), suggesting individuals may prefer a high-protein diet to a high-carbohydrate diet. The LCHP was found to be as effective or more effective than low-fat diets in reducing weight and the risk of cardiovascular disease after six months and one year. (18)

Cons: Certain precautions should be taken with a high-protein diet. A high intake of certain amino acids (e.g., valine, leucine, isoleucine, tyrosine, phenylalanine) in combination with a high-fat diet may be associated with an increased risk of metabolic disease. The potential acid load of high-protein diets may also be detrimental to kidney health. Incorporating nutritious plant-based protein sources may help to moderate the intake of fat from animal-based proteins. (33)

Keto diet for weight loss

The ketogenic diet, often referred to as the keto diet, is a high-fat, very low-carbohydrate dietary pattern, in which carbohydrate intake is limited to 50 grams per day on a 2,000 calorie diet. The purpose of the diet is to achieve a shift in metabolism from using carbohydrates to using primarily fatty-acid derived ketones for energy, a process referred to as ketosis. (28)

Pros: Individuals following the keto diet typically experience rapid weight loss in the first two weeks. Additionally, hunger cues may be reduced and lean body muscle is typically maintained during weight loss. (28) Research has shown that a 24-week keto diet in obese patients was associated with a significant reduction in body weight and BMI, as well as improvements in several cardiometabolic risk factors. (16) The keto diet may also improve aspects of health that may be impaired by weight gain and obesity, such as cognitive impairment, mood, and longevity. (32)

Cons: The keto diet has been reported as safe for up to two years, however, research has not explored any potential negative implications with long-term adherence to the diet. Short-term adverse effects, commonly referred to as the “keto flu”, include constipation, dizziness, fatigue, headaches, and vomiting. Long-term adverse effects may include kidney stones, nutrient deficiencies, and hepatic steatosis. (28)

Individuals with diabetes should consult a healthcare practitioner prior to beginning the keto diet. In addition, the keto diet is contraindicated in individuals with certain health conditions, including fat metabolism disorders, liver failure, pancreatitis, and porphyrias, as well as primary carnitine deficiency, carnitine palmitoyltransferase deficiency, carnitine translocase deficiency, and pyruvate kinase deficiency. (28)

Read about supplements that support the keto diet on the Fullscript blog.

Low-carb diet for weight loss

Low-carbohydrate (low-carb) diet plans vary from very low-carb, which restricts the intake of carbohydrates to a maximum of 50 grams per day. On a low-carb diet, the intake of carbohydrates is restricted to 130 grams per day. (20)

Pros: Low-carb diets may result in a number of benefits, such as decreased fasting insulin and blood glucose, reduced triglyceride levels, improved blood pressure, and rapid weight loss. (1) A meta-analysis reviewed studies comparing the effects of low-carbohydrate and low-fat diets in a total of 1797 overweight and obese adults individuals. The review demonstrated that while both diets were associated with significant weight loss, the low-carbohydrate diet resulted in greater weight loss and improvement in atherosclerotic cardiovascular disease (ASCVD) risk over eight to 24 months. These findings suggest that a low-carbohydrate diet is a safe and effective weight loss intervention for a period of up to two years. (35)

Cons: Several adverse effects have been reported with low-carb diets, including increased urinary calcium loss, loss of lean body mass, increased plasma homocysteine levels, and increased low-density lipoprotein (LDL) cholesterol. (1)

Low-fat diet for weight loss

Similar to low-carb diets, the definition of a low-fat diet varies. A low fat diet is typically considered to contain 20% of total calories from fat. (5) A diet that derives less than 15% of calories from fat is considered a very low-fat diet. (25)

Pros: A meta-analysis of randomized controlled trials examining the effects of low-fat dietary interventions on weight loss found that low-fat diets are more effective than a “usual diet” consumed by individuals. (38)

A low-fat diet (20% of total calories from fat) may be associated with other health benefits, such as a reduced risk of cognitive impairment in certain individuals. An 8.5-year dietary intervention study in postmenopausal women found that a low-fat diet was associated with a significantly reduced risk of possible cognitive impairment. (15) Similarly, a one-year trial comparing the effects of energy-restricted low-fat and low-carbohydrate diets in overweight and obese individuals found a greater improvement in psychological mood states following the low-fat diet. In the trial, both groups saw similar effects on weight loss, working memory, and speed of processing. (9)

Cons: Meta-analyses suggest that low-carbohydrate diets may be more effective at achieving weight loss than low-fat diets. (35)(38) The effectiveness of a low-fat diet for achieving weight loss may depend on an individual’s health status. Research suggests that normoglycemic (normal blood sugar level) individuals may lose more weight on a low-fat and high-carbohydrate diet, while diabetic individuals may lose more weight on a high-fat, low-carbohydrate diet. (19)

