Fad Diets: The Pros and Cons

By Brianna Hanson, Dietetic Intern
MUSC Health Metabolic & Bariatric Surgery Program

Hands around fruit with the word diet with a tape measure wrapped around wrists.

"Lose 40 pounds in two weeks!" "Burn fat fast with our new protein shake!" "Lose weight fast!" Have you ever heard these phrases before? Weight loss programs and diets often use catchy, seemingly easy weight loss solutions to promote their company or their products.

Are their promises of weight loss true and sustainable? Are they safe after bariatric surgery?

We are bombarded with new diet trends, social media influencers telling us what foods we should or should not eat, and food products tailored to weight loss. Among all of the noise and pseudoscience circulating in the world of nutrition, it may be hard to determine what is true and what is not about these claims. Time to break down a few popular diets and examine the pros and cons of some trending diets.

Ketogenic Diet

The Ketogenic diet has grown in popularity over the years. Despite its origin as a treatment for epilepsy, it has now become a more common diet for weight loss. The hallmark of this diet is the high amount of fat and low intake of carbohydrates. Carbohydrates are the body's main source of fuel but when this is severely restricted, as it is on a true keto diet, the body is forced to be fueled by another source (fat). The breakdown of the standard ketogenic diet is 70% of daily calories come from fat, only 20% for protein, and 10% carbohydrates. The diet can be modified to be higher in protein, reducing the fat content down to 60%, increasing protein to 35% of calories, and reducing the carbohydrate intake to 5% of calories.


  • More accessible and available keto alternatives to common foods (bread, chips, flour, sweeteners).
  • The severe decrease in carbohydrates can cause the body to hold less water, leading to quick weight loss.
  • May help manage blood sugar levels by decreasing intake of simple carbohydrates.


  • Carbs are your body's primary energy source, limiting your intake of these may cause brain fog, irritability, fatigue, and constipation. This collection of symptoms is known as "keto flu."
  • Weight loss on the diet may not lead to long-term weight loss or maintenance.
  • Eliminates healthy food from your diet, such as whole grains, fruits, and some vegetables. These foods are high in vitamins and minerals that your body needs.
  • The diet does not differentiate between healthy and unhealthy types of fat.

Considerations after bariatric surgery

  • Higher protein needs after surgery may be hard to achieve with a standard keto diet which is predominately fat.
  • High amounts of fat are not well tolerated by people after weight loss surgery, and fat sources tend to be rich in calories. Fat malabsorption may occur, leading to loose and frequent bowel movements, excessive gas production, and vitamin deficiencies.

Atkins / Low Carbohydrate Diet

The Atkins Diet, similar to the keto diet, is a low carbohydrate diet to aid in weight loss and disease prevention. The standard Atkins diet is less restrictive than the keto diet and has three variations of the diet designed to fit your goals.


  • Protein and fat are not digested as quickly as carbohydrates, which can suppress the appetite and keep your feeling full longer.
  • Limiting carbohydrates may help reduce the amount of non-nutritive foods you are consuming.
  • Fewer simple carbohydrates may help control your blood sugar, this is especially important for people with diabetes.


  • This diet excludes many healthy foods, including fruits and vegetables, that provide essential vitamins/minerals and fiber in the diet.
  • This diet also allows processed meats, which can raise your risk for heart problems and certain cancers.
  • A low-carb diet may cause constipation, low blood sugar, kidney issues, and electrolyte imbalances.

Considerations after bariatric surgery

  • It is recommended that post-op bariatric patients avoid high sugar and high-fat foods as their bodies cannot break down or absorb these foods as well. Steatorrhea (fatty stool) may occur from fat malabsorption, which can occur in people who have undergone this surgery.

*Certain vitamins/minerals may not be adequately absorbed by the body after bariatric surgery, it is important to take the vitamins and supplements recommended by a registered dietitian.

Paleo Diet

The Paleo diet is designed to resemble the diet of human ancestors who relied on hunting and gathering thousands of years ago. This diet includes meat, fish, eggs, vegetables, fruits, nuts, seeds, herbs, spices, and healthy fats and oils. Foods excluded from this diet include processed foods, sugar, soft drinks, grains, most dairy products, legumes, artificial sweeteners, vegetable oils, margarine and translate fats. This diet was designed with a focus on improving overall health, including improving insulin sensitivity, lowering blood pressure, weight management, improving cholesterol balance, better satiety, healthy blood glucose levels, and overall lower risks of early mortality.


