Dietician Insights: The Good and Bad of “Fad Diets”

Shannon Miller

February 27, 2019

You are not alone in your frustration around competing nutritional information. We are bombarded daily with new studies, articles, testimonials and blogs related to new findings in diets and weight loss. Asa House, a dietician at Composition ID Baltimore compares the facts around the most popular “fad diets” to examine their benefits, risks, and how they impact performance and health.

“Science moves fast. Sometimes what is confirmed one day can be disproved the next, which leaves endless lingering questions. Do we eat carbs? Does the keto diet have an effect on our long-term health? Is going vegan the ultimate the healthiest lifestyle? Should we limit food intake for part of the day, then indulge for the rest? It is easy to get overwhelmed.

Let’s be honest, most of us have tried a fad diet at some point in our lives. And let me guess: the results did not last or it was not sustainable. But being on a “diet” is temporary, and naturally so. With the exception of the vegan diet, most fad diets are not designed to be sustainable for most people. And with “temporary” mindset, would you expect anything other than “temporary” results?

First, it’s important to consider your goals. To lose weight? Develop better eating habits? Change body composition? In any case, a temporary commitment will only get temporary results. Weight loss requires a change in habits over time around both diet and lifestyle. There is no other way. Unless there is sustainable change, we risk getting stuck in the yo-yo trap of losing weight, then gaining it back. This pattern can be particularly detrimental to your health.

Change takes time, and if you are willing to step away from the “quick fix” mentality, you can achieve lasting results. It’s easy to fall for the simplistic, strict guidelines that leave little to figure out on your own, but that may not be tailored to your own nutritional needs or lifestyle. More often than not I hear people say: “I have to get back on my diet because I lost so much weight on it last time.” What made you “go off” the diet? It will happen again, I guarantee it!

I have worked with so many clients who were at the end of their rope. They tried all diets under the sun but weighed more than ever – and were more confused than ever. However, once they started eating consistently, pounds started to come off. Sometimes slowly – maybe a pound or two per month. However, more importantly, they stopped looking to the number on the scale as a measure of their success and started looking at the new healthy habits they were creating. These habits led to improved health and, as an added side effect, a healthy weight. Even if just one at a time, these habits were made for life.

So, decide on your goal. Find a sustainable way to get there. Stop looking for a quick fix and set up a plan that you feel comfortable with. This plan is going to be different for everyone. If you need help to create this plan, find a professional that looks beyond what is “hot” today and out tomorrow and brings into the equation you as a person: with your likes, dislikes, habits, wants and needs, and keeps you accountable for the goals you set up. A one-time visit will not be enough. Create a relationship and stick to it! Habits take time to become habits. Let it take time, it will be worth it in the end.”

Low Calorie

  • 400-1200 calories per day, depending on the stage. Examples: Medifast, Nutrisystem, or other fad diets like “the grapefruit diet,” or “the cabbage soup diet,” etc.


  • Use of meal replacement supplements.
  • Can result in initial significant weight loss.


  • Can trigger compensatory mechanisms, such as increased appetite, slowed metabolism and reduced energy expenditure from lost muscle mass.
  • High risk for weight regain, even beyond baseline.

Low Fat

  • Less than 30% of calories from fat.
  • No more than 10% of calories from saturated fat. 0% trans fat.
  • Naturally higher in carbs (50% of calories or higher)
  • Moderate protein (18-20% of calories)


  • Supports the idea of low energy-dense foods as a means to control calorie intake.
  • Usually recommended by the American Heart Association and similar institutions/organizations
  • Could benefit athletes trying to cut weight while keeping or gaining muscle mass


  • Should emphasize a low glycemic carb load or there will be a risk of filling up on less nutritional carbs, such as sweets and white flower type foods.
  • Could potentially leave you unsatisfied after meals if protein to carb ratio is not adequate.
  • Fat is important in a healthy diet and if too little, there can be issues with deficiencies in omega fatty acids and fat-soluble vitamins, such as vitamin A, D, E and K.
  • Supplementation with omega 3 might be needed.

Low Carb

  • Carb intake below 150g daily or less than 40% of calories.
  • Naturally higher in protein and with fat consistent at 30-40% of calories


  • Easy to follow since guidelines are clear.
  • Can generate initial significant weight loss, which can serve as motivation.
  • Since it’s higher in protein, satiety will increased, even with less food eaten.
  • Popular among people with chronic disease, such as diabetes.
  • Can help in cutting back on sugar.


  • Could be misleading since weight loss can be a result of reduced caloric intake by cutting out a whole food group.
  • Initial weight loss is mainly fluid loss from within the glycogen stores flushed out from lean body mass. Will easily be regained once carbs are reintroduced.
  • Insufficient consumption of carbs can limit athletic progress by reducing muscle synthesis and limiting high-intensity capacity.
  • Studies suggest that too much protein could be a risk factor for heart conditions, including high plant-based protein intake.
  • There are proven benefits to dietary fiber and micronutrients from whole grain and fruit in preventing disease and improving inflammation.