A study in individuals with hypertriglyceridemia (elevated triglyceride levels) found that compliance with a low-fat diet was considered to be difficult. The reported barriers to the diet included inconvenience, social pressure, cost, and a lack of flavor and variety. (39) The individuals’ average daily consumption of certain nutrients did not meet the reference daily intakes (RDIs) in the U.S., including calcium, iron, magnesium, and vitamins A and E. (17)(39)

Mediterranean diet for weight loss

The Mediterranean diet (MD) is a dietary pattern based on the traditional dietary and lifestyle habits of individuals living in the Mediterranean region. The diet is composed primarily of cold-pressed extra-virgin olive oil (EVOO), vegetables, fruits, whole grains, legumes, and nuts. The MD also allows for the moderate consumption of lean meats, fish, dairy, and red wine, and limits the consumption of red meat, refined and processed foods, and sugars. (10)

Pros: The health benefits of the MD include reducing the risk of overweight, obesity, and abdominal obesity. (2) Further, anti-inflammatory and antioxidant effects of the diet have been associated with a reduced risk of cardiovascular disease and cancer. (10) The MD may be more effective than a low-fat diet at improving fasting blood glucose and insulin levels in obese individuals with diabetes. (36)

Cons: As a result of its many benefits, the MD has been suggested as the “gold standard in preventive medicine”. However, further research is required to understand the health and weight loss effects of the other aspects of the Mediterranean lifestyle (e.g., the recommended physical activity) in combination with the diet. (27)

Paleo diet for weight loss

Also referred to as the caveman or hunter-gatherer diet, the paleolithic (paleo) diet consists exclusively of foods that were available to humans prior to modern agriculture. This includes the consumption of vegetables, fruit, nuts, seeds, eggs, animal proteins, and seafood, as well as the restriction of grains, legumes, dairy, processed oils, salt, and refined sugars. (24) The specific macronutrient breakdown of the diet may vary, but the paleo diet is often classified as a low-carb diet. (4)

Pros: A systematic review and meta-analysis examining the effects of dietary patterns on the components of metabolic syndrome found moderate evidence of weight loss following a paleo diet compared to a control diet based on current dietary recommendations. Compared to the control diet, additional health benefits of the paleo diet included greater improvements in the five components of metabolic syndrome (e.g., waist circumference, triglycerides, HDL cholesterol, blood pressure, fasting blood sugar). (26)

Cons: Potential negative effects of the paleo diet may include an increased exposure to environmental toxins found in fish and a reduced intake of certain nutrients (e.g., calcium, vitamin D). Researchers suggest that further clinical trials with larger groups of participants and longer study durations are required to better understand the effects of the diet. (24)

Vegan diet for weight loss

A vegan diet restricts the consumption of animals and animal-based products. While the foods included on a vegan diet may vary, typical foods consumed include fruit, vegetables, grains, nuts, seeds, beans, and legumes. (22)

Pros: While vegan diets may at first seem limiting or difficult to follow, a study examining the adherence to five different diets for weight loss (vegan, vegetarian, pesco-vegetarian, semi-vegetarian, and omnivore) found equal adherence and acceptability rate among all diets. At six months, non-adherent individuals assigned to the vegan and vegetarian diets were still found to have a significantly greater decrease in cholesterol intake than the other diet groups in the trial. (30)

Cons: In the absence of a well-planned vegan diet or dietary supplementation, individuals following a vegan diet may have insufficient intake of certain nutrients, including protein, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), retinol, vitamin B12, calcium, and zinc. (22)

Vegetarian diet for weight loss

Vegetarian diets restrict the intake of meat, poultry, and seafood. Unlike the vegan diet, the lacto-ovo vegetarian diet includes eggs, as well as animal-based foods like dairy and honey, in addition to all plant-based foods. (22)

Pros: Research suggests that compared to non-vegetarians, vegetarian individuals have a lower BMI and a reduced incidence of obesity. These benefits may be a result of dietary components, such as an increased fiber intake. (22) Further, a systematic review and meta-analysis assessed changes in body weight following vegetarian diets. The results suggest that following a prescribed vegetarian diet reduces mean body weight, with greater weight loss seen in individuals with a higher baseline weight. (7)

Cons: Vegetarian diets may be low in certain nutrients, such as protein, vitamin B12, and zinc. (22)

Additional considerations

While there is evidence to support some of the benefits seen in various weight loss diets, clinical research on diets has several limitations. Factors to consider when assessing the success of dietary research include the age and gender of participants, the level of adherence to the assigned diet, self-reporting of dietary intake, the duration of the trial, and which health outcomes are measured in the study (e.g., weight change from baseline, weight change compared to control group, waist circumference, BMI, body composition). (4) Confounding factors that may affect study outcomes include dietary supplements, physical activity levels, and varied caloric intake between participants when calories are not restricted. (4)

Overall, which is the best diet for weight loss? The effectiveness of a weight loss diet depends on the individual and a variety of factors, including health status, (29) metabolism, (5) diet quality, (5), and diet duration. (4) Consider working with your integrative practitioner to develop a personalized dietary approach that suits your weight loss goals.