Pros and Cons of Keto Diet, According to Nutritionists & Dietitians

Pros and Cons of Keto Diet, According to Nutritionists & Dietitians

Pros and Cons of Keto Diet, According to Nutritionists & Dietitians

By: Julie Mancuso, founder of JM Nutrition, Nataly Georgieva, eating disorder dietitian, MScFN, RD; Terence Boateng, sports dietitian, BASc, BSc, RD, CSEP-CEP, MHSc, Vanessa Phillips, BSc, MSc. About JM Nutrition


In this post:

  • What is the ketogenic diet?

  • Origins of the ketogenic diet

  • How does the keto diet work?

  • Pros and cons of keto diet


A high number of our clients continue to inquire about the pros and cons of the keto diet during nutritional counselling sessions with our nutritionists,  dietitians and nutrition coaches. It’s a common occurrence, largely due to the popularity of this ubiquitous fad diet. For this reason we decided to share our point of view on the matter.

Before we analyze the pros and cons of the ketogenic diet, let’s take a look at what the diet looks like, how it works and its origins.


What is the ketogenic diet?

In a broad sense, the ketogenic diet is any diet that produces a physiological state called ketosis, that is, an increase in ketone bodies.

According to, ketosis is a natural metabolic state that occurs when the body uses fat as its main fuel. The body is able to enter ketosis through a variety of methods that include “high-fat, low-carb diets, fasting periods or caloric restriction” (PubMed Central: Keto Microbiota).

Classically, the ketogenic diet consisted of a 4:1 ratio of fat to non-fat (carbohydrates and proteins), with 90% of calories coming from fat (PubMed Central: The Ketogenic Diet…).

Modified keto diet

Nowadays, a modified, slightly more moderate ketogenic diet predominates. This diet is composed of 5-10% calories coming from carbohydrates or below 50g per day, 30-35% of calories coming from protein and 55-60% calories coming from fat (PubMed Central: Ketogenic Diet).

Of course, the protein and fat ratios may change slightly with protein decreasing to as much as around 20% and fat increasing to as much as around 75%.


Keto diet origin

The origin of the keto diet is rather interesting. 

Since approximately 500 BC, Hippocrates noticed that the symptoms of patients suffering from epilepsy improved by prolonged periods of fasting.

“In earlier periods of history, children were kept on clear liquids for as long as two or three weeks until seizures improved”, according to

In the early 1920s the ketogenic diet was introduced as a method to “mimic the metabolism of fasting” (Online Library). For decades, the ketogenic diet was used as a treatment for epilepsy. However, in the advent of anti-epileptic drug treatments, the use of the ketogenic diet declined.

Related: Metabolism 101

Over the past 15 years, however, there has been an explosion of interest in the ketogenic diet. The interest, however, is not solely based on its effectiveness in treating epilepsy. A large proportion of interest exists for another reason. Although there are many pros and cons of the keto diet, the primary reason why such a high number of people try it is weight loss. 


How does the keto diet work?

Carbohydrates are the main source of energy for our body. This energy comes in the form of glucose. When carbohydrates are reduced significantly to a level of less than 50g per day, the body turns to breaking down fat into ketones for energy. This process typically takes a few days to complete. “Two metabolic processes come into action when there is low carbohydrate availability in body tissues: gluconeogenesis and ketogenesis”, according to PubMed Central.

Gluconeogenesis is the “synthesis of glucose from non-sugar precursors such as lactate, pyruvate” and so on, according to Science Direct.

When the availability of glucose drops even further, the internal production of glucose is not able to keep up with demand of the body and “ketogenesis begins in order to provide an alternate source of energy in the form of ketone bodies. Ketone bodies replace glucose as a primary source of energy”, again, according to PubMed Central. 


Pros and cons of keto diet

The pros and cons of the keto diet are many and varied. Let’s take a look at potential keto diet pros first.


Keto Diet Pros

1. Reduction of hunger

Without a doubt, hunger is a frequent challenge for many dieters. It is also one of the primary reasons why many diets fail in the long-term.

Many people report feeling hungry throughout the day when attempting various diets. This lack of satiety contributes to feelings of dieter discontent. Eventually, many dieters choose to abandon the given diet for this reason.

Eating low-carb, however, has an opposite effect.

Following a low-carb diet such as the ketogenic diet, can lead to a reduction in appetite. Because hunger is reduced, those on a low-carb, high-fat diet tend to eat less than those on a strictly low-fat diet, according to Tufts University. This is one of the more significant pros of the keto diet. 

2. Larger initial weight loss

In addition, studies have shown that the ketogenic diet is more effective for short-term weight loss than low-fat diets. Those on a low-carb, ketogenic diet lose more weight faster than those on a low-fat diet. Over a longer term, the differences are insignificant, however (The New England Journal of Medicine).

Related: Why Am I Not Losing Weight?

Weight loss with nutritionist and dietitian

3. Reduction in blood sugar and insulin levels

Another one of the more recognizable pros of the keto diet is that low-carb diets of this nature can benefit people with diabetes and insulin resistance, according to Bio Med Central.