  • High fat intake (70% of calories per day or more) moderate protein around (18-20% of calories) and low carb intake (5% of calories)
  • Was created in the 1920’s by doctors to minimize the occurrence of epileptic seizures. Initially, fasting had been used to treat seizure disorders but since fasting is not sustainable, the ketogenic diet was born as an alternative. The keto diet mimics fasting in the way it creates ketones. The exact mechanism of how this benefits those with seizures is still not fully understood but it’s thought to have to do with pH and electrical charge, which changes the paths or response of the neurotransmitters in the brain.


  • Clear guidelines!
  • Will also result in significant initial weight loss from emptying of glycogen stores and water, which could serve as motivation.


  • Although it was created to mimic fasting for improving seizure occurrence in epilepsy, there are no consistent studies that associate it with long-term weight loss.
  • It has been suggested that the main reason weight is lost on this diet is because an entire food group is cut out and this will naturally lead to eating less calories.
  • Also, even though protein intake is “moderate,” it is still higher than a standard diet and would result in increased satiety.
  • Not consuming enough carbs could limit athletic progress the same way a low carb diet would by reducing muscle synthesis and limiting high-intensity capacity.
  • Studies have suggested an increase in LDL cholesterol in the long term.
  • High intake of saturated fat is still considered harmful by most health organizations.
  • Again, the importance of dietary fiber and micronutrients from whole grain and fruit in preventing disease and improve inflammation cannot be replaced with fat or protein.
  • Hard to stick to in the long term and weight regain is common.
  • Supplements are required.
  • Unpleasant side effects, such as constipation and bad breath.


  • Refraining from food and fasting for a certain amount of time.
  • *Fasting mimicking diet: Consume 1100 calories the first day and cut down to 800 for the remaining 5 days. Foods are exclusively vegetables and higher fat foods, such as olive oil and nuts/seeds and very low in protein.
  • Done every month or every other month.
  • *Alternating days: for example, fasting or consuming 25% of calories on Monday, Wednesday and Friday and eating normal the other days.
  • *5:2 diet where you eat normal for 5 days and fast or consume 25% for 2 days. This can be 2 consecutive days or they can be spread out.
  • *Time restricted where you eat only within an 8-hour period time, for example between noon and 8pm or 9am and 5pm.


  • Fasting is suggested to benefit the body in several ways, including improved immune system, reduced visceral fat and longevity.
  • It has been recommended that those who start off with a time restricted fast work slowly increase fasting length of time in a row in order to get the full benefits.
  • Can provide the opportunity to start eating better by the “clean” feeling felt immediately following a fasting period.


  • Can be difficult to follow. (Hunger can be uncomfortable!)
  • Might halt training progress.
  • If nutrition between periods of fasting is not improved or if there is over-indulgent, any benefits from fasting would be counteracted.
  • If you are on daily medications, any fast that is based on water only and is longer than 12 hours would be contraindicated. (In this case, a juice fast would be recommended.)
  • Could lead to a disordered eating patterns, such as binge eating and preoccupation with food.
  • Some studies suggest that cutting down on protein consumption periodically, particularly leucine, and methionine, could have a similar effect on our aging process and immune status.
  • A complete rest from food, a water fast, can bring healing and overall wellbeing. However, it is really the diet that follows the fast that has the greatest impact on continued health.


  • Consuming no animal products, including eggs, dairy, or gelatins.
  • Main focus on vegetables, a few servings of fruit and with plant-based protein from legumes, nuts, seeds and produce.


  • Compared to meat eaters, studies have concluded that vegans seem to be leaner, healthier and tend to live longer.
  • Since whole grain, fruit and vegetable intake is higher, the effects of inflammation and the amount of free radicals among athletes might be minimized.
  • Is said to be more environmentally beneficial by reducing the release of greenhouse gases, land use and degradation, water pollution, and rainforest deforestation that occurs with animal farming.


  • Great risk for malnutrition if not done correctly.
  • “Vegan” does not automatically mean “healthy!” The “vegan junkie” refers to someone who eliminates animal products but replaces them with “vegan” junk food.
  • Getting enough protein can seem as a simple task but getting the correct amounts of correct amino acids require knowledge and planning. Especially for athletes!
  • Supplementation is required since the diet is lacking B12, creatine and Omega 3 in form of DHA and EPA.
  • Vegan diets are naturally higher in omega 6 and very limited in omega 3, which could cause an imbalance, much like in a standard American diet.
  • There are several vegan food sources that provide omega 3 in the form of ALA and some of this fatty acid can be converted into EPA and DHA, but only about 5-10%. It is VITAL that EPA and DHA are supplemented or the diet includes microalgae, which would be the only plant-based source of DHA.

Overwhelmed? Don’t be! It’s all about finding what’s right for your body and your lifestyle. Speak to one of our nutrition experts for more information.

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