  • This diet eliminates many processed foods that negatively impact our health.
  • Multiple studies have shown that following this diet can lead to fairly significant weight loss.
  • One study indicated a reduction of salt intake in patients with insulin resistance and metabolic syndrome and a lower intake of high-glycemic-index products.
  • High consumption of plant products provides many anti-inflammatory benefits.
  • The higher intake of protein and fats can lead to a greater sense of satiety.


  • This diet reduces carbohydrate intake, which is essential for several body systems, including brain function.
  • May be expensive and difficult to sustain long-term.
  • If you are an athlete or exercise frequently, you may not be consuming a sufficient amount of carbohydrates to optimize your performance.
  • Overconsumption of red meat may increase your risk of cancer and heart disease (WHO) due to its saturated fat content.
  • This diet removes some healthy foods, including grains, dairy products, and legumes.

Considerations after bariatric surgery

  • The paleo diet emphasizes vegetables and fruits, many of which are low in calories but may be large in volume. It is important to ensure you have a balanced diet and meet your nutrition goals with a limited volume tolerance.
  • Choose lean protein options to avoid eating high-fat meats and dairy products, which may not be absorbed properly.

Vegan or Vegetarian Diet

A vegetarian diet eliminates meat from the diet. A vegan diet removes all animal products and by-products from the diet, including meat, dairy, eggs, and honey. These diets are adapted for a variety of reasons, including moral convictions, environmental consciousness, or improving overall health.


  • Heart-protective benefits of vegetarianism include intake of legumes, high fiber whole grains, nuts, fruits and vegetables, and other low-glycemic foods.
  • Good for heart health, a study from the American Journal of Clinical Nutrition published a study indicating that vegetarians may be one third less likely to die or be hospitalized for heart disease.
  • Plant foods tend to be lower in fat, sodium, and cholesterol, resulting in a positive effect on blood pressure.


  • It can be difficult for some people to reach their protein goals, especially after surgery without consuming meat.
  • People on this diet are more susceptible to deficiencies in vitamin B12, vitamin D, omega-3 fatty acids, zinc, and iron.

Considerations after bariatric surgery

  • Post-op patients have high protein needs and this may be difficult for some to achieve on a more restrictive diet.
  • Vitamin deficiencies can be common in both vegans/vegetarians and those with a history of weight loss surgery. Speak with your medical care team to ensure you are receiving adequate nutrition.

Weight Watchers

Weight Watchers (WW) is a weight loss program featuring a point-based system that gives a numerical value for foods, drinks, and WW recipes. There is an allotment of points per day based on your weight loss goals. They offer in-person meetings or online programs. Leaders of the meetings help members create goals and discuss new topics and offer new tips during meetings.


  • It does not eliminate an entire food group. All foods can fit within moderation.
  • It can help people develop healthy habits and provide a community through their meetings.


  • Some people find it difficult or frustrating to track your points, workouts, and weight as much as is required with this program.
  • The program is facilitated by coaches, not physicians or other medical professionals.
  • Some participants may not learn or truly understand the fundamentals of a healthy diet since they depend on the program to determine "points" for each food.

Considerations after bariatric surgery

  • Lifestyle modifications greatly benefit the maintenance of weight loss and weight maintenance after bariatric surgery. Lifestyle changes are a foundational part of the Weight Watchers program, which can be a benefit post-surgery.

Intermittent Fasting

Intermittent fasting is an eating pattern that includes periods without food or very little food that our glycogen stores are depleted. There are variations of intermittent fasting; 16/8 is one of the most popular. 16/8 intermittent fasting limits intake of food and drinks containing calories to 8 hours of the day, while fasting for the other 16 hours. You are allowed to drink water, zero-calorie beverages (black coffee and plain tea) during the 16-hour fast.


  • Regardless of its label, most people experience a form of intermittent fasting during their sleep cycle. A normal, overnight fasting period can be helpful for
  • The fasting style is flexible and can be adjusted to fit your schedule.


  • This diet does not outline nutrient-dense foods, it only limits the time frame for meals and snacks. For some, this may encourage overeating/ overindulging before or after fasting.
  • More research is needed to determine the risk of this diet for people with diabetes who may be at risk for hyper- and hypoglycemia.

Considerations after bariatric surgery

  • This diet may be helpful for weight loss or weight control by limiting the time frame in which you eat.
  • Due to volume restrictions, it may be difficult to obtain all of your essential nutrients during a smaller window of time.


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