Related: Dietitian for diabetes

Studies show a “diet lower in carbohydrates led to greater improvements in glycemic control, and more frequent medication reduction or elimination than the low glycemic index diet. Lifestyle modification using low carbohydrate interventions is effective for improving and reversing type 2 diabetes” (PubMed Central).

4. Keto diet may be therapeutic for a wide variety of disorders and diseases

While further research is needed to confirm the therapeutic uses of the ketogenic diet, some preliminary findings are promising. A number of studies show that the ketogenic diet may be beneficial to those suffering from a myriad of diseases and disorders.

In recent years, there has been a surge of research done on the ketogenic diet as a potential support therapy for a number of diseases and disorders including obesity and related metabolic disorders.


“Recently, VLCKD (Very Low Carb Ketogenic Diet) has been demonstrated to be a powerful tool for some neurodegenerative disease, autism spectrum disorder (ASD), Alzheimer’s disease, glucose transporter 1 deficiency syndrome and autoimmune multiple sclerosis (AIMS)” (PubMed Central: Ketogenic Diet and Microbiota).

Some research has even suggested that the ketogenic diet is a promising nutritional support therapy to be used in conjunction with modern cancer treatments (chemotherapy, radiation) (PubMed Central: Promising Effect…), (PubMed Central: Ketogenic Diet in the Treatment of Cancer).

Moreover, there have been favourable results in using the ketogenic diet as a support therapy in type-2 diabetes due to its effectiveness in stabilizing blood sugar levels.

Although studies are incomplete and not fully conclusive, these pros of the keto diet cannot be overlooked. That said, however, it’s important to note that research here is still in its infancy. Certainly, more light will be shed on the subject in due time.

5. Keto diet may boost energy levels

Though less significant in scope, a feeling of increased energy is another pro of the keto diet.

Many keto dieters report feeling increased energy levels throughout the day. That said, the empirical evidence in this area is thin at the time of writing.

Because the ketogenic diet avoids significant peaks and valleys in blood sugar, there is a very stable, steady feeling of energy while on the diet. As a result, some dieters find that the keto diet helps them avoid energy dips and slumps throughout the day.


Keto Diet Cons

1. Ketogenic diet is too strict for many

One of the more prevalent day-to-day cons of the keto is that it is difficult to sustain over a long period of time.

Many find the elimination of a large amount of fruits and vegetables as well as other carbohydrates over a long period of time too restrictive. This makes it difficult to sustain.

The difficulty is compounded further by the fact that in order to remain in ketosis you must adhere to the diet strictly. This eliminates “cheat days” entirely. Such an all-or-nothing approach is something that many dieters find hard to tolerate, sometimes leading to stress or abandonment.

Discover more about the role diet plays in stress management.

According to Nutritional Therapy Practitioner, Vanessa Phillips, many people end up following a keto diet on weekdays, but are less strict on the weekend. Doing so may cause a weight loss plateau or even weight gain. In addition, cycling in and out of ketosis too quickly month on month may cause blood sugar spikes and insulin resistance, which may lead to a higher risk of obesity and type 2 diabetes.

Related: Dietitian for obesity management

2. The unpleasant symptoms associated with the “keto flu”

Undoubtedly, one of the keto diet cons is the keto flu.

Many people report feeling sick when they begin the keto diet. Some may have nausea and vomit. Others may experience headaches. While others still, may feel lethargy, fatigue and irritability. Some people even suffer from gastrointestinal distress (

To decrease the severity and/or frequency of these symptoms drink a great deal of water and get adequate sleep. 

Related: Hard To Digest Foods: Are You Ready For Some Surprises?

The flue-like symptoms generally subside within a week. Some people, however, may feel ill for slightly longer.

What causes the keto flu?

According to Harvard Health, no one really knows. “Is it related to a detox factor? Is it due to a carb withdrawal? Is there an immunologic reaction? Or is this the result of a change in the gut microbiome?”

Whatever the reason, it does not observably happen to everyone, after a switch to the ketogenic diet. Only to some.

3. Nutritional deficiencies

There is no way of getting around the fact that because the ketogenic diet eschews certain foods, and thus, nutrients, nutritional deficiencies are possible. This is one of the more important cons of the keto diet, particularly from the perspective of a nutritionist or dietitian. 

To be in ketosis, you need to consume high amounts of fats (generally 55-75% of daily caloric intake) and a very low amount of carbohydrates (typically 5-10% of daily caloric intake).

According to these figures, it is extremely difficult (if not impossible) to obtain all the daily recommended requirements of vitamins and minerals. This is especially true for the average keto dieter who subscribes to the principles of the diet without a full understanding of nutritional composition of food.

The fact that the ketogenic diet severely restricts the consumption of nutrient dense foods such as fruits and vegetables, it is likely that without proper professional guidance, vitamin and mineral deficiencies are bound to occur.

4. Kidney stones

Some people develop kidney stones while on the ketogenic diet.

High fat animal foods, which are staples on the ketogenic diet, may expose you to a higher risk of developing kidney stones.

According to Healthline, and supported by research published on PubMed, a “high intake of animal foods can cause your blood and urine to become more acidic, leading to increased excretion of calcium in your urine.

Some studies also suggest that the keto diet reduces the amount of citrate that’s released in your urine. Given that citrate can bind to calcium and prevent the formation of kidney stones, reduced levels of it may also raise your risk of developing them.”

Related: Kidney disease dietitian

5. Constipation

Another one of the more prominent cons of the keto diet is constipation, which plagues many of the dieters.

According to Registered Dietitian, Nataly Georgieva, the ketogenic diet restricts nutritious carbohydrate-containing foods such as whole grains, fruits, starchy vegetables, and pulses, which naturally contain plenty of fibre. When these foods are omitted from the diet, it is difficult to have adequate fibre intake to keep regular. Doing so may also lead to digestive discomfort and constipation.

If digestive health is of utmost importance or you already suffer from constipation, we advise you exercise caution. For more information you can contact our gut health dietitians and nutritionists.

Related: Digestive Health Basics

6. Diarrhea

Conversely, some dieters report bouts of diarrhea, when on the keto diet. This is likely due to the very high intake of fat, which requires more work for the body to break down, according to Georgieva. It may also be due to excessive consumption of sugar alcohols (e.g. erythritol, sorbitol, xylitol) in an attempt to keep carbohydrate intake low.

“Additionally”, states Nutritional Therapy Practitioner, Vanessa Phillips, “for those who have poor gallbladder function, have had gallbladder removal surgery, or who have experienced gallstones, consuming too many fats in one sitting may exacerbate diarrhea. Subsequently, this may exacerbate nutrient deficiencies that are already a risk for those following a strict keto diet.”

7. Dehydration

One of the most common side effects of the ketogenic diet is dehydration. As such, it is one of the cons of the keto diet. 

Dehydration occurs because people urinate more frequently when shifting into ketosis. During this transition, your body depletes its stored form of carbs, called glycogen. Given that the glycogen in your body is bound to water molecules, it releases water when it’s used up.

Furthermore, your body produces less insulin–a hormone that helps absorb glucose from your blood–on the keto diet because you consume fewer carbs. A drop in insulin levels can affect electrolytes, such as potassium and sodium, which play key roles in hydration. For example, your kidneys release excess sodium when insulin levels fall, promoting dehydration”, according to Healthline.

Learn more about the importance of water, dehydration and how much water you should drink.


8. High-fat risks

Because the ketogenic diet calls for the consumption of foods that are high in fat, many keto dieters feel this is a ticket to eating a wide variety of highly-palatable foods. The problem is that many of these high-fat foods contain the potentially harmful dietary fats. These fats, namely saturated and trans, should be limited.

It is true that some keto dieters consume goods fats such as avocado, olive oil, nuts and seeds as well. Typically, however, the bad fats are eaten in much greater quantities and with much greater frequency. Doing so over a long period of time can be certainly detrimental to the over all health, increasing the risk of chronic disease. This makes it one of the more significant cons of the keto diet.

9. Athletes beware!

JM Nutrition’s Registered Dietitian, Sports Nutritionist and Certified Exercise Physiologist, Terence Boateng, weighs in on the pros and cons of the keto diet debate:

“As a dietitian who works with athletes, many clients have asked about the effects of the ketogenic diet on sports performance and muscle mass. While this diet may have some benefits for general weight loss, I discourage its use among athletes. 

Reason being, carbohydrates are the primary fuel source for high-intensity training including strength training and weight lifting, as well as hard runs. Completely restricting this efficient fuel source results in athletes not being able to exercise as hard, and thus not getting all the desirable muscular adaptations from training.

Related: Strength Training Diet Myths and Misconceptions

Instead, I recommend a balanced approach that is tailored to the training routine and fuel demands of clients.” This can be accomplished with simple meal planning. After all, nutrition for combat sports differs from a diet for endurance activities such as running or cycling.


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The ketogenic diet has experienced a rise in popularity in recent years, primarily as a weight loss tool.

As with anything else, pros and cons of the keto diet exist.

What’s more, some preliminary research looks promising. 

It’s important to keep in mind that the keto diet is experiencing a relatively recent reemergence in popular culture. It will take some time to compile a satisfactory body of evidence to determine its long-term effects.  

Aside from solid evidence supporting its efficacy in managing intractable epilepsy, there is not a great deal of research to suggest any other long-term benefits of the diet. At least not yet. Only time will reveal more.

As such, we advise anyone considering trying the keto diet to exercise caution. After all, you don’t need to subscribe to a rigid diet model to to help you meet your goals. Other ways exist. We assure you.

As always, if you require personalized support, book an appointment or book a free consultation. We offer in-person appointments, as well as virtual nutritional counselling.


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Author: Julie Mancuso

Julie Mancuso

Julie Mancuso is a graduate of the University of Toronto, founder and owner of JM Nutrition, a nutritional counselling service by registered dietitians and nutritionists. For 15+ years, JM Nutrition has helped thousands reach their health, wellness and nutrition goals. Julie and her team regularly lend their expertise to a variety of health publications such as Reader's Digest, Livestrong, Business Insider, Food Network, Today's Parent, MyFitnessPal, Toronto Star, Elle Magazine, Best Life, Weight Watchers and many more.